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Membrane Bioreactor Technology: Opportunities and Challenges<br />By <br />Sami Rehman (Process Engineer) at Albion Water Ltd<br />
Contents<br />Membrane Bioreactor (MBR) systems process outline <br />Reasons for using MBR as an alternative to Activated Sludge<br />Challenges to address: e.g. membrane fouling and stability<br />Latest Research <br />Further Work <br />Summary<br />
MBR: The Process<br />Combination of membrane technology in a bioreactor and a biological stage => led to three generic types of MBR<br />First type = separation and retention of solids<br />Second type = bubble-less aeration within the bioreactor<br />Third type = extraction of priority organic pollutants from industrial wastewaters<br />
MBR: The Process<br />Raw sewage from equalization/holding tank passes through fine screens to remove substances that may clog or scratch membrane before entering MBR facilities<br />Membrane modules immersed inside aerobic tank where organic contents (BOD) in sewage is biologically degraded by activated sludge<br />MLSS concentration in MBR sys = 10-20 g/l compared to 3-4 g/l in conventional AS thus 30% lower retention time compared to conventional systems<br />Membranes separate solids from liquids in filtration process <br />Pore size of membranes: 0.1µm, not only SS are removed but also bacteria such as coliform bacteria<br />Immersed membrane filtration process eliminates requirement for gravity sedimentation tank/clarifier required by conventional ASS. By recirculating MLSS from aerobic to anoxic tanks, nitrate content removed<br />Additional coagulant or flocculant dosing can be used for phosphorus removal <br />Courtesy of Aquatech Pte Ltd<br />
MBR Configurations<br />Two Types: External and Internal <br />External – Mixed liquor filtered under pressure in specific membrane module<br />Internal or Submerged – Filtration in an aerated basin by suction to remove effluent<br />
Issues: Membrane Fouling<br />External modules can avoid fouling by carrying out tangential filtration especially when effluent is concentrated<br />There may be a higher cost – this is justified!<br />Necessary in such cases that shear stress on bioflocs is controlled, external membranes have high shear stress due to high recycle flow ratios<br />
Why MBR over activated sludge?<br />Traditional secondary clarifier replaced by membrane module. This module is more compact and quality of rejected water depends on changes in sludge settling velocities<br />MBR allows the biomass concentrations to be higher than for traditional plants (20-30 g/l)<br />
Latest Research<br />Combination of MBR and NF/RO membranes for indirect potable water reuse applications (Abdulhakeem Ali Alturkiet al., 2010)<br />Membrane bioreactor in water treatment (G. Wen et al., 2010)<br />Novel Anaerobic MBR technology for low cost methane production: pilot wastewater project 2010 proved a success at Ken’s Foods WWTP in MA, USA <br />
Further Work <br />More indepth study of membranes: MBR or integrated/combined systems approach eg MBR + NF/RO <br />Need to study membrane fouling further – establish better understanding for fouling process, identify which materials under what conditions (T, P and pH) will foul the least to optimize system design <br />
Summary <br />MBR presents an attractive alternative to conventional activated sludge (CAS) in treating wastewater<br />MBR is a more robust technology with a small footprint and produces a higher quality effluent due to high removal efficiencies as a result of high retention time compared with CAS <br />MBR can meet the increasingly stringent requirements for discharge of treated effluent placed on WWTP operators by environmental bodies like EA<br />Research suggests that MBR has a lot of potential and is poised to be the next generation to wastewater treatment<br />