Co-Composting is the controlled aerobic degradation of organics, using more than one feedstock (faecal sludge and organic solid waste). Thermophilic conditions, marked by temperatures that exceed 60 °C, are achieved when certain basic parameters (moisture, carbon-nitrogen (C:N) ratio, aeration) are met that result in the elimination of pathogens and rapid decomposition of the waste material. The process produces a safe, stable end product that can be used as a compost or soil amendment.Describes biological processes that occur in the presence of oxygen.
Decomposed organic matter that results from a controlled aerobic degradation process. In this biological process, microorganisms (mainly bacteria and fungi) decompose the biodegradable waste components and produce an earth-like, odourless, brown/black material. Compost has excellent soil-conditioning properties and a variable nutrient content. Because of leaching and volatilisation, some of the nutrients may be lost, but the material remains rich in nutrients and organic matter. Generally, excreta or sludge should be composted long enough (2 to 4 months) under thermophilic conditions (55 to 60 °C) in order to be sanitised sufficiently for safe agricultural use.Consists of urine and faeces that are not mixed with any flushwater. Excreta is relatively small in volume, but concentrated in both nutrients and pathogens. Depending on the characteristics of the faeces and the urine content, it can have a soft or runny consistency.Refers to (semi-solid) excrement that is not mixed with urine or water. Depending on diet, each person produces approximately 50–150 L per year of faecal matter of which about 80 % is water and the remaining solid fraction is mostly composed of organic material. Of the total essential plant nutrients excreted by the human body, faeces contain around 39 % of the phosphorus (P), 26 % of the potassium (K) and 12 % of the nitrogen (N). Faeces also contain the vast majority of the pathogens excreted by the body, as well as energy and carbon rich, fibrous material.Refer to biodegradable plant material (organic waste) that must be added to some technologies in order for them to function properly. Organic degradable material can include, but is not limited to, leaves, grass and food market waste. Although other products in this compendium contain organic matter, the term organics is used to refer to undigested plant material.Mixture of solids and liquids, containing mostly excreta and water, in combination with sand, grit, metals, trash and/or various chemical compounds. A distinction can be made between faecal sludge and wastewater sludge. Faecal sludge comes from on-site sanitation technologies, i.e. it has not been transported through a sewer. It can be raw or partially digested, a slurry or semisolid, and results from the collection and storage/treatment of excreta or blackwater, with or without greywater. Wastewater sludge (also referred to as sewage sludge) originates from sewer-based wastewater collection and (semi-)centralised treatment processes. The sludge composition will determine the type of treatment that is required and the end-use possibilities.The liquid produced by the body to rid itself of nitrogen in the form of urea and other waste products. In this context, the urine product refers to pure urine that is not mixed with faeces or water. Depending on diet, human urine collected from one person during one year (approx. 300 to 550 L) contains 2 to 4 kg of nitrogen. The urine of healthy individuals is sterile when it leaves the body but is often immediately contaminated by coming into contact with faeces.Describes technologies for on-site collection, storage, and sometimes (pre-) treatment of the products generated at the user interface. The treatment provided by these technologies is often a function of storage and is usually passive (i.e. requires no energy input), except a few emerging technologies where additives are needed. Thus, products that are ‘treated’ by these technologies often require subsequent treatment before use and/or disposal. In the technology overview graphic, this functional group is subdivided into the two subgroups: “Collection/Storage” and “(Pre-)Treatment”. This allows a further classification for each of the listed technologies with regard to their function: collection and storage, (pre-) treatment only or both.Refers to the methods through which products are returned to the environment, either as useful resources or reduced-risk materials. Some products can also be cycled back into a system (e.g. by using treated greywater for flushing).A functional group is a grouping of technologies that have similar functions. The compendium proposes five different functional groups from which technologies can be chosen to build a sanitation system:
User interface (U), Collection and Storage/Treatment (S), Conveyance (C), (Semi-) Centralised Treatment (T), Use and/or Disposal (U).
A sanitation system is a multi-step process in which sanitation products such as human excreta and wastewater are managed from the point of generation to the point of use or ultimate disposal. It is a context-specific series of technologies and services for the management of these sanitation products, i.e. for their collection, containment, transport, treatment, transformation, use or disposal. A sanitation system comprises functional groups of technologies that can be selected according to context. By selecting technologies from each applicable functional group, considering the incoming and outgoing products, and the suitability of the technologies in a particular context, a logical, modular sanitation system can be designed. A sanitation system also includes the management and operation and maintenance (O & M) required to ensure that the system functions safely and sustainably. Simple, single cell organisms that are found everywhere on earth. They are essential for maintaining life and performing essential “services”, such as composting, aerobic degradation
of waste, and digesting food in our intestines. Some types, however, can be pathogenic and cause mild to severe illnesses. Bacteria obtain nutrients from their environment by excreting enzymes that dissolve complex molecules into more simple ones which can then pass through the cell membrane.

The process by which biodegradable components are biologically decomposed by microorganisms (mainly bacteria and fungi) under controlled aerobic conditions.
The utilisation of products derived from a sanitation system.
Any cellular or non-cellular microbiological entity capable of replication or of transferring genetic material (e.g. bacteria, viruses, protozoa, algae or fungi).
Any substance that is used for growth. Nitrogen (N), phosphorus (P) and potassium (K) are the main nutrients contained in agricultural fertilisers. N and P are also primarily responsible for the eutrophication of water bodies.
A sanitation system in which excreta and wastewater are collected and stored or treated on the plot where they are generated.
An organism or other agent that causes disease.A diverse group of unicellular eukaryotic organisms, including amoeba, ciliates, and flagellates. Some can be pathogenic and cause mild to severe illnesses.
The means of safely collecting and hygienically disposing of excreta and liquid
wastes for the protection of public health and the preservation of the quality of public water bodies and, more generally, of the environment.

Waste matter that is transported through the sewer.
An open channel or closed pipe used to convey sewage. See C.3 and C.4
The organic molecule (NH2)2CO that is excreted in urine and that contains the nutrient nitrogen. Over time, urea breaks down into carbon dioxide and ammonium, which is readily used by organisms in soil. It can also be used for on-site faecal sludge treatment. See. S.18An infectious agent consisting of a nucleic acid (DNA or RNA) and a protein coat. Viruses can only replicate in the cells of a living host. Some pathogenic viruses are known to be waterborne (e.g., the rotavirus that can cause diarrheal disease).
Used water from any combination of domestic, industrial, commercial or agricultural activities, surface runoff/stormwater, and any sewer inflow/infiltration.

Faecal sludge has a high moisture and nitrogen content, while organic solid waste (from food or agricultural waste) is high in organic carbon and has good bulking properties which promotes aeration. By combining the two, the benefits of each can be used to optimise process and product. Three commonly used methods of Co-Composting are (1) open windrow, (2) in-vessel and (3) a combination of open-windrow and passively-aerated static pile. In open windrow Co-Composting, the mixed material ( sludge and organic waste) is piled into long heaps called windrows and left to decompose. In-vessel Co-Composting requires controlled moisture, air supply and mechanical mixing. The third method uses a combination of static-pile and open-windrow. Waste sits in a static-pile for around two to three months and then it is moved to windrows for further decomposition.

Design Considerations

Key components in the design of a Co-Composting facility include space for sorting and waste separation, drying beds, composting units, screening, storage of compost and discards, hygiene and disinfection infrastructure, on-site wastewater treatment system, staff facilities and a buffer zone. Depending on the climate and available space, the facility may need to be covered. The facility should be located close to sources of organic waste and faecal sludge to minimize transport costs, but still a distance away from living areas to minimise any perceived or real health risks. Windrow  piles should be at least 1 m high and insulated with a 30 cm layer of compost, soil, or grass soil to promote an even distribution of heat. In colder climates heaps work best at 2.5 m high and 5 m wide. Sludge must be dewatered in Unplanted Drying Beds T.9 prior to mixing with organic waste. A sealed or impervious composting pad (the surface where the heaps are located) must be constructed to collect the leachate which can then be reintegrated into the piles or treated.

Materials

Co-Composting facilities can be constructed using locally available material. The compost pad can be made out of concrete, or well-compressed clay. If required, a cover/roof can be made from local materials such as bamboo, grass matting, or wood, plastic or metal sheeting. Water may be a required additive, depending on the climate. Prefabricated composting vessels of different sizes are available on the market.

Applicability

Because of the high level of organisation and labour needed to sort organic waste, manage the facility and monitor treatment efficiency, this technology is unlikely to be practical in the acute response phase. However, it can be considered a viable option in the stabilization and recovery phases of an emergency. Experience has shown that Co-Composting facilities operate best when they are established as a business with compost as the marketable product that can generate revenue to support cost recovery. However, compost sales cannot be expected to cover the full cost of the service.

Operation and Maintenance

The operation requirements for Co-Composting facilities are high. Well-trained maintenance staff must carefully monitor quality and quantity of input material, the C:N ratio, and manage moisture and oxygen content. Staff should also carefully track turning schedules, temperature, and maturing times to ensure high-quality treatment. Organic waste must first be sorted so it is free from non-organic materials. Turning must be periodically done with either a front-end loader or by hand using a pitch fork or shovel. Robust grinders for shredding large pieces of organic solid waste (i.e., small branches and coconut shells) and pile turners help to optimize the process, reduce manual labour, and ensure a more homogenous end product.

Health and Safety

Health risks can be minimised if workers adopt basic precautions and hygienic practices and wear personal protective equipment. If material is found to be dusty, proper ventilation should be provided and workers should wear masks. To ensure pathogens are Removed to a safe level, the World Health Organization (WHO) recommends that compost temperature should be maintained between 55–60 °C for at least one week. If there is any doubt, compost should be stored for at least a year before use. If resources exist, helminth egg inactivation should be monitored as a proxy measure of sterilisation. WHO guidelines should be consulted for detailed information.

Costs

Costs of building a Co-Composting facility vary depending on the method chosen and the cost of local materials and if machinery such as aerators and grinders are included in the design. The main costs to consider are the overall operation requirements including transport and supply of faecal sludge and organic solid waste and disposal of compost.

Social Considerations

Before considering a Co-Composting system, the concept should be discussed with the affected community. If the community has experience of separating their organic waste and composting, this can be an enabling factor. Identifying that compost made from human waste is an acceptable product for potential users (market survey) and ensuring that the compost product conforms to local guidelines/standards are necessary prerequisites. Without these, different treatment processes should be identified.

Case Studies & Related Content

Anaerobic Baffled Reactor - maturation ponds
Suggested by: (Save the Children International) at 20.03.2021