There are two types of treatment systems, namely dry and wet systems for the treatment of brown and black water. Dry systems use no flush water whereas wet systems use flush water, but only very low amounts just to transport faecal matter to the treatment plant located close to the origin of faecal matter. The non-diluted or less diluted faecal matter has to be sanitised before reuse in agriculture. This can be done with composting, dehydration, vermicomposting and anaerobic fermentation/digestion.In the following sections the theoretical background of these processes is briefly discussed.