Fabrication Of Novel Low-cost SiO₂/PVC Nano-composite Membrane And Their Antifouling Mechanism For Oil Extraction Wastewater

At present,most oilfields in our country still choose water injection technology to produce oil,resulting in a large amount of produced water.If the oil extraction wastewater was not properly disposed,it will bring great damage to the local ecological environment.Traditional technologies for wastewater treatment in the oil field such as gravity de-emulsification,coagulation,and flocculation present several disadvantages,including low efficiency,high operational costs and recontamination problems,especially difficult to remove the emulsified oil in the water.In recent years,membrane separation technology,especially the ultrafiltration?UF?technology obtained the rapid development.And UF membranes can effectively remove emulsified oil from the wastewater because of their appropriate pore sizes?2¹00 nm?.However,the problems including membrane fouling and high membrane cost seriously hinder their wide application.Herein,a novel low-cost and good antifouling UF membrane was fabricated with regular and hydrophilic nano-SiO₂particles as additives,and was used to the treatment of oil extraction wastewater.Orthogonal experiment showed that the best formula is 6%PVP,PVC 12%,82%DMAC,and the optimal preparation conditions are that pre-evaporation time is 15 s,coagulation bath temperature is 60oC.The effect of different nano-SiO₂ content on the casting solution system and membrane performance showed that:when the amount of nano-SiO₂ exceeds 3 g,it could increase the difficulty of degassed and stretch film as well as reduce the membranes'mechanical properties for the pinhole defect.With reasonable nano-particles addition,modified membranes could present obvious increase in the mechanical properties,pure water flux,hydrophilicities,antifouing performance.Comprehensive consideration of all the membranes'performance,it is determined that the membrane modified with hydrophilic nano-SiO₂ presents best performance and the optimal nano-SiO₂ amount is 1.5 g.Compared with the unmodified membrane,the membranes modified by regular and hydrophilic nano-SiO₂?at optimal addition of 1.5 g?presented more steady initial fluxes and higher flux recovery ratios in every filtration cycle.Meanwhile,both modified membranes exhibited high removal efficiencies of suspended solids?more than 98%?and oil components?up to 95%?.Antifouling mechanism analysis shows that there would form a hydrophilic layer on the membrane surface when nano-Si O₂ added into.And this layer could effectively protect the membrane surface from the hydrophobic pollutants.However,3 h long-term cross-flow filtration experiments displayed that the advantage of good hydrophilicity on the modified membrane surface is not obvious.Reasonable choice of pretreatment time of ozone and ultraviolet can further improve the membrane fouling in the treatment of oil extraction wastewater.Compared with the process of without any pretreatment,the flux recovery ratio of modified membrane after of 30 min ozone and 30 min ultraviolet treatment of produced water,increased by 25.7%and 29.8%,respectively.