The working principle of MBR (Membrane Bioreactor) wastewater treatment involves the integration of biological treatment and membrane filtration.  Here is a description of the operational principles of MBR wastewater treatment:

1.  Biological Treatment: The wastewater is first subjected to biological treatment in an activated sludge process, similar to conventional wastewater treatment.  Microorganisms, such as bacteria and protozoa, are introduced to the wastewater, where they break down and consume organic pollutants through aerobic or anaerobic digestion.

2.  Membrane Filtration: The partially treated wastewater is then passed through a membrane filtration system.  MBR utilizes a semi-permeable membrane, typically made of polymeric materials, with very small pore sizes.  This membrane acts as a physical barrier, allowing only water and dissolved substances to pass through while retaining suspended solids, bacteria, and other contaminants.

3.  Membrane Cleaning: Over time, the membrane may become fouled or clogged with accumulated solids and biofilm.  To maintain the filtration efficiency, the MBR system employs various cleaning methods, such as backwashing, air scouring, or chemical cleaning, to remove the fouling layer and restore the membrane's permeability.

4.  Solids Separation: The retained solids and biomass, known as activated sludge, are concentrated in the MBR system due to the membrane's ability to retain them.  This concentrated sludge is then returned to the biological treatment process to maintain the microbial population and ensure effective pollutant removal.

5.  Treated Effluent: The permeate, which is the treated wastewater that has passed through the membrane, is of high quality with low turbidity, suspended solids, and pathogens.  It can be discharged directly or undergo further treatment processes, such as disinfection or advanced oxidation, to meet specific water quality standards for reuse or environmental discharge.