The faecal sludge collected from septic tanks has higher biochemical oxygen demand (BOD) as well as a higher solid content when compared to sewerage. Faecal sludge treatment entails separation of solid and liquid matter, their treatment, reuse and disposal. The objectives are to:

1. Reduce the water content of sludge, thus making it easier to work with and transport.
2. Reduce the oxygen demand and suspended solids content of the liquid fraction that is discharged to the environment.
3. Reduce pathogens from the liquid effluent, to allow its safe disposal or end use.
4. Reduce pathogen concentrations in sludge sufficiently to allow its safe end use (waste-to-energy and waste-to-compost) or disposal as part of the solid waste stream.

Sewage is untreated domestic/municipal waste water, which contains mostly of grey water and black water and gets conveyed through the sewerage system or into an onsite sewage facility. Sewage is characterized by its rate of flow, physical condition, chemical and toxic constituents, and its bacteriological status.

Faecal sludge is the mixture of human excreta, water and solid wastes (such as toilet paper and menstrual hygiene materials) that gets collected in onsite sanitation systems.

Septage is a specific type of faecal sludge and refers to the partially digested faecal solids that accumulate in septic tanks. Faecal sludge and septage is emptied out of pits or septic tanks and is much more concentrated than sewage.

Grey water is the wastewater from kitchen and bathrooms i.e. from sinks, bathtubs, showers, dishwashers, and clothes washers and does not contain excreta. Wastewater from a community, containing solid and liquid excreta, is known as black water, as per the Central Public Health and Environmental Engineering Organization (CPHEEO). Black water is generated from the toilet, which contains human excreta whereas grey water can be generated from other activities like cooking, washing cloths and dishes.

Faecal sludge and septage management (FSSM) refers to the management of all stages of the sanitation value chain such as collection, emptying, transport, treatment, disposal and reuse of faecal sludge from pit latrines, septic tanks or other onsite sanitation systems. The term FSSM is not just about creating infrastructure for each stage, it also includes creating enabling environment for the system to run smoothly and sustainably.