VERFAHREN ZUR SCHLAMM-ABWASSER- AUFBEREITUNG, INSBESONDERE ZUR ENTFERNUNG STICKSTOFF- UND KOHLENSTOFFHALTIGER STOFFE AUS HAUSHALTS- UND INDUSTRIEABWAESSERN

A multistage treatment is disclosed for the removal of carbonaceous BOD and nitrogenous pollutants from wastewaters, wherein the influent wastewater undergoes successive nitrification-denitrification in the presence of recycled activated sludge containing a mixed culture biomass comprising heterotrophic and autotrophic organisms. The initial mixing of the wastewater with recycled sludge is effected in the presence of sufficient oxygen to maintain oxic conditions. The mixed liquor from the initial oxic treatment, without intermediate separation of solids, is passed to an anoxic stage wherein nitrites and nitrates (NOx, x = 2,3) formed by oxidation of ammonium compounds are reduced to nitrogen gas. Any number of oxic treating stages each followed by an anoxic stage may be employed. The final treating stage prior to solids separation from the mixed liquor may be either oxic or anoxic. The separated solids constitute the activated sludge recycled to at least the initial mixing stage. A short residence time, resulting in a high food to biomass ratio, is maintained in the initial oxic stage or the first subsection thereof, in order to avoid sludge bulking and to promote an active dense biomass.