Chemosphere 84 (2011) 832–839
Contents lists available at ScienceDirect
Chemosphere
journal homepage: www.elsevier.com/locate/chemosphere
Global potential of phosphorus recovery from human urine and feces
James R. Mihelcic a,⇑, Lauren M. Fry b, Ryan Shaw b
a
b
Civil and Environmental Engineering, University of South Florida, United States
Civil and Environmental Engineering, Michigan Technological University, United States
a r t i c l e
i n f o
Article history:
Received 9 September 2010
Received in revised form 10 January 2011
Accepted 21 February 2011
Available online 22 March 2011
Keywords:
Phosphorus
Material flow
Human excrement
Ecosanitation
Wastewater
Sanitation
a b s t r a c t
This study geospatially quantifies the mass of an essential fertilizer element, phosphorus, available from
human urine and feces, globally, regionally, and by specific country. The analysis is performed over two
population scenarios (2009 and 2050). This important material flow is related to the presence of
improved sanitation facilities and also considers the global trend of urbanization. Results show that in
2009 the phosphorus available from urine is approximately 1.68 million metric tons (with similar mass
available from feces). If collected, the phosphorus available from urine and feces could account for 22% of
the total global phosphorus demand. In 2050 the available phosphorus from urine that is associated with
population increases only will increase to 2.16 million metric tons (with similar mass available from
feces). The available phosphorus from urine and feces produced in urban settings is currently approximately 0.88 million metric tons and will increase with population growth to over 1.5 million metric tons
by 2050. Results point to the large potential source of human-derived phosphorus in developing regions
like Africa and Asia that have a large population currently unserved by improved sanitation facilities.
These regions have great potential to implement urine diversion and reuse and composting or recovery
of biosolids, because innovative technologies can be integrated with improvements in sanitation coverage. In contrast, other regions with extensive sanitation coverage like Europe and North America need to
determine how to retrofit existing sanitation technology combined that is combined with human behavioral changes to recover phosphorus and other valuable nutrients.
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
Management of human waste is a critical part of daily life, and it
is an important factor in human health (Esrey et al., 2001). The
goals of most modern day sanitation systems are to prevent exposure of humans to harmful pathogens that are found in excrement
and to minimize adverse impact on aquatic ecosystems from the
input of oxygen consuming pollutants and nutrients such as nitrogen and phosphorus. Most sanitation systems in the developed
world seek to carry away waste via a sewer collection system, remove pathogens and pollutants in an energy and material intensive treatment system, and then release the contents back into
nature, often in large volumes of dilute waste that can cause water
quality problems (Muga and Mihelcic, 2008). In the developing
world, various types of latrines are often proposed as an appropriate technology to concentrate and contain the excrement (Mihelcic
et al., 2009). Furthermore, when sewers are used in the developing
world, because of limited resources, they often focus more on car⇑ Corresponding author. Address: Civil and Environmental Engineering,
University of South Florida, 4202 East Fowler Ave., ENB 118, Tampa, FL 33620,
United States. Tel.: +1 813 974 9896; fax: +1 813 974 2957.
E-mail address: [email protected] (J.R. Mihelcic).
0045-6535/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.chemosphere.2011.02.046
rying away waste than providing adequate treatment (WHO,
2006). In addition, sewers may not be an appropriate technology
in areas of the world that are water stressed (Fry et al., 2008)
and centralized treatment systems that require large and expensive collection systems may not be the most appropriate technology for communities that are looking for sanitation coverage
beyond latrines (Fuchs and Mihelcic, 2011).
Globally 2.6 billion people, 72% who live in Asia, still do not
have access to improved sanitation facilities (WHO and UNICEF,
2010). Furthermore, while open defecation has decreased globally
from 25% in 1990 to 17% in 2008, it is still widely practiced in SubSaharan Africa by 27% of the population and in Southern Asia by
44% of the population (WHO/UNICEF, 2010). Also, nutrient discharges (phosphorus and nitrogen) to surface waters are expected
to increase substantially between 2000 and 2050 from the combined impact of increasing population, urbanization, and provision
of sewers. This increase is especially great in southern Asia where
phosphorus discharges are expected to increase by a factor of 4–5
(Van Drecht et al., 2009).
Improved sanitation can improve health by limiting contact
between humans and their excreta. It is defined by the Joint Monitoring Programme for Water Supply and Sanitation through the
World Health Organization and UNICEF (WHO/UNICEF, 2010) as
J.R. Mihelcic et al. / Chemosphere 84 (2011) 832–839
a connection to a public sewer, connection to a septic system, or
use of a pour-flush latrine, ventilated improved pit latrine, composting latrine, and simple pit latrine. When integrated with treatment or appropriate containment, current human waste collection
systems found in the developed and developing world do much to
minimize human contact with the pathogens in excrement, but little to ensure that nutrients will be recovered and returned to agricultural and natural systems in a way that benefits food production
and aquatic ecosystems.
There is however growing awareness of the valuable nutrients
being lost in human excreta collection, containment, and treatment systems. For example, it has been reported that for Swedish
diets, 88% of the excreted nitrogen and 67% of the excreted P are
present in urine (Jönsson et al., 2004). The remainder is discharged
with the feces. In countries where the diet is less digestible (as
might be expected in the developing world), urine will contain a
smaller percent of the total nutrients with more subsequently
present in the feces. For example, data from a Chinese diet reported
urine contained approximately 70% of the excreted nitrogen and
25–60% of the excreted phosphorus (Gao et al., 2002). The nitrogen
initially present in urine consists of approximately 75–90% urea
with the remainder being mostly ammonium ion. Urea breaks
down rapidly to ammonium ion and carbon dioxide in the present
of water and urease. Ninety-five to 100% of the phosphorus in urine
exists as inorganic phosphate ions. Also present are potassium and
sulfate ions. This overall chemical composition makes urine a preferable fertilizer because the nutrients are available in plant-available chemical forms (Jönsson et al., 2004). In regards to the
nutrients found in feces, the beneficial reuse of wastewater biosolids in agricultural settings is already widely recognized for
improving of soil properties.
In terms of phosphorus, it has been estimated that globally
there are 0.3–1.5 million metric tons of phosphorus reused annually from the 3 to 3.3 million metric tons of phosphorus generated
in human excreta (i.e., feces and urine) and graywater (Liu et al.,
2008; Cordell et al., 2009a). In regards to national material flows,
it is estimated that 8000 metric tons of phosphorus are discharged
with human excreta annually in Australia and 40–50% of that phosphorus reaching a treatment plant is applied to agricultural soils as
biosolids (Cordell and White, 2009). Furthermore, the potential
production of phosphorus from urine in Europe has been estimated
as 0.3 kg phosphorus per person per year (Lienert et al., 2003). Reuse of these nutrients currently occurs primarily through wastewater reuse (i.e., water reclamation) and land application of biosolids.
The available phosphorus from human excreta is reported to also
be split near equally between rural and urban areas (i.e., 1.6 million metric tons excreted in urban environments, 1.7 million metric tons excreted in rural environments) (Liu et al., 2008). This split
is likely to become more urban in the future because an estimated
70% of the world’s population is expected to reside in cities by the
year 2050 (UNFPA, 2007).
Closing the nutrient loop related to sanitation is now especially
important because of the critical need to address the looming
phosphorus crisis (see Vaccari (2009) and other articles in this special issue). Also, a new paradigm emerging in water and wastewater management is to emphasize the resources (water, energy, and
nutrients) that can be recovered from wastewater in addition to
the constituents that must be removed (Guest et al., 2009). Given
all this information, there is thus a tremendous opportunity to
not only provide appropriate and sustainable technology to the
2.6 billion people that lack improved sanitation that incorporates
efficient nutrient recycling, but also integrate new ideas and technology with existing sanitation collection and treatment systems.
Accordingly, the objective of this study is to geospatially quantify the mass of phosphorus available from human urine and feces
on a global, developing region, and country specific basis, taking
833
care to integrate the results with availability of sanitation technology. The analysis is performed for two scenarios of population
(2009 and 2050) and on a country specific basis. This important
material flow is related to the presence or absence of improved
sanitation technologies and also considers the global trend of
urbanization. We also present our results using the United Nation’s
regional grouping of countries in terms of their development
status.
Of the main sources of available phosphorus (phosphate rock,
animal manure, human excreta), human excreta makes up the
smallest mass (Cordell et al., 2009a). However phosphorus material flows from human excreta should increase in the future as population and affluence (as measured by individual protein
consumption) both increase, while greater demand for total food
calories and protein will also increase the need for phosphorus fertilizer. And while others have reported global phosphorus material
flows from human excreta (e.g., Liu et al., 2008; Cordell et al.,
2009a), no one has geospatially related this information on a country and regional basis in terms of current development status and
the availability of improved sanitation facilities. This information is
important because proposed methods to remove phosphorus from
wastewater are still largely based on biological and chemical removal from the dissolved to particulate form (de-Bashan and Bashan, 2004). However, new perspectives, technologies and
behaviors are needed to drive innovations in providing infrastructure required to meet the future needs of increasing population
and affluence along with an urbanizing world (Boyle et al., 2010).
One perspective that has been used by humans for centuries
and is gaining renewed attention as a method to recover nutrients
from human excreta is urine diversion. This contrasts with the
more established technologies of processing and returning biosolids to agricultural settings. Urine diversion and reuse has been
shown to be technologically feasible in both the developed and
developing world settings (Maurer et al., 2003; Rauch et al.,
2003; Wilsenach et al., 2007; Shaw, 2010; Shaw et al., 2010). The
average human produces 0.8–1.6 L of urine per day (Lentner
et al., 1981) which makes up less than 1% of total wastewater flow
in developing country wastewater collection systems. The mass of
phosphorus produced annually in this urine on a per capita basis is
reported to range from 0.2 to 0.4 kg (Drangert, 1998; Kvarnström
et al., 2006).
Human urine contains very few, if any, pathogens but contains
significant nutrients. Few diseases are transferred through urine,
and the risk of transfer for these through the use of urine fertilizer
is insignificant, with the exceptions being: (1) schistosomiasis or
(2) the possible contamination of urine with feces, both of which
can be eliminated or minimized by appropriate collection, storage,
and application (WHO, 2006). Unwanted micropollutants in urine
are primarily steroidal hormones and pharmaceuticals which can
be removed to different degrees through natural attenuation or
with existing engineering treatment technologies (Jönsson et al.,
2004; Escher et al., 2006) which are energy and material intensive,
and thus may not be appropriate in all areas of the world.
Understanding the potential for nutrient reuse on a geospatial
basis is also important. For example, some agricultural practices
do not always replace the nutrients lost in the system from harvesting crops. In addition, soils are losing nutrients at an alarming
rate, especially in Africa (Connor, 2006) where three-quarters of
Africa’s farmland is plagued by severe soil degradation caused by
wind and soil erosion and the loss of vital mineral nutrients. This
degradation partly explains why agricultural productivity in Africa
has remained largely stagnant for 40 years while Asia’s productivity has increased threefold. African farmers must have access to
affordable mineral and organic fertilizers if they are to stand any
chance of reversing the decline of soil fertility (Connor, 2006). Urine and feces are two such sources of affordable fertilizer. In fact,
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J.R. Mihelcic et al. / Chemosphere 84 (2011) 832–839
Population in 2009
5.00e+001 - 1.70e+007
1.71e+007 - 5.01e+007
5.02e+007 - 1.41e+008
1.42e+008 - 3.15e+008
3.16e+008 - 1.35e+009
Projected population in 2050
5.10e+001 - 2.61e+007
2.62e+007 - 7.59e+007
7.60e+007 - 1.74e+008
1.75e+008 - 4.04e+008
4.05e+008 - 1.61e+009
Total protein intake (g/c/day)
24.4 - 50.8
50.9 - 64.9
65.0 - 81.4
81.5 - 100.0
100.1 - 136.7
Percent protein from vegetable sources
28.3% - 42%
42.1% - 53.4%
53.5% - 66.5%
66.6% - 79%
79.1% - 93%
Fig. 1. Data used in development of this study’s results. 2009 and 2050 population (United Nations Environment Programme, 2010), total protein intake, and the percent
protein that is derived from vegetable sources (Food and Agriculture Organization of the United Nations 2010a,b).
Sub-Saharan Africa provides an immediate opportunity for use of
sanitation derived fertilizers because it already has very low levels
of chemical fertilizer use (Rosemarin et al., 2008). In addition, Asia
with its expanding population, lack of freshwater reserves relative
to global population, and large population not served by improved
sanitation facilities provides a realistic opportunity to introduce a
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J.R. Mihelcic et al. / Chemosphere 84 (2011) 832–839
new perspective for nutrient recovery from human excrement and
wastewaters.
2. Methods and data
A few studies have determined the precise nutrient content of
urine (e.g., see Esrey et al., 2001; Gao et al., 2002; Jönsson et al.,
2004). The problem is compounded because the chemical content
of urine and feces depends on the digestible content of an individual’s diet. This is because digested nutrients enter the metabolism
and are excreted with urine, while undigested fractions are excreted with feces. The Food and Agriculture Organization of the
United Nations (FAO) provides per capita protein consumption
data on a country specific basis. This data can be used to estimate
the phosphorus excreted by an individual on a country specific basis as follows (Jönsson et al., 2004):
Phosphorus ¼ 0:011 ðtotal food protein
þ plant food proteinÞ
ð1Þ
In Eq. (1), the units of phosphorus are the total phosphorus in urine
and feces in grams per capita per day (g/c/d) and both protein values have units of grams of protein per capita per day. Total food
protein is the sum of protein derived from animal and plant food
sources.
Eq. (1) was developed from data collected in Sweden on the
mass of urine and feces excreted on a per capita basis, the nitrogen
and phosphorus content of these two items, and country specific
food intake information (Vinnerås, 2002; Jönsson and Vinnerås,
2004). And because plant protein contains approximately twice
as much phosphorus per gram of protein than animal protein
(Jönsson et al., 2004), the amount of phosphorus in the excreta (urine plus feces) is obtained from the sum of animal protein intake
and two times the plant protein.
Results were then modified to determine the phosphorus present in urine and feces. For this we used a value of 50%, assuming
equal distribution of phosphorus in urine and feces. One study conducted in Sweden suggested that urine will contain somewhat less
than 67% of total excreted phosphorus (Jönsson and Vinnerås,
2004) and Chinese data (Gao et al., 2002) indicates that urine contains approximately 25–60% of human excreted phosphorus. And
as was previously discussed, in countries where the diet is less
digestible, urine should contain a smaller percent of the excreted
phosphorus excreted with subsequently more present in the feces.
The most current average national total protein and vegetable
protein consumption data (g/capita/day) that are available (from
2007) were drawn from FAO food balance sheets where available
(FAO, 2010a). If 2007 data were not available, the next available
2005 data were drawn from the FAO’s Nutrition Country Profiles
(FAO, 2010b). Urban, rural, and total population by country in
2009
National Sanitation Coverage in 2008 (%)
2009
P Produced Per Capita Annually in 2009 (kg)
9-21
0.18-0.36
21-37
0.36-0.42
37-60
0.42-0.49
60-85
0.49-0.55
85-100
0.55-0.62
0.62-0.73
2009
Total P Produced Annually in 2009 (metric tonnes)
2050
Total P Produced Annually in 2050 (metric tonnes)
18.4-10200
22.9-7740
10300-26800
7750-21900
26900-54800
22000-43400
54900-99200
43500-85400
99300-195000
85500-250000
1960000-7780000
251000-819000
Fig. 2. (Upper left) national sanitation coverage in 2008. (Upper right) total phosphorus produced in urine and feces annually per capita in 2009. (Lower left and right) total
phosphorus produced in urine and feces on a country specific basis in years 2009 and 2050. Note the different scale representing the 2050 scenario.
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J.R. Mihelcic et al. / Chemosphere 84 (2011) 832–839
2009 and 2050 (projected) were obtained from the United Nations
Environment Programme (UNEP, 2010). The data used to produce
our results are provided in Fig. 1. Note that in this figure vegetable
protein consumption data were converted to percent protein obtained from vegetable sources to make the data more visually
clear. Protein consumption data were available for 180 countries,
representing 98% of the global population in 2009. Countries were
grouped into specific ‘‘developing regions’’ as developed by the
United Nations and listed in the most current Joint Monitoring Report (WHO/UNICEF, 2010). This report also provided 2008 information on availability of improved sanitation coverage (as defined in
the Introduction).
3. Results and discussion
Results varied by region, according to total protein intake, percentage of protein from vegetable sources, and total population.
The total phosphorus produced each year (for the years 2009 and
2050) in specific countries on a per capita basis and a total produced on a country basis is shown in Fig. 2. Fig. 2 shows that
depending on their protein intake, the mass of phosphorus produced annually on a capita basis in their combined urine and feces
ranges from 0.18 (Democratic Republic of Congo) to 0.73 kg (Israel). The lower row of this figure shows that the total phosphorus
discharged in combined urine and feces for individual countries
ranges from 18.4 metric tonnes (Lichtenstein) to 7.78 105 metric
tonnes (China). The specific mass of phosphorus available specifically from human urine or feces can be obtained by taking the values in Fig. 2 and multiplying by an assumed percent of the nutrient
expected to be excreted in urine or feces (assumed to be 50% in this
study). This is an important consideration in identifying the types
of technology and behavior changes required to recover the nutrients. The potential phosphorus recovery from urine and feces increases under the 2050 population scenario because of
population increases (our results assume no change in diet).
Table 1 shows results of the analysis using the regional grouping of countries in terms of their ‘‘development status’’ as defined
by the United Nations and used in the WHO/UNICEF Joint Monitoring Report along with the percent of population served by improved sanitation in 2008. This table shows there are large
regional sources of human-derived phosphorus that are available
for agricultural reuse and could be derived from either urine or
composted feces or digested biosolids. This is especially important
for Sub-Saharan Africa and the three development regions of Asia
that have large numbers of population currently unserved by im-
proved sanitation facilities. For example three developing regions
of Asia alone have the potential to recover over 1 million metric
tons of phosphorus from urine in the year 2050 (and a similar value from composted or digested feces). This value will be even
higher if protein consumption increases by 2050 (though increases
in protein production will require greater phosphorus fertilizer inputs). Regions like Africa and Asia have great potential to immediately implement urine diversion, composting of feces, and/or
biosolids recovery via new and existing technologies as sanitation
coverage is provided over the next several decades. Other regions
with extensive existing sanitation coverage (e.g., Europe and North
America) would need to determine how to retrofit existing wastewater collection and treatment technology (e.g., addition of struvite precipitation).
Fig. 3 geospatially shows similar data as Table 1. Again phosphorus data is presented on a per capita basis and also a regional
basis using groupings of countries in terms of their development
status (specific regions are listed in Table 1). Fig. 3 also provides
2008 sanitation coverage averaged for each developing region
(WHO/UNICEF, 2010). In addition to the opportunities for recovery
of phosphorus in Africa and Asia which are currently implementing
sanitation coverage on a broad scale, Fig. 3 also shows the large potential for recovering phosphorus from human excrement (currently and in future years) in the Americas and Europe. The data
provided in this figure on existing sanitation coverage is important
because it provides information on whether implementing urine
and feces collection on a large scale will require retrofitting existing technology, using new technology, and/or consideration of
what type of specific household behavioral changes might be
needed.
Table 2 shows that in 2009 the global phosphorus available
from urine (and similar mass from feces) is 0.88 million metric tonnes in urban areas and 0.80 metric tonnes in rural areas (results are
supported by those of Liu et al., 2008). In 2050 the available phosphorus in urban areas from urine and feces that is due to only population growth will increase to over 1.5 million metric tons.
However, the available phosphorus in urine and feces in rural areas
will decrease to 0.64 million metric tones because of projected decreases in population. This data points to an important challenge,
that is, the world is urbanizing with most population growth over
this century projected to occur in urban areas, thus presenting
challenges related to spatially connecting urban sources of human-excrement derived phosphorus with rural areas of agricultural activity.
It is important to note that our estimates do not take into account future changes in diet (i.e., total protein intake and per ca-
Table 1
Sanitation coverage, population, and mass of phosphorus produced annually in human excreta (urine and feces) and urine in the United Nations regional grouping of countries in
terms of their development status (50% of phosphorus is estimated to be in the urine of human excreta; thus, the mass of phosphorus in feces would equal the mass listed in
urine).
Sanitation
coverage
in 2008 (%)
Commonwealth of Independent States
Developed
Eastern Asia
Latin American and the Caribbean
Northern Africa
Oceania
South-Eastern Asia
Southern Asia
Sub-Saharan Africa
Western Asia
89
99
56
79
89
51
68
35
31
84
2009
2050
Total
population
(thousands)
Total P in human
excreta per
year (metric tons)
Total P in urine
(metric tons),
50% of total P
Total
population
(thousands)
Total P in human
excreta per year
(metric tons)
Total P in urine
(metric tons),
50% of total P
272 404
718 279
1420 661
891 449
166 579
2476
577 928
1665 803
841 099
180 725
154 807
417 708
815 089
475 410
105 707
1126
239 751
698 750
342 959
107 204
77 404
208 854
407 545
237 705
52 853
563
119 875
349 375
171 480
53 602
253 804
709 606
1489 135
1127 144
244 256
3566
760 744
2340 667
1750 341
285 771
142 908
414 792
854 546
597 013
155 196
1578
315 545
978 730
706 031
163 544
71 454
207 396
427 273
298 507
77 598
789
157 772
489 365
353 016
81 772
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J.R. Mihelcic et al. / Chemosphere 84 (2011) 832–839
2009
2009
Regional Sanitation Coverage in 2008 (%)
Average P Produced Per Capita Annually in 2009 (kg)
31
79
0.404
0.490
35
84
0.427
0.526
51
89
0.444
0.550
56
99
0.451
0.569
0.452
0.611
68
2009
2050
Total P Produced Annually in 2009 (metric tonnes)
Total P Produced Annually in 2050 (metric tonnes)
1126
342959
1578
414792
105707
417708
142908
597013
107204
475410
155196
706031
154807
698750
163544
854546
239751
815089
315545
978730
Fig. 3. Results depicted according to ‘‘developing region’’ defined by the United Nations. (Upper left) national sanitation coverage in 2008. (Upper right) total phosphorus
produced in urine and feces annually per capita in 2009. (Lower left and right) total phosphorus produced in urine and feces on a regional basis in years 2009 and 2050. Note
the different scale representing the 2050 scenario.
Table 2
Total phosphorus in human excreta and in urine in urban and rural areas of the world
in 2009 and 2050 (50% of phosphorus is estimated to be in the urine of human
excreta; thus, the mass of phosphorus in feces would equal the mass listed in urine).
Total P in excreta
(metric tons)
Total P in urine
(metric tons)
2009
Total
Urban
Rural
3358 048
1755 942
1601 546
1678 744
877 691
800 493
2050
Total
Urban
Rural
4329 417
3055 623
1273 234
2164 429
1527 532
636 337
pita protein intake from vegetable sources is assumed the same in
2009 and 2050). In reality, it is likely that diets will change as
countries develop and food intake changes on a global level
(WHO, FAO, 2003). Increases in food intake and shifting of calories from staples of roots and tubers towards livestock products
and to meat, poultry, milk, and other dairy products will increase
demand for phosphorus fertilizers. Urbanization also results in a
more varied diet richer in animal proteins and fat (WHO, FAO,
2003). Changes in global diets will also drive the demand for
phosphorus fertilizers.
Furthermore, while dietary energy and protein intake have been
steadily increasing on a global basis; the change is not equal across
regions. That is, the per capita supply of vegetable protein is
slightly higher than that of animal protein in developing countries,
while the supply of animal protein is three times higher than that
of vegetable protein in industrialized countries. In addition, per capita food energy supply has declined from both animal and vegetable sources in the countries in economic transition, while it has
increased in the developing and industrialized countries (WHO,
FAO, 2003). In global terms, the WHO/FAO reported that the supply
of calories has remained relatively constant in Sub-Saharan Africa
while caloric intake has increased by almost 1000 kcal/capita-day
in East Asia, primarily in China.
Global phosphorus demand is currently approximately 15 million metric tons. Future scenarios for 2050 suggest the demand
could range from 4 to 110 million metric tons with a likely demand
of 67 million metric tons (Cordell, 2010). Our calculations show
that the total phosphorus available in excreted human waste (urine and feces) in 2009 is therefore approximately 22% of global
phosphorus demand. This is supported by other estimations (Liu
et al., 2008; Cordell et al., 2009a) The phosphorus available in urine
alone could account for 11% of the total global phosphorus demand
assuming 50% of phosphorus is present in urine. Importantly, only
0.3–1.5 million metric tons of phosphorus are estimated to be cur-
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J.R. Mihelcic et al. / Chemosphere 84 (2011) 832–839
rently recovered from human waste annually by wastewater reuse
and reclamation and biosolids application (Liu et al., 2008; Cordell
et al., 2009a). In addition, our discussion does not take into considerations the many inefficiencies and losses that occur in the whole
system of mining phosphate reserves and producing agricultural
commodities (see Cordell et al. (2009b) for discussion on this topic). Also, our comparisons do not account for scenarios where demand for phosphorus demand increases 2% per year until 2050
from increases in population, demand for meat and dairy demand,
and cultivation of biofuels (Cordell et al., 2009b).
Our 2009 estimates of potential global phosphorus derived from
human urine and feces was approximately 3.4 million metric tons
of phosphorus available per year. If this value is assumed to remain
constant over the next 90 years (resulting in 2.9 million metric
tons globally in 2050), it represents only 2% of the approximately
15 000 million metric tons of phosphorus in phosphate rock that
are economically recoverable with current technology and represent approximately 50–100 years of readily available phosphorus
mining reserves (Cordell et al., 2009a; Vaccari, 2009). However,
all the urine collected from one individual has been reported to
provide enough useable nutrients (phosphorus, nitrogen) to fertilizer 300–400 square meters of crops per year (Jönsson et al., 2004).
Furthermore, the World Health Organization has stated that nutrients obtained from recycled excreta can help to relieve poverty
through: (1) reductions in malnutrition through improved nutritional variety and household food security, (2) increased income
from sale of surplus crops, and, (3) money saved on fertilizer which
can be put to other productive uses (WHO, 2006). Recovery of
phosphorus (and nitrogen) from urine and pollution prevention efforts that reduce phosphorus from laundry and dish detergents
also have the potential to greatly reduce phosphorus (and nitrogen) loadings to wastewater treatment plants and the environment. Obviously consideration of the potential to recover
nitrogen from human excrement (especially urine) is important.
In recent decades, closed-loop sanitation systems have received
attention as a way to reduce health risks while at the same time
recovering useful nutrients and returning them back to food systems quickly (Esrey et al., 2001). Closed-loop sanitation uses excreta collection methods that facilitate the decomposition of
pathogens and other excreted material into beneficial products
that can be used directly for crop production, which can then help
alleviate malnutrition and possibly increase income (WHO, 2006).
One important component of closed-loop sanitation technology
such as a compost latrine is the diversion of urine from the collection of feces, which keeps moisture levels low, promoting oxygenated conditions and speeding up destruction of pathogens through
desiccation (WHO, 2006; Mehl et al., 2011). Urine diversion is also
a technology that addresses the need for an alternative means for
providing sanitation coverage in urban areas of developing countries. Urine diversion (e.g. urine-separating compost toilets) is currently used more frequently in rural rather than urban settings.
However, urine diversion has many advantages in urban settings.
For example, removing urine from the wastewater collection system reduces energy and materials requirements at the treatment
plant , reduces peak ammonia loadings to the treatment plant
which can act as a substitute for plant expansion, and 3) reduces
the impact of combined sewer overflows on aquatic environments
(Rauch et al., 2003). In addition, urine diversion technology has
been shown to be feasible in several urban developed country settings. This includes a Swiss study which measured attitudes in a
small focus group towards a Swedish based technology implemented at the household level (Pahl-Wostl et al., 2003). In that
study, acceptance of urine diversion toilets was quite high (assuming no increase in cost) with the majority of participants expressing interest in moving to an apartment with the technology and
purchasing food fertilized with urine.
Table 2 demonstrated the important role urbanization will play
in the distribution of phosphorus produced from urine. Currently,
slightly over 50% of the global population is urban, whereas in
2050, the percentage of the population that is urban is projected
to grow to nearly 70% (UNFPA, 2007). Accordingly, much of the
world’s future population that will be unserved by improved sanitation will be situated in the world’s cities. In terms of the current
situation in regards to reuse of human wastes in urban and rural
areas, Liu et al. (2008) suggests that ‘‘it could be appropriate to assume’’ that about 20% of urban human wastes are currently reused
and 70% of rural human wastes are currently reused. Traditionally,
water-consumptive sewers where urine is mixed and diluted with
solid excreta and graywater are thought to be the most feasible option for managing human waste in urban environments. However,
even in developing world cities where sewers exist, few are connected to wastewater treatment facilities that can recover nutrients from the waste. In these situations oxygen depleting
pollutants and nutrients can cause localized water quality problems which in turn harm the ability of the world’s poor to generate
needed income through employment as fishers. Additionally,
water-intensive sanitation technologies may not be appropriate
for many of the world’s cities which are under water stress or will
be in the future (Fry et al., 2008). The combined importance of
water conservation and nutrient recovery from human excreta in
these urban areas of developing countries suggests the need for
an alternative strategy for providing sanitation coverage.
This study geospatially quantified the mass of phosphorus
available from human urine globally, regionally, and by specific
country. The analysis was performed over two scenarios of population (2009 and 2050). This important material flow was related to
the presence or absence of improved sanitation technologies and
also considers the global trend of urbanization. The potential for
obtaining needed phosphorus from human urine is in its infancy,
yet has great potential as a source or phosphorus. This is especially
important because as the world moves toward meeting the
Millennium Development Goal sanitation target, engineers and urban planners might consider designing urine diversion systems
appropriate for urban areas.
Acknowledgment
We thank the US Peace Corps for assistance provided through
the Master’s International Program in Civil & Environmental
Engineering.
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