Decoupling and Optimization of Both P and N Removal in an Advanced IFAS-EBPR-MBR System

An advanced continuous-flow IFAS-EBPR-MBR system has been established with the aim to decouple the nitrogen (N) removing and phosphorus (P) removing microbial populations and to achieve simultaneous optimization of N and P removal for obtaining high quality effluent. Effluent phosphorus as low as 0.03 mg-P/L and effluent total nitrogen of less than 2 mg-N/L have been reached with stable performance at steady state at both 15-days and 8-day SRTs. To understand the population distribution in the reactor, both P uptake and release and polyphosphate accumulating organisms (PAOs) population abundance studies were conducted with mixed liquor (ML), with carrier media only or with combination of ML and media. The results indicated that most of the PAO activity was in the ML and the PAO activity in the biofilm was insignificant. Population study showed that about 50% of total cells in ML were PAOs and more than 70% of these PAOs were Accumulibacter type. Fixed film contained less than 2-5% of total PAOs, which contained more than 50% of Accumulibacter type and, nearly all of the PAOs resided in the loosely attached portion of the biofilm on the media. Membrane/nitrate recycle brings both biomass and nitrate from the membrane chamber back to the anoxic zone and change in recycle ratio affected the biomass (MLSS) distribution in different zones of the reactor as observed for recycle ratio of 1Q, 1.5Q and 2.5Q, respectively. Nitrate recycle also impacted the COD, nitrogen species and phosphorus profiles in different reactor zones along the process. Lowest effluent nitrate was found at recycle ratio of 2.5 (