Membrane Bioreactors in Municipal Used Water Purification

Membrane bioreactor is a process for biological wastewater treatment based on suspended activated sludge. Sludge flocs and particles are separated from the treated wastewater with membranes. Depending on the application, a big variety of systems and membrane types can be used. In municipal applications, often ultrafiltration membranes with a pore size of 0.01–0.1 μm or microfiltration membranes with a pore size of up to several μm are used. Both membranes are submerged and operated outside-in. Advantages of the membrane bioreactors include the smaller footprint compared to many other biological treatment systems, the excellent effluent quality including partial mechanical disinfection, and large independency of the sludge settling properties. Downsides of the membranes are higher operational cost compared to conventional treatment technologies (including energy, chemicals, and wear parts). The right system should carefully be chosen based on effluent requirements and existing structures or spatial requirements. WABAG used the MBR technology in many WWTP where either space was very limited (e.g., WWTP Zermatt in a man-made cavern inside the mountain) or where the effluent requirement asked for a membrane solution. MBR applications typically include plants, where treatment capacity had to be increased substantially within existing structures of a conventional treatment plant. WABAG mainly applies hollow fiber UF membranes.