Treatment of oil-containing wastewater using surface-modified ultrafiltration membranes

Introduction. The results of the study of modified polymer ultrafiltration membranes used to separate stable emulsions of process waters of circulating water supply cycles, pipe and electric welding shops, and the heat-generating assembly of a metallurgical enterprise are presented. Materials and methods. Experiments on filtration of wastewater containing colloidally dissolved and suspended impurities of petroleum products were carried out while maintaining a constant filtration pressure of 0.2 MPa. The filtering mode is dead-end. Before each series of experiments, the emulsion was injected with coagulant in prescribed doses. The filtration process was performed using a laboratory filtration cell. A hollow fibre ultrafiltration membrane made of polyvinylidene fluoride was used as a filter element. To increase hydrophilicity, the membrane surface was subjected to a two-stage modification with sequential treatment with solutions of tannic acid and potassium permanganate in buffer solutions with different pH values. Results. It was found that the modified membranes provide a high degree of removal of petroleum products and organic compounds that determine the COD value. The optimal coagulant dose was determined to be 20–25 mg/L of Fe 3+ , at which the minimum content of petroleum products (up to 0.2 mg/L) and COD (up to 190 mg/L) in the filtrate is achieved. The specific productivity of the membranes was 17–12 L/(h·m 2 ) at coagulant doses of 5–25 mg/L. A further increase in the coagulant dose is not advisable due to the lack of significant improvement in treatment efficiency and the increase in reagent costs. Conclusions. The results obtained confirm the promise of using modified ultrafiltration membranes for the removal of emulsified petroleum products during wastewater treatment and post-treatment.