Enhanced BNR with MBR – Two years of successful operation

The application of membrane bioreactor (MBR) technology has grown exponentially in terms of number of plants and capacity over the past decade. Earlier applications of MBR technology was directed mainly for water reuse and recycling applications. More recently the types of applications have grown significantly to include advanced nutrient removal for direct discharge into sensitive receiving water bodies and upgrade of aging infrastructure to increase capacity as well as effluent quality. There is a growing interest in enhanced biological nutrient removal (EBNR) using the MBR technology to capitalize on the benefits of these two advanced technologies. Enhanced BNR and MBR is a unique combination since the enhanced BNR process provides excess phosphorous accumulation in the biomass and the MBR process provides excellent solids-liquid separation which ensure virtually no solids in the treated effluent.The Cauley Creek ZeeWeed® MBR plant was expanded from 2.5 mgd to 5.0 mgd and converted from a chemical P removal process to enhanced biological phosphorous removal process. Modeling and simulation using BioWin showed that a modified Johannesburg configuration was the preferred approach. The expanded plant was commissioned in fall 2004 and has been meeting all effluent discharge limits over the past two years with significantly lower ferric and caustic consumption. The results over the first two years of operation showed that the dosages for both ferric chloride and caustic were reduced by 60% as compared to chemical P removal during Phase I. The plant consistently achieved effluent TP of 0.1 mg/L or less, effluent ammonia-N of 0.2 mg/L, and effluent TN of 4–5 mg/L.