Membrane Bioreactors Scale Up to Gain Size and Market
Twenty-first century technology is gaining momentum in the staid business of wastewater treatment. Since the federal Water Pollution Control Act of 1972 fueled the buildout of the nation’s current crop of wastewater treatment plants, municipalities have mostly relied on conventional activated-sludge processes to meet secondary-treatment standards. That is changing now as vendors and engineers tweak membrane systems originally developed to treat drinking water for the more corrosive environment of wastewater. The results are positive, now often producing effluent that greatly exceeds federal standards for secondary treatment at roughly the same cost.
MBRs, or membrane bioreactor systems, combine either flat-plate or hollow-strand plastic membranes spotted with tiny pores and a conventional activated-sludge biological system. Cassettes or banks of membranes are submerged in CAS tanks where air is bubbled through to promote oxidation and mixing. Wastewater is sucked through the membranes’ pores, which are small enough to filter out not only suspended solids but bacteria and viruses. The resulting effluent can be used for nonpotable purposes.