Driving Membrane Bio-Reactors to Limit of Technology

Available technologies for low effluent nitrogen rely on multi-stage systems with sequential aerobic and anoxic zones for nitrification and denitrification. Membrane bioreactors (MBR) use the Bardenpho configuration to achieve low effluent TN. At lower temperature, the endogenous denitrification in the second anoxic zone is low requiring the addition of a carbon source. The membrane reactor serves as the final re-aeration zone, but is larger than is required for the process. Ammonia set free in the anoxic zone and endogenous breakdown of biological cells in the membrane reactor result in an increase in the nitrates. Using an attached growth system after the membranes is not feasible and would defeat the purpose of selecting the membrane reactor in the first place. The question is then, can the effluent nitrate concentration be reduced in an MBR to the same level as that of a denitrification filter. A BioWin™ simulator was used to study the difficulties encountered in driving the TN down to the lowest possible level.