Using Excess Biomass Sludge Acclimated in Side Stream Partial Nitrification to Evaluation Partial Nitrification and Abrupt Cold Shock Effect in main stream

In this study biomass acclimation in a side stream partial nitrification sequencing batch reactor (SBR) was performed under optimum conditions (T 30ºC, SRT 9± 1 days and hydraulic retention time (HRT) 1.2 day). Excess sludge for solids retention time (SRT) regulation was added to another batch reactor (main stream) which performed under different conditions for partial nitrification evaluation and calculating temperature dependency factor. The results of main stream reactor showed that temperature was an important factor that affected specific ammonia oxidation rate (sAOR) after cold shock by about 98.5%. It was demonstrated that abrupt cold shock caused a significant reduction in the sAOR; up to 25, 55 and 78% for temperature reduction from 30 to 25, 20 and 15ºC, respectively. Therefore, the temperature dependency factor was calculated about 1.0965 and 1.106 based on indirect and direct comparison, respectively. NO2/ NOx ratio analysis showed that temperature, initial ammonia, MLVSS and time affected nitrite accumulation ratio by 49.7, 14.6, 3.7 and 30.7%, respectively. Results indicated that maximum NO2/ NOx ratio was about 94.9% and was reduced to 89.4% after 270 minutes.