Two pilot plants applied to anaerobic-anoxic-oxic (A2O) process with immobilized nitrifying pellets added in the oxic tank were operated supplying different influents, which one consisted of municipal wastewater mixed with so much supernatant returning from sludge treatment facilities and the other consisted of a major portion of municipal wastewater. The operating experiments were carried out comparing with a pilot plant applied to nitrified liquor recycling process with the same pellets added in the oxic tank supplying influent composed of a major portion of municipal wastewater. The influent to the pilot plants was different primary clarifier effluent, which was flown into municipal wastewater treatment works from combined sewer system.
As the results, declining S-BOD removed with T-P released in anaerobic tank could be expressed in the relation between T-P released and S-BOD removed / T-P released ratio, and the regression equation could be expressed as an exponential function. Namely, the bigger S-BOD removed / T-P released ratio increased progressively, the smaller T-P released produced.
And, the relationship between NOX-N removed and S-BOD removed by denitrifying reaction in the anaerobic and anoxic tanks could be shown as the regression equation by two different straight lines having nearly the same gradient, of which were applied either for immobilized nitrifying pellets added A2O process or for the same pellets added nitrified liquor recycling process. It was estimated that the S-BOD requirement to NOX-N removed for the pellets added A2O process was slightly higher than those for the pellets added nitrified liquor recycling process.