Seasonal change of microbial population and activities in a building wastewater reuse system using a membrane separation activated sludge process

The seasonal change of microbial population and activities in an existing building wastewater reuse system using membrane separation activated sludge process (MSAS) were investigated, and they were also compared with those in a municipal wastewater treatment plant using conventional activated sludge (CAS) process. The operating conditions of MSAS process, such as sludge retention time, biomass concentration, the ratio of food to microorganism (F/M) and so on, are much different from CAS process. Acridine orange direct count (AODC), plate count of heterotrophic bacteria (HPC), MPN of ammonia oxidizing bacteria (MPNa) and microfauna were measured. In the MSAS process, the AODC and MPNa/HPC were high, but the HPC/AODC was low. This means that the MSAS process tended to maintain a high ratio of ammonia oxidizing bacteria and also tended to keep dead cells. The microfauna in the MSAS process was unstable and changed a lot seasonally, but it wouldn't affect the treatment efficiency. Moreover, the specific activities of nitrification, denitrification and organic removal fluctuated largely and seasonally, and were lower than those in the CAS process. However, their volumetric activities were higher than those in the CAS process because the MSAS process could maintain very high biomass concentration. Dehydrogenase activity, ATP content and oxygen utilization rate were measured to estimate the bacterial activities and viability. The OUR and ATP has different relationship in the both processes. Polysaccharides were also determined as metabolic products.