The effect of temperature and sludge age on COD removal and nitrification in a moving bed sequencing batch biofilm reactor

This study investigates the effect of temperature and the sludge age on the performance of a moving bed sequencing batch biofilm reactor (MBSBBR) for COD removal and nitrification. The experiments are conducted in a lab-scale MBSBBR operated at three different temperatures (20, 15 and 10 °C) with a synthetic feed simulating domestic sewage characteristics. Evaluation of the results revealed that removal of organic matter at high rates and with efficiencies over 90% was secured at all operation conditions applied. The nitrification rate was significantly influenced by changes in temperature but complete nitrification occurred at each temperature. The nitrification rates observed at 20 and 15 °C were very close (0.241 mg NO_X-N/m² d, 0.252 mg NO_X-N/m² d, respectively), but at 10 °C, it decreased to 0.178 mg NO_X-N/m² d. On the other hand, the biomass concentration and sludge age increased while the VSS/TSS ratios that can be accepted as an indicator of active biomass fraction decreased with time. It is considered that, increasing biofilm thickness and diffusion limitation affected the treatment efficiency, especially nitrification rate, negatively.