Membrane bioreactors (MBRs)and wastewater treatment

The treatment of urban wastewater (UWW) or industrial wastewater (IWW) is governed either by regulations based on the greater or lesser fragility of the receiving environment in the case of direct discharge, or by the required quality of use in the case of a desire to reuse treated water.

For discharges of domestic effluent into the natural environment, so-called "normal" zones have been defined, where treatment is mainly focused on eliminating particulate fractions and carbonaceous pollution, and "sensitive" zones, where additional elimination of nitrogen and phosphate fractions is necessary.

For domestic effluent, so-called "conventional" processes - whether intensive (e.g. activated sludge or bacterial beds, biofilters), extensive (e.g. lagooning, infiltration systems) or combined - can meet discharge requirements, while each offering more or less reliable performance due to their sensitivity to sudden variations in the flow to be treated (in the case of free-culture systems), the state of flocculation of purification populations (in the case of activated sludge) or inadequate control of biomass distribution and flow within porous packings (systems with fixed cultures in trickling beds, or even biofilters).

For industrial effluents, regulations also specify the conditions for discharge into the natural environment, or even the urban network, but there is growing interest in systems that allow partial or total reuse of treated water.

The purpose of this article is to present membrane bioreactors used in wastewater treatment, to highlight the originality of this multifunctional process in terms of treatment quality and reliability, and to give some tools for controlling the physical and biological processes specific to the process.

As the membrane bioreactor is the combination of a biological reactor and physical separation by porous membranes, the document includes a general presentation of the system, the specific characteristics of each unit stage and their coupling, examples of sizing and applications, and development prospects.