Since the 1980's, Membrane Bioreactors (MBR) have been successfully used to treat municipal, commercial and industrial wastewaters for discharge and reuse applications. Today, with thousands of installations operating worldwide, MBR technology is shaping the way we view wastewater treatment and water conservation around the world.

EWT MBR Technology® process produces a high quality discharge permeate that will meet the most stringent of discharge requirements and allow water re-used. EWT MBR Technology® process employs simple flat sheet membrane panels housed in stainless steel units and aerated by a coarse bubble system below each unit.

A series of these membranes are submerged within an activated sludge treatment tank. The aeration necessary for treatment of the liquors also generates an upward cross-flow over the membranes; essential to keep fouling of the filtration surface to a minimum. An advantage of this design is that the membrane panels are securely retained and do not touch or abrade each other whilst the units also act as a flume to ensure effective tank mixing and even distribution of the biomass.

The membrane panels are manufactured with a pore size in the range of 0.1 to 0.4 microns which in operation becomes covered by a dynamic layer of protein and cellular material. This further enhances the effectiveness of this filtration performance by providing an effective pore size of less than 0.01 microns, which is in the ultra filtration range.

The hydraulic flow determines the required number of membrane units. Each membrane unit may contain up to 400 flat sheet membrane panels housed within a rectangular box, together with an integral aeration system in the bottom section of the unit.

Treated effluent is removed from the membrane units using gravity head (typically 1 – 1.2 m), or a pumped suction operation can be utilised.

Advantages

Membrane Bioreactor Technology has a number of inherent advantages. The system does not require flocs to be formed to remove the solids by settlement and therefore the biomass can operate at very high levels of MLSS, generally in the order of 12,000-18,000 mg/l, and as high as 22,000 mg/l. This high concentration enables a low tank volume and a long sludge age to be utilised, which substantially reduces sludge production.

The process requires no primary or secondary settlement stages and no additional tertiary treatment or UV stages to achieve very high disinfection quality: typically better than 5:5:5 BOD: Suspended Solids: Ammonia.

Operation and Maintenance

Operating experience of EWT membrane bioreactor plants has consistently shown an effluent of high quality that has little dependence on variations in feed strength: disinfection of bacteria and viruses is to below the EU limits for bathing water or recreational water standards.

By minimising the effect of fouling through controlled cross flow velocities over the membrane surface cleaning is required typically only twice per year using a backwash of very dilute sodium hypochlorite solution into each membrane unit. The process is designed to run without supervision and by using high quality plastics and stainless steel, the membrane panels and units have long life expectancies in the most part beyond 10 years.