Abstract: The invention provides a system 10 for treatment and purification of domestic household effluent, and for the elimination within said system of organic solid wastes, comprising elements 12 and 14 for separately collecting first and second constituents of the sewage of a domestic residential unit, lavatory sewage comprising said first sewage constituent, and bath, shower, wash basin, laundry, kitchen sink sewage and the like comprising said second sewage constituent, a first and a second dual-purpose vessel 22 and 24, each vessel having at least one inlet port 18 and 20 and at least one outlet port 26, 28, 30, 32 and being arranged so that during the time period that one of said vessels 22 receives said first sewage constituent and acts as a collector and settling tank, the remaining vessel 24 operates as an anaerobic reaction vessel, the vessel operating as an anaerobic reaction vessel carrying out a decomposition process during which the volume of sludge 34 contained therein is greatly reduced by conversion