Composting toilets as a sustainable alternative to urban sanitation - A review

Abstract

In today's flush based urban sanitation systems, toilets are connected to both the centralized water and wastewater infrastructures. This approach is not a sustainable use of our water and energy resources. In addition, in the U.S., there is a shortfall in funding for maintenance and upgrade of the water and wastewater infrastructures. The goal of this paper was to review the current knowledge on composting toilets since this technology is decentralized, requires no water, creates a value product (fertilizer) and can possibly reduce the burden on the current infrastructure as a sustainable sanitation approach. We found a large variety of composting toilet designs and categorized the different types of toilets as being self contained or central; single or multi chamber; waterless or with water/foam flush, electric or non-electric, and no-mix or combined collection. Factors reported as affecting the composting process and their optimum values were identified as; aeration, moisture content (50-60%), temperature (40-65°C), carbon to nitrogen ratio (25-35), pH (5.5-8.0), and porosity (35-50%). Mass and energy balance models have been created for the composting process. However there is a literature gap in the use of this knowledge in design and operation of composting toilets. To evaluate the stability and safety of compost for use as fertilizer, various methods are available and the temperature-time criterion approach is the most common one used. There are many barriers to the use of composting toilets in urban settings including public acceptance, regulations, and lack of knowledge and experience in composting toilet design and operation and program operation.

Full text

Review
Composting toilets as a sustainable alternative
to urban sanitation – A review
Chirjiv K. Anand, Defne S. Apul
⇑
Department of Civil Engineering, The University of Toledo, MS 307, 2801 W. Bancroft St., Toledo, OH 43606, USA
article info
Article history:
Received 1 March 2013
Accepted 10 October 2013
Available online 21 November 2013
Keywords:
Composting toilet
Dry sanitation
abstract
In today’s flush based urban sanitation systems, toilets are connected to both the centralized water and
wastewater infrastructures. This approach is not a sustainable use of our water and energy resources. In
addition, in the U.S., there is a shortfall in funding for maintenance and upgrade of the water and waste-
water infrastructures. The goal of this paper was to review the current knowledge on composting toilets
since this technology is decentralized, requires no water, creates a value product (fertilizer) and can pos-
sibly reduce the burden on the current infrastructure as a sustainable sanitation approach. We found a
large variety of composting toilet designs and categorized the different types of toilets as being self con-
tained or central; single or multi chamber; waterless or with water/foam flush, electric or non-electric,
and no-mix or combined collection. Factors reported as affecting the composting process and their opti-
mum values were identified as; aeration, moisture content (50–60%), temperature (40–65 °C), carbon to
nitrogen ratio (25–35), pH (5.5–8.0), and porosity (35–50%). Mass and energy balance models have been
created for the composting process. However there is a literature gap in the use of this knowledge in
design and operation of composting toilets. To evaluate the stability and safety of compost for use as fer-
tilizer, various methods are available and the temperature–time criterion approach is the most common
one used. There are many barriers to the use of composting toilets in urban settings including public
acceptance, regulations, and lack of knowledge and experience in composting toilet design and operation
and program operation.
Ó2013 Elsevier Ltd. All rights reserved.
Contents
1. Introduction . . . ...................................................................................................... 330
2. Types of sanitation technologies . . . . . . ................................................................................... 330
3. Composting toilet systems. . . . . . . . . . . ................................................................................... 332
3.1. Evolution of composting toilets . . . . . . . . . . . ............. ............................................................ 332
3.2. Types of composting toilets . . . . . . . . . . . . . . ............. ............................................................ 333
3.2.1. Self-contained and central composting toilets . . . . . . ........................................................... 333
3.2.2. Single and multiple chambered . . . . . . . . . . . . . . . . . . ........................................................... 333
3.2.3. Waterless and water based toilets. . . . . . . . . . . . . . . . ........................................................... 333
3.2.4. Electric and non-electric toilets . . . . . . . . . . . . . . . . . . ........................................................... 334
3.2.5. Urine separating and combined collection systems . . ........................................................... 334
3.2.6. Commercially available toilets.............................................................................. 334
4. Choosing a composting toilet system . . ................................................................................... 336
5. Factors affecting aerobic composting in toilets . . . . . . . . . . . . . ................................................................ 336
5.1. Aeration . . . . . . . . . . . . . . ...................................................... ................................... 336
5.2. Moisture content . . . . . . . ................ ......................................................................... 336
5.3. Temperature . . . . . . . . . . ................................ ......................................................... 336
5.4. Carbon and nitrogen content and nutrient balance (C/N ratio) . . . . . ............. ......................................... 337
5.5. pH............................. ............................................................................... 337
0956-053X/$ - see front matter Ó2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.wasman.2013.10.006
⇑
Corresponding author. Tel.: +1 419 530 8132.
E-mail addresses: chirjiv@gmail.com (C.K. Anand), defne.apul@utoledo.edu (D.S.
Apul).
Waste Management 34 (2014) 329–343
Contents lists available at ScienceDirect
Waste Management
journal homepage: www.elsevier.com/locate/wasman

5.6. Particle size and porosity . . . . . . . . . . . . . ....... ..................................................................... 337
6. Compost safety and application to plants. . . . . . . . . . . . ...................................................................... 338
7. Mathematical modeling of compost process . . . . . . . . . ...................................................................... 338
8. Design of composting toilets . . . ......................................................................................... 339
9. Guidelines and regulations for composting toilets. . . . . ...................................................................... 339
10. Case studies on composting toilets . . . . . . . . . . . . . . . . ...................................................................... 339
11. Barriers to use of composting toilets in urban areas . . ...................................................................... 340
12. Conclusions......................................................................................................... 341
Acknowledgements . . . . . . . . . . ......................................................................................... 341
References . ......................................................................................................... 341
1. Introduction
The current water infrastructure in developed countries re-
quires a lot of energy and produces one quality of potable water
for all uses, such as drinking, irrigation, and toilet flushing. In the
U.S., the water and wastewater treatment systems use approxi-
mately 3% of total U.S. electricity (EPRI, 2002). Using energy inten-
sive processes to produce water and then using this high quality
water for flushing toilets is inefficient management of both water
and energy resources. In addition, the current water infrastructure
is aging which results in water loss through leaks and bursts in
pipes. According to USEPA’s funding gap analysis, there is a roughly
$17-billion shortfall between current annual capital expenditures
and the amount of spending required to maintain the existing
water and wastewater infrastructure (USEPA, 2002). While repair
and rehabilitation are necessary and unavoidable, alternatives
should also be explored to reduce the burden on the current infra-
structure and develop more sustainable options.
What are some possible alternatives? High quality potable
water is needed in the buildings; supplying lower quality water
to save on energy or cost is therefore not a viable option However,
the practice of using potable water for flushing toilets (non-potable
purpose) can be mitigated with the use of alternative technologies.
For example, technologies such as the use of grey water or har-
vested rainwater in toilet flushing would reduce the need for pota-
ble water; yet that would still require the connection to the
wastewater infrastructure. In these flush-based technologies, the
waste is still first diluted with water for easy conveyance. Then, en-
ergy is spent at the wastewater treatment plant to biodegrade the
organic matter and separate the solids from the wastewater.
Another alternative technology is the composting toilet, which
has thus far been used primarily in rural areas, and areas with
water shortages (Fittschen and Niemczynowicz, 1997; Cordova
and Knuth, 2005; Kaczala, 2006; Tønner-Klank, 2007). Composting
toilets require little to no water and can therefore disconnect the
toilet from both the water supply and wastewater infrastructure.
Such water and wastewater savings can be significant at system le-
vel since toilet flushing constitutes the highest percentage of water
use in residential (27%) (Vickers, 2001), office (51%), school (60%)
and hotel (33%) buildings (Schultz communications, 1999). An-
other advantage of composting toilets is in nutrient cycling and
transportation. Similar to solids obtained from traditional waste-
water treatment plant, the solids obtained from composting toilets
can also be used as a fertilizer; yet they would be free from the ur-
ban runoff contamination and may require less transportation if
they can be applied where compost is produced.
By being decentralized, requiring little to no water, and produc-
ing a value product (fertilizer), composting toilets offer good prom-
ise as a sustainable solution to water and wastewater
infrastructure issues. In addition, the operation of composting toi-
lets is well aligned with the ecological design principles. When ap-
plied to the water and sanitation infrastructure, ecological design
principles point to human dimension (e.g. incorporating stakehold-
ers in design), learning from nature (e.g. decentralization; elimina-
tion of the concept of waste; meeting multiple functions such as
treating human waste while producing a value product, limited en-
ergy input to the system, and system design specific to location
and scale), and integrating nature (e.g. relying on nature’s pro-
cesses for treatment) (Apul, 2010). From a sustainability perspec-
tive, a stronger connection to these ecological design principles
gives composting toilets an advantage over the conventional
systems.
Composting toilets also fit in with today’s understanding of sus-
tainable construction since they reduce water and wastewater
flows within a building. In the U.S. the most common green build-
ing rating system is the U.S. Green Building Council’s (USGBC)
Leadership in Energy and Environmental Design (LEED). Compost-
ing toilets are recognized by the USGBC and they have been used to
achieve LEED certifications. More specifically, the use of compost-
ing toilets in a new construction or major renovation building can
help earn the water use reduction and innovative wastewater tech-
nologies credits within the water efficiency (WE) category of LEED
(LEED, 2005).
In spite of these benefits, the lack of knowledge and awareness
of composting toilets remains a barrier to their acceptance and
implementation. Starting in 1970s, as wastewater treatment re-
search received much attention and saw major developments,
the topic of composting toilets has been neglected by the sanita-
tion community including researchers and professionals. Yet, with
the new sustainability paradigm of the 21st century, interest in
composting toilets has been growing. With this growing interest
and yet gaps in knowledge about the engineering of composting
toilets, it is now timely to revisit the status of composting toilets
and bring awareness to this technology so they can be better eval-
uated for possible adoption as an alternative sustainable sanitation
system.
The goal of this paper was to review the current state of knowl-
edge on composting toilets use in developed countries and identify
knowledge gaps. Since the science and engineering of composting
human waste is not very well developed and there is limited peer
reviewed literature on this topic, information was pulled not only
from peer reviewed but also from grey literature. We begin by dis-
cussing the different types of sanitation, differentiating their work-
ing from the composting toilets. We discuss the technological
development of different types of composting toilets that can be
used in different locations based on site conditions. The design of
composting toilets and its relation to the science of composting
are also presented. A few case studies are included to bring out
some advantages as well as barriers in implementation of this
technology.
2. Types of sanitation technologies
Sanitation technologies can be water based or composting
based (Fig. 1). In water based systems, the flushed water source
330 C.K. Anand, D.S. Apul / Waste Management 34 (2014) 329–343

can be potable water, rainwater, or grey water and the treatment
can be achieved via various methods such as conventional
wastewater treatment (Tchobanoglous et al., 2002), septic tanks
(McCray et al., 2005), constructed wetlands (Kadlec and Knight,
2008), or living machines (eco-machines) (Living machines,
2012; Todd Ecological, 2012; Kumar et al., 2011; Morgan and
Martin, 2008; Kavanagh and Keller, 2007). Though all these sanita-
tion technologies provide the same function of treating human
waste, potable water based systems with conventional wastewater
treatment or with septic tanks are primarily the ones used in the
developed world.
Composting based sanitation systems are known as compost-
ing toilets, dry toilets, biological toilets, bio-toilets, or waterless
toilets (Del Porto and Steinfeld, 1998). They are typically made
of plastic, ceramic, or fiberglass. A composting toilet has two pri-
mary components; the toilet and the composting tank. The other
parts of a composting system often include a fan and vent pipe to
remove any odor. There is typically a drain to remove excess
leachate and access doors to empty compost. Composting systems
require little or no use of water for conveyance of wastes. Similar
to the conventional toilet, the toilet in a composting system is a
waste collector. The waste is collected into the composting tank
where it is digested aerobically. Some systems may use earth-
worms (vermicomposting) as an alternative to aerobic compost-
ing (Yadav et al., 2010; Hill and Baldwin, 2012). Bulking agents
or amendments (e.g. sawdust, leaves, and food waste) are often
added to help co-manage different types of waste, adjust carbon
to nitrogen ratio, and increase porosity of the compost. Sawdust
is a popular amendment because it creates an environment for
bacteria to thrive with its high porosity, high water and air reten-
tion and high drainage properties (Kitsui and Tesezawa, 1999). In
addition, the low density of saw dust (0.19 g/cm
3
;Zavala and
Funamizu, 2006) can reduce energy requirements of mixing.
Composting toilets are often equipped with a mechanical mixer
that homogenizes the compost matrix to maintain conditions
favorable for aerobic digestion where organic matter is oxidized
Fig. 2. Composting toilet system.
Fig. 3. Composting toilet system design approaches.
Sanitation systems
Water based
(Potable, rainwater, or greywater based)
Composting based
(Dry, pint flush, foam flush)
Treatment method
(Municipal wastewater, septic tanks,
constructed wetlands, or living machines)
Treatment method
(Composting)
Solids management
Fig. 1. Sanitation technologies.
C.K. Anand, D.S. Apul / Waste Management 34 (2014) 329–343 331

into ammonia, carbon dioxide, and humus. The end product from
these toilets contains stable, high molecular weight dissolved or-
ganic matter (Narita et al., 2005) that can be recycled as soil
fertilizers.
Solids are produced as a result of both water and compost-
ing based sanitation approaches. The solids from wastewater
treatment are typically dried, digested, and sometimes com-
posted before they are moved out of site to be landfilled, incin-
erated, applied to crops as fertilizers, or used for energy
recovery. The only treatment of solids from dry or non-water
based toilets is typically the composting process. After this
treatment, they are considered ready for application to non-edi-
ble plants as natural fertilizers.
3. Composting toilet systems
3.1. Evolution of composting toilets
The very first dry toilet called the earth commode, made of
wood, was invented in 1860 by Henry Moule (Del porto and Stein-
feld, 1998). The flush mechanism of this toilet released soil into the
commode every time the flush was used. The closet was shallow,
allowing aerobic decomposition. In 1873, a dry ash commode
was introduced, that was connected to the fireplace and automat-
ically filled the commode with ash every time the lid of the toilet
was lifted (Davis, 1996). This version of the dry toilet had a bucket
under the toilet, where all the waste was collected. The version
after this replaced the bucket with drawers. The compost from this
toilet was recommended to be dried in an iron drawer under a
kitchen range. There were no major complaints of odors or annoy-
ance from the use of these toilets (Ward, 1868). The next modifica-
tion to this design was the installation of pipe to the composting
toilet so that the toilet and the composting chamber could be in-
stalled at different levels in a multi-story building. In 1940s Appas-
aheb Patwardhan invented a double chambered composting toilet
in India (Del Porto and Steinfeld, 1998). He collected night soil (hu-
man waste), composted it, and applied it to crops. There was very
little use of water in these toilets (Patil, 1996). Use of two cham-
bered toilets, with aeration chimneys was also seen in Vietnam
in the 1960s (Del Porto and Steinfeld, 1998).
Commercial composting toilets progressed technologically
when different brands invented better toilets. In 1939, with an
aim of pollution prevention in Baltic Sea, Rickard Lindstorm in-
vented a single chambered composting toilet, after observing the
conversion of horse manure to soil (Del Porto and Steinfeld,
1998; Clivus Multrum, 2012). This toilet had partitions and air
ducts. In 1964, this toilet, originally made in concrete, was made
in fiberglass and introduced into the market under the company
name Clivus Multrum. Sun-mar, another composting toilet com-
pany, introduced incinerating composting toilet for use in cottages
in 1966 in Sweden (Sun-Mar, 2013). These toilets used incineration
and reduced the waste to ashes. After this stage, composting toilets
Fig. 4. Self-contained composting toilet (Envirolet). Source:http://www.enviro-
let.com/enwatsel.html.
Fig. 5. Central composting tank connected to multiple toilets from one story (a) and from multiple stories (b) Source: www.sun-mar.com/products/centrex3000.php.
332 C.K. Anand, D.S. Apul / Waste Management 34 (2014) 329–343

were developed further and marketed for large and small-scale use
in many different designs.
3.2. Types of composting toilets
Composting toilets are currently available in many different
types of designs. Design possibilities include either the top or the
bottom option in Fig. 3. We aimed to make this categorization of
design approaches based on the types of systems available in the
market. The design of a composting toilet can follow any one of
the paths along the lines from left to right. In other words, a com-
posting toilet can be self-contained or central, have single or multi-
ple chamber tanks, be operated electrically, or manually, be water-
based or waterless, separately collect urine or collect urine and
feces through one pipe, and be installed in single or multi-storied
buildings.
3.2.1. Self-contained and central composting toilets
Self-contained composting toilets were introduced in the mar-
ket in 1970s (Sun-mar in 1971, Biolet in 1972). In a self-contained
composting chamber (Fig. 4), the toilet and the composting cham-
ber are one unit.
In 1977, Sun-mar introduced a central composting toilet (Sun-
Mar, 2013). Central composting systems have larger tanks com-
pared to self-contained composting toilets. The tank has connec-
tions to multiple toilets that can be located on the same or
different floors (Fig. 5). If a transport medium such as water or
foam is not used, vertical piping is necessary to convey fecal matter
into the composting tank (Fig. 5b). Angled piping can be used with
water or foam flush composting toilets (Fig. 5a).
3.2.2. Single and multiple chambered
All waste (fresh and old) is composted in a single chamber in
single chambered composting toilets (Fig. 2). Some current brands
that manufacture single chamber composting toilets include Clivus
Multrum, CTS, Phoenix, Bio-toilet, and Sun-Mar. As the drawbacks
of having a single chamber came into sight, these toilets were
improved over time. In an earlier design where hot air was being
blown into the composting toilet, issues were observed with liquid
at the bottom not evaporating efficiently while the fresh waste at
the top of the pile was drying out too much causing difficulty in
mechanical agitation and reductions in microbe concentration
and composting rate (Sun-mar, 2013). This version of composting
toilet in Sun-mar was improved when the heater was removed
from the top and instead placed in the base of the toilet in a sealed
compartment. This change in design improved the speed of com-
posting and ease of operation by allowing evaporation of excess li-
quid in the base; yet still keeping the compost moist (Sun-mar,
2013).
Single chambered composting toilets have the disadvantage of
having the same operating conditions throughout the toilet and
for all stages of composting. This problem can be overcome by
batch composting using multi-chambered composting tanks that
provide extra chambers to separate composted material from fresh
wastes. Multi-chambered composting tanks can also increase the
design capacity of the toilet since the filled chamber can be re-
placed with an empty chamber.
Multi-chambered composting toilet systems typically have two
or three chambered composting tanks. Two chambered compost-
ing tanks contain a chamber for composting and another cham-
ber/tray for finishing (Fig. 4). Another version of multi-chamber
composting is carousel composting (Fig. 6) or composting using
interchangeable composters. In carousel composting, at any given
time, the toilet is connected to only one chamber so that the waste
enters only that chamber. Once that chamber is filled, the tank is
rotated such that waste falls into an empty chamber (Peasey,
2000). By the time the fourth chamber is filled, the waste in the
first chamber is composted, finished, and ready to be removed
(Del Porto and Steinfeld, 1996). Some brands that manufacture
these toilets include Eco-Tech Carousel, all Vera systems, BioLet
NE.
A multi-chamber bio-drum based system is another type of
multi-chambered composting system where the waste is rotated
in a drum that has different chambers for composting, evaporating,
and finishing for each batch of waste (Fig. 7). The bio-drum in-
cludes a screen in the rear to help leach out excess water from
the waste into an evaporating chamber. When the compost seems
ready, it is shifted to a finishing chamber, by rotating the drum
backwards. In the finishing chamber, fresh waste is not allowed;
the compost is isolated and allowed to finish while drying out.
The finishing chamber is safe to be accessed by the user for re-
moval of compost since the user is not exposed to fresh wastes.
3.2.3. Waterless and water based toilets
In waterless toilets, vertical piping is used to convey the waste
and water may be used for cleaning the toilet but not for waste
conveyance. Water based toilets can have angled piping and in-
clude micro-flush toilets (1 pint = 0.47 L) and foam flush toilets
(6 oz = 0.17 L). The foam is a biodegradable soap that serves the
purpose of improving user comfort, cleaning, and waste
conveyance.
Fig. 6. Carousel composting tank. Source:http://www.ecological-engineering.com/
carousel.html.
Fig. 7. Drum based composting chambers. Source:http://www.sun-mar.com/
tech_drum.html,http://sun-mar.com/tech_our.html.
C.K. Anand, D.S. Apul / Waste Management 34 (2014) 329–343 333

3.2.4. Electric and non-electric toilets
The electric versions of the composting toilets include fans and
heating system that use electricity. The fan in electric composting
toilets draws the air into the toilet, preventing any odors in a
restroom. In Biolet systems, this air inside the toilet is heated using
a thermostatically controlled heater. The warm air evaporates the
excess liquid in the composting toilets and is vented out through
the vent pipes (Biolet, 2010). Non-electric systems can remove ex-
cess moisture and therefore work better if they are coupled with
either urine diversion or a leachate drainage system.
In electric toilets, the electricity can also be used to convey the
waste by creating a vacuum. Most toilets are generally gravity
based but some are vacuum flush toilets that use suction for easy
movement of wastes through the pipes. The toilet in vacuum flush
systems is not directly connected to the composting tank (Fig. 8). A
vacuum (negative pressure) generator unit intercepts the pipe that
connects toilet to tank. These toilets use 0.2 L of water per flush
and are available in single tank or double tank models as shown.
A Y-connection in dual tank systems can divide the waste into
the two tanks.
3.2.5. Urine separating and combined collection systems
About 500 L of urine and 50 L of feces are produced per person
per year (Drangert, 1998). Combined collection systems collect all
this waste into one composting chamber. In urine separating toi-
lets (also known as no-mix toilets) (Fig. 9) urine is collected and
managed separately, typically with end use as a fertilizer. Urine
separation in flushed toilets is now well accepted in some Euro-
pean countries (Lienert and Larsen, 2009). Urine separating com-
posting toilets (e.g. Seperatte toilets) and urine separating
vermicomposting toilets (Hill and Baldwin, 2012) are also com-
mercially available. Urine separation has the advantages of reduc-
ing unwanted odor and excess moisture in the compost pile. In
addition, urine can be an effective fertilizer because of its high
nutrient and low pathogen content. Humans release 7–10 times
more nitrogen, 2–3 times more potassium, and 2–3 times more
phosphorus in urine than in feces (Table 1). Urine separation
combined with vermicomposting especially seems to hold good
promise. Lab studies simulating vermicomposting of feces resulted
in highly mature compost with complete inactivation of total col-
iforms (Yadav et al., 2010). Recently Hill and Baldwin (2012) com-
pared the field performance of urine separating vermicomposting
toilets with combined collection composting toilets. Their results
significantly favored the urine separating vermicomposting toilet,
which performed much better in mass reduction, pathogen
destruction, compost quality, and operational cost.
3.2.6. Commercially available toilets
Table 2 is a compilation of some of the popular commercially
available composting toilet models. There is a wide variety in type,
capacity, and price of the models but the initial costs are generally
higher than a flushed toilet. Yet, their life cycle costs, energy use,
Fig. 9. Urine separating toilet (water based). Source:http://www.ecovita.net/
ekologen.html.
Table 1
Amount of nutrients physiologically excreted by one person in one year.
Source Phosphorus (kg/person/year) Potassium (kg/person/year) Nitrogen (kg/person/year)
UF T UF T UF T
Drangert (1998) 0.4 (67%) 0.2 (33%) 0.6 (100%) 0.9 (71%) 0.3 (29%) 1.2 (100%) 4.0 (88%) 0.5 (12%) 4.5 (100%)
Magid et al. (2006) 0.55 (75%) 0.18 (25%) 0.73 (100%) 0.91 (71%) 0.37 (29%) 1.28 (100%) 4.00 (9%) 0.37(91%) 4.37 (100%)
Vinneras et al. (2006)
a
0.36 (67%) 0.18 (33%) 0.54 (100%) 1.00 (73%) 0.37 (27%) 1.37 (100%) 4.00 (88%) 0.55 (12%) 4.55 (100%)
U = Urine; F = Feces, T = Total.
a
Proposed values for design purposes. Percentages were calculated from Table 6 of Vinneras et al. (2006).
Fig. 8. Vacuum based composting systems (single and double tank models). Source:
http://enviroletvf.com/files/dometic_envirolet_vf_catalog.pdf,http://www.enviro-
let.com/vf.html.
334 C.K. Anand, D.S. Apul / Waste Management 34 (2014) 329–343

Table 2
Commercially available composting toilet technologies (adapted from Berger (2009)).
Company Models Automatic/manual Electric/non-electric Minimum and maximum
capacity for available
models
Price ($ USD) Web address
BioLan With or without urine diversion,
waterless
Manual Both – 826 http://www.biolan.fi/english/
default.asp?active_page_id=1
BioLet Self-contained and central; dry
toilets
Manual and automatic mixing models
available; Models also equipped with
automatic liquid control
Electric and non-electric
(has fan and heater); solar
powered fan;
Full time use : 3–4 people 1000–2499 http://www.biolet.com/
Part time use: 4–6 people
Bio-Lux Self-contained; Can be powered by
windmill or solar panels
Heat and sawdust mixing are electricity
based, but can be controlled manually
Electric 16–20 times/day to 160–
200 times
6800–57,000 http://www.seiwa-denko.co.jp/
biolux/top.html#JavaScript
Clivus
Multrum
Self-contained and central, Foam
flush, waterless, grey water, no urine
diversion
Semi-automatic Electric for fan and non-
electric, solar powered
3–7 people 2500–5000 http://www.clivusmultrum.com/
EcoEthic Waterless Automatic and semi-automatic Both 3–4 people full time use http://www.ecoethic.ca/
Eco Toilets Dual flush, urine separating, and
central, low flush, waterless
Non-electric 5 people including periodic
loading from visitors
http://www.ecotoilets.co.nz/
Eco John Waterless Incinerating Toilet, Waste
combustion system, waterless
system
Non-electric 3–10 people 3000 http://ecojohn.com/
Eco Tech Multi-chambered tank, Urine
Diversion Available
Electricity for fan and
heating if required
4–6 people 2000–4000 http://ecotechproducts.net/
Ekolet Multi-chambered tank Electricity for fan 900–4000 http://www.ekolet.com/?lang=eng
Envirolet Double tank; water flush; foam flush Both Electric 2–16 people based on 3 uses
per capita per day
1779–5529 http://www.envirolet.com/
Green Toilet Vacuum, flame burning, electric fuel,
waste freezing
Electric 2–4 people 23,457–396,172 http://www.pikkuvihrea.fi/fi/
Nature Loo Self contained, Vermi composting,
Urine diverting
Manually and electrically operated Electric 1–6 people (permanent
basis) based on 2 uses per
capita per day
671–3381 http://www.nature-loo.com.au/
Naturum Urine diverting Manual Electricity for fan 1700 http://www.biolan.fi/suomi/
default4.asp?active_page_id=534
Pheonix Central systems, dry systems, gravity
micro-flush
Manual Electric 2–8 people 5000–7000 http://www.compostingtoilet.com/
Rota Loo Multi cambered tank, Urine diversion
available, central systems
4–8 people 600 onwards http://www.rotaloo.com/
Terra Nova Self-contained and central, urine
diversion available,
Electricity for fan, 5–40 uses/day 3000–6000 http://www.berger-
biotechnik.com/compost-toilets/-
terranova-grp/index.php
Separette
Villa
Urine diverting, incinerating toilets, Both Unlimited user capacity
available
1134–3899 http://www.separett.com/
Sun-mar Self-contained and central dry and
flush
Both 1–8 people 1595–2195 and
up for higher
capacity
http://www.sun-mar.com/
C.K. Anand, D.S. Apul / Waste Management 34 (2014) 329–343 335

and associated greenhouse gas emissions can be lower than those
of potable water flushed toilets due to reduced operational costs
and impacts (Anand and Apul, 2010).
The capacity of the toilets is reported in different units by each
company (Table 2). Some specify the number of people, others
specify the number of uses and yet others specify full or part time
use and whether the loading is estimated for daily or occasional
visitor use. The lack of consistency in how toilet capacity is pre-
sented is due to a lack of standardized or established design guide-
lines for composting toilets.
Commercial composting tanks are typically of fixed size. If the
number of people using the toilet is more than the capacity of
the tank, then the system is scaled up by adding more tanks. These
units are best installed in new construction but a retrofit to
existing buildings is also possible. In the U.S. each state has differ-
ent rules on manufacturing, installation, and operation of toilets
and end use of the compost. These regulations must be referred
to before investing in a manufactured composting toilet. The
mechanics of a composting toilet are not very complicated. Contac-
tors or owners can custom build a composting toilet by modeling
after the designs shown in Table 2.
4. Choosing a composting toilet system
Selection and installation of a suitable composting system de-
pends on local factors such as climatic conditions, water availabil-
ity, infrastructure (single or multi story building), population
density, and end-product management (Esrey et.al, 1998). The lo-
cal temperature conditions and electricity availability will help to
decide whether an electric or a non-electric toilet may be required.
Depending on the availability of water or conveyance require-
ments water based or waterless toilets can be adopted. The infra-
structure type and the services available at a site may support
only one particular model or provide options. Examples of such in-
stances are construction work required in new or existing build-
ings for installation of piping; space for installation and
maintenance of composting tanks in the basement of an already
existing building; composter load considerations, and position of
the composter (ground level or above ground level). Availability
of a nearby garden or agricultural land may also affect the decision
of installation of a dry sanitation system unless the composted
material is collected and sold to farmers or transported to an agri-
cultural area. Composted material is often disposed of in dump-
sters in urban areas where other ways to manage it may not be
available or convenient.
5. Factors affecting aerobic composting in toilets
Composting is the process of decomposition of organic matter.
Microorganisms oxidize organic compounds under aerobic condi-
tions producing carbon dioxide, ammonia, volatile compounds,
and water. Energy is released during decomposition some of which
is used by the microrganisms for reproduction and growth; the rest
is released as heat. The primary organisms involved in the decompo-
sition of organic matter in a compost pile are bacteria, actinomycetes
and fungi (Trautmann and Olynciw, 1996). For microorganisms to
survive and carryout the process of composting in the composting
chamber, suitable environmental conditions need to be maintained.
The factors affecting the process of composting include water
content, temperature, carbon to nitrogen ratio, pH, particle size,
porosity, oxygen concentration. These parameters depend on the
formulation of the compost mix (Bernal et al., 2009). During com-
posting, how the process is managed by agent addition, aeration,
mixing, heating, and leachate collection will affect the water
content, temperature, and oxygen concentration of the compost.
Most of these factors affecting composting are inter-related. Gen-
erally, composting systems do not have any monitors to check
the condition of the compost. The maintenance needs manual
attention. AlasCan, onsite recycling and wastewater treatment sys-
tems provide the treatment systems with a monitor to check liquid
levels, pH levels, electric usage, and temperature (Del Porto and
Steinfeld, 1998). It also has sprinkler systems for automatic liquid
distribution and programmed mixers for regular mixing to aid in
heat distribution.
5.1. Aeration
Adequate aeration is necessary to maintain aerobic conditions
for composting. Lack of oxygen in the pile can cause anaerobic con-
ditions which leads to odor issues and lowers the rate of compost-
ing. On the other hand, excess airflow is not recommended either
since it can remove too much heat and water vapor from the com-
post. The volume fraction of oxygen ein compost can be calculated
using Eq. (1) (Richard et al., 2002):
¼V
g
V
g
þV
w
þV
s
ð1Þ
V
g
is volume of gas; V
w
is volume of liquid and V
s
is volume of solids.
As shown in Eq. (1), the amount of air space in compost is affected
by the moisture content of the compost; the more the moisture, the
less available space for air. Miller et al. suggest that the optimum
oxygen concentration is between 15% and 20% (Miller, 1992).
5.2. Moisture content
Moisture in compost is necessary for adequate microbial activ-
ity since the aqueous medium makes the nutrients physically and
chemically accessible to micro-organisms. Urine, moisture in feces,
and water from pint or foam flush toilets contribute to the mois-
ture content in compost. The moisture content of feces is 82% (Zav-
ala et al., 2002). The composting pile produces additional moisture
as a result of microbial activity and biological oxidation of organic
matter (Epstein, 1997).
Too much moisture in the compost pile can create anaerobic
conditions. Composting systems can have provisions to remove
leachate and reduce the excess moisture content of the compost.
If the moisture level is too low (below 40%); the dry conditions
slow down the process of decomposition and require addition of
water for activation (Yamada and Kawase, 2006). Liang et al.
(2003), in their experiments on biosolids composting, observed a
lag in initiation and lower rate of microbial activity at low moisture
content (30–40%), at all temperatures.
Many studies have been published on the required level of
moisture content in composting systems. Liang et al. (2003) ob-
served that a moisture content of 50% is the minimal requirement
for composting. Others noted that a moisture content <64% is suit-
able for aerobic degradation whereas moisture content above 60%
or 65% favors both aerobic and anaerobic degradation of feces due
to high moisture content inhibiting oxygen movement in the pile
(Zavala and Funamizu, 2005, 2006). Many studies showed that
the optimum moisture content for proper composting is 50–60%
(Schultz, 1960; Poincelot, 1974; Zavala and Funamizu, 2006; Jen-
kins, 1999; Gajalakshmi and Abbasi, 2008), and Zavala and Funam-
izu (2006) proposed that a moisture content of 65% be considered
the critical level above which should be avoided.
5.3. Temperature
Different phases of composting are indicated by differing
temperatures. Composting begins with and the readily degradable
336 C.K. Anand, D.S. Apul / Waste Management 34 (2014) 329–343

organic matter is degraded by mesophilic organisms that function
at a temperature range of 19–45 °C(Depledge, 2013). The heat pro-
duced during this process causes the temperature of the compost
to rise above 45 °C where thermophilic organisms become active
(Zavala and Funamizu, 2006;Jenkins, 1999). The rate of compost
biodegradation is faster in thermophilic phase than in mesophilic
phase (Zavala et al., 2004a). Maximum degradation of organic mat-
ter and destruction of pathogens occur during the thermophilic
phase at a temperature range of about 50–65 °C(Bernal et al.,
2009; Nataka et al., 2003). An early study reported the optimum
temperature range for composting as 40–65 °C(de Bertoldi et al.,
1983). A more recent study suggested 60 °C as the optimum tem-
perature for feces degradation (Zavala and Funamizu, 2006). At
temperatures over 65

C, the compost activity reduces, as most
thermophilic organisms cannot survive this temperature (Germer
et al., 2010). As the supply of fats, proteins, and complex carbohy-
drates decreases in the pile, the temperature of the pile reduces.
During this cooling stage, the compost appears ready to be applied
on agricultural lands. However, coarser organic matters still need
to be digested. As the temperature reduces, the organisms from
the mesophilic range work on decomposing the remaining organic
matter. The last stage of composting is the curing/maturing stage
where compost is set aside allowing the organisms left in the com-
post pile to complete the composting process (Trautmann and
Olynciw, 1996; Jenkins, 1999).
To maintain an optimum temperature profile various strategies
can be used including insulation (Huang, 1993; Epstein, 1997;
Niwagaba et al., 2009), turning, and electrical heaters. Niwagaba
et al. (2009) noted that insulation is essential for maintaining tem-
perature in the compost even when outside temperature is greater
than 25 °C. Germer et al. (2010) reported that optimum tempera-
tures could not be obtained when feces from ventilated pit latrines
was mixed with shredded bush vegetation but sufficiently high
temperatures were observed under the addition of food waste to
feces. Since high temperatures in a compost pile are typically con-
centrated in the central parts, mixing and turning can be used to
create a more uniform temperature profile (Huang, 1993; Epstein,
1997). Turning can also increase the temperature. Vinnerås et al.
(2003) observed that the temperature in a pilot study was just
above 40 °C until the compost was turned after which the temper-
ature rose above 65 °C.
5.4. Carbon and nitrogen content and nutrient balance (C/N ratio)
Nitrogen and carbon content of human feces is around 65 mg-
N/g-dry and 500 mg-C/g-dry, respectively (Hotta and Funamizu,
2009;Bai and wang, 2010). During composting, both the carbon
and nitrogen content of the compost are reduced. Hotta and Fun-
amizu (2007) note that 66% of fecal nitrogen decomposes to
ammonia whereas 34% remain as biologically inert type of nitro-
gen. In other studies, nitrogen losses from 17% to 94% have been re-
ported in presence of sawdust as the bulk matrix (Bai and Wang,
2010; Wang and Wang, 2008; Zavala et al., 2005; Hotta et al.,
2007). In thermophilic conditions all nitrogen loss to ammonia
gas can be from inorganic nitrogen whereas the organic nitrogen
can be fully retained in the compost (Bai and Wang, 2010). This
is because ammonifying bacteria are mesophilic and their absence
in thermophilic conditions would hinder ammonification. In the
case of fecal carbon, approximately 80% of fecal carbon is mineral-
ized to CO
2
(a greenhouse gas) whereas further 20% remains in the
composted material (Hotta and Funamizu, 2007). Loss of carbon
and nitrogen in gaseous emissions of CO
2
and ammonia reduce
the amount of fertilizer nutrients available to fertilizers and there-
fore the agronomic value of the compost. However, in their review
of animal manure compost quality literature, Bernal et al. (2009)
note that high mineralization results in mature compost with bet-
ter nutrient availability since leaching and volatilization are ex-
pected to be less when mature compost is applied to plants.
When bulking agents with little biodegradability and high ligno-
cellulose content (e.g. sawdust) are used the nitrogen loss can be
decreased (Sanchez et al., 2001).
Animal manure composting has been studied more extensively
than human waste composting. Uenosono et al. (2002) reported a
nitrogen loss of 70% from animal manure composting. A review of
compost maturity of animal manure found fairly large variations of
nitrogen (2–60%) and carbon loss (9–67% for organic matter and
30–72% for organic carbon) (Bernal et al., 2009). The variability
in nutrient loss values has been attributed to manure type (beef,
dairy, poultry or pig), bulking agent type (straw, woodchip, cotton
waste, sawdust), and composting process (turned or unturned
windrow, in vessel system, forced ventilation, static pile) (Bernal
et al., 2009).
The practical management of compost focuses not on managing
the loss of carbon or nitrogen but on adjusting the ratio of carbon
to nitrogen in the compost pile. Researchers and compost manag-
ers use the carbon to nitrogen ratio as a rule of thumb for optimiz-
ing the composting process. They use the ratio of the total carbon
to total nitrogen, yet it is really the ratio of biodegradable fractions
that affect the composting process (Guardia et al., 2010).
Carbon to nitrogen ratios of 25–35 have been recommended for
composting of municipal waste and sewage sludge (Bishop and
Godfrey, 1983;de Bertoldi et al., 1983). Since the carbon to nitro-
gen ratio of human feces (C:N = 8) is deficient in carbon, a large
amount of carbon has to be added to the compost pile to adjust
the carbon to nitrogen ratio. Fresh grass cuttings, wood chips,
and kitchen wastes are examples of high carbon content bulking
materials. Fresh grass cuttings and leaves have a carbon nitrogen
ratio of 15:1. Dried leaves might have an even higher ratio (De-
pledge, 2013). Toilet paper has a carbon to nitrogen ratio of 200–
350:1(Compost ingredients, 2012). Saw dust has a carbon to nitro-
gen ratio of 190:1 and is recommended to be used on a dry weight
ratio of feces/sawdust as 1:4 (Bai and wang, 2010) resulting in a
carbon to nitrogen ratio of approximately 16. Large amounts of
food and matured compost amendment (1 feces: 3 food waste: 1
straw amendment) were also used by Vinnerås et al. (2003).
5.5. pH
pH affects the growth response of microorganisms in a compost
pile. Different bacteria survive at different pH levels. de Bertoldi
et al. (1983) and Miller (1992) recommended a pH range of 5.5–
8.0 for optimum composting. More recently, Bernal et al. (2009)
suggested a pH range of 6.7–9.0 in a review of animal manure com-
posting. Maintaining pH in 6.7–9.0 range helps to control nitrogen
losses by ammonia volatilization (Bernal et al., 2009). pH typically
drops as the composting process progresses due to the breakdown
of carbonaceous material to organic acidic intermediates by acid
forming bacteria (de Bertoldi et al., 1983). The pH of the compost
pile is observed to increase with increase in temperature (Epstein,
1997;de Bertoldi et al., 1983).
5.6. Particle size and porosity
Particle size plays a role in balancing the surface area for growth
of microorganisms and maintaining adequate porosity for aeration
(Bernal et al., 2009). The larger the particle size, the higher the
porosity and the lower the surface area to mass ratio. Compost
with large particles does not decompose adequately due to mi-
crobes’ inaccessibility to the interior parts of the compost particles.
On the other hand, very small particle size may compact the mass
and reduce the porosity. A porosity of 35–50% is recommended for
composting (Bernal et al., 2009).
C.K. Anand, D.S. Apul / Waste Management 34 (2014) 329–343 337

6. Compost safety and application to plants
Use of compost in plants can replace the use of chemical fertil-
izer and help close the nutrient cycle loop. Salmon et al. (2004)
estimated that 4.9–6.4% of annual commercial fertilizer used in
Australia could be replaced by human compost. Matured compost
can also be used as a soil amendment and can be a good alternative
to other materials since it gives a smaller final volume of compost
to handle (Vinnerås et al., 2003). The size of the compost can be re-
duced by about 10–30% of its original volume when the compost-
ing is managed well (Del Porto and Steinfeld, 1998; Arnold, 1990;
USEPA, 1999a,b).
There are two primary safety considerations with the use of
compost as soil amendment or as fertilizer. One issue is related
to toxic chemicals in compost. It has been shown in bioassay
experiments that feces from a healthy human may have low toxic-
ity but compost obtained from composting toilets can be toxic due
to biological reactions in the compost pile or accumulation of toxic
compounds in the toilet system (Kakimoto et al., 2006). The source
of toxic compounds in compost may be the pharmaceuticals and
estrogens excreted by humans. If these chemicals are not biode-
graded during the composting process, they can pollute the soil
and groundwater and accumulate in the environment. Antibiotics
and particularly amoxicillin is one of the most commonly used
pharmaceuticals by humans. Amoxicillin can quickly degrade in
composting toilets and this degradation is attributed not to bacte-
ria but to non-biological factors such as phosphate, ammonia and
pH level in the toilet matrix (Kakimoto and Funamizu, 2007a,b).
Another unwanted effect of amoxicillin is that it reduces the bacte-
rial activity and initial bacterial count in compost resulting in
lengthening of the degradation time of feces and reduction of the
maximum biodegradation rate (Kakimoto and Funamizu, 2007a,b).
Another safety consideration with the use of compost as soil
amendment or as fertilizer is its pathogen content. Compost can
contain many types of pathogenic bacteria, viruses, protozoa, hel-
minth and fungi that can cause various diseases (Wichuk and
McCartney, 2007). During composting, these pathogens are re-
duced by several processes including thermal destruction, compe-
tition between indigenous microorganisms and pathogens,
antagonistic relationships between organisms, the action of antibi-
otics produced by certain fungi, natural die-off in the compost
environment, production of toxic byproducts such as gaseous
ammonia, and nutrient depletion (Wichuk and McCartney, 2007).
In developing countries, ash has been added to compost to raise
pH and kill pathogens (Vinnerås et al., 2003). For human safety,
the product from a composting toilet should not have more than
200 most probable number (MNP) per gram of fecal coli form bac-
teria (Del Porto and Steinfeld, 1998).
Since microbiological parameters are difficult to measure, tem-
perature is often the primary criterion used to determine if the
compost is safe for use as a fertilizer. For inactivation of microor-
ganisms, a temperature of 55–65 °C is required and composting
at 55 °C can kill Escherichia coli, Listeria and Salmonella spp. within
three days (Grewal et al., 2006). Aside from high temperatures,
pathogens are also killed due to competition with thermophilic mi-
crobes that sustain in high temperature (Feachem et al., 1983).
Time–temperature combinations are used to assess pathogen
die-off. Feachem et al. (1983) suggested time–temperature combi-
nations of 1 h at P62 °C, 1 day at P50 °C, and 1 week at P46 °C for
pathogens to die-off in composting human waste. Depledge (2013)
reported that one month of 44 °C temperature or 12 months of
43 °C, temperature can be sufficient to kill all pathogens.
There are no regulations specifically for decentralized human
compost. However, there are time–temperature regulatory criteria
for pathogen reduction in compost (biosolids) obtained from
domestic wastewater treatment. Biosolids are classified as Class
A if they do not contain detectable levels of pathogens (USEPA,
2012). USEPA requires a minimum temperature of 55 °C for
15 days or longer and minimum of 5 turnings for windrow com-
posting of Class A biosolids (USEPA, 1999a,b). For aerated static
piles and in-vessel reactors the class A biosolids have to maintain
a temperature greater than 55 °C for 3 days.
While temperature–time criteria can be used as a measure of
safety of the compost, this criterion is virtually impossible to mea-
sure with available technology for the entire compost. The compost
is expected to have non-uniform temperature profile (with higher
temperatures in the middle due to higher microbial activity there)
but only a limited number of measurements can be taken from
throughout the compost. This limitation may incorrectly lead to
deeming compost safe if the measurements are taken from areas
with higher temperature. Non-uniform temperatures are the most
commonly cited explanation for pathogen regrowth and survival
during composting (Wichuk and McCartney, 2007). Zavala and
Funamizu (2006) suggest that the compost infection risk can be re-
duced to an acceptable level by mixing the sawdust amended com-
post 20 times per day over 2 days or by mixing 15 times per day
over three days after the last using event of the toilet. The mixing
helps to maintain uniform temperatures and thus reduce the
pathogens via advancing the process of composting.
A high level of stability and maturity are desired for use of com-
post as a fertilizer. The terms stability and maturity are sometimes
used interchangeably but they refer to different properties of the
compost. Stable compost is expected to have low microbial activ-
ity, be free of pathogens, and an advanced degree of organic matter
decomposition with resistance to further decomposition (Bernal
et al., 2009; Wichuk and McCartney, 2010). A mature compost is
one that does not cause adverse effects when used as or applied
to plant-growing media (Wichuk and McCartney, 2010). In a ma-
ture compost, plant growth potential (seedling emergence, vigour)
is high since phytotoxic substances and organic matter are decom-
posed. Due to high level of organic matter decomposition, a low ra-
tio of ammonia to nitrate nitrogen and volatile fatty acids is
expected (TMECC, 2002). The carbon to nitrogen ratio also has to
be low (less than 25) to be considered mature. Stability and matu-
rity typically go hand in hand since phytotoxic compounds are pro-
duced by the microorganisms in unstable composts (Bernal et al.,
2009).
There is a large number of tests available for determining com-
post maturity and stability. These tests were compiled and re-
viewed by Wichuk and McCartney (2010). Physical and sensory
tests include pile temperature, color, and odour. Biological tests in-
clude respiration, phytotoxicity and enzyme acitivty. Chemical
tests include carbon to nitrogen ratio, organic matter, humification
parameters, cation exchange capacity, electrical conductivity, pH,
ammonia and nitrate, spectroscopy, and dissolved organic carbon.
Since a single, stand-alone test for both compost stability and
maturity does not exist, it is best to use a combination of tests.
However, there is disagreement in the literature as to what the
best combination should be (Wichuk and McCartney, 2010). In
addition, applicability of these tests to human waste compost is
not very well known. For example, Hill et al. (in press) recently
showed that ammonia and CO
2
analysis based Solvita commercial
test kits commonly used for evaluating compost maturity and sta-
bility do not provide accurate results for compost from composting
toilets.
7. Mathematical modeling of compost process
Mathematical modeling of compost process is based on the gen-
eral approach of applying mass and energy balance principles to
the compost and models of different complexity involving as few
338 C.K. Anand, D.S. Apul / Waste Management 34 (2014) 329–343

as 6 to as many as 30 parameters have been developed (Mason,
2006). Microbial kinetics and oxygen consumption are used in
designing wastewater treatment plant activated sludge processes.
A similar approach can be used for composting to estimate the
time varying and ultimate decomposition of compost process
(Yamada and Kawase, 2006;Mason, 2006). Prior studies have
shown reasonable success in predicting the time varying tempera-
ture, moisture, solids content, and oxygen utilization rate of the
compost (Mason, 2006;Zavala et al., 2004b). However, to our
knowledge these mathematical models have not been used in
designing and sizing composting tanks.
8. Design of composting toilets
Composting toilet technology is not new. However, its design
and performance are still in early stages. The recommendations
made on manuals of composting toilets are typically based on
experiences and not on technical information (Zavala and Funam-
izu, 2006). Criteria for proper design of the composting toilet have
been broadly listed as safety, functionality, economy, aesthetics,
and social and environmental affordability (Zavala and Funamizu,
2006). Design considerations for a composting toilet should in-
clude an adequately sized composting chamber, ventilation
(means of aeration) to assist in decomposition of wastes and to re-
duce odor, supply of carbon to maintain carbon to nitrogen ratio, a
drain for excess fluid, and an access door for removal of composted
material (Depledge, 2013;Zavala and Funamizu, 2006). In addition,
a heater can be included to maintain temperatures and evaporate
excess moisture.
The size of the composting chamber depends on the number of
users and the chamber emptying frequency, water used for clean-
ing the toilet bowl, evaporation rate of all the water that goes into
the toilet, and the organic loading rate for adjusting the carbon
nitrogen ratio. No studies have been conducted on the amount of
water used for cleaning of the toilets; therefore, this factor is ne-
glected in designing of a composting toilet chamber (Zavala and
Funamizu, 2006). There are no standard methods for sizing a com-
posting chamber. Two methods for sizing the composting chamber
have been suggested in the literature.
The first method calculates the volume of the composting
chamber (Vin m
3
, See (Eq. (2))) based on the emptying interval
in years (N), the average number of users (P), and the annual sludge
produced per person (R)(Pickford and Reed, 1992; Bhagwan et al.,
2008). The emptying interval (N) can be taken as the design life
(e.g. 10 years) if the toilet is designed not for emtyping (as I pit la-
trines). The recommended Rvalue is 0.05 m
3
/yr/person (Bhagwan
et al., 2008).
V¼NPRð2Þ
The second method was developed by Zavala and Funamizu
(2006) who reported that organic loading (feces to sawdust ratio)
to a composting tank is much less than water loading and therefore
the water mass balance should govern the sizing of the composting
tank. Their approach included accounting for water loading from
urine and feces and drying/evaporation of water needed to main-
tain moisture content of 60%. A required drying surface area was
calculated as 643 cm
2
per capita. The bulk volume of compost ma-
trix was estimated at 17 L and 34 L per capita if compost is with-
drawn every six months and every year, respectively. Including
the shape of the mixing mechanism and free space over the com-
post matrix surface for air circulation, the height of the compost
was estimated at 36 and 63 cm for compost withdrawn every six
months and annually, respectively. These estimates do not con-
sider the enhanced drying due to mixing which would decrease
the estimated volumes and heights.
It is beneficial to include a fan in the composting toilet design so
as to remove the odorous gases generated from composting (Sal-
mon et al., 2004). An exhaust fan can be designed based on the size
of the vent pipe and the volume of air to be exchanged from the
chamber. It is recommended to have a screen at the outer opening
of the ventilation pipe to avoid files and other insects entering the
composting chamber (Depledge, 2013; Salmon et al., 2004). Solar
power and wind powered fans have also been used to power the
fans in composting toilets (Depledge, 2013;USEPA, 1999a;Berger,
2004).
9. Guidelines and regulations for composting toilets
Prior to installation of composting toilets, local or state regula-
tions need to be referred. In the U.S., the regulations were devel-
oped by counties, municipalities and state departments of
environmental quality and show some variation as well as a gen-
eral lack of detailed guidelines (Jenkins, 1999).
As per most of the regulations, composting toilets are permitted
on sites where soil conditions are unsuitable for onsite sewage
treatment and disposal systems or water under pressure is not
available from the municipality and in flood prone areas. The toi-
lets are required to have a toilet seat and a riser as well as contin-
uous ventilation to avoid any odor issues. Other general statements
are included in the regulations such as the composting tank design
requiring sufficient volume for accommodating the people served.
Similarly, care should be taken that the maintenance work of the
toilets does not endanger public health or create any nuisance.
Most states have a minimum regulation of certification of toilets
by National Sanitation Foundation (NSF) or a national testing lab-
oratory. The certification ensures that only safe designs be permit-
ted and some commercial composting toilet models are NSF
certified.
The regulations for compost management are also non-
uniform throughout the world due to a lack of strong scientifi-
cally proven information on how composting should be
performed and what are the critical points for proper composting
to ensure safety (Briton, 2000). In the United States the Biosolids
503 rule establishes requirements for final use or disposal of
sewage sludge (USEPA, 2012). There are no rules specifically for
composting but the Biosolids 503 rule is typically extended to
composting as well.
In addition to the above commonly stated rules, some states
include the following additional regulations. Written permissions
from the department of health is required for handling of products.
The composting tank cannot be placed near a food storage or
preparation area. Disposal of any liquids should be to a sanitary
sewer system. The residue from the tank should be removed, when
the tank is 75% filled. State of Connecticut requires a minimum vol-
ume of 64 m
3
for the composting tank. Most of the above men-
tioned barriers do not help in promoting the use of a composting
toilet. These regulations need to be modified or edited for better
approval of these toilets.
10. Case studies on composting toilets
Use of composting toilets in buildings has been reported on
many green technology type web pages. In contrast, there is a scar-
city of published literature on this topic. Here, we report a few
example case studies obtained from gray literature. One example
of large scale installation of composting toilets is the ecological set-
tlement in Bielefeld, Germany which has more than 100 flats, up to
4 stories high and a kindergarten school (Berger, 2004). This site
has 70 composting toilets installed initially in 1986, extended to
500 toilets later. Most of the systems involved were manufactured
C.K. Anand, D.S. Apul / Waste Management 34 (2014) 329–343 339

by Clivus Multrum. All the composting systems were provided
with in-built insulation. Up to four toilets were connected to one
composting toilet. Decomposition of the biological waste took
about two years from each tank before it was emptied for the first
time. The apartments did not initially have approval to install com-
posting toilets as by law all apartments needed to be installed with
water-flushed toilets. Permits were obtained for each of the apart-
ments for installation of composting toilets. The systems required
regular maintenance. In cases where the inhabitants did not wish
to personally look into maintenance, packages for the same could
be purchased as a service from the provider. The excess fluid from
the system is either connected to a grey water system or used in a
garden. The decomposition process reduces the volume of the
waste by about 10% in 2–3 years. This waste is then removed from
the composting tank. The waste removed is finished for one more
year before application to plants. After the first emptying, the tank
is emptied once every year.
At the building scale, various installations of composting toi-
lets have been reported in educational buildings. For example, in
Weston, Masacchusetts a private K-12 school facility (Garthwaite
Center) was not permitted to use the local sewer system (Kieran,
2008). So building designers used waterless urinals and Phoenix
brand composting toilets in the two-story building. In Swan-
nanoa, North Carolina, Clivus Multrum brand composting toilets
were installed in two of the 10 toilets of a 38-student college
dorm (North Carolina Green Building Technology Database,
2003). At this facility, students add a cup of sawdust every time
they use the toilet and the compost is removed almost every
month. A pump is installed to drain out any liquid/urine to the
sewer. An exhaust fan is run continuously to create a negative
pressure and control odor. The exhaust from the fan was not al-
lowed to be sent through the recovery ventilators as a part of
abiding county codes. The state of North Carolina does not allow
composting and use of the waste so; the waste is collected and
sent to a landfill.
A centralized composting toilet system is installed at the C.K.
Choi Building for the Institute of Asian Research at University of
British Columbia (Institutional Green Buildings, 2010;Thomas,
2008). This is a three story office and classroom type building with
Clivus Multrum brand composting toilets connected to composters
in the basement via steel chutes. The composting toilets are noted
to be odor free due to basement installation of composters and the
presence of a fan. Daily maintenance, such as wiping the toilet and
adding wood chips or bark mulch is carried out by the University
maintenance staff. When the building was designed, the concept
was to use the products from composting as fertilizers. However,
currently, the leachate is drained to the sewer and the compost
product is disposed of in a sanitary landfill because they do not
meet the local regulatory environmental and health and safety
standards.
A larger scale single building implementation of composting
toilets can be found in Charlest Strut University Campus in
Thurgoona, Australia (Salmon et al., 2004;Crockett et al., 2003).
At this facility 25 composting toilets are installed. The leachate
from composting toilets is discharged to a wetland system and
the compost is buried onsite. Midges were found in the compos-
ter but not externally or in the toilet room. Flies did not cause
any problems; however, spiders colonized the air vents and the
composters due to the plentiful supply of midges. To maintain
regular airflow, the spider webs required regular removal. The
maintenance operations such as raking of the compost pile and
cleaning of the vents was not found objectionable by the mainte-
nance staff. Midges could be controlled by placing a filter at the
opening of the vent. Positive responses were obtained from the
users at the campus with some behavior change toward use of
green sanitation.
11. Barriers to use of composting toilets in urban areas
One barrier to poor adoption of composting toilets is the lack of
awareness of this technology. Engineers and water/construction
industry can be resistant to accepting a technology they are unfa-
miliar with (Cordova and Knuth, 2005). Similarly, the public may
not accept the technology because of perceived odor and mainte-
nance issues. Composting toilets can require the user to be more
active in managing their waste compared to the flush and forget
approach currently used in developed areas. Maintenance require-
ments such as turning of the compost, addition of bulking agents,
emptying the chamber, and cleaning the toilet without much use
of water can be unacceptable for the user. Also, composting toilets
may be perceived as second-class, inconvenient and burdensome
all of which would interfere with the adoption of the technology
(Cordova and Knuth, 2005).
Much of this lack of awareness and negative image of compost-
ing toilets is likely to arise from insufficient experience and litera-
ture on this topic. There are no well known urban success stories
regarding composting toilets. Research on the rate of composting
of human waste and process based design of composting toilets
is immature resulting in composting toilet designs that rely mostly
on experience and not as much on science. Scientific research on
field performance of composting toilets and especially the achieve-
ment of thermophilic temperatures is immature and inconclusive
(Hill and Baldwin, 2012;Vinnerås et al., 2003). Detailed design
and sizing guidance regarding ventilation, heating, and use of bul-
king agents are still unaddressed issues. In single chambered toi-
lets, fresh waste containing pathogens can leach into and
contaminate the finished compost negating any sanitation
achieved (Hill and Baldwin, 2012). Multi chambered toilets can
overcome this problem but there exist no design guidelines
addressing this issue in either single or multi chambered toilets.
Design advancements can also be made to make the handling
and monitoring of composting of waste easier. One possibility is
to develop designs that allow the user to monitor and appropri-
ately adjust the levels of temperature, moisture content and other
factors. This can reduce the maintenance barrier and make the
technology more acceptable. There is a lack of development in
the safe handling and application of compost as well. Safe use
and handing of compost and its application to crops is a barrier
to the implementation of composting toilets due to the pathogen
and pharmaceutical risk factor.
There are also barriers related to the urban setting (Cordova and
Knuth, 2005; Salmon et al., 2004). There is a large stock of existing
buildings and their retrofitting with composting toilets may not be
easy. Use of composting toilets in high density and high rise build-
ings is even less developed. It would require a large basement,
which may not be available in many cases. Access to bulking mate-
rial and management of the end product may be difficult in urban
settings. Local plumbing codes may also be prevent the use of com-
posting toilets since they may require a toilet to be connected to
the central water and wastewater treatment system or may have
other provisions regarding the management of the compost.
One of the largest scale urban applications of composting toilets
has been tried in Mexico. Experience from this also identified pro-
grammatic issues as barriers to the success of the composting toilet
technology (Cordova and Knuth, 2005). Weaknesses in program
operation and issues with scaling up of the operation, incomplete
service provision and political motivations have been noted as bar-
riers to adoption of composting toilets in urban areas.
Currently, the cost of composting toilets is estimated from the
purchase of a composting toilet which is higher than a flush based
toilet. From a user’s perspective and in presence of low water and
sewer utility rates, composting toilets are not currently economi-
cal. Therefore, the cost is a barrier from a building designer or a
340 C.K. Anand, D.S. Apul / Waste Management 34 (2014) 329–343

home owner perspective. However, the true cost of large scale use
of composting toilets is not known since system level analyses
comparing composting toilets to centralized infrastructures have
not been researched.
12. Conclusions
Composting literature review in this paper focused on increas-
ing awareness and developing good understanding of composting
toilets as an alternative urban sanitation technology. The goal of
the paper was to review the current knowledge on composting toi-
lets and identify the knowledge gaps. The following major points
are drawn from the review:
– While some composting toilets may use small amounts of foam
or water for waste conveyance, in general, composting toilets
can be considered a dry system not requiring connections to
water and wastewater infrastructures.
– Composting toilets exist in greater diversity compared to the
conventional water based toilets. Possible designs of compost-
ing toilets are self contained or central; single or multi cham-
ber; waterless or with water/foam flush, electric or non-
electric, and no-mix or combined collection. A fan, heater,
leachate drainage, and compost access door are some elements
of composting toilets.
– Factors affecting composting process and their optimum values
are: aeration, moisture content (50–60%), temperature (40–
65 °C), carbon to nitrogen ratio (25–35), pH (5.5–8.0), and
porosity (35–50%).
– Mass and energy balance models have been created for the
composting process. However, such models have not been
utilized in design and operation of composting toilets with
one exception where a water mass balance approach was
demonstrated for sizing of composting chamber.
– Compost can be a high quality fertilizer with its rich nutrient
content but the safety of compost is a concern due to presence
of pathogens and phytotoxic compounds. Stability and maturity
of the compost can be assessed using many different methods
but there is no agreement on which combination of tests are
most accurate and there is limited literature on applicability
of these tests to compost from human waste.
– There are limited case studies on composting toilets but com-
posting toilets have been used in communities and in different
types of facilities.
– There are no clear and uniform regulations related to compost-
ing toilets. Existing regulations can either prevent the sole
installation of the toilet or the application of compost can
become a barrier to use of composting toilets.
– There are many barriers to the use of composting toilets in
urban settings including public acceptance, regulations, and
lack of knowledge and experience in composting toilet design
and operation and program operation. It will be necessary to
overcome these barriers before composting toilets can take
their place as a sustainable sanitation approach in the devel-
oped areas.
The primary recommendation for research direction based on
this review is on better understanding the composting process in
toilets so this information can be used in composting toilet design
and operation. Experimental and modeling studies considering real
conditions such as effects of bulking agents, toilet paper, fan, mix-
er, and heater on the performance of the composting toilet and the
safety of the compost product will be helpful in improving the de-
sign and operation of composting toilets and subsequently their
public acceptance. In addition, system level economic and
environmental analysis (e.g. life cycle costing, environmental life
cycle assessment, city level assessment) of composting toilets is
missing in the literature but would be helpful in evaluating this
technology as a sustainable alternative to centralized water based
sanitation.
Acknowledgements
This study was partially funded by the Lake Erie Protection
Fund and Water Resources Center of Ohio. We thank Todd Rains
and Robert Nix from University of Toledo learning ventures for cre-
ating figure 2.
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