Treatment of phosphate-containing oily wastewater by coagulation and microfiltration

The oily wastewater generated from pretreatment unit of electrocoating industry contains oils, phosphate, organic solvents, and surfactants. In order to improve the removal efficiencies of phosphate and oils, to mitigate the membr ane fouling, coagulation for ceramic membrane microfiltration of oily wastewater was performed. The results of filtration tests show that the membrane fouling d ecreased and the permeate flux and quality increased with coagulation as pret reatment. At the coagulant Ca(OH)2 dosage of 900 mg/L, the removal efficiency of phosphate was increased from 46.4% without coagulation to 99.6%; the removal of COD and oils were 97.0% and 99.8%, respectively. And the permeate flux was about 70% greater than that when Ca(OH)2 was not used. The permeate o btained from coagulation and microfiltration can be reused as make-up water, and the recommended operation conditions for pilot and industrial application are t ransmembrane pressure of 0.10 MPa and cross-flow velocity of 5 m/s. The comparis on results show that 0.2 μm ZrO2 microfilter with coagulation could be used to perform the filtration rather than conventional ultrafilter, with very substanti al gain in flux and removal efficiency of phosphate.