Membrane distillation coupled with a novel two-stage pretreatment process for petrochemical wastewater treatment and reuse

A novel hybrid system was designed for petrochemical wastewater treatment and reuse by coupling membrane distillation (MD) with a two-stage pretreatment process comprising oil/water separation and photocatalytic organics degradation. The oil/water separation process removed oil emulsions from water, while the follow-up photocatalysis process degraded dissolved oil and volatile organic pollutants. The pretreated water was then introduced to the MD process to produce distilled water. A modified stainless steel mesh/glass microfiber filter was used for removal of oil emulsions and exhibited excellent performance and durability (92% oil rejection in the first cycle and 87% after 10 consecutive cycles). In the photocatalysis stage, TiO2 P25 was used as the photocatalyst to effectively decompose the remaining organic compounds and to inactivate microorganisms under UV light irradiation. The two-stage pretreatment reached 99.5% total organic degradation and 6.02 log bacteria removal. The advantages of the hybrid system are to prevent MD membrane fouling and produce high quality distillate with low TDS and minimal volatile organics that are difficult to remove by a conventional MD process.