Organic and nitrogen removal with minimal COD requirement by integration of sequestered denitrification and separate nitrification in a low-loaded activated sludge process

A separate sludge system incorporating sequencing batch reactor (SBR) for s equestered denitrification and an immobilized fixed-film reactor for nitrif ication was investigated in this study. Emphases were placed on the, preser vation of organic matter as an electron donor for denitrification and the i mprovement of nitrification efficiency by using an immobilization technique with alginate coating. To preserve organic materials in the sludge require d for denitrification, a study was made with a contact process. The contact or, when operated with a short detention time, gave incomplete metabolism o f organic matter. With 64% of the influent soluble chemical oxygen demand ( SCOD) was adsorbed to activated sludge within 30 min. The specific mass of organic matter uptaken was 55 mg SCOD/g mixed liquor suspended solids (MLSS ), which enhanced the denitrification efficiency up to 63% in the following denitrification step. Thus, the required COD in the proposed system can be saved up to 63% as an available electron donor for the conventional aerobi c process. The immobilized nitrification unit showed over 90% of nitrate pr oduction rate up to 50 mg/l of influent ammonia load.