Reuse of human excreta is the safe, beneficial use of treated
human excreta after applying suitable treatment steps and risk management approaches that are customized for the intended reuse application. Beneficial uses of the treated excreta may focus on using the
plant-available nutrients (mainly nitrogen, phosphorus and potassium) that are contained in the treated excreta. They may also make use of the organic matter and energy contained in the excreta. To a lesser extent, reuse of the excreta's water content might also take place, although this is better known as
water reclamation from
municipal wastewater. The intended reuse applications for the nutrient content may include:
soil conditioner or
fertilizer
A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
in
agriculture
Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled peop ...
or
horticultural
Horticulture is the branch of agriculture that deals with the art, science, technology, and business of plant cultivation. It includes the cultivation of fruits, vegetables, nuts, seeds, herbs, sprouts, mushrooms, algae, flowers, seaweeds and no ...
activities. Other reuse applications, which focus more on the organic matter content of the excreta, include use
as a fuel source or as an energy source in the form of
biogas
Biogas is a mixture of gases, primarily consisting of methane, carbon dioxide and hydrogen sulphide, produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste and food waste. I ...
.
There is a large and growing number of treatment options to make excreta safe and manageable for the intended reuse option.
Some options include: Urine diversion and dehydration of feces (
urine-diverting dry toilets), composting (
composting toilets or external
composting processes),
sewage sludge treatment technologies and a range of
fecal sludge treatment processes. They all achieve various degrees of pathogen removal and reduction in water content for easier handling. Pathogens of concern are enteric bacteria, virus, protozoa, and
helminth eggs in feces.
As the helminth eggs are the pathogens that are the most difficult to destroy with treatment processes, they are commonly used as an
indicator organism in reuse schemes. Other health risks and environmental pollution aspects that need to be considered include spreading micropollutants,
pharmaceutical residues and
nitrate in the environment which could cause
groundwater pollution and thus potentially affect
drinking water quality
Drinking water quality standards describes the quality parameters set for drinking water. Despite the truth that every human on this planet needs drinking water to survive and that water may contain many harmful constituents, there are no univers ...
.
There are several "human excreta derived fertilizers" which vary in their properties and fertilizing characteristics, for example: urine, dried feces, composted feces,
fecal sludge,
sewage,
sewage sludge.
The nutrients and organic matter which are contained in human excreta or in domestic
wastewater (
sewage) have been used in agriculture in many countries for centuries. However, this practice is often carried out in an unregulated and unsafe manner in
developing countries
A developing country is a sovereign state with a lesser developed Industrial sector, industrial base and a lower Human Development Index (HDI) relative to other countries. However, this definition is not universally agreed upon. There is al ...
.
World Health Organization
The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level o ...
Guidelines from 2006 have set up a framework describing how this reuse can be done safely by following a "multiple barrier approach".
[WHO (2006)]
WHO Guidelines for the Safe Use of Wastewater, Excreta and Greywater - Volume IV: Excreta and greywater use in agriculture
World Health Organization (WHO), Geneva, Switzerland Such barriers might be selecting a suitable crop, farming methods, methods of applying the fertilizer and education of the farmers.
Terminology
Human excreta,
fecal sludge and
wastewater are often referred to as wastes (see also
human waste). Within the concept of a
circular economy in sanitation, an alternative term that is being used is "resource flows".
The final outputs from the
sanitation
Sanitation refers to public health conditions related to clean drinking water and treatment and disposal of human excreta and sewage. Preventing human contact with feces is part of sanitation, as is hand washing with soap. Sanitation syste ...
treatment systems can be called "reuse products" or "other outputs".
These reuse products are general
fertilizer
A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
s,
soil conditioners,
biomass
Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms biom ...
, water or energy.
Reuse of human excreta focuses on the nutrient and organic matter content of human excreta unlike
reuse of wastewater which focuses on the water content. An alternative term is "use of human excreta" rather than "
reuse" as strictly speaking it is the ''first'' ''use'' of human excreta, not the second time that it is used.
Technologies and approaches
The resources available in wastewater and human excreta include water,
plant nutrients,
organic matter
Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have c ...
and energy content.
Sanitation
Sanitation refers to public health conditions related to clean drinking water and treatment and disposal of human excreta and sewage. Preventing human contact with feces is part of sanitation, as is hand washing with soap. Sanitation syste ...
systems that are designed for safe and effective
recovery of resources can play an important role in a community's overall
resource management.
Recovering the resources embedded in excreta and wastewater (like nutrients, water and energy) contributes to achieving
Sustainable Development Goal 6
Sustainable Development Goal 6 (SDG 6 or Global Goal 6) is about "clean water and sanitation for all". It is one of 17 Sustainable Development Goals established by the United Nations General Assembly in 2015, the official wording is: "Ensure ava ...
and other
sustainable development goals.
It can be efficient to combine wastewater and human excreta with other
organic waste such as
manure, food and crop waste for the purposes of resource recovery.
[Andersson, K., Rosemarin, A., Lamizana, B., Kvarnström, E., McConville, J., Seidu, R., Dickin, S. and Trimmer, C. (2016)]
Sanitation, Wastewater Management and Sustainability: from Waste Disposal to Resource Recovery
Nairobi and Stockholm: United Nations Environment Programme and Stockholm Environment Institute.
Treatment options
There is a large and growing number of treatment options to make excreta safe and manageable for the intended reuse option.
Various technologies and practices, ranging in scale from a single rural household to a city, can be used to capture potentially valuable resources and make them available for safe, productive uses that support human well-being and broader
sustainability
Specific definitions of sustainability are difficult to agree on and have varied in the literature and over time. The concept of sustainability can be used to guide decisions at the global, national, and individual levels (e.g. sustainable livin ...
. Some treatment options are listed below but there are many more:
* Urine diversion and dehydration of feces (which is done with
urine-diverting dry toilets)
* Composting (
composting toilets or external
composting processes)
*
Sewage sludge treatment technologies, which is installed downstream of various
wastewater treatment technologies
*
Fecal sludge treatment processes, such as sludge drying beds,
constructed wetlands.
*
Anaerobic digestion with biogas production
*
Waste-to-energy process
*
Omni Processor
A guide by the
Swedish University of Agricultural Sciences provides a list of treatment technologies for sanitation resource recovery: Vermicomposting and
vermifiltration, black soldier fly composting,
algae
Algae ( , ; : alga ) are any of a large and diverse group of photosynthetic, eukaryotic organisms. The name is an informal term for a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from ...
cultivation,
microbial fuel cell, nitrification and distillation of urine,
struvite
Struvite (magnesium ammonium phosphate) is a phosphate mineral with formula: NH4MgPO4·6H2O. Struvite crystallizes in the orthorhombic system as white to yellowish or brownish-white pyramidal crystals or in platy mica-like forms. It is a soft m ...
precipitation, incineration,
carbonization
Carbonization is the conversion of organic matters like plants and dead animal remains into carbon through destructive distillation.
Complexity in carbonization
Carbonization is a pyrolytic reaction, therefore, is considered a complex proces ...
, solar drying, membranes, filters, alkaline dehydration of urine, ammonia sanitization/urea treatment, lime sanitization.
[McConville, J., Niwagaba, C., Nordin, A., Ahlström, M., Namboozo, V. and Kiffe, M. (2020)]
Guide to Sanitation Resource-Recovery Products & Technologies: A supplement to the Compendium of Sanitation Systems and Technologies
1st Edition. Swedish University of Agricultural Sciences (SLU), Department of Energy and Technology, Uppsala, Sweden.
Reuse options
The most common type of reuse of excreta is as fertilizer and soil conditioner in agriculture. This is also called a "closing the loop" approach for
sanitation
Sanitation refers to public health conditions related to clean drinking water and treatment and disposal of human excreta and sewage. Preventing human contact with feces is part of sanitation, as is hand washing with soap. Sanitation syste ...
with agriculture. It is a central aspect of the
ecological sanitation approach.
Reuse options depend on the form of the excreta that is being reused: it can be either excreta on its own or mixed with some water (
fecal sludge)
or mixed with much water (domestic wastewater or
sewage).
The most common types of excreta reuse include:
*
Fertilizer
A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
and irrigation water in agriculture, and horticulture: for example using
recovered and treated water for irrigation; using composted excreta (and other organic waste) or appropriately treated
biosolids as
fertilizer
A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
and
soil conditioner; using treated source-separated urine as
fertilizer
A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
.
* Energy: for example digesting feces and other organic waste to produce
biogas
Biogas is a mixture of gases, primarily consisting of methane, carbon dioxide and hydrogen sulphide, produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste and food waste. I ...
; or producing combustible fuels.
* Other: other emerging excreta reuse options include producing protein feeds for livestock using
black soldier fly larvae, recovering organic matter for use as building materials or in paper production.
Resource recovery from fecal sludge can take many forms, including as a fuel, soil amendment, building material, protein, animal fodder, and water for irrigation.
Reuse products that can be recovered from sanitation systems include: Stored
urine
Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excreted from the body through the urethra.
Cellular ...
, concentrated urine, sanitized
blackwater Blackwater or Black Water may refer to:
Health and ecology
* Blackwater (coal), liquid waste from coal preparation
* Blackwater (waste), wastewater containing feces, urine, and flushwater from flush toilets
* Blackwater fever, an acute kidney disea ...
, digestate, nutrient solutions, dry urine, struvite, dried feces,
pit
Pit or PIT may refer to:
Structure
* Ball pit, a recreation structure
* Casino pit, the part of a casino which holds gaming tables
* Trapping pit, pits used for hunting
* Pit (motor racing), an area of a racetrack where pit stops are conducted
* ...
humus, dewatered sludge,
compost
Compost is a mixture of ingredients used as plant fertilizer and to improve soil's physical, chemical and biological properties. It is commonly prepared by decomposing plant, food waste, recycling organic materials and manure. The resulting ...
, ash from sludge,
biochar, nutrient-enriched filter material,
algae
Algae ( , ; : alga ) are any of a large and diverse group of photosynthetic, eukaryotic organisms. The name is an informal term for a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from ...
,
macrophytes, black soldier fly larvae, worms,
irrigation water,
aquaculture, biogas.
As fertilizer
Comparison to other fertilizers
There is an untapped fertilizer resource in human excreta. In Africa, for example, the theoretical quantities of nutrients that can be recovered from human excreta are comparable with all current fertilizer use on the continent.
Therefore, reuse can support increased food production and also provide an alternative to chemical fertilizers, which is often unaffordable to small-holder farmers. However, nutritional value of human excreta largely depends on dietary input.
Mineral fertilizers are made from mining activities and can contain heavy metals. Phosphate ores contain heavy metals such as cadmium and uranium, which can reach the food chain via mineral phosphate fertilizer. This does not apply to excreta-based fertilizers (unless the human's food was contaminated beyond safe limits to start with), which is an advantage.
Fertilizing elements of organic fertilizers are mostly bound in carbonaceous reduced compounds. If these are already partially oxidized as in the compost, the fertilizing minerals are adsorbed on the degradation products (
humic acids) etc. Thus, they exhibit a slow-release effect and are usually less rapidly leached compared to mineral fertilizers.
Urine
Urine
Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excreted from the body through the urethra.
Cellular ...
contains large quantities of
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seve ...
(mostly as
urea), as well as reasonable quantities of dissolved
potassium
Potassium is the chemical element with the symbol K (from Neo-Latin '' kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosp ...
.
The nutrient concentrations in urine vary with diet.
[Joensson, H., Richert Stintzing, A., Vinneras, B., Salomon, E. (2004)]
Guidelines on the Use of Urine and Faeces in Crop Production
Stockholm Environment Institute, Sweden In particular, the nitrogen content in urine is related to quantity of protein in the diet: A
high protein diet
A high-protein diet is a diet in which 20% or more of the total daily calories comes from protein.Longe, Jacqueline L. (2008). ''High-protein diet''. In ''The Gale Encyclopedia of Diets: A Guide to Health and Nutrition''. Gale. pp. 524-526. Most ...
results in high urea levels in urine. The nitrogen content in urine is proportional to the total food protein in the person's diet, and the phosphorus content is proportional to the sum of total food protein and vegetal food protein.
Urine's eight main ionic species (> 0.1 meq L−1) are
cations
Na,
K,
NH4,
Ca and the
anions,
Cl,
SO4,
PO4 and
HCO3.
Urine typically contains 70% of the nitrogen and more than half the
potassium
Potassium is the chemical element with the symbol K (from Neo-Latin '' kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosp ...
found in
sewage, while making up less than 1% of the overall volume.
The amount of urine produced by an adult is around 0.8 to 1.5 L per day.
Applying urine as fertilizer has been called "closing the cycle of agricultural nutrient flows" or ecological sanitation or
ecosan
Ecological sanitation, commonly abbreviated as ecosan (also spelled eco-san or EcoSan), is an approach to sanitation provision which aims to safely Reuse of excreta, reuse excreta in agriculture. It is an approach, rather than a technology or a d ...
. Urine fertilizer is usually applied diluted with water because undiluted urine can
chemically burn the leaves or roots of some plants, causing plant injury, particularly if the soil moisture content is low. The dilution also helps to reduce odor development following application. When diluted with water (at a 1:5 ratio for container-grown
annual crops with fresh growing medium each season or a 1:8 ratio for more general use), it can be applied directly to soil as a fertilizer.
The fertilization effect of urine has been found to be comparable to that of commercial nitrogen fertilizers.
[
] Urine may contain pharmaceutical residues (
environmental persistent pharmaceutical pollutants).
[Winker, M. (2009). ''Pharmaceutical Residues in Urine and Potential Risks related to Usage as Fertiliser in Agriculture'' ]UHH University Library UHH or Uhh can refer to:
* University of Hawaii at Hilo
* University of Hamburg
The University of Hamburg (german: link=no, Universität Hamburg, also referred to as UHH) is a public research university in Hamburg, Germany. It was founded on 2 ...
https://doi.org/10.15480/882.481 Concentrations of heavy metals such as
lead
Lead is a chemical element with the Symbol (chemistry), symbol Pb (from the Latin ) and atomic number 82. It is a heavy metals, heavy metal that is density, denser than most common materials. Lead is Mohs scale of mineral hardness#Intermediate ...
,
mercury, and
cadmium
Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, silvery-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Like zinc, it demonstrates oxidation state +2 in most of ...
, commonly found in sewage sludge, are much lower in urine.
[
]
Typical design values for nutrients excreted with urine are: 4 kg nitrogen per person per year, 0.36 kg phosphorus per person per year and 1.0 kg potassium per person per year.
[Jönsson, H., Richert Stintzing, A., Vinnerås, B. and Salomon, E. (2004]
Guidelines on the use of urine and faeces in crop production
EcoSanRes Publications Series, Report 2004-2, Sweden [This source seems to truncate the Jönsson & Vinnerås (2004) table by omitting the potassium row. The full version may be found at the original source a
RG#285858813
!-- -->] Based on the quantity of 1.5 L urine per day (or 550 L per year), the concentration values of macronutrients as follows: 7.3 g/L N; .67 g/L P; 1.8 g/L K.
These are design values but the actual values vary with diet.
Urine's nutrient content, when expressed with the international fertilizer convention of N:P
2O
5:K
2O, is approximately 7:1.5:2.2.
Since urine is rather diluted as a fertilizer compared to dry manufactured nitrogen fertilizers such as
di-ammonium-phosphate, the relative transport costs for urine are high as a lot of water needs to be transported.
The general limitations to using urine as fertilizer depend mainly on the potential for buildup of excess nitrogen (due to the high ratio of that macronutrient),
and inorganic
salt
Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quanti ...
s such as
sodium chloride
Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35 ...
, which are also part of the wastes excreted by the
renal system.
Over-fertilization with urine or other nitrogen fertilizers can result in too much ammonia for plants to absorb, acidic conditions, or other
phytotoxicity.
Important parameters to consider while fertilizing with urine include salinity tolerance of the plant, soil composition, addition of other fertilizing compounds, and quantity of rainfall or other irrigation.
It was reported in 1995 that urine nitrogen gaseous losses were relatively high and plant uptake lower than with labelled
ammonium nitrate. In contrast,
phosphorus was utilized at a higher rate than soluble phosphate.
Urine can also be used safely as a source of nitrogen in carbon-rich
compost
Compost is a mixture of ingredients used as plant fertilizer and to improve soil's physical, chemical and biological properties. It is commonly prepared by decomposing plant, food waste, recycling organic materials and manure. The resulting ...
.
Human urine can be collected with sanitation
Sanitation refers to public health conditions related to clean drinking water and treatment and disposal of human excreta and sewage. Preventing human contact with feces is part of sanitation, as is hand washing with soap. Sanitation syste ...
systems that utilize urinals or urine diversion toilets. If urine is to be separated and collected for use as a fertilizer in agriculture, then this can be done with sanitation
Sanitation refers to public health conditions related to clean drinking water and treatment and disposal of human excreta and sewage. Preventing human contact with feces is part of sanitation, as is hand washing with soap. Sanitation syste ...
systems that utilize waterless urinals, urine-diverting dry toilets (UDDTs) or urine diversion flush toilets. During storage, the urea in urine is rapidly hydrolyzed by urease, creating ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogeno ...
. Further treatment can be done with collected urine to stabilize the nitrogen and concentrate the fertilizer. One low-tech solution to odor is to add citric acid
Citric acid is an organic compound with the chemical formula HOC(CO2H)(CH2CO2H)2. It is a colorless weak organic acid. It occurs naturally in citrus fruits. In biochemistry, it is an intermediate in the citric acid cycle, which occurs in t ...
or vinegar
Vinegar is an aqueous solution of acetic acid and trace compounds that may include flavorings. Vinegar typically contains 5–8% acetic acid by volume. Usually, the acetic acid is produced by a double fermentation, converting simple sugars to ...
to the urine collection container, so that the urease is inactivated and any ammonia that do form are less volatile. Besides concentration, simple chemical processes can be used to extract pure substances: nitrogen as nitrates (similar to medieval nitre beds) and phosphorus as struvite
Struvite (magnesium ammonium phosphate) is a phosphate mineral with formula: NH4MgPO4·6H2O. Struvite crystallizes in the orthorhombic system as white to yellowish or brownish-white pyramidal crystals or in platy mica-like forms. It is a soft m ...
.
The health risks of using urine as a source of fertilizer are generally regarded as negligible, especially when dispersed in soil rather than on the part of a plant that is consumed. Urine can be distributed via perforated hoses buried ~10 cm under the surface of the soil
Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former ...
among crop plants, thus minimizing risk of odors, loss of nutrients due to votalization, or transmission of pathogen
In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a ger ...
s. There are potentially more environmental problems (such as eutrophication
Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytopla ...
resulting from the influx of nutrient rich effluent into aquatic or marine ecosystems) and a higher energy consumption when urine is treated as part of sewage in sewage treatment plants compared with when it is used directly as a fertilizer resource.
In developing countries, the use of raw sewage or fecal sludge has been common throughout history, yet the application of pure urine to crops is still quite rare in 2021. This is despite many publications that advocate the use of urine as a fertilizer since at least 2001. Since about 2011, the Bill and Melinda Gates Foundation is providing funding for research involving sanitation systems that recover the nutrients in urine.
Feces
According to the 2004 "proposed Swedish default values", an average Swedish adult excretes 0.55 kg nitrogen, 0.18 kg phosphorus, and 0.36 kg potassium as feces per year. The yearly mass is 51 kg wet and 11 kg dried, so that wet feces would have a NPK% value of 1.1:0.8:0.9.
Dried feces
Reuse of dried
feces
Feces ( or faeces), known colloquially and in slang as poo and poop, are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the large intestine. Feces contain a rela ...
(feces) from urine-diverting dry toilets after post-treatment can result in increased crop production through fertilizing effects of nitrogen, phosphorus, potassium and improved
soil fertility
Soil fertility refers to the ability of soil to sustain agricultural plant growth, i.e. to provide plant habitat and result in sustained and consistent Crop yield, yields of high quality. through organic carbon.
[Rieck, C., von Münch, E., Hoffmann, H. (2012)]
Technology review of urine-diverting dry toilets (UDDTs) - Overview on design, management, maintenance and costs.
Deutsche Gesellschaft fuer Internationale Zusammenarbeit GmbH, Eschborn, Germany
Composted feces
Compost
Compost is a mixture of ingredients used as plant fertilizer and to improve soil's physical, chemical and biological properties. It is commonly prepared by decomposing plant, food waste, recycling organic materials and manure. The resulting ...
derived from
composting toilets (where organic kitchen waste is in some cases also added to the composting toilet) has, in principle, the same uses as compost derived from other organic waste products, such as
sewage sludge or municipal organic waste. One limiting factor may be legal restrictions due to the possibility that pathogens remain in the compost. In any case, the use of compost from composting toilets in one's own garden can be regarded as safe and is the main method of use for compost from composting toilets. Hygienic measures for handling of the compost must be applied by all those people who are exposed to it, e.g. wearing gloves and boots.
Some of the
urine
Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excreted from the body through the urethra.
Cellular ...
will be part of the compost although some urine will be lost via leachate and evaporation.
Urine
Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excreted from the body through the urethra.
Cellular ...
can contain up to 90 percent of the
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seve ...
, up to 50 percent of the
phosphorus, and up to 70 percent of the
potassium
Potassium is the chemical element with the symbol K (from Neo-Latin '' kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosp ...
present in human excreta.
The nutrients in compost from a composting toilet have a higher plant availability than dried feces from a typical
urine-diverting dry toilet. The two processes are not mutually exclusive, however: some composting toilets do divert urine (to avoid over-saturation of water and nitrogen) and dried feces can still be composted.
[Berger, W. (2011)]
Technology review of composting toilets - Basic overview of composting toilets (with or without urine diversion).
Deutsche Gesellschaft für Internationale Zusammenarbeit GmbH, Eschborn, Germany
Fecal sludge
Fecal sludge is defined as "coming from onsite sanitation technologies, and has not been transported through a sewer." Examples of onsite technologies include pit latrines, unsewered public ablution blocks, septic tanks and dry toilets. Fecal sludge can be treated by a variety of methods to render it suitable for reuse in agriculture. These include (usually carried out in combination) dewatering, thickening, drying (in sludge drying beds),
composting, pelletization, and
anaerobic digestion.
Municipal wastewater
Reclaimed water can be reused for irrigation, industrial uses, replenishing natural water courses, water bodies,
aquifers and other potable and non-potable uses. These applications, however, focus usually on the water aspect, not on the nutrients and organic matter reuse aspect, which is the focus of "reuse of excreta".
When wastewater is reused in agriculture, its nutrient (nitrogen and phosphorus) content may be useful for additional fertilizer application.
Work by the
International Water Management Institute and others has led to guidelines on how reuse of municipal wastewater in agriculture for irrigation and fertilizer application can be safely implemented in low income countries.
Sewage sludge
The use of treated
sewage sludge (after treatment also called "
biosolids") as a
soil conditioner or fertilizer is possible but is a controversial topic in some countries (such as USA, some countries in Europe) due to the chemical pollutants it may contain, such as heavy metals and
environmental persistent pharmaceutical pollutants.
Northumbrian Water
Northumbrian Water Limited is a water company in the United Kingdom, providing mains water and sewerage services in the English counties of Northumberland, Tyne and Wear, Durham and parts of North Yorkshire, and also supplying water as Es ...
in the
United Kingdom
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the European mainland, continental mainland. It comprises England, Scotlan ...
uses two
biogas plants to produce what the company calls "poo power" - using
sewage sludge to produce energy to generate income.
Biogas
Biogas is a mixture of gases, primarily consisting of methane, carbon dioxide and hydrogen sulphide, produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste and food waste. I ...
production has reduced its pre 1996
electricity
Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as describ ...
expenditure of 20 million
GBP by about 20%.
Severn Trent and
Wessex Water also have similar projects.
Sludge treatment liquids
Sludge treatment liquids (after
anaerobic digestion) can be used as an input source for a process to recover phosphorus in the form of
struvite
Struvite (magnesium ammonium phosphate) is a phosphate mineral with formula: NH4MgPO4·6H2O. Struvite crystallizes in the orthorhombic system as white to yellowish or brownish-white pyramidal crystals or in platy mica-like forms. It is a soft m ...
for use as fertilizer. For example, the Canadian company Ostara Nutrient Recovery Technologies is marketing a process based on controlled chemical precipitation of phosphorus in a fluidized bed reactor that recovers struvite in the form of crystalline pellets from sludge dewatering streams. The resulting crystalline product is sold to the
agriculture
Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled peop ...
,
turf and
ornamental plants sectors as fertilizer under the registered trade name "Crystal Green".
Peak phosphorus
In the case of phosphorus in particular, reuse of excreta is one known method to recover phosphorus to mitigate the looming shortage (also known as "
peak phosphorus") of economical mined phosphorus. Mined phosphorus is a limited resource that is being used up for fertilizer production at an ever-increasing rate, which is threatening worldwide
food security. Therefore, phosphorus from excreta-based fertilizers is an interesting alternative to fertilizers containing mined phosphate ore.
Health and environmental aspects of agricultural use
Pathogens
Multiple barrier concept for safe use in agriculture
Research into how to make reuse of urine and feces safe in agriculture has been carried out in Sweden since the 1990s.
In 2006 the
World Health Organization
The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level o ...
(WHO) provided guidelines on safe reuse of wastewater, excreta and greywater.
The multiple barrier concept to reuse, which is the key cornerstone of this publication, has led to a clear understanding of how excreta reuse can be done safely. The concept is also used in water supply and food production, and is generally understood as a series of treatment steps and other safety precautions to prevent the spread of pathogens.
The degree of treatment required for excreta-based fertilizers before they can safely be used in agriculture depends on a number of factors. It mainly depends on which other barriers will be put in place according to the multiple barrier concept. Such barriers might be selecting a suitable crop, farming methods, methods of applying the fertilizer, education of the farmers, and so forth.
[Richert, A., Gensch, R., Jönsson, H., Stenström, T., Dagerskog, L. (2010)]
Practical guidance on the use of urine in crop production
Stockholm Environment Institute (SEI), Sweden
For example, in the case of urine-diverting dry toilets secondary treatment of dried feces can be performed at community level rather than at household level and can include
thermophilic composting
Compost is a mixture of ingredients used as plant fertilizer and to improve soil's physical, chemical and biological properties. It is commonly prepared by decomposing plant, food waste, recycling organic materials and manure. The resulting m ...
where fecal material is composted at over 50 °C, prolonged storage with the duration of 1.5 to two years, chemical treatment with ammonia from urine to inactivate the pathogens, solar sanitation for further drying or heat treatment to eliminate pathogens.
Exposure of farm workers to untreated excreta constitutes a significant health risk due to its
pathogen
In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a ger ...
content. There can be a large amount of enteric bacteria, virus, protozoa, and
helminth eggs in feces.
This risk also extends to consumers of crops fertilized with untreated excreta. Therefore, excreta needs to be appropriately treated before reuse, and health aspects need to be managed for all reuse applications as the excreta can contain
pathogens even after treatment.
Treatment of excreta for pathogen removal
Temperature is a treatment parameter with an established relation to pathogen inactivation for all pathogen groups: Temperatures above 50 °C have the potential to inactivate most pathogens.
Therefore, thermal sanitization is utilized in several technologies, such as thermophilic composting and thermophilic
anaerobic digestion and potentially in sun drying. Alkaline conditions (pH value above 10) can also deactivate pathogens. This can be achieved with ammonia sanitization or lime treatment.
The treatment of excreta and wastewater for pathogen removal can take place:
* at the toilet itself (for example, urine collected from
urine-diverting dry toilets is often treated by simple storage at the household level); or
* at a semi-centralized level (for example, by
composting); or
* at a fully centralized level at
sewage treatment plants and
sewage sludge treatment plants.
Indicator organisms
As an
indicator organism in reuse schemes,
helminth
Parasitic worms, also known as helminths, are large macroparasites
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adap ...
eggs are commonly used as these organisms are the most difficult to destroy in most treatment processes. The multiple barrier approach is recommended where e.g. lower levels of treatment may be acceptable when combined with other post-treatment barriers along the
sanitation
Sanitation refers to public health conditions related to clean drinking water and treatment and disposal of human excreta and sewage. Preventing human contact with feces is part of sanitation, as is hand washing with soap. Sanitation syste ...
chain.
Pharmaceutical residues
Excreta from humans contains
hormones and
pharmaceutical residues which could in theory enter the food chain via fertilized crops but are currently not fully removed by conventional wastewater treatment plants anyway and can enter drinking water sources via household wastewater (sewage).
[von Münch, E., Winker, M. (2011)]
Technology review of urine diversion components - Overview on urine diversion components such as waterless urinals, urine diversion toilets, urine storage and reuse systems.
Gesellschaft für Internationale Zusammenarbeit GmbH In fact, the pharmaceutical residues in the excreta are degraded better in terrestrial systems (soil) than in aquatic systems.
Nitrate pollution
Only a fraction of the nitrogen-based fertilizers is converted to produce plant matter. The remainder accumulates in the soil or is lost as run-off.
This also applies to excreta-based fertilizer since it also contains nitrogen. Excessive nitrogen which is not taken up by plants is transformed into nitrate which is easily leached. High application rates combined with the high water-solubility of nitrate leads to increased
runoff into
surface water as well as
leaching into
groundwater
Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidat ...
. Nitrate levels above 10 mg/L (10 ppm) in groundwater can cause '
blue baby syndrome' (acquired
methemoglobinemia). The nutrients, especially nitrates, in fertilizers can cause problems for
ecosystem
An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...
s and for human health if they are washed off into
surface water or leached through the soil into groundwater.
Other uses
Apart from use in agriculture, there are other possible uses of excreta. For example, in the case of fecal sludge, it can be treated and then serve as protein (
black soldier fly process),
fodder, fish food, building materials and
biofuels
Biofuel is a fuel that is produced over a short time span from biomass, rather than by the very slow natural processes involved in the formation of fossil fuels, such as oil. According to the United States Energy Information Administration (E ...
(
biogas
Biogas is a mixture of gases, primarily consisting of methane, carbon dioxide and hydrogen sulphide, produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste and food waste. I ...
from
anaerobic digestion, incineration or co-combustion of dried sludge, pyrolysis of fecal sludge, biodiesel from fecal sludge).
Fuel
Solid fuel, heat, electricity
Pilot scale research in Uganda and Senegal has shown that it is viable to use dry feces as for combustion in industry, provided it has been dried to a minimum of 28% dry solids.
Dried sewage sludge can be burned in
sludge incineration plants and generate heat and electricity (the
waste-to-energy process is one example).
Resource recovery of fecal sludge as a solid fuel has been found to have high market potential in
Sub-Saharan Africa.
Hydrogen fuel
Urine has also been investigated as a potential source of
hydrogen fuel.
Urine was found to be a suitable wastewater for high rate hydrogen production in a
Microbial Electrolysis Cell (MEC).
Biogas
Small-scale
biogas
Biogas is a mixture of gases, primarily consisting of methane, carbon dioxide and hydrogen sulphide, produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste and food waste. I ...
plants are being utilized in many countries, including Ghana, Vietnam and many others. Larger centralized systems are being planned that mix animal and human feces to produce biogas.
Biogas is also produced during
sewage sludge treatment processes with
anaerobic digestion. Here, it can be used for heating the digesters and for generating electricity.
Biogas is an important waste-to-energy resource which plays a huge role in reducing environmental pollution and most importantly in reducing greenhouse gases effect caused by the waste. Utilization of raw material such as human waste for biogas generation is considered beneficial because it does not require additional starters such as microorganism seeds for methane production, and a supply of microorganisms occurs continuously during the feeding of raw materials.
Food source to produce protein for animal feed
Pilot facilities are being developed for feeding
Black Soldier Fly larvae with feces. The mature flies would then be a source of protein to be included in the production of feed for chickens in South Africa.
Black soldier fly (BSF) bio-waste processing is a relatively new treatment technology that has received increasing attention over the last decades. Larvae grown on bio-waste can be a necessary raw material for animal feed production, and can therefore provide revenues for financially applicable waste management systems. In addition, when produced on bio-waste, insect-based feeds can be more sustainable than conventional feeds.
Building materials
It is known that additions of fecal matter up to 20% by dried weight in clay bricks does not make a significant functional difference to bricks.
Precious metals recovery
A Japanese sewage treatment facility extracts
precious metals from
sewage sludge, "high percentage of gold found at the Suwa facility was probably due to the large number of precision equipment manufacturers in the vicinity that use
old The facility recently recorded finding 1,890 grammes of gold per tonne of ash from incinerated sludge. That is a far higher gold content than Japan’s Hishikari Mine, one of the world’s top gold mines,
.which contains 20-40 grammes of the precious metal per tonne of ore."
This idea was also tested by the US Geological Survey (USGS) which found that the yearly sewage sludge generated by 1 million people contained 13 million dollars worth of precious metals.
Other materials
With pyrolysis, urine is turned into a pre-doped, highly porous, carbon material termed "urine carbon" (URC). URC is cheaper than current
fuel cell
A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen fuel, hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most bat ...
catalysts while performing better.
History
The reuse of excreta as a fertilizer for growing crops has been practiced in many countries for a long time.
Society and culture
Economics
Debate is ongoing about whether reuse of excreta is cost effective.
The terms "sanitation economy" and "toilet resources" have been introduced to describe the potential for selling products made from
human feces or
urine
Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excreted from the body through the urethra.
Cellular ...
.
Sale of compost
The NGO
SOIL
Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former ...
in
Haiti
Haiti (; ht, Ayiti ; French: ), officially the Republic of Haiti (); ) and formerly known as Hayti, is a country located on the island of Hispaniola in the Greater Antilles archipelago of the Caribbean Sea, east of Cuba and Jamaica, and ...
began building
urine-diverting dry toilets and
composting the waste produced for agricultural use in 2006. SOIL's two composting waste treatment facilities currently transform over 20,000 gallons (75,708 liters) of human excreta into organic, agricultural-grade compost every month. The compost produced at these facilities is sold to farmers, organizations, businesses, and institutions around the country to help finance SOIL's waste treatment operations. Crops grown with this soil amendment include spinach, peppers, sorghum, maize, and more. Each batch of compost produced is tested for the
indicator organism ''
E. coli'' to ensure that complete pathogen kill has taken place during the
thermophilic composting process.
Policies
There is still a lack of examples of implemented policy where the reuse aspect is fully integrated in policy and advocacy.
[SEI (2009)]
Sanitation policies and regulatory frameworks for reuse of nutrients in wastewater, human excreta and greywater
- Proceedings from SEI/EcoSanRes2 Workshop in Sweden. Stockholm Environment Institute, Sweden When considering drivers for policy change in this respect, the following lessons learned should be taken into consideration: Revising legislation does not necessarily lead to functioning reuse systems; it is important to describe the “institutional landscape” and involve all actors; parallel processes should be initiated at all levels of government (i.e. national, regional and local level); country specific strategies and approaches are needed; and strategies supporting newly developed policies need to be developed).
Regulatory considerations
Regulations such as Global
Good Agricultural Practices
Good agricultural practice (GAP) is a certification system for agriculture, specifying procedures (and attendant documentation) that must be implemented to create food for consumers or further processing that is safe and wholesome, using sustaina ...
may hinder export and import of agricultural products that have been grown with the application of human excreta-derived fertilisers.
[Elisabeth Kvarnström, Linus Dagerskog, Anna Norström and Mats Johansson (2012]
Nutrient reuse as a solution multiplier
(SIANI policy brief 1.1), A policy brief by the SIANI Agriculture-Sanitation Expert Group, Sweden
Urine use in organic farming in Europe
The
European Union
The European Union (EU) is a supranational political and economic union of member states that are located primarily in Europe. The union has a total area of and an estimated total population of about 447million. The EU has often been ...
allows the use of source separated urine only in conventional farming within the EU, but not yet in organic farming. This is a situation that many agricultural experts, especially in Sweden, would like to see changed.
This ban may also reduce the options to use urine as a fertilizer in other countries if they wish to export their products to the EU.
Dried feces from urine-diverting dry toilets in the U.S.
In the United States, the EPA regulation governs the management of
sewage sludge but has no jurisdiction over the byproducts of a urine-diverting dry toilet. Oversight of these materials falls to the states.
Country examples
China
Treatment disposal of human excreta can be categorized into three types: fertilizer use, discharge and biogas use. Discharge is the disposal of human excreta to soil, septic tank or water body. In China, with the impact of the long tradition, human excreta is often used as fertilizer for crops. The main application methods are direct usage for crops and fruits as basal or top application after fermentation in a ditch for a certain period, compost with crop stalk for basal application and direct usage as feed for fish in ponds. On the other hand, as much as many people rely on human waste as an agricultural fertilizer, if the waste is not properly treated, the use of night soil may promote the spread of infectious diseases.
India
Urine is used as organic manure in India. It is also used for making an alcohol-based bio-pesticide: the ammonia within breaks down lignin, allowing plant materials like
straw
Straw is an agricultural byproduct consisting of the dry stalks of cereal plants after the grain and chaff have been removed. It makes up about half of the yield of cereal crops such as barley, oats, rice, rye and wheat. It has a numbe ...
to be more easily fermented into alcohol.
Kenya
In Mukuru, Kenya, the slum dwellers are worst hit by the sanitation challenge due to a high population density and a lack of supporting infrastructure. Makeshift pit latrines, illegal toilet connections to the main sewer systems and lack of running water to support the flushable toilets present a sanitation nightmare in all Kenyan slums. The NGO Sanergy seeks to provide decent toilet facilities to Mukuru residents and uses the feces and urine from the toilets to provide fertilizer and energy for the market.
Uganda
Reuse of wastewater in agriculture is a common practice in the developing world. In a study in
Kampala, although famers were not using fecal sludge, 8% of farmers were using wastewater sludge as a soil amendment. Compost from animal manure and composted household waste are applied by many farmers as soil conditioners. On the other hand, farmers are already mixing their own feed because of limited trust in the feed industry and the quality of products.
Electricity demand is significantly more than the electricity generation and only a small margin of the population nationally has access to electricity. The pellets produced from fecal sludge are being used in gasification for electricity production. Converting fecal sludge for energy could contribute towards meeting present and future energy needs.
In
Tororo District in eastern Uganda - a region with severe
land degradation
Land degradation is a process in which the value of the biophysical environment is affected by a combination of human-induced processes acting upon the land.
It is viewed as any change or disturbance to the land perceived to be deleterious ...
problems -
smallholder farmers appreciated urine fertilization as a low-cost, low-risk practice. They found that it could contribute to significant yield increases. The importance of social norms and cultural perceptions needs to be recognized but these are not absolute barriers to adoption of the practice.
Ghana
In Ghana, the only wide scale implementation is small scale rural digesters, with about 200 biogas plants using human excreta and animal dung as feedstock. Linking up of public toilets with biogas digesters as a way of improving communal hygiene and combating hygiene-related communicable diseases including cholera and dysentery is also a notable solution within Ghana.
See also
*
Manure
*
Ecological sanitation
*
Fecal sludge management
*
Nightsoil
Night soil is a historically used euphemism for human excreta collected from cesspools, privies, pail closets, pit latrines, privy middens, septic tanks, etc. This material was removed from the immediate area, usually at night, by workers employe ...
*
Resource recovery
*
Compost
Compost is a mixture of ingredients used as plant fertilizer and to improve soil's physical, chemical and biological properties. It is commonly prepared by decomposing plant, food waste, recycling organic materials and manure. The resulting ...
Notes
References
External links
Documents on reuse of excretain the library of the
Sustainable Sanitation AlliancePhotos on reuse of excretain photo database of the
Sustainable Sanitation Alliance
{{Recycling
Agriculture
Excretion
Repurposing
Sanitation
Feces