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.