Concentrated (> 5 percent) oily wastes are produced by various metal-working operations (rolling mills, metal cutting and working). The ability of conventional cross-flow membrane technology to treat a concentrated oily waste directly or the residual from the conventional membrane system is limited because of the low permeate flux observed at high oil concentrations. Conventional cross-flow systems rely on high recirculating velocities (approxapprox 10 ft/s) to scour or clean the membrane surfvace so that satisfactory permeate flux is maintained. As the concentration of the feed increases, the maintenance of a high velocity is difficult because of the increase in feed viscosity.
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