EFFECTS OF TEMPERATURE AND MEAN CELL RESIDENCE TIME ON BIOLOGICAL NUTRIENT REMOVAL PROCESSES

The effects of temperature and mean cell residence time (MCRT) on biol ogical nitrogen and phosphorus removal were investigated by operating two pilot-scale continuous-flow reactors in parallel over a range of t emperatures and MCRTs. One system was operated as a high-rate Virginia Initiative Plant (VIP) biological nutrient removal (BNR) process, and the other was operated as a conventional, fully aerobic activated slu dge process for comparison. Results showed that less aerobic volume wa s needed for complete nitrification in the BNR process than in the con ventional process when conditions of temperature and MCRT were suitabl e for complete nitrification. However, the BNR system was more prone t o nitrifier washout than the conventional system. Nitrification rates and the degree of nitrification achieved by the BNR system and the con ventional system were equal when compared on the basis of aerobic MCRT . Enhanced biological phosphorus removal (EBPR) was adversely affected by colder temperatures, with lower MCRTs being most affected. EBPR wa s not possible at a 5 day system MCRT and 10-degrees-C. Nitrification, however, was more sensitive to MCRT and temperature effects than EBPR under all conditions studied. Operation of the BNR process at the low est MCRT that provided complete nitrification provided the best combin ed nitrogen and phosphorus removal when EBPR was chemical oxygen deman d (COD)-limited. Higher MCRTs were considered optimal when EBPR was li mited by phosphorus because of lower sludge productions.