Feasibility of the on-site treatment of sewage and swill in large buildings

Three concepts are proposed for the on-site treatment of sewage and swill in large buildings, like hospitals. The production and anaerobic treatment of night soil in combination with swill in a slurry digestion system and separate production and treatment of grey water is the most attractive concept. The slurry digestion could either be carried out in a CSTR-system at mesophilic conditions or in an Accumulation-system at ambient temperatures. The reactor volume needed for the digestion of a mixture of swill and night soil (or primary sludge) in an Accumulation (AC)- and Completely Stirred Tank Reactor (CSTR)-system at different process temperatures is calculated based on literature values. From the results it should be concluded that mesophilic digestion (30°C) and a SRT of 20–30 days is to be recommended for the digestion of a mixture of night soil and swill in a CSTR system. The latter coincides with the installation of 40–60 l reactor volume per person. Depending on the applied temperature and therefore the minimum storage time and percentage inoculation, a r eactor/storage volume of 431 or 951 litres per person should be installed at 20 and 15°C, respectively when an Accumulation system is applied. An Accumulation-system has the advantage that storage and digestion are combined, implying a completely closed system, also for the storage. The latter is of highest importance for the indoor treatment, as proposed in the paper.