Composting toilet
A composting toilet is a type of dry toilet that treats human waste by a biological process called composting. This process leads to the decomposition of organic matter and turns human waste into compost-like material. Composting is carried out by microorganisms under controlled aerobic conditions. Most composting toilets use no water for flushing and are therefore called "dry toilets".
In many composting toilet designs, a carbon additive such as sawdust, coconut coir, or peat moss is added after each use. This practice creates air pockets in the human waste to promote aerobic decomposition. This also improves the carbon-to-nitrogen ratio and reduces potential odor. Most composting toilet systems rely on mesophilic composting. Longer retention time in the composting chamber also facilitates pathogen die-off. The end product can also be moved to a secondary system – usually another composting step – to allow more time for mesophilic composting to further reduce pathogens.
Composting toilets, together with the secondary composting step, produce a humus-like end product that can be used to enrich soil if local regulations allow this. Some composting toilets have urine diversion systems in the toilet bowl to collect the urine separately and control excess moisture. A vermifilter toilet is a composting toilet with flushing water where earthworms are used to promote decomposition to compost.
Composting toilets do not require a connection to septic tanks or sewer systems unlike flush toilets. Common applications include national parks, remote holiday cottages, ecotourism resorts, off-grid homes and rural areas in developing countries.
Terminology
The term "composting toilet" is used quite loosely, and its meaning varies by country. For example, in Germany and Scandinavian countries, composting always refers to a predominantly aerobic process. This aerobic composting may take place with an increase in temperature due to microbial action, or without a temperature increase in the case of slow composting or cold composting. If earth worms are used then there is also no increase in temperature.Composting toilets differ from pit latrines and arborloos, which use less controlled decomposition and may not protect groundwater from nutrient or pathogen contamination or provide optimal nutrient recycling. They also differ from urine-diverting dry toilets where pathogen reduction is achieved through dehydration and where the feces collection vault is kept as dry as possible. Composting toilets aim to have a certain degree of moisture in the composting chamber.
Composting toilets can be used to implement an ecological sanitation approach for resource recovery, and some people call their composting toilet designs "ecosan toilets" for that reason. However, this is not recommended as the two terms are not identical.
Composting toilets have also been called "sawdust toilets", which can be appropriate if the amount of aerobic composting taking place in the toilet's container is very limited. The "Clivus multrum" is a type of composting toilet which has a large composting chamber below the toilet seat and also receives undigested organic material to increase the carbon to nitrogen ratio. Alternatives with smaller composting chambers are called "self-contained composting toilets" since the composting chamber is part of the toilet unit itself.
Applications
Composting toilets can be suitable in areas such as a rural area or a park that lacks a suitable water supply, sewers and sewage treatment. They can also help increase the resilience of existing sanitation systems in the face of possible natural disasters such as climate change, earthquakes or tsunami. Composting toilets can reduce or perhaps eliminate the need for a septic tank system to reduce environmental footprint.These types of toilets can be used for resource recovery by reusing sanitized feces and urine as fertilizer and soil conditioner for gardening or ornamental activities.
Basics
Components and use
A composting toilet consists of two elements: a place to sit or squat and a collection/composting unit. The composting unit consists of four main parts:- storage or composting chamber
- a ventilation unit to ensure that the degradation process in the toilet is predominantly aerobic and to vent odorous gases
- a leachate collection or urine diversion system to remove excess liquid
- an access door for extracting the compost
Some composting toilets divert urine to prevent the creation of anaerobic conditions that can result from over saturation of the compost, which leads to odors and vector problems. This usually requires all users to use the toilet in a seated position. Offering a waterless urinal in addition to the toilet can help keep excess amounts of urine out of the composting chamber. Alternatively, in rural areas, men and boys may be encouraged just to find a tree.
Construction
The composting chamber can be constructed above or below ground level. It can be inside a structure or include a separate superstructure.A drainage system removes leachate. Otherwise, excess moisture can cause anaerobic conditions and impede decomposition. Urine diversion can improve compost quality, since urine contains large amounts of ammonia that inhibits microbiological activity.
Composting toilets greatly reduce human waste volumes through psychrophilic, thermophilic or mesophilic composting. Keeping the composting chamber insulated and warm protects the composting process from slowing due to low temperatures.
Odorous gases
The following gases may be emitted during the composting process that takes place in composting toilets: hydrogen sulfide, ammonia, nitrous oxide and volatile organic compounds. These gases can potentially lead to complaints about odours. Some methane may also be present, but it is not odorous.Pathogen removal
Waste-derived compost recycles fecal nutrients, but it can carry and spread pathogens if the process of reuse of waste is not done properly. Pathogen destruction rates in composting toilets are usually low, particularly of helminth eggs. This carries the risk of spreading disease if a proper system management is not in place. Compost from human waste processed under only mesophilic conditions or taken directly from the compost chamber is not safe for food production. High temperatures or long composting times are required to kill helminth eggs, the hardiest of all pathogens. Helminth infections are common in many developing countries.In thermophilic composting bacteria that thrive at temperatures of oxidize waste into its components, some of which are consumed in the process, reducing volume and eliminating potential pathogens. To destroy pathogens, thermophilic composting must heat the compost pile sufficiently, or enough time must elapse since fresh material was added that biological activity has had the same pathogen removal effect.
One guideline claims that pathogen levels are reduced to a safe level by thermophilic composting at temperatures of 55 °C for at least two weeks or at 60 °C for one week. An alternative guideline claims that complete pathogen destruction may be achieved already if the entire compost heap reaches a temperature of for one hour, for one day, for one week or for one month, although others regard this as overly optimistic.
Design considerations
Environmental factors
Four main factors affect the decomposition process:- Sufficient oxygen is necessary for aerobic composting
- Moisture content from 45 to 70 percent
- Temperature between and, which is achieved through proper chamber dimensioning and possibly active mixing
- Carbon-to-nitrogen ratio of 25:1
Additives and bulking material
Leachate management
removal controls moisture levels, which is necessary to ensure rapid, aerobic composting. Some commercial units include a urine-separator or urine-diverting system and/or a drain at the bottom of the composter for this purpose.Aeration and mixing
Microbial action also requires oxygen, typically from the air. Commercial systems provide ventilation that moves air from the bathroom, through the waste container, and out a vertical pipe, venting above the roof. This air movement passes carbon dioxide and odors.Some units require manual methods for periodic aeration of the solid mass such as rotating the composting chamber or pulling an "aerator rake" through the mass.
Comparisons with other types of toilets
Pit latrines
Composting toilets convert feces into a dry, odorless material which is very different to the wet fecal sludge produced in pit latrines which has to be taken care of through a fecal sludge management system. Composting toilets do not cause groundwater pollution due to their safe containment of feces in above-ground vaults compared to pit latrines, allowing composting toilets to be sited in locations where pit-based systems are not appropriate.Composting toilets may have higher capital costs than pit latrines, but lower lifecycle costs. They require more involvement by the user than the "drop and forget" approach of pit latrines.