FSM is required in densely populated areas where a proportion of the population is not connected to a sewerage network, and pit latrine coverings and reconstruction are not possible. This is the situation in most urban areas in developing countries, but such services are also used in developed countries where sewerage systems are unavailable. FSM services are typically provided by formal and informal private sector service providers, local governments, water authorities and utilities. However, FSM services are often unavailable in many developing countries, or are often informal, irregular, unhealthy, and insecure if they are available. This can cause surface water and groundwater pollution, the spread of pathogens in the environment and adversely affect public health. This can result in incredible services with relatively high costs in the homes they need.
Faecal sludge collection services can be made available on a scheduled basis or on a call-for-service basis (also known as on-demand, on-request or non-scheduled services). The collected faecal sludge may be transported to treatment plants using a vacuum truck; a tank and pump mounted on a flatbed truck; a small tank pulled by a motorcycle; or in containers on a hand cart. Mobile or permanent transfer stations can be used to improve the efficiency of faecal sludge transportation by transferring the waste to larger tankers for haulage to treatment. The wider use of multiple decentralized sludge treatment facilities within cities (to avoid long haulage distances) is currently being researched and piloted.
The collected faecal sludge should preferably be processed at dedicated faecal sludge treatment plants, instead of being co-treated with sewage in municipal sewage treatment plants, unless these plants are able to take the additional load, and facilities to separate liquids and solids are available.
A variety of mechanized and non-mechanized processing technologies may be used, including constructed wetlands, anaerobic digestion, and waste stabilization ponds. The treatment process can produce useful products such as treated effluent that can be used for irrigation.