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COMPARISON OF URINE DIVERTING TOILET SYSTEMS TO CONVENTIONAL
WASTEWATER TREATMENT AND ASSESSMENT OF THE FEASIBILITY OF
REPLACING THE LATTER WITH THE FORMER
by
Nathan Krebs
A Thesis
Submitted in partial fulfillment
of the requirements for the degree
Master of Environmental Studies
The Evergreen State College
March 2013
© 2013 by Nathan Krebs. All rights reserved.
ii
This Thesis for the Master of Environmental Studies Degree
by
Nathan Krebs
has been approved for
The Evergreen State College
by
________________________
Robert H. Knapp, Jr. Ph.D.,
Member of the Faculty (Physics and Sustainable Design)
________________________
Date
iii
ABSTRACT
Comparison of Urine Diverting Systems to Conventional Wastewater Treatment and
Assessment of the Feasibility of Replacing the Latter With the Former
Nathan Krebs
Developed and developing nations alike face challenges around the seemingly
disparate issues of water shortages, energy consumption, water pollution and shortage of
agricultural inputs. Conventional sanitation systems in industrialized societies are
expensive to build and maintain, consume large amounts of energy, lead to extensive
water use because they require water as a transport medium and, because wastewater
contains large amounts of plant nutrients, wastewater is implicated as a major source of
water pollution. In less developed areas of the globe, human excreta often causes major
health and environmental problems when it is directed untreated into water ways.
Agriculture worldwide requires fertilizer inputs to maintain the fertility of soil. While
these concerns are widely studied by researchers in distinct disciplines, a cooperative and
interdisciplinary approach may arguably be more effective at adequately handling these
problems than the piecemeal offerings of individualized fields of study.
Urine diverting toilet systems represent a rather revolutionary departure from
status quo sanitation systems. Such systems treat human excreta as a valuable reusable
resource rather than a waste. The sanitation system becomes a means of not only
sanitizing human excreta, but also a means of capturing a resource to be directed back to
agriculture as a fertilizer. However, as these systems have only been implemented on
relatively small scales, their overall feasibility remains unproved. The research presented
here seeks to compare conventional systems to alternative urine diverting systems,
analyzes the potential feasibility of the alternative technology both from a technical
aspect and also from the standpoint of the potential perception and acceptance of the
technology by the anticipated users.
Table of Contents
Section 1- Introduction
Section 2- Background Information
Section 3- Urine Diverting Technologies
Section 4- History of Nutrient Reuse: Shifting Perceptions
Section 5- System Comparison and Analysis
Section 6- Conclusions
Works Cited/Bibliography
Page 1
Page 6
Page 27
Page 42
Page 50
Page 74
Page 80
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ACKNOWLEDGEMENTS
I am very grateful to all of the friends and family who supported me as I worked to
complete this document. Especially, I would like to thank Rebbeckah, my loving wife for
continuing to support me and encouraging me to see this through to completion. Thank
you to Rob Knapp for all of your wise guidance and input, both on this project and as I
worked my way through the MES program. And thank you to mom and dad for all your
love and support through the years. You will never know how much it is appreciated.
v
Section 1- Introduction
Interdisciplinary approaches are gaining popularity and recognition for their
essential role in finding solutions to growing environmental problems. Specialized fields
of study have long been important for providing understanding of the physical world and
developing ways that societies may benefit from natural systems. However, the interface
of human societies and their environment takes place on a complex and interconnected
front. In many human interactions with the natural world, a lack of a comprehensive
understanding of natural systems' roles lead to ventures that are successful in some
regards, but complete failures in others.
For instance, hindsight shows that society and environmental systems may have
been better served had engineers working on the construction of dams in the Pacific
Northwest during the middle of the last century stepped outside of their tidy professional
boundaries to discuss means to mitigate the potential harmful impacts of dams with
fishery scientists and biologists. These massive construction projects were generally quite
successful in providing irrigation water and electricity, but also resulted in widespread
destruction of habitat for salmon and other wildlife native to impacted riverine habitats.
The impacts of the decisions made decades ago continue to carry, in many ways, a
damaging legacy to cultural, environmental, and economic systems in the region.
Since the middle of the twentieth century, human food systems have become
increasingly complex and technical in many regards. Following World War II, western
agricultural systems, largely influenced by specialized chemists, plant geneticists, and
agricultural scientists, experienced a massive infusion of fertilizers and crop treatments.
1
These inputs were largely made possible through a heavy subsidization by fossil fuels
and government policies and have allowed for tremendous increases in yields over past
decades. The benefits of the increased yields are obvious. Food is generally more easily
available and cheaper than it has ever been in history. However, the reliance of the food
system on finite resources makes it vulnerable to market forces as those resources
become depleted and costly.
Sanitation systems represent the other end of the existing" linear" agricultural
system (i.e. this system has defined inputs and outputs, as opposed to a cyclical system in
which outputs are recycled in some manner to become inputs into the system) . Human
excreta, the primary component of concern in what is commonly known as
"wastewater."By treating excreta as a waste it becomes essentially an externalized cost of
producing and consuming food. Human excreta can be a public health concern due to the
potential for disease transmission from contact with excreta. In the name of protecting
public health, specialists such as wastewater engineers and public health officials,
developed modern sanitation systems that have proved largely successful at limiting
human contact with excreta, but require large, expensive and technologically advanced
systems to move vast quantities from points of potential contact between individuals and
excreta to large treatment facilities.
In the process, large quantities of energy, water, and other resources are needed to
treat the water that is, due to its role as a transport medium, intentionally polluted by the
system. The system is then tasked with handling vast quantities of sludge removed from
water. Due to the presence of various pollutants present in the wastewater stream, and
especially due to the presence of large quantities of plant nutrients present in excreta, this
2
waste product often becomes an environmental pollutant in itself. Indeed, the current
widespread consideration and treatment of human excreta as a waste product has
presented environmental problems not easily solved by existing systems.
In addition to the large amounts of inputs, the agricultural system, and in turn
sanitation system, can be critiqued based on its linear nature. The system in many ways is
weakened by its distinct inputs and outputs. The inputs (fossil fuels, mined resources,
water, infrastructure, etc) are in many cases finite or limited in their availability. The
outputs are largely implicated as pollutants of land, air and water.
Myriad technologies have long been in existence that could allow the closure of
the resource "loop" with regard to the inputs to the agricultural system and the outputs of
the sanitation system. One such system is urine diverting (UD) technology. This system
allows for the sanitary capture and reuse of urine (a fraction of the wastewater stream of
high importance for nutrient reuse and sequestration) in agriculture. These alternative
systems are designed to not only effectively remove pathogenic organisms and pollutants
that cause environmental and human health problems, but also to capture the plant
nutrients that are found in human excreta in order to make them available for reuse in
agriculture. This paper will seek to examine the issues surrounding the choices societies
make with regard to managing their waste/resource streams and consider issues regarding
the feasibility of shifting from a system of sewered "wastewater" systems to urine
diverting systems.
In order for this technology to become widely adopted, there are many potential
barriers. Some of these barriers are technological. There are concerns about whether urine
collection and storage technology can be scaled up to function in the context of large
3
towns and cities. Technology to transfer urine-sourced fertilizer resources to agriculture
and means of application are still largely unproven.
In addition to the technological barriers, there are many barriers based on the
perception of the technology by a wide variety of stakeholders. Human excreta is a taboo
topic in many societies. There are many reasons, some of them being quite reasonable,
that using fertilizer products sourced from excreta to grow food gives many people pause.
There are also many rather irrational and emotional reactions that factor in. In addition to
the difficulty many individuals have regarding the mental problem of using sewage for
fertilizer, there also are challenges that arise when an attempt is made to replace or
augment established systems and practices (e.g. infrastructure). In many cases these
challenges arise from strong paradigmatic convictions held by key stakeholders. Finding
a way to overcome or convince these convictions is often the challenge of a new
technology, no matter how innovative or sensible it may be.
It is widely accepted that industrial agriculture is not currently on a sustainable
path due to its linear nature, massive resource throughputs, irresponsible use and handling
of plant nutrients, and the resultant environmental damage that stems from these
attributes. Additionally, there are many concerns about the ability of sewer-based
industrial wastewater systems to adequately and efficiently sanitize human excreta. Urine
Diverting systems represent an alternative that may be capable of adequately collecting
and sanitizing human excreta while also providing a reasonable means for reuse of the
plant nutrients contained in excreta. However, these systems require a radical
reconsideration of the meaning of human excreta and shift the value of it from being a
valueless waste product to being a valuable resource. In so doing, the technology also
4
essentially demands a reconsideration of the barriers that exist between existing
disciplines. These technologies have the potential to dramatically increase the
sustainability of both agricultural and sanitation systems. However, there exist
technological and attitudinal barriers for the extensive implementation of these systems.
These barriers and their interactions are the subjects of this paper.
5
Section 2- Background Information
Flush and Forget: Conventional wastewater treatment plants
The “flush and forget” (Langergraber & Muellegger, 2005) system of sanitation,
based on vast networks of sewer pipes connected to centralized treatment plants, has long
been considered the superior system for reducing the potential health threats posed by
improperly handled human excreta. Sewer systems have existed for centuries and have
flourished especially within the last two hundred years (Bracken, Wachtler, Panesar, &
Lange, 2007). In response to the horribly unsanitary conditions that arose around
industrializing towns and cities in Europe in the seventeenth and eighteenth centuries,
systems were designed to minimize odor, filth and health concerns associated with
human excreta. As indoor restrooms became more prevalent, especially in western
industrialized countries during the nineteenth century, flush toilets and sewers came to
dominate as the most common form of sanitation.
However, the construction of sewers and sewage treatment plants has proved
insufficient to control water pollution, other associated environmental issues, and human
health problems. In many cities, water treatment plants have become locations where
concentrated wastewater is introduced into the environment. In the United States, the
Clean Water Act of 1972 established a set of rules and regulations to govern the
wastewater treatment industry. Many other counties have analogous legislation to
regulate wastewater treatment and the subsequent return to the environment. However, as
populations continue to grow, costs of operation increase, infrastructure ages, and the
6
nature and quantity of contaminants change and increase, treating water to legally
acceptable levels is proving more and more difficult (U.S. EPA, 2004).
Overview of Conventional Wastewater Treatment Plant Operation
Conventional wastewater treatment plants (WWTPs) are quite technologically
advanced. Most of these systems use water as a medium to transfer excrement via pipes
into networks of sewers, where toilet water (blackwater) mixes with other domestic
wastewater (greywater), industrial wastewater streams and possibly stormwater runoff
before arriving at centralized treatment facilities. Treatment facilities use myriad
physical, chemical and biological treatment processes to bring water to some level of
sanitization before it is returned to the environment. The following synopsis of the
treatment processes at conventional WWTPs is based on the “Primer for Municipal
Wastewater Treatment Systems,” published by the U.S. Environmental Protection
Agency (EPA) (2004).
In some systems solids are simply removed by a primary process of filtration and
settling. This process first removes large objects such as sticks and rags that may be
suspended in the wastewater stream by the use of screens and grates. Sand and gravel are
then removed in sedimentation chambers. This step is very important to limit wear and
tear on pumps and other machinery and is especially important in combined sewer
systems where storm water runoff can contribute road debris when it is added to the
wastewater stream. After the largest particles are removed, dissolved inorganic and
organic material and suspended solids are still present. Additional solids may be removed
7
by further gravity sedimentation, filtration or chemical coagulation. The sludge collected
during primary processing is generally either hauled to a landfill or incinerated.
In the United States and many other industrialized countries, secondary treatment
is required as a minimum level of treatment before wastewater can be returned to the
environment. These more advanced systems use biological agents such as bacteria, algae
and fungi to consume and remove additional organic materials from the water.
Wastewater is passed through biologically active holding tanks utilizing either attached
growth apparatus (where the biological agents are affixed to a stone or plastic media) or a
suspended growth system. Both types of systems require the water to be continually
aerated to ensure that the biological agents have plenty of oxygen to thoroughly remove
dissolved organic matter. Secondary treatment potentially removes about 90% of
suspended biodegradable matter.
For the approximately 70% of WWTPs in the United States employing secondary
treatment, the final step in the process is to disinfect the wastewater before it is returned
to the environment. This is generally done in one of three ways. The use of chlorine gas
is very effective at killing bacteria and viruses, but the use of this method has declined in
many areas because chlorine is also highly toxic to beneficial aquatic life. Therefore, if
this method is employed, precise dechlorination processes are necessary before the water
can be released. Ozone, an unstable molecule produced by exposing oxygen to very high
voltage, is also very effective at sanitizing water. The gas readily breaks down to reform
oxygen and leaves no harmful residue in the water. However, it is expensive to treat
water with ozone due to the large amounts of electricity used. Ultraviolet radiation kills
potentially pathogenic microorganisms by penetrating cellular tissues and damaging
8
genetic material. UV treatment is quite effective and leaves no harmful residue in the out
flowing water. However there are substantial energy penalties to this method of
sterilization.
The other approximately 30% of WWTPs in the United States employs a third
stage of treatment. Tertiary, or advanced treatment is necessary to further purify
wastewater, and specifically to remove the plant nutrients nitrogen and phosphorus before
the nutrients can be absorbed by aquatic vegetation. This is because the deleterious
effects of excess nutrient loading of waterways are generally associated with high levels
of algae and plant growth (e.g. Anderson, et al., 2008). Eventually the overgrowth blocks
out sunlight at the surface, causing a die-off of the algae. As the algae decompose by
natural biological processes, oxygen is consumed. The resulting low levels of dissolved
oxygen can cause severe harm to aquatic systems and has been implicated in large-scale
fish kills, marine mammal mortality, shellfish mortality, illness in humans from eating
affected shellfish, and loss of certain types of aquatic vegetation (Anderson et al., 2008).
In addition to pollution of aquatic environments, nitrogen groundwater pollution is
another concern. Groundwater pollution is most often associated with agricultural sources
of nitrogen. However, the connection between wastewater treatment processes and
aquifer pollution can be quite direct in places that allow secondarily-treated wastewater to
be used in irrigation.
Nitrogen often occurs in the wastewater stream in the form of ammonia.
Ammonia can be directly poisonous to some aquatic life and can also stimulate the
growth of algae. Nitrification is a process whereby toxic ammonia is converted into nontoxic nitrates by nitrifying bacteria. Once the toxicity of the ammonia is addressed,
9
nitrogen removal from the wastewater stream typically takes place by biologically
converting it to nitrogen gas. This is accomplished in an anaerobic environment where
bacteria are forced to use the oxygen linked to the nitrates for their metabolic activity,
which isolates nitrogen as nitrogen gas. The non-toxic gas is simply vented to the
atmosphere.
Phosphorus, another plant/algae nutrient found in wastewater, must also often be
removed prior to releasing the effluent to lakes, streams or estuaries. Such removal may
be done through coagulation-sedimentation processes or by using biological nutrient
removal systems. The coagulation-sedimentation process requires the addition of alum,
lime, or iron salts to be added to the wastewater. These chemicals bond with phosphorus
and, because the resulting particles are heavier than water, they fall out of solution as
sediment. Up to 95% of phosphorus can be captured in this process. However, the
resulting chemical sludge is fairly expensive to dispose of, making this process less
desirable as an option for municipal wastewater treatment. In the biological nutrient
removal system, bacteria and other microorganisms are supported on a suspended growth
system. These systems generally treat nitrogen by converting it to nitrogen gas in a
similar manner as the denitrifying systems described above. Phosphorus is removed in
the solid material of the microorganisms collected from the effluent.
The solid portions, or sludge, of the wastewater stream are collected and generally
are either incinerated, buried in landfills or applied to the land in some manner. The
proportion of sludge that is disposed of or reused in some capacity varies widely. In some
Swedish municipalities, for instance, nearly all of the sludge produced is spread on
agricultural lands, while the national average is closer to about 30% (Kvarnstrom &
10
Nilsson, 1999). In the United States about half of the sewage sludge produced is applied
to the land either as an agricultural soil amendment or as a soil conditioner in disturbed
lands such as construction sites and strip-mines where vegetation re-growth is desired
(U.S. EPA, 2004). Because sewage sludge may contain heavy metals, pathogens, and
other pollutants, the use of sewage sludge is regulated in the United States by Federal
Regulation 40 CFR Pert 503.
Problems Inherent to Conventional WWTP Operations
Modern sewage systems have done an admirable job of improving sanitary
conditions for many populations globally. However, this benefit to society has not come
without a price. Drawbacks to conventional sewer-based sanitation systems include high
energy consumption, considerable usage of freshwater, economic costs and
environmental pollution.
Energy Consumption
A substantial amount of energy is required in the process of purifying water that
has been contaminated by human excreta. Depending on the location and design of a
given system, electric pumps may be required to move large volumes of water to
centralized treatment facilities. Massive mechanical apparatuses are also required at
treatment plants to aerate water as it moves through the system. The energy costs of
aeration alone in the United States accounts for at least one percent of all electricity
consumption in the country (Rabaey, 2009). The handling of sludge at treatment plants
accounts for at least as much additional energy use (Rabaey, 2009). Many other aspects
11
of the process result in additional energy consumption. These range from the production
of chemicals (e.g. chlorine) involved in the sanitation process, to the maintenance and
manufacture of large machinery required for the treatment operations. The energy costs
of pumping, storing, and treating the water used as flush water are also not accounted for
here. Depending on what energy costs are included, it is possible to come to diverse
conclusions about the energy costs of WWTPs. However, it is difficult to deny the large
magnitude of energy used in treatment processes. According to a large study coordinated
by the EPA "estimates the annual energy usage at approximately 100 billion kWh per
year. At an average energy cost of $0.075 per kWh, the cost for providing safe drinking
water and providing effective wastewater treatment is approximately $7.5 billion per
year" (EPA, 2010).
Water Use
Because of the tremendous volume of water required by such systems,
consumption of freshwater is a major concern, especially as shortages in per capita
availability of freshwater become more prevalent in many areas around the globe.
Jenkins (2005) states that “by some estimates it takes one to two thousand tons of water
to flush one ton of human waste.” A study of water use in the United Kingdom found
that around one third of total domestic water use is used for flushing toilets (Burkhard,
Deletic, & Craig, 2000). This figure agrees with Vinnerås and Jönsson (2002), who state
that in Sweden the average person uses about 59 m3/yr, of which 19 m3 is used for toilet
flushing. The EPA estimates that Americans use about 4.8 billion gallons of water to
flush toilets every day (“How to Conserve Water and Use It Effectively”, 2010). These
12
statistics are concerning, as freshwater supplies around the world are in shorter supply
every year. For instance, in the United States, groundwater use outpaces replacement
rates by 21 billion gallons per day (Jenkins, 2005).
In addition to the sheer volume of water used by sewer-based sanitation systems,
water used for flushing in most parts of the world is purified drinking water. This means
that not only are freshwater supplies being depleted, but also that energy and other
resources are invested into the purification of the water used for flushing, which is then to
be polluted prior to anyone having had a chance to drink it.
High Cost of Maintenance and Operation
Because of the high levels of inputs, wastewater treatment systems have relatively
high operating costs. The operation of sanitation systems in industrialized countries
generally is the responsibility of municipalities. According to Langergraber and
Muellegger (2005) “conventional systems are directly cross subsidized and the chances to
ever become financially sustainable are low.” In western, industrialized economies,
wastewater treatment can require expenditures of 2% of Gross Domestic Product (Larsen
& Gujer, 2001). The true costs of water supply and the resulting water treatment are
rarely covered by the fees paid by consumers. On average, municipalities must pay 65%
of the cost for treating wastewater that is not covered by user fees (Renzetti, 1999). In the
U.S., a recent report by the U.S. Conference of Mayors, Mayors Water Council estimates
that local governments spent $93 billion in 2008 to pay for water and wastewater
infrastructure. It is estimated that about 60% of these costs go to operations and
13
maintenance, with the approximately 40% of these funds going to new capital investment
(Anderson, 2010).
A primary point made by this report is that the current level of funding dedicated
to the existing water infrastructure is not sustainable. Additionally, due to the
degeneration of the aging infrastructure, there are grave concerns about the ability of
municipalities to pay for future maintenance, upgrades, and replacement of water
infrastructure components that are coming to an end of their useful lives. The wastewater
infrastructure alone in the United States is comprised of over 16,000 publicly owned
treatment facilities, 100,000 pumping stations, 600,000 miles of sanitary sewers, and
200,000 miles of storm sewers (Anderson, 2010). The Congressional Budget Office
predicts that between $13-20.9 billion (2001 $US) will need to be spent annually to repair
the nation’s wastewater treatment system in order to meet existing levels of service and
comply with existing regulations. This expenditure is in addition to $20.3-25.2 billion
annually for operation and maintenance costs and does not include increased costs
associated with growing populations and tightening regulations.
Water Pollution
From an environmental perspective, perhaps the most significant concern
regarding conventional sanitation systems is their management of plant nutrients,
specifically nitrogen and phosphorus, and micro-pollutants, such as pharmaceuticals and
endocrine disrupting compounds. Myriad studies have demonstrated that micropollutants are showing up in increasing concentrations in surface water, groundwater and
drinking water (e.g. Winker, Faika, Gulyas, & Otterpohl, 2008).
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Many pharmaceuticals that are introduced into the environment via WWTP
outflow pipes are classified as endocrine disruptors. This class of chemicals can disrupt
hormone development in aquatic organisms even at very low concentrations (Daughton
& Ternes, 1999). Also, natural and synthetic hormones from anthropogenic sources have
been implicated in the destruction of aquatic ecosystems, especially fish populations
(Escher, Pronk, Suter, & Maurer, 2006). The toxic effects of the broad range of
pharmaceutical compounds have only been studied for a relatively short period of time
and they are still not well understood. However, according to Daughton and Ternes
(1999) the drug interactions in aquatic environments that are understood “…are known to
elicit subtle but dramatic effects on aquatic life at very low concentrations…” and
“…may point to an ill-defined vulnerability in aquatic ecosystems”. Conventional
wastewater treatment systems are a primary route by which micro-pollutants enter the
environment, but no widespread technologies have yet been introduced to conventional
WWTPs that allow for the removal of micro-pollutants from the effluent stream (Larsen
& Gujer, 2001).
In addition to their failure to handle micropollutants, many WWTPs globally and
about 70% of those in the U.S. do not effectively remove biologically available nitrogen
and phosphorus from the outgoing water. Nutrients not absorbed by the treatment
processes are introduced into the environment where they can become pollutants if they
are allowed to flow into naturally nitrogen- or phosphorus-limited bodies of water. In
addition to the nutrients that escape from systems that are fully equipped to remove them,
there are a great number of sewer systems around the world that dump sewage ranging
from insufficiently treated to completely untreated into water bodies. In cities throughout
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the Southern hemisphere the high cost of implementing sewage treatment system has
resulted in over 90% of effluent being left completely untreated (Drangert, 1998). Even
in Europe, according to Lienert, Tove and Larsen (2009), “only 79 of 542 major cities
have full (tertiary) sewage treatment.” Of those cities without full tertiary treatment, 223
rely on secondary treatment systems, 72 have only incomplete primary treatment, and
168 have “no or an unknown form of treatment for their wastewater” (Bracken et al.,
2007).
In the United States, The American Society of Civil Engineers gave the country’s
wastewater treatment system a grade of D- on their 2009 “Report Card for America’s
Infrastructure” (ASCE, 2009). This low grade is based on the crumbling state of
America’s wastewater treatment system, its antiquated equipment and especially on the
fact that the overall system allows over 10 billion gallons of untreated sewage to be
discharged into the nation’s surface waters every year (ASCE, 2010).
Consequent discharge of improperly treated sewage into the environment presents
a serious health risk due the pathogens that can be found in human excreta. Also, as
noted previously, pollution from nutrients that are allowed to flow through the treatment
process and into marine environments and bodies of freshwater can result in
eutrophication, the cause of significant ecological and economic losses around the globe.
The human disruption of the nitrogen cycle, a cycle largely driven through Earth's
marine and aquatic ecosystems, over the last century has been tremendous. Through
various activities such as burning fossil fuels, and fixing atmospheric nitrogen into
synthetic fertilizers, humans produce roughly 160 million metric tons of biologically
available nitrogen annually. This compares to between 90 and 120 million metric tons
16
fixed by natural systems (Dybas, 2005). Of the additional nitrogen that humans add to the
system, relatively small amounts are taken up by crops. The remaining nitrogen added to
the system invariably ends up in aquatic ecosystems.
When nitrogen (and in some cases, phosphorus) are added in large volumes to
aquatic ecosystems that are limited by these nutrients, large blooms of algae known as
harmful algal blooms (HABs) can occur. In fact, the frequency, severity, and duration of
HABs is expanding dramatically (e.g. Dybas, 2005). These blooms can have direct
harmful effects on humans when toxins produced by harmful algae species are
bioaccumulated into shellfish consumed by humans. More commonly and with more
widespread harmful implications, the added nutrients are causing marine dead zones
around the world caused by blooming and consequent oxygen-consuming decay of algae
in marine environments. The occurrence of these situations, which cause large fish kills
and areas of very poor ecosystem production, is expanding at an astonishing rate, with the
waters affected by HABs doubling every decade (Dybas, 2005). Reducing the amount of
nitrogen synthesized from atmospheric sources (perhaps by recycling nitrogen through
the human food chain) could have a positive effect of reducing the over-addition of
biologically available nitrogen to the system.
Concerns regarding conventional modern agricultural inputs
As the wastewater industry has sought technologically advanced methods for
removing plant nutrients from wastewater, agriculture has relied on the production of
synthetic fertilizers and mining of mineral fertilizers to replace the nutrients removed
from fields when food crops are harvested. As societies have trended toward
17
industrialization over the last century, negative flows of nutrients from agricultural lands
have become more pronounced (Magdoff et al., 1997). Incidentally, the three main
nutrients required for plant growth- nitrogen, phosphorus, and potassium- are all found in
human excreta. Nitrogen and phosphorus supplies will be the emphasis of this paper.
Plants require nitrogen for protein synthesis and up to five percent of plant dry
matter is nitrogen. Atmospheric nitrogen is quite abundant, constituting about 79% of the
atmosphere. However, in general, plants have no way of absorbing nitrogen from the air
for their own cellular use. Some plants (e.g. legumes) have developed symbiotic
relationships with soil microorganisms that are capable of “fixing” atmospheric nitrogen.
For plants that have this capability, it is an energy intensive process that ceases when just
enough nitrogen is made available. Therefore, for many plants (nitrogen fixers and
others) nitrogen is one of the primary factors limiting growth (Heinonen-Tanski & van
Wijk-Sijbesma, 2005).
Phosphorus is a vital element in DNA, RNA and enzyme reactions that are
necessary for plant growth. Although phosphorus is equally as vital as nitrogen, plants
require about one tenth as much phosphorus as nitrogen to maintain growth (HeinonenTanski & van Wijk-Sijbesma, 2005). Different soil types have varying amounts of
naturally available phosphorus. In most agricultural areas, phosphorus should be added
once per growing season to ensure a sufficient supply to growing plants.
Historically, natural levels of phosphorus in soil were relied upon to supply plants
with their requirements. Human excreta, animal manure and bone were sources of
phosphorus that were used to supplement naturally occurring phosphorus. Over the
course of history soil reserves were depleted and local contributions could no longer keep
18
up with the demand for nutrients. In order to meet the needs of growing populations it
became necessary in many areas to supplement naturally occurring phosphorus with
imported fertilizer. When large guano deposits, which had accumulated over countless
centuries off of the South American coast and in the South Pacific, were discovered, they
provided the world with a steady supply of phosphorus. These limited supplies quickly
became depleted though, and were exhausted around the end of the 19th century (Cordell,
Drangert, & White, 2009).
Phosphorus in modern agricultural systems is primarily obtained from mined rock
phosphate.
Global reserves of rock phosphate were once considered to be inexhaustible.
However, after more than a century of intensive pressure, it is now widely recognized
that global reserves of high quality rock phosphate are quickly being diminished and that
they may be exhausted in the next 50-100 years (Cordell et al., 2009). There are currently
no viable alternative sources that can replace the 20 million tonnes of rock phosphate that
are currently mined each year (Cordell, et al., 2011).
A growing shortage, and the resulting price increase, of an essential agricultural
input will inevitably lead to increased food prices, potentially lower yields, and decreased
food security (Cordell et al., 2009). In fact “some researchers assume that within a
century, the severity of the phosphorus crisis will result in increasing food prices, food
shortages and geopolitical rifts” (Langergraber & Muellegger, 2005).
In addition to their declining availability, phosphate fertilizers from rock
phosphate can have high levels of heavy metals, depending on the source of rock
phosphate (Maurer, Pronk, & Larsen, 2006). As stocks of higher quality (lower heavy
metal content) rock phosphate become depleted, stocks with higher levels of heavy
19
metals will more extensively be brought to market. These heavy metals can be
transmitted to agricultural lands, where they can accumulate and be taken up into food
crops and on up the food chain into humans.
Nitrogen fertilizer does not face the same resource availability issues that
phosphorus does per se, but there are some compelling reasons to reconsider the methods
used to obtain plant-available nitrogen for agricultural purposes. The Haber process is
the industrial process used to combine vast atmospheric stores of non-reactive nitrogen
gas and hydrogen under high pressure into reactive ammonia. Ammonia produced by the
Haber process can be used as a high nitrogen fertilizer, converted into other nitrogensupplying compounds such as urea, ammonium nitrate and ammonium sulfate, or be
combined into NPK combination fertilizers.
The Haber process produces each unit of nitrogen quite efficiently and therefore it
can be argued, assuming that natural gas prices remain low, that there is little economic
incentive to seek alternative sources of nitrogen fertilizer (Wilsenach & van Loosdrecht,
2006). However, because of the tremendous quantities produced worldwide, and the rate
at which demand continues to grow, the production of nitrogen fertilizers constitutes a
significant percentage of annual global natural gas consumption and accounted for
approximately 1% of total world energy consumption in 2001 (Ramirez & Worrell,
2005). Annual applications of nitrogen fertilizers continue to grow at impressive rates.
To this point that has meant a steady increase in the quantity of natural gas used for the
production of nitrogen fertilizers (just less than 500 PJ in 1961 compared with just over
2500 PJ in 2001) (Ramirez & Worrell, 2005).
20
Natural gas is used in the Haber process both as means of providing heat, and
also as a source of hydrogen as a raw material for the process (obtained by mixing
methane gas with steam). With natural gas being one of the primary inputs to the Haber
process, farmers have come to be at the mercy of fluctuating natural gas markets. For
instance, an increase in the price of natural gas in 2003, and the resulting increase in the
cost of fertilizer, was cited as the cause of the collapse of the largest farmer owned cooperative in the United States (“Expensive Fertilizer Blamed”, 2003). The increase in
cost of nitrogen fertilizers was around 32% between April 2007 and April 2008. Prices
also rose substantially the following year (Huang et al, 2009). Although the price of
natural gas has come down in recent years (due to new reserves becoming available by
hydraulic fracturing) the point remains that the existing nutrient sources for the world
food supply is inextricably linked to the ever-fluctuating whims of energy markets. All
markets seek consistent estimates input costs. Given the inevitable uncertainty already
faced by farmers from weather, pests, and market forces, the development of a more
consistently priced source of nitrogen (e.g. from urine diverting systems) would likely be
beneficial to agricultural systems.
In Ethiopia, the rising cost of energy and the fact of limited phosphorus reserves
are causing annual price increases of up to 20% (Meinzinger, Oldenburg, & Otterpohl,
2008). There are additional signs of stress worldwide as farmers in the poorer nations of
the world struggle to pay higher and higher prices for fertilizers (e.g. Cordell et al. 2009).
As a result of rising costs for production inputs, among other factors, Mitchell (2008)
notes that the price of fertilizer from 2002 to 2007 in $/acre of input has risen markedly
21
for corn ($42.51 in 2002 to $93.96 in 2007), soybeans ($6.79/$13.94), and wheat
($17.71/$33.33).
The rising cost of farm inputs does not only affect farmers. As noted by R. Neal
Elliott of the American Council for an Energy-Efficient Economy (ACEEE) in his
testimony before Congress (2005)“negative economic impacts on the agricultural
community ripple throughout the entire economy affecting every household because
these increased farm energy costs are passed thorough to the consumer in higher food and
agricultural product costs.” Although energy prices are just one factor that contribute to
the price of food, the trend of rising food costs has become clear. Prices of internationally
traded food commodities increased 130 percent from January 2002 to June 2008 and 56
percent from January 2007 to June 2008 (Mitchell, 2008).
Economic and ecological costs associated with nitrogen are not only attributable
to fertilizer costs, however. As noted previously, an overabundance of nitrogen has been
the cause of damage to fish populations, changes in levels of marine vegetation, beach
pollution, damage to coral reefs, and ground water pollution (Heal, 2000). These
deleterious effects are due to the fact that humans have, through the use of synthetic
fertilizers, altered the global nitrogen cycle to the point that “the quantities of nitrogen
added to the soil…now exceed the totals fixed through natural processes” (Heal, 2000).
However, “less than half of the nitrogen added to the soil (in the form of synthetic
fertilizers) is taken up by plants” and “nitrogen and its compounds are highly mobile, so
the majority runs off into groundwater and ends up in lakes or the sea or seeps through
the ground into aquifers” (Heal, 2000).
22
Plant nutrients available in human excreta
Human excreta contain many of the micronutrients required for plant growth and
contain especially high levels of nitrogen and phosphorus. In fact, each person excretes
plant nutrients each year approximately proportional to the nutrients required to grow the
amount of food (in the form of grains) that that person will require in a year (Drangert,
1998). On average, humans produce about 500 kg of urine and about 50 kg of feces per
year (Heinonen-Tanski & van Wijk-Sijbesma, 2005). Urine consists of approximately
93-96% water. Fecal matter contains a high proportion of water as well, typically
between 70-85% . Because the kidneys are the primary excretion organs in the human
body, the majority of nutrients are found in the urine portion. Of all the nitrogen in
human excreta, about 90% is found in urine. Additionally, 50-65% of phosphorus and
50-80% of potassium are found in urine (Heinonen-Tanski & van Wijk-Sijbesma, 2005).
Agricultural nutrients in human urine are produced by the body in forms that are
readily available to plants. The nitrogen, for instance, in urine is excreted as urea. Urea
is one of the primary industrially produced forms of nitrogen fertilizer. In addition to
having a high nutrient content, urine from a healthy individual is also generally free of
pathogens when it leaves the body (Heinonen-Tanski & van Wijk-Sijbesma, 2005),
although there are some diseases that may be spread through urine and it should be
handled with care. Methods and technologies for ensuring the hygienic handling of urine
will be addressed in another section of this paper.
Although fecal matter contains less of the three primary agricultural nutrients, it
still has agricultural value as a nutrient rich form of soil-building source of organic
material. The plant nutrients found in feces are not as readily available to plants as those
23
found in urine. For instance, according to Vinnerås and Jönsson (2002), only about 50%
of the nitrogen in feces is water soluble and therefore immediately available to plants.
For this reason, properly processed/composted feces represent a kind time-release source
of nutrients. Fecal material also represents a potentially valuable source of organic
matter that can increase the humus content of soil, thereby increasing its ability to hold
water and maintain fertility (Langergraber & Muellegger, 2005). Despite the potential
benefits of feces, the reuse of feces will not be the primary focus of this paper.
Resources available for use from the waste stream
Urine represents only about one percent of the total wastewater volume (Maurer
et al., 2006). However, blackwater (urine and feces combined) contributes up to 95% of
the nitrogen content and 90% of total phosphorus in typical wastewater streams. Urine
alone accounts for about 87% of the nitrogen and 50% of the phosphorus in the
wastewater stream (Langergraber & Muellegger, 2005). When urine is diluted in a
conventional toilet, it contaminates the water used to flush, thus increasing the
“magnitude of the pollution by mixing relatively small quantities of potentially harmful
substances with large amounts of water” (Chandran, Pradhan, and Heinonen-Tanski,
2009). In addition to contaminating large amounts of clean drinking water, conventional
treatment systems move the valuable nutrients from a relatively concentrated form into a
much more dilute form, thus making their reuse much more difficult.
When the urine/flush water solution reaches the sewer, the entire volume of water
within the sewer becomes contaminated. If this water is destined for a treatment plant
capable of tertiary treatment to remove the plant nutrients, because of the mixing of the
24
water streams, a significantly higher volume of water must be treated that would not
otherwise have required costly advanced treatment. Thus, a much larger treatment
facility is required, causing higher construction and operating costs (e.g. more
precipitation chemicals are required (Tidåker et al, 2007)). If the destination plant does
not employ technology for nutrient removal, the nitrogen and phosphorus will be released
back into the environment at the end of the pipe, leading to potential environmental
degradation by misplaced nutrients. In addition to the possibility of small volumes of
blackwater contaminating large volumes of wastewater, if nutrient recovery is an
objective, other wastewater sources are often to blame for contaminating and diluting the
nutrient-rich blackwater stream.
Many countries allow the use of sewage sludge as a soil amendment in various
uses ranging from food production to forestry. In theory, this practice can be seen as a
positive in terms of sustainable reuse of resources. However, sewer systems often divert
runoff from stormwater drains, industrial effluent, greywater (water from all domestic
drains other than toilets, e.g. sinks and showers), and toilet water into a single stream. It
becomes very difficult, if not impossible to separate out heavy metals, micro-pollutants
and chemicals prior to the sludge being dispersed as a source of agricultural nutrients.
Therefore, the use of sewage sludge in agriculture is rightfully restricted and even banned
by many government policies. For instance, the United States Department of Agriculture
(USDA) Organic Standards prohibit the use of sewage sludge in the growing of organic
food. In Switzerland consumer pressure convinced the government to issue a complete
ban on the use of sewage sludge in agriculture (Lienert & Larsen, 2009). In 2002, a
National Academy of Sciences panel concluded that the potential mix of biological and
25
chemical wastes in sewage sludge represents such a complicated and unpredictable set of
dangers. It therefore warned that existing management practices allowing the use of
sewage sludge on agricultural lands do not protect public health (Snyder, 2005).
In addition to the various contaminants that are found in the wastewater stream,
some “contaminants” that limit the use of sewage sludge in agriculture are added as part
of the treatment process. For instance, phosphorous can be removed using chemical
precipitation processes or by biological systems as outlined previously. In the case of the
common chemical treatment for phosphorus, where iron and aluminum salts are added to
the wastewater stream, the recovery of and reuse of phosphorus becomes impossible (deBashan & Bashan, 2004). Because of the cross-contamination of valuable nutrient-rich
resources such as urine that occur in conventional wastewater treatment systems, if
nutrient recycling from human excreta sources is desired, new treatment processes will be
necessary.
In fact, technology already exists and is currently being deployed on varying
scales around the globe. The various technologies and methods that exist for collecting
and handling excreta are described in the upcoming chapter. Additionally, processes for
treating excreta for reuse as nutrient fertilizers will be addressed.
26
Section 3- Urine Diverting Technologies
In response to the situations described above, many technical suggestions have
been presented that allow human excreta to be used to supplement or replace synthetic
fertilizers in agriculture and limit the negative consequences of conventional wastewater
treatment. Some technologies remove both urine and feces from the wastewater stream.
Also, because urine represents the largest portion of the nutrients of interest, many
technologies have been devised to specifically remove urine from the wastewater stream
before it arrives at the treatment plant. Additionally, technologies and methods have been
devised to prepare and use collected excreta in agriculture
Collection Technologies
Feces and Urine Collecting Systems
In addition to the site-built and custom toilets of that have been built over the
centuries, toilets that separate both urine and feces from the wastewater stream have been
commercially available since at least the 1970s. These first source separating toilets were
designed as dry toilets. Dry toilets do not use water to flush excreta into a sewer
(although in some innovative toilets, such as the Aquatron toilet, discussed by Vinnerås
and Jönsson (2002), a very small amount of water is used to clean the bowl, but is kept
separate from the fecal matter as it enters the holding tank). In most dry systems, urine is
diverted by a dedicated pipe into a holding tank. Feces pass, typically by gravity, into a
separate holding compartment. The size of holding tank, depending on the size of the
27
building it serves, is usually compact enough to fit in the basement or else can be buried.
In some of the more advanced systems a source of carbon, such as sawdust, (proper
composting requires a ratio of carbon to nitrogen of 20-35:1 (Jenkins, 2005)) is added to
the high-nitrogen feces to allow composting to take place inside of the toilet.
Additionally, depending on the level of sophistication, mechanisms to mix and aerate the
composting material, fans to minimize odors, and dual holding tanks that allow one side
to compost while the other collects new material may be included.
Both the feces and the urine storage tanks require periodic emptying, with the
frequency being determined by the size of the holding tanks, the number of people using
them, and the percentage of each user’s daily trips to the restroom that employ that
holding tank (i.e. some people may use such a toilet at work or in public buildings, but
have a conventional flush toilet at home). With proper treatment (options to be discussed
in succeeding section), either in the holding tank or in a separate container, the feces and
urine may be used as a nutrient source for agricultural purposes.
From the perspective of maximizing nutrient recovery, such systems would be the
most ideal. However, implementing nutrient-recovering toilets into a system that is
already embedded with water-based flush toilets and sewers will be a complicated matter.
Capturing the feces portion of the waste stream presents additional complications. For
instance, the feces portion must be moved by a mechanical method generally, as opposed
to urine which, being a liquid, can be moved by pump or gravity feed. Feces are also
more likely to be smelly and messy to handle. As such, this paper will focus primarily on
the feasibility of recovery of urine.
28
Urine Collecting Systems
Many modern urine separating, or urine diverting (UD) toilets, (also referred to as
NoMix, ecological sanitation, and EcoSan) represent a compromise between
conventional flush toilets and full-capture composting toilets. Sweden has been the
location of much pioneering effort regarding new urine separation technologies. Starting
during the 1990s, “thousands were installed in pilot projects” (Larsen et al., 2009). Such
pilot projects have also been undertaken in several other European and Asian cities.
Upon approach, a urine separating toilet will generally bear a strong resemblance
to a conventional flush toilet. The main functional difference is that instead of having
one large bowl and a single drain, there are two separate bowls with two separate drains.
The front bowl is designed to catch the urine portion. In this bowl there is generally a
very small amount of water (.1 l/flush) that is used for flushing. There is a dedicated
flushing mechanism that is distinct from the mechanism for flushing the back bowl,
which is intended for fecal matter. The back bowl is very similar to a conventional toilet
and is usually plumbed into an existing sewer system.
Urine diverting systems only capture urine, while allowing feces to enter the
wastewater stream. This is an improvement over conventional systems from an
environmental and economic standpoint because, as discussed previously, urine contains
a much higher percentage of the available nutrients. Keeping the nutrients in urine from
entering the wastewater stream reduces the load that conventional WWTPs must handle.
From a water conservation standpoint, there is also a significant savings in water over a
conventional system, as typical urine separating toilets use only one tenth of a liter per
flush (.1 l/flush) of water to flush the urine bowl, as opposed to four to six liters per flush
29
for a conventional toilet (codes for water use by conventional toilets vary by location and
only apply to newly installed toilets) (Vinnerås & Jönsson, 2002). In some toilets no
water is used for flushing urine.
There are several methods used for relaying the urine to storage or treatment
facilities. The most obvious is to use gravity to simply transport pure urine to a storage
tank. Some toilets also add a small amount of flush water to the urine portion to aid in
flushing. This makes the toilet function better and helps to meet the objective of reduced
water consumption. There are many proprietary designs on the market that employ
various valves and mechanisms to assist in flushing, odor control and reduction of
precipitation and flocculation of urine in pipes. The Aquatron® is one such example of
the myriad devices appearing on the market. This product allows the use of a
conventional flush toilet, but allows the feces and urine/water portions to be separated. In
this case the urine and about 98% of the water are diverted into a separate holding tank
via an apparatus that operates on gravity and centrifugal force. The water/urine portion
may enter a standard leech field or be stored as irrigation water. The feces are diverted to
another holding tank for treatment by composting or vermiculture.
Treatment Technologies
Although UD toilets are useful for capturing nutrients, in most cases they must
still be connected to a system that allows for the collected material to be sanitized in
some way prior to use. Urine from a healthy individual is theoretically free of pathogens.
However, in many cases it is not prudent to assume sterility and measures should be
taken to ensure the safety of urine to be applied for agricultural purposes. This is because
30
source-separated urine may be contaminated by fecal matter at the toilet. It is also the
case that some pathogens, such as Salmonella typhi and S. paratyphi, Salmonella strains
associated with typhoid fever, and Schistosoma haematobium, may be passed through the
urine of an unhealthy individual (Vinnerås, Nordin, Niwagaba, & Nyberg, 2008). Feces
may contain any number of enteric pathogens and bacteria. Additionally, while excreta
are generally very low in pollutants such as heavy metals (Jönsson et al., 1997), in many
societies they may contain high levels of micropollutants. The following are some
potential methods and technologies for ensuring that excreta may be used safely.
Storage
The most straight-forward method of sterilization for pure urine, and the only
method to have been used on any scale outside of laboratory experiments (Maurer et al.,
2006) is to simply store the urine for a period of time prior to use. Length of storage
time, pH level and temperature “are the critical factors affecting the survival of different
enteric organisms” (Chandran et al., 2009). For many of the pilot projects underway in
Sweden, storage has been the chosen method of hygienization. It is generally recognized
that urine stored at 20°C for six months may generally be considered safe to use for
agricultural purposes (e.g. Drangert, 1998 and Maurer et al. 2006).
The risk of urine-oral transmission of such bacterial infections as mentioned
above is significantly lower than the risk from fecal-oral transmission. This is because
most bacteria in urine are inactivated even after a relatively short storage time (Chandran
et al., 2009). Chandran et al. (2009) studied the survival of enteric organisms (S. enterica,
E. coli, and Ent. faecalis) and the coliphage MS2. The study sought to determine the
31
survival rates at temperatures relating to temperate (15°C) and tropical (30°C) climates.
The authors found that all of the micro-organisms and the virus survived for less than one
week in urine stored at 30°C, at a pH of around nine. Thus, in warm climates, relatively
short storage times are necessary. At 15°C, a temperature deemed representative of
temperate climates, the study found complete die-off after nine weeks.
Vinnerås et al. (2008) also found temperature to be important to the die-off of
studied micro-organisms and viruses, but also examined control samples with varying
temperatures, but no ammonia concentrations (and therefore low pH). The same study
“confirmed that the temperature works synergistically with NH3 when threshold
concentrations are reached.” The study found that above 34°C, and with ammonia
concentration of 40 mM, all micro-organisms and viruses studied showed rapid mortality.
However, below 20°C, the study reports that “there ought to be restrictions on the use of
urine as a fertilizer for food crops.” These studies indicate not only that temperature plays
an important role in the time it take for urine to become sterile, but also that the pH of the
urine also plays a role. According to this research finding, it can be assumed that in
cooler climates it may be necessary to add supplemental heat to storage tanks and/or
place storage tanks in relatively warm locations such as underground parking garages if it
is desired to use the urine within a shorter timeframe than mentioned by Maurer et al
(2006).
Storage of urine presents several potential limitations. First, with long storage
times being required in many cases, large volumes of storage are required. While it is
quite conceivable for an individual household to store sixth months’ worth of urine on
site, it would be much harder to imagine a storage tank to contain all of the urine
32
produced in six months by the tenants of a high-rise apartment building in a large city.
Hence, space considerations may be a limiting factor for storage as a method of
sterilization.
From a nutrient recapture perspective, storage tanks also may suffer from
excessive nitrogen loss due to ammonia evaporation if they are left to vent to the
atmosphere (Maurer et al., 2006). This problem may be alleviated by making the stored
urine more acidic. This can be accomplished by dosing the storage tank with a
supplemental acid as described in the next section.
Acidification
As mentioned previously, the addition of a strong acid can help to reduce loss of
nitrogen by ammonia evaporation from urine storage tanks. The reduction in nitrogen
losses is attributed to a reduction in ammonia produced. Under normal circumstances,
shortly after leaving the body, pH levels in stored urine rise as urea undergoes chemical
decomposition by hydrolysis to eventually form ammonia gas, which, given a pathway to
the atmosphere, easily evaporates. Hellström et al. (1999) found that a one-time dosing of
60 meq of sulphuric or acetic acid to experimental 10 l cans of urine was sufficient to
substantially inhibit the decomposition of urea to ammonia.
Acidification may also serve to sterilize stored urine. At a low pH, many bacteria
are rendered unviable. Additionally, high pH levels may have a positive impact on
pharmaceuticals found in stored urine. Maurer et al. (2006) report that Butzen et al.
(2005) found an inactivation level between 50-95% for various antibiotic and antiinflammatory drugs.
33
Evaporation
The reduction of nitrogen losses to ammonia evaporation by techniques such as
acidification may be most helpful due to their role in other volume reduction strategies.
In some areas of the world, for example, around many major cities, the cost of
transporting large volumes of relatively heavy liquid urine to outlying agricultural lands
will preclude the use of urine directly in agriculture. There are several methods for
concentrating the nutrients in separated liquid urine and thereby reducing the volume and
weight of the finished product.
Evaporation of the liquid is one obvious method of volume reduction. Potential
issues with evaporation are energy use, loss of ammonia (and thereby valuable nitrogen)
due to evaporation (Maurer et al., 2006), and sterilization. Evaporation does not, by itself
provide any sterilization. However, if heat is applied to speed evaporation, the storage
time required to sterilize can be reduced. Energy consumption can be minimized by
employing energy recovery systems and losses due to ammonia evaporation can be
minimized by acidifying the urine (Maurer et al. 2006 and Hellström et al., 1999).
Although there are situations where evaporation may make sense (e.g. dry warm
climates), it is likely not a feasible method for large-scale volume reduction of urine for
nutrient reuse. This is due in part to the potential nitrogen losses associated with the
practice. Also, the large surface areas required to allow efficient water loss may preclude
this as being a sensible concentration method in many locations.
34
Freeze/thaw
The repeated freezing and thawing of collected urine is another potential means of
volume reduction. Studies have shown a concentration of 80% of nutrients in about 25%
of the original volume (Maurer et al 2006). This method could potentially be used in
certain climates if systems could be devised to recycle the inevitable heat that is
produced/consumed by this system. If virgin energy is used, the energy inputs to this
system would likely render this process cost prohibitive.
Struvite production
Another method of volume reduction and means of capturing nutrients in urine,
especially phosphorus, is to facilitate the formation of the precipitate magnesium
ammonium phosphate (MgNH4PO4∙6H2O), also known as struvite, MAP, and AMP
(Maurer et al. 2006). Precipitation of struvite requires a molecular ratio of
1(Mg2+):1(NH4+):1(PO43-) (de-Bashan & Bashan, 2004). The precipitation generally
requires the supplementation of Mg, “usually in the form of MgO, Mg(OH)2, MgCl2, or
bittern (a magnesium-rich brine from table salt production)” (Maurer et al. 2006).
Finished struvite is a dry, granulized product that is very similar in appearance to
conventional fertilizer.
Struvite is a very promising means to produce an effective fertilizer product as
well as a method for limiting the release of plant nutrients and other pollutants into the
environment. Lind et al. (2000) added MgO to fresh and synthetic urine containing 0.5 g
P/l at a Mg:P ratio of 1.71:2.21. The resulting struvite (and other minor mineral crystals)
35
resulted in the concentration of considerable percentages of available micronutrients as
well as 100% of available phosphorus.
Struvite offers several major advantages as a means of volume reduction/nutrient
concentration, sterilization, purification, and fertilizer production. From a nutrient
recycling perspective, struvite provides a means of capturing phosphorus in the form of a
slow-release fertilizer that has considerable market potential (Maurer et al. 2006).
Because ammonium generally exists in urine at higher ratios relative to phosphorus,
phosphorus recovery rates can be quite high (Ganrot, Z. et al., 2007). Some nitrogen and
potassium, along with myriad other plant micronutrients have also been shown to be
absorbed into struvite crystals (Lind et al., 2000).
Struvite production may also have the major benefit of removing the majority of
micro-pollutants from urine. Escher et al. (2006) find that struvite production, “due to the
formation of very clean precipitates,” removes 97% (±2%) of pharmaceuticals, and 98%
(±2%) of estrogens. Ronteltap et al. (2007) confirm this research, finding that around
98% of tested hormones and pharmaceuticals remained in solution after struvite
precipitation. Thus, as the micro-pollutants become highly concentrated in a solution with
a volume much reduced from the original. Presumably, as technology advances process
could be made to continue to further remove the micro-pollutants from the remaining
contaminated water so that they could be disposed of in a responsible manner. Regardless
of whether the struvite is destined to be used in agriculture, a strong argument can be
made for urine separation and subsequent struvite precipitation if for no other reason than
to remove micro-pollutants from the wastewater stream.
36
The fate of pathogens in struvite precipitated from urine is also of vital concern if
struvite is to be used in agriculture. Decrey et al. (2011) performed a comprehensive
study of a human virus surrogate (phage ФX174) and the eggs of helminth Ascaris suum
to determine the effect of struvite precipitation on pathogens found in urine. The presence
of the virus was reduced by 1000-fold. Inactivation was fastest at high temperatures (20
and 36 °C) and low relative humidity (35%). Struvite precipitation had the opposite effect
of concentrating the Ascaris eggs to levels 100 times higher than the urine. Over the
three day testing period, only drying at temperatures of 35-36 °C had any appreciable
impact on egg inactivation. This study shows that a prudent and conservative approach to
using struvite in agriculture would require some form of drying treatment after
precipitation to limit the potential for pathogens to survive in struvite. Further study is
needed to determine what level of pathogen survival can be considered safe and also the
survival rates of those pathogens once they reach agricultural soils.
Zeolite adsorption
“Zeolites are natural crystalline aluminosilicates. They are among the most
common minerals present in sedimentary rocks. Zeolites occur in rocks of diverse age,
lithology and geologic setting…” (Ramesh et al., 2011). Zeolites have many uses for
agricultural and environmental engineering purposes. Among the possible applications
and benefits of zeolites are: promotion of crop growth due to enhanced nutrient use by
plants, acting as carriers of fertilizers, insecticides, fungicides and herbicides, and to
inactivate heavy metals in soils (Ramesh et al., 2011).
37
Research from Lind et al. (2000) indicates that zeolites may also be used as a
means to capture ammoniacal nitrogen from urine. The zeolites Clinoptilolite,
wollastonite and a mixed zeolite were added at a rate of 0.5 g/25 ml of synthetic urine
and NH4Cl solution. Variables included grain size of adsorbent, type of adsorbent,
concentration of NH4Cl and urine, and contact time of adsorbent to solution. The results
indicate that 50-80% of available nitrogen adsorption is possible using these methods.
Clinoptilolite, the NH4 specific zeolite, showed the best results.
In addition to the separate study of zeolite adsorption of nitrogen from urine, Lind
et al. (2000) also investigated the combined effect of struvite formation and zeolite
adsorption. Zeolite varieties were added to urine samples at the same time as MgO and
also to the supernatant resulting from struvite precipitation. The data generally show very
positive results with respect to nutrient recovery. The highest rate of nitrogen fixation in
struvite and adsorption (80% of available N) occurred when Clinoptilolite was added at
the same time as MgO.
Composting
In systems that do collect feces, fecal material must be treated with additional
caution, as it is much more likely to contain significant levels of enteric pathogens than is
urine. Depending on the region and relative health of the population producing the feces,
these can include bacteria such as E. Coli, viruses, protozoa, and helminth eggs.
Composted feces should generally be considered safe to use as a fertilizer source once it
has maintained a temperature of 55-60°C for several days (Heinonen-Tanski & van WijkSijbesma, 2005). This composting may take place at centralized composting facilities or
38
within toilets that are designed for such a purpose. The World Health Organization
suggests pasteurization at 70°C for one hour (Winker et al., 2009). In all cases where
human excreta are to be used as a source of fertilizer, the product should be tested in
region-specific manners prior to use to ensure that it is free of pathogens that may
otherwise be introduced into the food supply.
Ecological sanitation
Ecological sanitation, or EcoSan, is a term that has been used to describe
integrated sanitation systems that not only treat human excreta, but also allow for the
reuse of nutrients. Harada et al. (2006) detail one example of an ecological sanitation
system that is commonly employed in rural and peri-urban regions of Japan, a country
with a strong history of collecting and recycling human excreta into agriculture as “night
soil”. According to the authors, about 30% of the population in rural and peri-urban
areas uses systems similar to the one described.
In this situation, urine separating dry toilets are used in households, where the
diverted liquid and solid portions are collected and stored. Holding tanks are periodically
pumped by vacuum tanker trucks. The collected solids are mixed with other sources of
organic waste and (potentially) livestock excreta. This mixture then enters fermentation
chambers, often referred to as biodigesters. The fermentation treatment can be split into
thermophilic digestion (50-55°C) and mesophilic digestion (35-40°C). These processes
break down the organic material in an anaerobic environment and produce methane
(natural gas), which can be used to fuel the vacuum trucks and for providing heat for the
digestion process. The thermophilic digestion process alone, which typically is 16+ days,
39
may be enough to disinfect pathogens, although the authors assert that performance
testing should be carried out for varying systems. Fermented sludge can also be either
composted, as referred to previously, to ensure its safe use as an agricultural input, or be
incinerated.
The separation of urine has several distinct benefits. From the context of methane
production, the separation of urine is vital. Urine contains high amounts of urea, which
quickly converts to ammonia once outside the body. Because methane fermentation is
inhibited by such high concentrations of ammonia (14,000-35,000 mg/l of urine), the
separation of urine is a necessary step in the process.
Agricultural Reuse Technology
Many studies have shown that human urine can be used directly on fields as a
quality fertilizer (e.g. Heinonen-Tanski et al., 2007). As urine is a liquid, it is already in a
form that existing agricultural equipment is capable of handling. Direct use of urine
conveniently can be done using existing agricultural implements. However, as with all
fertilizer applications, especially if environmental considerations are to be made, it is
important to apply urine in a matter that ensures that the plant nutrients will be delivered
to the soil in a way that minimizes nutrient loss and encourages plant uptake.
Consequently, urine should be applied in a manner that reduces the evaporation of
ammonia, such as injecting it into a covered furrow 1-4 cm deep, spreading during the
evening, and just before rains (Heinonen-Tanski & van Wijk-Sijbesma, 2005). Ideal
rates of application depend primarily on the crop being fertilized, the region, and the
locale-specific nitrogen content of the urine supply (Heinonen-Tanski & van Wijk-
40
Sijbesma, 2005). Application of urine also should be timed so that the nutrients are
available at the time that crops are most able to absorb them (i.e. only during the growing
season). Products such as struvite and zeolite fertilizers will need to be applied in a
manner that takes into account their specific nutrient release characteristics. For instance,
Ganrot et al. (2007) show that timing of application of struvite and zeolite fertilizers may
have an impact on the growth rate of plants due to the slow release nature of these
fertilizers.
These dry fertilizer products produced from urine such as struvite and zeolites
may benefit from the fact that they are similar in appearance and application procedure to
many of the pelletized fertilizer products that are already common within agriculture. On
the other hand, spreading raw liquid urine is also a rather simple task that can easily be
accomplished using readily-available farming implements. However, while the ease of
application and ability to fertilize crops is similar for these two fertilizer products, their
rates of adoption may be expected to differ. While the functional ability of the above
referenced technologies' abilities to perform their intended purposes are vitally important
to their being implemented, the willingness of the public to purchase and use the
technologies depend on much more than the products' abilities to perform. The
perceptions and cultural mores around reuse technology will be discussed in the
following chapter.
41
Section 4- History of Nutrient Reuse: Shifting Perception
Angyal (1941) notes that when people are asked what they find disgusting, there
is near-universal agreement among respondents that excreta is the most disgusting subject
they can think of. This author further notes that the progression of disgusting experiences
exists. Being in the presence of excreta is a somewhat disgusting experience according to
those surveyed. The more intimate experiences of having excreta on ones clothes and
getting it on one’s skin are progressively more disgusting experiences. Having excreta in
one’s mouth and then even ingesting them are cited as the most disgusting possible
experiences that were cited. This pattern has been replicated in more recent clinical
studies (e.g. Simpson et al., 2007). Given the results of these studies it would be expected
that some people respond with disgust at the idea of using excreta to produce food.
However, this certainly has not been the case throughout much of human history.
In fact, methods of using human excreta as resources have a well-documented precedent.
In many parts of Asia, especially China, Korea and Japan, human excreta, known as
“night soil,” have been applied to agricultural fields for thousands of years and continue
to be applied to this day (although as western mentalities encroach on the traditional, the
practice is declining somewhat). The practice of using human excreta to grow food crops
also has deep historical precedence in Europe. It was common practice until the middle
of the twentieth century (Heinonen-Tanski & van Wijk-Sijbesma, 2005). In fact “water
toilets were not first accepted in some Nordic towns in about 1900, the main argument
against them being that agriculture would lose its resource for fertilization” (HeinonenTanski & van Wijk-Sijbesma, 2005).
42
In addition to agricultural activities, urine has been used for many other purposes.
For instance urine was used to launder clothing by the Romans and the Celts, and in
medical practices in India (Bracken et al., 2007). The use of urine in agriculture and
other sectors of the economy actually led many individuals to the lucrative business of
actively seeking out sources of excreta by engaging in such ventures as managing public
toilets and contracting with households to collect the valuable resource (Bracken et al.,
2007).
Despite the obvious acceptance of human excreta as a resource in humanity’s
relatively recent past, attitudes shifted over the previous two centuries in many parts of
the world. Fewer and fewer societies actively recognize human excreta as a useful
resource and modern water-based sanitation systems preclude the recovery and reuse of
the material. The currently pervasive belief, especially in western cultures, is that human
excreta are disgusting “wastes” that must be disposed of. Drangert (1998) describes this
shift in attitudes as “urine blindness.” The term is defined as a general consideration of
urine (specifically) not as a resource, but rather as a smelly mixture with feces. Jenkins
(2005) regards “fecophobia”, an “irrational fear” of human excreta perpetuated by
sanitation experts as the cause of the trend away from the recovery and use of human
excreta.
Bracken et al. (2007) outline four reasons to more fully explain the shift away
from systems that allow the capture and reuse of human excreta. The first explanation is
that the systems required for collecting and reusing human excreta presented
insurmountable logistical and public health challenges in many cities as populations
exploded and the volume of material to be dealt with dramatically increased during the
43
last century and a half. Second, the widespread misunderstandings regarding the
mechanisms for the spread of disease contributed to the notion that human excreta should
be disposed of in the waste stream. The miasma was one such notion that falsely
proposed that illness was caused by the inhalation of volatile substances. Because bad
odors were considered to be the cause of illness, it followed that bad-smelling things
were to be gotten rid of. Increasing prevalence of piped domestic water during the
nineteenth century is the third reason cited for the shift away from nutrient collection
simply because it allowed for a sewer system based on flushing toilets to become
possible. Bracken et al. (2007) cite the resulting dilution of the nutrients caused by
water-based sanitation systems as the final factor that made the capture and reuse of
human excreta-derived nutrients nearly impossible. The arrival on the market of cheap
synthetic fertilizers during the twentieth century rendered “efforts to recover and reuse
the nutrients and organic material from the large volumes of sewage completely obsolete”
(Bracken et al, 2007).
The research referred to above indicates that there are major psychological
hurdles that must be overcome if urine separating technology is going to become socially
feasible, especially in industrialized countries. The broad trend over the last century has
been toward a throughput pipeline in the agricultural and sanitation sectors. Plant
nutrients have been seen as one-time-use resources that are to be used just one time and
then discarded after they are consumed by humans and enter the wastewater stream. At
that point, they in fact become a pollutant that the wastewater sector must clean up and
remove before the water can be returned to the environment. This mentality has spread
not only to the professionals who make decisions regarding the structure of the system,
44
but it has also become commonly accepted by the general population to the point that it is
not even thought about. The ability to just “flush and forget” has allowed societies to do
just that.
Several studies have been carried out to consider what factors are important in
shaping attitudes regarding the collection and potential reuse of human excreta. The
studies provide insights regarding public perception of UD technology. Given the
dominance of the existing paradigm, these studies find surprisingly high acceptance of
UD technology and also of the idea of recycling nutrients from human excreta to
agriculture. However, they also show that many people have reservations about of safety,
convenience, and other issues.
Leinert and Larsen (2009) compiled and sorted a literature review of 75
publications regarding 38 pilot projects and studies on the acceptance of urine separating
technology in seven European countries. Eighteen of the studies were from private
homes, 15 came from “institutions and exhibitions”, and five surveys considered farmers’
opinions of UD technology and the use of human excreta as a source of fertilizer. Survey
categories included topics such as general acceptance of the concept of ecological
sanitation and UD technology, perception of the technology, and acceptance of fertilizer
from human excreta. Some of the data from these studies pertaining to the acceptance
among different groups of people of both the technology and the idea of nutrient reuse
are outlined below.
45
Perceptions Regarding Reuse Technology
In contrast to conventional sanitation systems in which individuals are able “to
adopt an out of sight, out of mind attitude” (Burkhard et al., 2000), the relatively
decentralized technologies that are necessarily involved in urine separating systems
require some level of involvement from end-users. Hence, inquiry was made about users’
experiences with urine separating technology. Overall acceptance of the idea of UD
technology was quite high at 84% (±13%). When asked about using UD toilets at their
workplace or in public buildings, 79% (±4%) responded favorably. There was an equally
high acceptance (79% (±13%)) of using a urine separating toilet at home.
Likewise, the overall perception of the technology was positive. The design was
approved of by 79% (±11%). Eighty five percent (±9%) were satisfied with the hygiene
of UD toilets. The comfort of the toilets was also rated quite high, with 85% (±11)
approving. There are some areas where improvements can be made regarding the design
of urine separating toilets. “Cleaning was judged more laborious, with only 52% (±17%)
finding it equaled conventional toilets” (Leinert & Larsen, 2009). Respondents in many
studies reported blockages (due to precipitate crystals) in urine drains. Many users also
found issues with flushing toilet paper. The small amount of water used for the urine
bowl is often not enough to flush toilet paper. The studies found that users found that
using the large flush on the back bowl was a solution to this problem. However, this
completely negates the desired water-saving effect of the technology (Leinert & Larsen,
2009). This concern will either require a redesign of the toilet, or perhaps a change of
behavior on the part of the user, such as disposing of toilet paper used after urinating in a
trash can or in the feces bowl without flushing. The study found that 49% (±20%) of
46
users would be willing to take such actions. Other issues noted regarding the design and
function of the toilets were that both sexes must sit to urinate and the smell associated
with the toilets.
Perceptions Regarding Nutrient Reuse
Certainly acceptance of the technology itself is an important aspect if urine
separation is to be implemented. If nutrient reuse is also a desired outcome, society will
also need to accept food grown from nutrients derived from urine. Research into this
subject also yields somewhat promising, and perhaps, surprising results.
When asked about their opinion of using human excreta to grow food, the public
opinion was found to be quite high, with 85% (±13%) finding it to be a “very good idea”
(Leinert & Larsen, 2009). A study conducted in Switzerland by Pahl-Wostl, Schönborn,
Willi, Muncke, and Larsen (2003) echoes this finding, with 80% stating that they would
prefer vegetables grown with a urine fertilizer over those grown with artificial fertilizer.
However, a strong concern about pharmaceuticals and hormones entering the food supply
was also voiced. Pahl-Wostl et al. (2003) found that “citizens requested absolute
certainty that potential threats to human health could be excluded for using urine-based
fertilizer.”
Farmers were more skeptical of urine-based fertilizers than the general public.
Although “50% (of farmers) regard urine fertilizer as a good idea…only 34% would use
or purchase it” (Leinert & Larsen, 2009). Lack of a need for a new source of fertilizer,
ecological concerns (e.g. heavy metal and micro-pollutant contamination), fears of
47
liability, smells and concerns about consumer acceptance were among the reasons
provided for their skepticism.
Obviously, these studies reveal only the acceptance and perceptions of a European
sample of the world population. As such, the results are likely not representative of the
global population. Some cultures will be more inclined to accept urine separation and
nutrient reuse than others. However, this research does indicate that, at least in some
cultures, there is considerable tolerance of the idea for nutrient reuse from urine, despite
the general aversion to the excreta from which the nutrients are derived.
It is also of interest that the idea of nutrient reuse is gaining traction in the
wastewater sector. As Mitchell (2011) notes “this year’s International Water Association
Leading Edge Technology conference, held as part of Singapore International Water
Week that attracted up to 10,000 delegates from across the globe, opened with a
workshop explicitly focused on carbon and nutrient recovery.” Further evidence of a
shifting paradigm in wastewater management is seen when wastewater industry groups
such as the Water Services Association of Australia makes statements such as “Given the
need to maximize the efficient use of recycled water, it is highly likely that the days of
extending sewage collection systems over ever- increasing distances to be connected to
coastal sewage treatment plants are coming to an end” (Water Services Association of
Australia, 2009). Further interest in more fully integrating systems is obvious in the
pursuit of urine separating systems already noted in European countries (e.g. Germany,
Sweden, Switzerland and Denmark). Hence, it seems that the concept of nutrient reuse
from human excreta faces no inherent problem with attitudinal feasibility. However, there
48
are major psychological and technological hurdles that will have to be overcome before
the broader society will accept the practice of nutrient capture from excreta.
49
Section 5- System Comparison and Analysis
There are many ways that a technology can be judged. Ultimately, the technology
must effectively perform the task that it is designed to perform. Additionally, though, the
technology can be judged based on its ability to perform a beneficial task compared to the
negative consequences that stem from its use. Thus far, a description of the pertinent
attributes of conventional and UD sanitation systems has been provided so that a
comparison can be drawn between the two technologies and a determination made about
whether the less common technology (UD systems) can feasibly replace ubiquitous
conventional sewer-based systems.
Both systems have been shown to adequately and effectively provide for their
primary intended use: to limit human contact with excreta and to handle excreta in a
sanitary manner to prevent potential health impacts. However, when directly compared to
conventional systems, there are many reasons that make UD technology a very attractive
alternative technology. Some of the metrics that have been brought up previously will be
considered in this section for the purpose of drawing a direct comparison. Also
considered are some of the barriers that remain with regard to the implementation of UD
technology.
Urine diverting technology vs. conventional sanitation systems
As noted in section two, there are multiple significant challenges facing the
existing modes of handling human excreta. While there are ways that the existing system
can be repaired, many of the issues stem from the inherent essential design and logic of
50
the systems. Given the changing world, a growing body of knowledge indicates the
possibility that a more sensible investment will be in the employment of new
technologies that more directly meet the emerging needs of coming centuries.
Urine diverting systems, and other less-centralized alternative systems, show
much promise for being used to mitigate the noted problems of high net energy use,
extensive water consumption, high costs of operation and maintenance, and excessive
environmental pollution. In addition to the ability to reduce the demand for some
resources, these systems also offer a means of recapturing and reusing other valuable
resources.
Energy Use
Urine diverting technology offers the potential to reduce energy consumption
because a potential for resource conservation exists both from reduced inputs for
sanitation and also by providing a nutrient resource. For instance, in a study carried out
by Magid et al. (2006), the potential energy savings of several urine separating systems
were compared to a reference conventional sewage treatment system in the medium-sized
town of Hillerød, Denmark. All energy inputs/outputs in the model were normalized to
kWh equivalents. For each of the 12 systems analyzed, the study used a simple equation
that concludes that for either a conventional or alternative system:
Energy consumption = (Fertilizer savings + Water savings) – (Transport energy)
51
In the case of the reference (existing) system, per capita annual energy
consumption for treating household wastewater was figured to be 7.3 kWh. It should be
noted that it is entirely clear in the study that the accounting of energy cost for the
reference system actually includes the energy required to grow the food that ultimately
produced the nutrients being handled by the system. If that energy use was not included,
the actual energy use of the system should be somewhat higher. Additionally, the
transport cost seems to be assumed at zero. A true lifecycle cost of using drinking water
for flush water could arguably also include some cost for initial treatment of the water.
However, the authors note that conservative assumptions and estimates were made with
regard to the costs of the conventional system so as not to overly inflate the indicated
potential savings from the experimental systems.
With the exception of an experimental system that relies only on wet composting
of combined excreta and household organic matter (with mechanical aeration systems) all
of the experimental systems had at least better energy consumption characteristics than
the conventional reference system. In most cases the experimental systems actually
produced more energy than they consumed. For instance, in a system that separates urine
and feces from greywater, combines the excreta with other household organic material
prior to treatment at a biogas plant, and then re-circulates the nutrients into agriculture, a
net energy production of 118 kWh/person/year was estimated. For a system that consists
of only urine collection and reuse, a more modest energy savings of around 20
kWh/person/year was demonstrated, with the savings resulting from not only the
reductions in energy used for treatment, but also from energy savings from reduced
synthetic fertilizer use. Although this study was necessarily based on some predictions
52
and assumptions, it suggests that such systems warrant investigations for future, largerscale, cost effective implementation.
This study, though, is also illustrative of the difficulty in developing a generalized
comparison of UD systems and conventional systems. For instance, as mentioned above,
it matters greatly if methane gas production is included in the overall system energy
balance. Also, the distance that recovered nutrients are transported will have a large
impact on energy use. If methods of nutrient concentration such as struvite production are
employed, the energy cost to transport goes down dramatically due to the smaller volume
and lighter weight of the product. However, in cases where direct comparisons have been
done (see also e.g. Wilsenach et al., 2006 or Tidåker et al., 2005) it appears hopeful that
UD technologies can compete as more energy efficient alternatives to conventional
systems. Given the newness of the technology, the systems also have much room for
improvements, leaving room for increased efficiency gains.
Water consumption
Fresh water is another resource that is heavily relied upon by sewer-based
sanitation systems. While there are ways to reduce the rate at which fresh water is cycled
through the system, such as low-flow toilets, and using rainwater as the flushing medium,
it is impossible to even come close to eliminating the use of fresh water because of the
inherent design of sewered systems. UD toilets, by comparison, represent a technology
that could potentially virtually eliminate the use of fresh water in sanitation systems.
It is true that UD systems that capture only the urine portion will only conserve
the portion of water that would have been used for flushing urine. Considering the fact
53
that most individuals use the toilet for urinating around three to five times as often for
urinating as they do for defecating, there are significant savings to be made by simply
conserving this portion of the flush water, even if system design involves flushing solids
into a conventional sewer-based system. There are potential technological barriers for UD
technologies, though. Some of these barriers relate to the technologies themselves, while
others have more to do with the way that human operators use the technology.
With any evolving technology, it can be expected that earlier versions will exhibit
more operational problems than later ones. Generally speaking, the technical problems
most commonly reported in relation to UD technology concern the ability to flush and
odor/appearance issues. Many of these problems are related to floc accumulation in
plumbing lines that results from the precipitation of the myriad minerals that are present
in urine. As these precipitates form in the plumbing, they can cause the improper flushing
and also potentially bad odors. Some models of toilets that use a small amount of water to
flush, likely because manufacturers aim to limit water consumption, have also been
reported to flush poorly. This may especially be true for women due the fact that they are
accustomed to flushing tissue after urinating. A common solution employed by users and
noted by researchers has been to flush twice. This practice dramatically reduces the
potential water savings of the toilet. Fortunately, as the technology develops, many of
these issues are likely to be engineered out of existence. Additionally, many of these
problems can be avoided in the first place by encouraging different behaviors on the part
of users.
54
Pollution
As discussed in section two, pollution of ground, surface, and marine waters
downstream of conventional treatment plants is a major problem. Significant threats to
human health and negative economic impacts are the result of conventional systems'
designs and limitations. Urine separation presents a major opportunity to limit the
negative consequences to human and environmental health, two factors that, many would
argue, are inextricably linked.
Urine separating toilets remove the vast majority of primary plant nutrients from
the wastewater stream. Once the nutrients are removed, they may be more easily treated,
concentrated and recycled into agriculture, thereby reducing pressure on other natural
resources and ecosystems. But, even if the nutrients are not to be reused, simply by
separating them from the waste stream, a major pressure is removed from the
conventional treatment system. Although there are still costs associated with the handling
of separated urine, the dramatically reduced and concentrated volume is easier to handle
and could potentially represent a significant economic benefit by reducing the work load
of WWTPs (Wilsenach et al., 2006 and Berndtsson, 2006).
The economic benefit of reducing pollution by plant nutrients in aquatic
environments and groundwater aquifers could be quite substantial. Improved functioning
of fisheries, improved biodiversity, increased recreation opportunities, improved drinking
water quality, and reduced human health impacts are but a few of the benefits that could
be claimed by reducing the levels of anthropogenic plant nutrients that are introduced to
the environment.
55
In addition to an often incomplete removal of plant nutrients, as mentioned
previously, conventional treatment systems have no means by which to deal with the
recently recognized issue of micro pollutants. The direct, and possibly synergistic, effects
of hormones and pharmaceutical residues found in wastewater are not completely
understood. However, as mentioned in previous sections, the data collected thus far
indicate that there are substantial negative environmental, human health, and economic
impacts that are resulting from water pollution by micro pollutants. By removing urine,
and the micro-pollutants it contains, from the conventional wastewater stream, it becomes
much easier to remove or deactivate the micro-pollutants (e.g. Maurer et al., 2006 and
Escher et al., 2006). In particular, removing micro pollutants from “hot spots” such as
hospitals would be beneficial (Larsen et al. 2010).
As mentioned in the previous section, options are available that offer promising
means of separating the micro pollutant residue from urine and the nutrients that it
contains. Such locations as hospitals and nursing homes represent locations that
potentially offer many strategic opportunities to take advantage of the additional benefits
of UD technologies. In these locations, where heavy investment in infrastructure is
already available and where there is an exceptionally high level of micro pollutant
production, even if nutrient reuse is not the desired end result, simply removing the micro
pollutants from separated urine prior to their release into the environment would
represent a major improvement over the status quo. And this advantage could seemingly
be attained at a reasonable price when all potential costs are factored in to the equation.
56
Cost of Operation and Maintenance
The reasons listed above provide significant reasons why societies might consider
a shift toward alternative sanitation systems. Future replacement of existing sanitation
systems and the provision of sanitation in areas currently lacking it are other
considerations. As discussed in section two, sanitation systems in much of the
industrialized world (specifically in the United States) are aging and in need of major
repairs, renovations or replacement. Given the significant potential advantages of
alternative sanitation systems, investment in the improvement of these technologies could
present a more forward-thinking investment than simply rebuilding the conventional
systems that are already in existence. Also, considering the substantial costs of operation
and maintenance of conventional systems and the potential savings that accrue to society
from the reduction in use of natural resources by UD systems, it is likely that UD systems
can at least be cost competitive with conventional systems.
In fact, a simple search of the internet indicates that a sewer-connected UD toilet
is available for approximately $700 (http://www.ecovita.net/ekologen.html). It is
certainly possible to obtain a simple, moderately water efficient toilet for about a third of
that price. However, when compared to the myriad options for the more stylish and water
conservative commodes, the price is actually very near the conventional competition. In
fact, a search of a common "big-box" building supply store's website
(http://www.homedepot.com) indicates that the cost of the UD toilet is actually cheaper
than many of the fancier conventional toilets. While there are also minor additional costs
associated with UD systems (storage tanks, separate urine drain lines), if UD toilets were
57
to become more commonplace, the advantages associated with mass production would be
expected to make the toilets/systems even more cost competitive.
In areas of the world that do not rely on already-constructed sewer systems, such
as rural regions of Europe and North America, and also many parts of Africa and Asia,
UD systems represent a viable method to provide cost effective and ecologically sound
sanitation (e.g. Meinzinger et al., 2008 and Vinnerås & Jönsson, 2002). Likewise, in
locales where pharmaceutical use is low and there is no existing wastewater
infrastructure, separation and direct use may be feasible. The development of sanitation
systems to allow for the protection of human health all across the world is certainly a
desirable objective. However, on a planet with an ever-growing number of mouths to
feed and a finite amount of natural resources, many consider it foolhardy to continue to
construct sanitation systems based on an outmoded paradigm. Along those lines, even
within societies where centralized sewer-based sanitation systems are available, there are
still countless opportunities to for choices to be made to begin moving away from the
dominant paradigm and toward alternative systems.
Fertilizer resource reuse
Perhaps the most important aspect of UD technology is the capacity it provides to
convert a waste stream into a resource stream. All of the other relative benefits between
UD and conventional systems that have been listed stem at some level from this
characteristic. Conservative estimates indicate that, for example, fertilizer products from
UD toilets could meet at least 10-20% and 20-30% of the demand for mineral fertilizers
in Germany and Sweden, respectively. In sub-Saharan Africa, the quantity of nutrients
58
available from human excreta exceeds the local demand for mineral fertilizer, (Winke et
al., 2009). As noted previously, urine can be used as fertilizer directly or can be
processed into fertilizer products.
Human urine has potential value as a fertilizer. However, there are difficulties in
quantifying the exact value of human urine versus conventional fertilizer. An example of
this can be seen in Berndtsson (2006). In this study, a urine/water mixture was collected
from a UD system in an apartment building on the campus of Lund University in
Sweden. The urine was collected and hauled to a local farm for use as fertilizer. The
nitrogen content of the collected urine was measured for a year. The researchers
estimated that an average of 125 people stayed in the dormitory for about 15 hours per
day. The measured nitrogen and phosphorus collected was 150 kg/yr and 11 kg/yr,
respectively. It was thus assumed that this is the amount of fertilizer nutrients that could
be displaced based on the given parameters.
The basic comparison described above is often as far as many comparisons can be
taken. But, this comparison doesn't tell the whole story of the relative value. As pointed
out by Berndtsson (2006), factors such as heavy metal pollution are not easily quantified.
As noted in section two, in the case of conventional fertilizers, heavy metal pollution is a
growing concern as sources of rock phosphate are depleted. Heavy metal contamination
certainly has a negative financial impact on agricultural fields. As human urine is
effectively free of heavy metals, there is an economic benefit to be gained by changing
the source of the nutrients for use as fertilizer. However, internalizing the value of
reduced heavy metal contamination is an example of the difficulty of comparing not only
59
the value of the quantity of product available, but also the value of the quality differences
between conventional fertilizers and urine-based fertilizers.
Relating to the issues of both quantity and quality of urine-based fertilizers are
growing concerns over the future provision of phosphorus to agricultural systems. The
efficient use of phosphorus will be one of the most pressing challenges of this century
(Cordell et al. 2011). Phosphorus, being an essential element to all life, is a key
ingredient in conventional fertilizers. The worldwide production and consumption of rock
phosphate amounts to approximately 20 million metric tons annually (Cordell et al,
2011). At this rate of consumption, this non-renewable source will become more
increasingly scarce and prices will increase as world markets grapple with "peak
phosphorus" at some point around the middle of this century (Cordell et al, 2011).
Increasing costs of phosphorus will have a direct impact on the ability to provide
adequate food for growing world populations and to do so at a reasonable price. As noted
previously, urine accounts for approximately 50% of the urine in the wastewater stream
(Langergraber & Muellegger, 2005). Therefore, the ability of UD technology to recycle
phosphorus through agricultural systems is a very significant advantage over
conventional systems.
The recognition that wastewater and excreta contain a set of resources (energy,
water, nutrients) that need to be captured and reused, rather than treated as a waste
stream, is not limited only to isolated scientists in laboratories. The promising benefits of
UD technology are beginning to be acknowledged by entities such as wastewater trade
groups. For instance "this year’s International Water Association Leading Edge
Technology conference, held as part of Singapore International Water Week that attracted
60
up to 10,000 delegates from across the globe, opened with a workshop explicitly focused
on carbon and nutrient recovery" (Mitchell et al., 2011). Hence, it is becoming more
widely accepted that urine diverting technology is a viable technology.
The comparisons between UD as an alternative to conventional systems show that
there are indeed potential gains to be made should societies choose to employ UD
technology. However, the implementation of technologies does not depend exclusively
on whether or not they can fulfill their intended roles. The decision has to be made to
employ technologies, and that decision often depends on how society and individuals
perceive of a given technology.
How to Change Perceptions
The importance of the inter-relatedness of technology and perception cannot be
overstated. As has been described, the technology of UD systems is relatively simple, and
the engineering challenges that exist can likely be overcome. However, altering societies’
perceptions and user behaviors will likely be the most difficult aspect in spreading the use
of UD technology.
The four explanations provided by Bracken et al. (2007) and those from Jenkins
(2005) and Drangert (1998), indicate that the trend away from the reuse of human excreta
has been caused in part by fear or other attitudinal barriers, and also to a large degree by
shifts in technology. As has been described previously, there are developing technologies
that could likely be implemented on larger scales than they currently are, especially in
parts of the world where water-based sanitation systems have not been fully embedded as
61
the dominant technology. However, these technologies cannot and will not be put into
practice if societal attitudes do not allow for them.
Harms from existing systems must be known
Part of the reason why alternative sanitation options have not become common is
that it is widely accepted that the existing system does an adequate job at providing
sanitation services. Pahl-Wostl et al. (2003), in a focus group-based survey, noted high
public confidence in the current sanitation system. In many regards the public is correct
in placing its trust in conventional systems. However, as has been widely noted in this
paper and elsewhere, there are major challenges that face the conventional sanitation
system with regards to environmental protection and the protection of human health.
Pahl-Wostl et al. (2003) also found that much of the public perception was based on very
little specific knowledge and that, furthermore, “the average citizen is not interested in a
technology that is invisible and outside the realm of decisions made in daily life”.
In order for the technology to enter the realm of decisions made in daily life,
individuals and public policy makers must witness the implications of the decisions that
are made each day. For instance, in the case of communities along waterways, large-scale
fish kills caused by algal blooms fueled by an over-abundance of plant nutrients from the
local WWTP may start local conversations that may encourage the reconsideration of
piping wastewater into the waterway. Or, as communities face challenges of meeting
their needs for freshwater, the efficacy of conventional sewer systems may come into
question when the need to flush excreta away is compared to the need for fresh water to
drink.
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With regards to the issues of nutrient reuse, the linkage between choice of
technology and end result is not as readily apparent, and so may be a more challenging
point to be recognized. It is easy for the public to quickly grasp the concept that more
toilets flushing leads to more water use and, in turn, if there are fewer toilets flushing
(and more UD toilets) that water conservation could be achieved. However, the fact that
plant nutrients are added to crops via synthetic fertilizer using substantial quantities of
natural resources, food is eaten, excreta produced, toilets are flushed, myriad
environmental problems are caused, and that nutrients are piped out of the system has
more steps and is more difficult for people to grasp. It seems likely that market forces
will most likely be required to encourage adoption of UD technology for the purpose of
nutrient recapture. As prices for fertilizer inputs become more and more costly, it will
become necessary to adapt to meet the needs of food production. Given the need to
provide plant nutrients to grow food, means to obtain nutrients (e.g. UD toilets) will
likely become more widely used.
Reuse must be safe
There are many good reasons why human societies have largely established
varying levels of taboo around excreta. There are, after all, illnesses that are easily
transmitted between individuals via vectors related to sanitation systems (or lack thereof).
Laboratory and small-scale tests have indicated much promise for the potential to develop
technologies that would allow for the safe treatment of separated urine and also for its
reuse. However, in order for these technologies to be accepted, a fear of reusing resources
linked so intimately to human excreta must be overcome.
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An interesting parallel can be seen in relatively new technology of direct
purification and reuse of sewage as drinking water. An example of this technology can be
found in Orange County, California, a city in a region that is already experiencing a
shortage of freshwater. This water treatment plant directly recycles water from raw
sewage through a series of specialized processes. The finished result is purified water that
is safe for human consumption directly from the outflow of the plant. However, although
the Orange County, CA water treatment plant is technically capable of producing clean
drinking water, the public psyche demands that it be pumped to a holding reservoir
before being dispersed to the drinking water system (Royte, 2008).
Hence, technology can provide a means of changing perception, if the technology
can delink the connection between a concern and an end result. For example, in the case
of using human excreta to grow food, it is unlikely in many societies that direct use of
urine will be tolerated even though the practice can be made potentially just as safe as
many currently allowed practices. This is because the primary fear in this case is of
“contaminating” food with excreta. On the other hand, a product like struvite would have
a much higher probability of being accepted. The dry, solid nature of struvite may present
an advantage over other means of reusing excreta. As Angyal (1941) notes, touching a
dry, solid material is much less likely to be offensive than touching a wet, sticky material.
The latter material would be more likely to stick to the skin and cause one to be “soiled”.
Struvite, because it is a dry pelletized product, would be less offensive than a wet product
that is more reminiscent of raw human excreta. In a way similar to the lake water being
more acceptable than directly recycled water in Orange County, nutrients in struvite are
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isolated by a technical process that would likely make the finished product more
acceptable to the public.
Technology must be user friendly
As noted previously, even when a technology operates properly when
manufacturer’s directions are followed, malfunctioning is a possibility when used
improperly by an untrained or careless operator. Hence, the improper use of technology
can cause as many problems as faulty technology. In many cases the perception of the
user of the technology will dictate to what extent the technology is properly used.
Lienert and Larsen (2009) state that “…to be fully accepted, No-Mix (urine
diverting) toilets must reach the high standards of conventional bathroom installations…”
In order to determine the extent to which UD toilets have been able to meet this
challenge, the authors compiled data from 75 publications regarding 38 pilot projects in
seven European countries to determine users’ perspectives of a range of aspects of UD
technology. This literature review reveals many interesting trends. With regard to users’
opinions of UD toilets themselves, many of the respondents found the toilets overall
satisfactory with, for example, 79% (±11%) responding positively about the design.
However, when asked more specific questions, concerns tended to arise. For instance,
only 56% (±22%) found that the flushing equaled that of a conventional toilet. Also, only
52% (±17%) found that cleaning UD toilets was as easy as cleaning a conventional toilet.
These survey results indicate that, at least in societies where conventional sanitation
systems exist, UD technology has much room for improvement to gain a fuller
acceptance among users. Acceptance and understanding of UD technology will have a
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major impact on how well the technology meets its objectives (nutrient reuse, reduced
water consumption, etc.).
Many studies (e.g. Lienert and Larsen (2009) and Berndtsson (2006)) have
indicated that even when users are generally in favor of the technology (urine separation
and reuse in agriculture), they often have incomplete understanding of the details of the
system. For instance among the findings form a survey of UD toilet users in a Swedish
dormitory carried out by Berndtsson (2006) found that while 74% of respondents felt
they knew why the specialized toilets were in use, only 43% felt they knew what
happened to the collected urine. The general response to the concept of the system was
very favorable with 77% responding that capturing urine for reuse was a good idea.
However, nearly half of the female respondents said that they always used the big (feces)
flush after urinating. The authors note that a lack of education regarding a novel
technology, combined with a disinterest in the general topic of sanitation, led users to
improperly use the toilets in a large number of cases. Lack of knowledge and
understanding was also a major factor in poor functioning of the system in this case (only
about half of the theoretically expected amounts of plant nutrients were collected).
The studies cited above indicate that UD technology must not only “work”, but it
must also meet users’ expectations and be simple enough to use that users understand
how to appropriately use the technology. In order to move towards these goals, cultural
norms must be understood and catered to wherever possible. For example, in many
western industrialized countries, it is not customary for men to sit while urinating.
However, many early designs of UD technology virtually required men to sit in order to
direct the stream of urine into the smaller front bowl. As a result, it is easy to predict that
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many men would simply urinate into the larger feces bowl from a standing position and
thereby use an unnecessary volume of water to flush and flush the urine into the sewer.
This sort of conservation defeating behavior will be even more common if users
do not understand how the system operates. This is illustrated in the example of women
who acknowledge using the large flush to flush urine. This problem is likely to be
reduced as the technology becomes more common and users become more accustomed to
using it. It is likely that public ad campaigns, for instance in toilet stalls where UD toilets
may be installed in public buildings, would be very helpful to encourage the
dissemination of technical knowledge within society. Additionally, ensuring that the
proper technology is deployed (e.g. installing UD urinals in men's restrooms in addition
to standard toilets) will also help to ensure that the public utilizes the technology in as
near to optimum a manner as possible.
Existing Technology is Embedded and Obdurate
Despite very compelling arguments to be made for new technologies, often it is
very difficult for new technologies to achieve widespread use. In her work “Unbuilding
Cities: Obduracy in Urban Socio-technical Change”, Anique Hommels (2005) provides
detailed insight into why it is so often difficult to alter the built environment. She claims
that many of the "common sense" explanations for obduracy of human constructions are
often not sufficient. Rather, she provides examples in three different cities to illustrate
three principal reasons for why it can often for the built environment to adapt to a
changing world. The following is a synopsis of these main points from this in-depth study
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of technological fixity with emphasis on the ways that these concepts help to explain the
challenges that are faced by UD technology.
In many ways conventional sanitation systems offer a prime example of the
phenomena Hommels refers to. Although, as has been previously described, technology
is readily available that could meet the requirements for sanitation, ease pressures on the
environment, and provide useful resources to human endeavors. However, the obduracy
of conventional systems will likely make it difficult for alternative systems to be adopted.
Hommels provides three concepts that she feels properly explain why it is
difficult for aspects of cities to be "unbuilt" and new structures built in their place. These
concepts are "dominant frames", "embeddedness", and "persistent traditions". Each
concept applies to and helps to further explain the challenges that UD systems face to
become a viable alternative to conventional systems.
Dominant Frames
Hommels begins her description of dominant frames as: "conceptions of
technology's obduracy that focus on the roles and strategies of actors involved in the
design of technological artifacts" and "highlights the struggle for dominance between
groups of actors with diverging views and opinions" (p. 22). Dominant frames is a useful
concept to describe the paradigms that constrain the thinking surrounding technological
decision making within cities, primarily at the local level. The concept applies both to
designers and users of technologies.
As has been described previously, users of sanitation systems have become
generally accustomed to the idea of "flush and forget". Human excreta is profoundly
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framed as a "waste" that should be gotten rid of. In this case, the meaning and function of
existing sanitation technology are fixed in the public mind as a means by which to simply
remove this waste product.
Likewise, Hommels notes, dominant frames can be used to describe the
"professional worldviews" that limit the thinking of professionals such as planners,
architects, civil engineers, etc. These worldviews impact the decisions that are made.
They dictate what technologies and practices are acceptable and comfortable. Berndtsson
(2006) explains that “The existing technical and administrative infrastructure is to
support conventional wastewater handling. There is neither support nor infrastructure for
the collection, transportation, and use of human urine." Additionally, due to the restricted
worldviews of those who created and maintain the existing system, there exists an
inherent bias which, as Berndtsson notes causes "all extra work, costs and responsibilities
associated with the system (to be) incurred by the owner and user.”
The dominant frames model draws attention to the constructions built according
to the dominant "meaning and values they attribute to technology" (p.36). To illustrate
the resulting obduracy, one could consider a hypothetical situation where a community
has a problem with eutrophication in local bays. This community has been in existence
for centuries, but is now growing faster as people move there as a nearby large city
reaches a capacity and people choose to live farther out of the city and commute in. The
community is located on the coast on a peninsula that causes individual neighborhoods to
be widely spread apart with moderate infilling in between. The low-lying land upon
which the community sits precluded the construction of a sewer-based sanitation system
back when the initial infrastructure of roads, lot layout, etc. was designed. However, it is
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now widely accepted that one major source of the nutrient pollution in the surrounding
waterways are the septic systems that are ubiquitous to the entire community.
As the planners and residents of the community grapple with the problem,
according to the dominant frames concept, they would be strongly inclined to attempt a
massive undertaking of installing a retrofit sewer-based sanitation system. This would be
a massive investment, requiring not only new plumbing to be installed under every street,
but pump stations and a new treatment plant. It seems that this would be a prime
opportunity for the widespread implementation of alternative sanitation systems.
However, acceptance among both designers and users of the proposed technology would
be very difficult due to the conceptual limitations that the dominant paradigm places on
their realities. The conceptions of reality make up a framework that dictates that the
conventional technology remains obdurate and also encourages its continued expansion.
Interactions of social groups and institutions with differing dominant frames could
be another way in which innovation may be quashed. For instance, government
regulations may require certain levels of sanitation from WWTPs based on levels of
existing technology. So, even if a forward thinking city or town created incentives and
encouraged the installation of UD toilets in its boundaries, it still may not reap all the
potential benefits. If this town were regulated by a more rigid and conventionallyinclined state, provincial, national, etc. government, a government body with higher
authority may hinder innovation by requiring a conventional technology (e.g. tertiary
treatment) where it would not otherwise be required to properly remove the already low
levels of plant nutrients from out flowing waters (due to widespread use of UD
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technology). If the town were thus required to invest in this much more expensive
technology, the financial benefits of UD technology would be greatly reduced.
Embeddedness
Embeddedness refers to technological "artifacts" analyzed within social networks.
The concept is an explicit recognition of the co-evolution of society and technology and
that "the technical is socially constructed, and the social is technically constructed"
(p.27). It refers to the relatedness between technologies and other social networks.
Embeddedness "refers to the difficulty of changing elements of socio-technical
ensembles that have become closely intertwined” (p.30).
Conventional sanitation systems are a good example of an embedded technology.
In fact, there are several ways in which the technology is embedded. First, sewer-based
systems are embedded within physical social networks. Plumbing is connected to every
single toilet that is connected to the system. This plumbing is connected to pipes that run
inside buildings' walls, into their crawlspaces or basements, through their foundations,
then under the yard or sidewalk or parking lot adjacent to the building. From there, the
plumbing connects to larger pipes that are buried under networks of streets in every
neighborhood connected to the WWTP. These pipes may be connected to pump stations
and storm water drainage systems. Altering the sewer system at any point represents a
disruption to other social and technological systems.
In addition to being physically embedded within the built environment,
conventional sanitation systems are heavily linked to value-based social systems.
Sanitation systems of any kind represent massive capital investments. Investments in a
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sanitation system represent a commitment to the technology. The more money that is
sunk into the system, the harder it becomes to abandon the investment and thus the more
obdurate it becomes. Thus, when a WWTP becomes under-sized to support a growing
community, a hypothetical city may consider a decision between investing millions of
dollars into a new WWTP, or keeping the original and to begin diverting money into an
alternative system to work in parallel with the existing system. However, this decision is
hardly ever considered in part due to the amount of capital invested into the existing
system.
Persistent Traditions
Choices made in the past and the present continue to influence the future
development and implementation of technologies. The obduracy of socio-technical
artifacts that stem from these choices represent what Hommels refers to as persistent
traditions. It is important to note that persistent traditions is distinct from dominant
frames. Where dominant frames refers mostly to decision making at a localized level,
persistent traditions represent wider cultural views and decisions. Hommels refers to the
concept of "momentum", and notes that as decisions are made in favor of certain
technologies trajectories are set (p. 31). It can then become very difficult to alter these
trajectories.
Such trajectories are not formed at such a local level as in the case of dominant
frames. Rather, they permeate throughout society and become engrained via social
institutions and practices. Hommels refers to the case of the poly-phase electrical supply
system adopted during the 1890s as an example of how traditions become persistent (p.
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31). First, investments were made in this particular supply system, creating a demand for
products that was then met by manufacturers who adapted to make products that met the
requirements of the new system. As momentum grew for the "winning" technology,
educational institutions began to teach students about the new systems and began
churning out workers capable of building and maintaining the expanding infrastructure.
As the system became larger and more ubiquitous, professional trade groups developed
and best practices within the paradigm came to be disseminated in professional journals.
Research institutions aimed at solving "critical problems" help to further perpetuate the
momentum of the existing system and contribute to its lasting obduracy. It is not difficult
to see the parallels between the decisions made on a societal level that led to the adoption
of the electrical grid as we have come to commonly accept it and the decisions that led to
the adoption of sewer-based sanitation systems.
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Section 6- Conclusions
The widespread use of urine diverting toilets would represent a radical departure
from the conventional system in that it would require a much less centralized approach to
the handling of human urine. The trend for the last century in many realms, especially in
the United States and other industrialized countries, has been towards centralized systems
rather than away from them. The production of electricity is a prime example: rather than
opting for building- or neighborhood-scale production of electricity, choices have been
made that ensure that electricity largely comes from city- or regional-scale facilities.
There is nothing inherently "wrong" with centralized facilities. In fact, they often
represent a way to increase efficiency of a system. However, just like with the electrical
grid, there are also losses of efficiency (and resulting resource use) that come with
transport to and from centralized facilities. By definition, conventional sewer-based
systems use water as a transport medium. Reduction of water use has to be considered
one of the prime objectives for creating more sustainable societies. However,
conventional centralized, sewer-based systems face a monumental task when it comes to
meaningfully reducing water consumption. Likewise, few options exist that allow for
efficient long distance transport of urine to centralized facilities without using water as a
transport medium. Therefore, if reduction of water use and improved nutrient retention
are to be considered as primary objectives of sustainable sanitation systems, the main
infrastructure of the system will likely need to change and become less centralized. There
is evidence that such changes are already slowly occurring.
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While the trend toward centralization has been the rule for the most recent past,
there is evidence that new ways of thinking are creeping into the existing paradigm. For
instance, the value of on-site provision of a building's needs are coming to be recognized.
The Leadership in Energy and Environmental Design (LEED) rating and certification
system is but one example of rating systems that allows for a comparison of the
environmental sustainability of new and remodeled existing buildings. These rating
systems are becoming increasingly popular and often favor a shift toward
decentralization by encouraging onsite production and collection of energy, food, and
water, and also of onsite handling of waste and byproducts. Since 2000, 9 billion square
feet of buildings have been LEED certified, and an additional 1.6 million are certified
each day (www.usgbc.org, 2011). This trend indicates that building methods and
practices may be starting to shift in favor of decentralized technologies such as UD
systems.
Larsen and Maurer (2011) mention that on-site treatment of industrial wastewater
has long been a commonly accepted practice in the wastewater community. Additionally,
they note that source separation and UD technology are generally accepted within the
field as sensible means by which to provide sanitation to parts of the world that currently
lacks infrastructure. However, they also point to a 1997 issue of Water, Science and
Technology, the publication of the International Water Association, as a specific point in
time when the concept of source separation came to be seen as having potential
applications in the realm of urban, industrialized, residential wastewater treatment. Since
that time they note the abundance of studies that have been produced that address some
the potential benefits of source separation mentioned in this paper (efficient use of
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resources, ability to treat more concentrated streams, micro-pollutant removal). In
addition to highlighting the reasons why such systems are being more widely recognized
as viable alternatives to conventional systems, the authors go on to note that
"decentralized treatment options could become more attractive if treatment technology
for source-separated waste streams becomes integrated into household technology instead
of the prototype wastewater treatment plants that we know today."
Therefore, if UD systems are to become more common, it is likely that more,
smaller storage/treatment facilities would be required to replace the relatively few and
larger facilities that are common to sewer-based systems. Storage and/or treatment of
urine on-site would also be a possible solution. Many truly “sustainable” visions for
future buildings would take this one step further and actually use the nutrients within the
building on roof top gardens, etc. In order for positive changes to (continue to) occur, the
obduracy of the existing system will be challenged.
In order to get around the obduracy of the existing system, UD systems may need
to operate in parallel for some time until investment in the current order can be fully
amortized. This will be possible if the new technology can be installed as new buildings
and developments are constructed. Within new developments of single family homes, it
would be possible to have a semi-centralized storage and/or treatment facility to serve a
neighborhood of homes equipped with UD toilets. Such a system could conceivably
operate via vacuum lines to transfer urine to a holding facility. Alternately, pump trucks
such as those that currently empty septic systems could pass through neighborhoods on a
regular schedule in a similar manner that garbage collection trucks do. If collection is to
be done by truck, minimizing the distance to the treatment facility would be necessary to
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limit energy inputs. Once collected at a neighborhood facility, a volume-reducing
treatment, e.g. struvite production could take place prior to shipping, or materials could
be piped from intermediate storage facilities to larger, regional treatment facilities. From
the regional facilities finished products could be carried by rail or trucked to agricultural
areas. Ideally, as this system evolves, agriculture would also become less centralized. By
infilling urban and suburban land with agricultural land, the distance for fertilizer
products to travel would be greatly reduced.
The use of U.D. systems could conceivably have other, more broad-reaching
environmental, social and economic impacts. For instance, pharmaceuticals may be
produced differently once nutrient recapture becomes a more important goal. The focus
that U.D. systems place on the lifecycles of excreta, nutrients, and pollutants in
wastewater could be cause for the re-evaluation of how pharmaceuticals are
manufactured and the ways that their chemicals move through human bodies and the
environment at large. These changes could make it easier to regulate pharmaceuticals and
to keep them out of the environment.
Perhaps the most important and radical change that would potentially come about
if UD technology were widely adopted would be the re- connection of the human
developers and users of the technology to their environment and the systems that sustain
their lives. As Drangert (1998) notes, the existing "flush and forget" sanitation system in
most industrialized countries falls within the professional realm of water engineers,
physicians, and chemists. This professional involvement has undoubtedly had a positive
impact on public health as water quality throughout the industrialized world has
improved markedly over the last century. However, Drangert (1998) states that these
77
professional groups are also often restrained by their professional training and their
interest in maintaining the integrity of their professional paradigms and have difficulty
"seeing" the larger issues that surround their fields of expertise and coming up with
solutions outside of their limited worldview. So, in addition to the incremental changes
that have already been witnessed in the fields of water and waste management it is quite
likely that, in a world facing ever-changing challenges, new methods and bold new ways
of thinking will need to be brought to bear on the growing problems.
The "sanitize and reuse" option provided by UD systems promote the inclusion of
many more professional groups (e.g. ecologists, agriculturists) and also brings user
groups at least somewhat more in touch with an important stage in the human food cycle.
Encouraging the cooperation of seemingly disparate segments of the economy as
wastewater treatment and agricultural inputs could have rippling effects through the rest
of society. Where a water chemist may be able to easily suggest a solution for removing
nitrogen from wastewater, an agriculturist may be able to assist with considering the
requirements of plants if those nutrients were to be reused as a fertilizer. The resulting
technology would likely look quite different.
Evidence exists that expanding awareness and including more groups into the
discussion can aid in finding ways of reducing environmental harm and other societal
problems. For instance, there has already long been a movement afoot to increase the
awareness among consumers about where their food comes from. This increased
awareness has led to an explosion of the market for local and organic food. The Organic
Trade Association in the United States (2011) claims that sales of organic food and
beverages rose in the period between 1990 and 2010 from $1 billion to $26.7 billion in
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2010. The growth in this market has been largely due to grassroots organizations
pressuring producers, distributers, governments, etc. to provide products to meet the
demand for food with fewer chemical inputs.
Implementing urine diverting toilet technology provides a means to further that
understanding and awareness that has begun with such shifts as the organic food
movement. As stated previously, much effort will need to go into convincing consumers
that food grown with fertilizer sourced from urine is safe and acceptable. However, in a
similar way as the organic movement has grown, as pilot UD systems are installed and
become available as options, awareness and acceptance are likely to grow. This pattern
could create a feedback loop where additional people come to recognize the benefits and
grow to support the technology. It is quite conceivable (and indeed has already begun to
occur in some European towns) that as systems are installed, the growing understanding
will in turn beget more systems and eventually revolutionize the way that humanity
handles its excreta and fertilizes its crops.
79
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