Membrane bioreactors (MBRs) are accepted in the municipal and industrial wastewater market as providing high quality effluent. The majority of the installed systems in the United States to date use immersed systems where the membranes are submerged either directly in the bioreactor
or in a separate membrane tank. One key reason immersed systems were developed was to avoid the high energy cost of pumping needed to maintain proper cross-flow velocities for external or side-stream membrane systems. While side-stream technology has been used for years in many industrial
applications and has proven to provide high quality liquid/solid separation, the high cost of operation has limited its practical use in membrane bioreactor applications. This paper discusses a new technology which uses two-phase flow to provide a cost-effective and proven way to apply
external, or side-stream, tubular membranes to membrane bioreactors. Using a simple airlift to sustain the cross flow velocity and turbulence required, high membrane flux and permeability can be maintained while significantly reducing the pumping energy required with traditional cross-flow
systems. As a result, the benefits of an accessible, external tubular membrane system design can now be applied in a cost effective way to membrane bioreactors. These benefits include proven, long-life of rugged tubular membranes, sustainable high flux and permeability, low operating costs,
and simple and safe membrane access and cleaning regimes.
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