A Sustainable Path to Membrane Quality Effluent

The current trend when combining biological and membrane processes is to challenge the membrane with as high a fouling environment as possible, which results in very costly operating procedures that are required to mitigate membrane fouling. This has resulted in current membrane / biological designs (MBR) which require various combinations of high membrane area, high energy consumption, excessive pre-screening and large equalization basins. Increasing economic, environmental and political concerns will not sustain the high energy and membrane costs and associated CO2 emissions of the MBR process scheme. To date, a membrane & biological process approach which has fundamental dual goals of minimizing both membrane area and energy consumption has not only presumably contained mutually exclusive goals, it has in large part been unexplored as an option.A highly efficient membrane / biological process, IMAS (Integrated Membrane Activated Sludge), has been developed to dramatically lower the membrane fouling rate without additional energy input or an increase in the amount of membrane area. In fact, both energy usage and membrane area are significantly reduced compared to a conventional MBR. A research study at Duke University has been initiated to compare IMAS, which uses suspended growth biomass, to IMFAS (Integrated Membrane Fixed Film Activated Sludge), a biological / membrane process which combines both suspended & fixed growth biomass in the activated sludge process. The IMFAS process is expected to increase the efficiency of the combined activated sludge and membrane process by further reducing both the hydraulic retention time of the biological component and the solids settling time of the high rate primary liquid/solids separation component.Both IMAS and IMFAS create a low membrane fouling environment via particle management, primarily controlling the composition and size of suspended particles. This enables the membrane to tolerate a wide range of suspended solids concentrations, with the concentration range being between that of a conventional MBR and a conventional activated sludge process. The low fouling nature of the suspended particles allows the transmembrane pressure drop to remain consistently low, even when challenged with high peak flow periods and varying influent turbidities. The design and operation of these technologies creates a complimentary synergy between the biological and membrane processes, allowing for the highest total system efficiency to be achieved, while maintaining a compact footprint and generating minimum waste sludge.