UPGRADING OIL REFINERY EFFLUENTS BY CROSS-FLOW ULTRAFILTRATION

The oil refinery wastewaters conventionally treated still contain abou t 20 mg/l total hydrocarbons and 30 mg/l suspended solids sloughed fro m a biological reactor and their temperature is about 35 degrees C. Th e new European standards will require less than 5 mg/l hydrocarbons an d less than 10 mg/l suspended solids. Such standards could be met by a n ultrafiltration operation. The M9 Carbosep membrane was selected aft er this inorganic membrane proved to be a total barrier for the hydroc arbons contained in a synthetic emulsion made with an Iranian crude oi l while giving highest water flux. A systematic study of the influence of the different operational parameters was then effected with a mixe d suspension containing hydrocarbons and biological solids sampled fro m an activated sludge plant. Aggregation processes of hydrocarbons on the bacterial flocs were observed leading to larger particles with an optimal hydrocarbons/biological solids ratio, This induces a significa nt flux increase up to 150 l/h.m(2). The progressive fouling can be li mited by use of helical baffles introduced in the filtration element o perated at 0.5 bar. Experimental data were fitted to a model of cake d eposition with retroflux while the steady state results were recalcula ted in terms of two dimensionless groups whose plots lead to straight lines. Copyright (C) 1996 IAWQ. Published by Elsevier Science Ltd.