The Membrane BioReactor is a biological water filtration plant combining a traditional cleaning process on activated sludge with a membrane separation system (generally microfiltration or ultrafiltration), replacing a normal secondary separator. The system is extremely useful as it reaches high activated sludge concentrations in the biological reactor (10-15 kgSS/m3), which can’t be reached in traditional systems. The use of membranes instead of a separators avoids possible sludge leakages, extremely frequent in industrial plants, often leading to many problems (variable immediate capacities with the consequent increase of the surface hydraulic load, presence of light sludge, filament bacteria bulking, etc).
The MBR can by set with a two different installation configurations:
- with external filtration (MBR side-stream);
- with submersed filtration (MBR submerged membrane), where the membranes are immersed in the same activated sludge vessel, in direct and constant contact with the waste.
The waste, following pre-treatments, such as solid and grease removal and thin grilling, is conveyed to the activated sludge vessel where, as in the traditional separators, the organic substance is degraded. In the case of external/sidestream filtration, the waste is conveyed to the external filtration process while in the case of the internal/submersed configuration, the waste is sucked through filtrating membranes. The permeate (the filtered liquid crossing the membranes) is then pumped to an external disinfection system, to a reverse osmosis treatment or directly to the outlet, according to the specific operating scopes.
During the filtration process, air intermittently flows inside the lower unit part where the membranes are located, preventing any sludge build-up and thus avoiding the membrane fouling. As to keep the membrane perfectly operating in time, a counter-washing is forecast (washing under counter-current), leading to the complete removal of any material accumulation on their surfaces. The accumulated sludge during the membrane filtration process is well stabilized thanks to the sludge aging and the lower organic load concentrations, depending on the consistently high active biomass concentrations and it can be directly pumped to be disposed without any biological stabilization treatments.