The Treatment of Petroleum Refinery Wastewaters Using Membrane Sequencing Batch Reactors

In the present study membrane sequencing batch reactor (MSBR) was employed for the treatment of petroleum refinery wastewaters (PRW) taken from either the effluent or influent of the dissolved air flotation (DAF) unit at Tehran refinery. An MSBR was operated for around 90 days with effluent of DAF and avaerage COD and O&G removal of 81±7% and 82% ±0.7% respectivley was obtained. TOC removal efficiencies very similar to COD removal efficiencies were also attained. During part of the operation of the MSBR PRW containing abnormally high furfural concentration was used as feed; during this period SVI of the activated sludge inside the reactor dramatically increased but nevertheless COD removal efficiencies and MLSS were maintained above 78.7% and 510 mg/l respectively and the initial values were restored when normal PRW was fed again to the MSBR. Change in volume exchange ratio (VER) - a very important parameter in the operation of MSBRs - was also studied and the results indicated a pronounced increase in the COD removal perfromance of MSBR when VER was decreased from 0.5 to 0.33. The kinetic study of COD decrease during a single cycle of the MSBR showed that, at HRT=8 hours, maximum COD removal was achieved before the end of the cycle which might explain the higher COD removal efficiencies obtained at VER of 0.33 compared to 0.5. Comaprison of the COD removal efficiency obtained in MSBR after achievement of steady state when influent and effuent of DAF unit of Tehran Petroleum refinery was used as feed showed lower - but still acceptable - removal efficiencies when MSBR was used to treat the influent compared to effluent of the DAF unit.