Study On Forward Osmosis Technology Used For Treating High-salinity Oil-bearing Wastewater

Forward osmosis(FO),an emerging osmotic driving membrane separation process,can be directly applied to high-salinity oil-bearing(HSOB)wastewater treatment,which has good separation performance,simple pretreatment process,low costs and extensive application prospect.At present,FO is still in the infancy of industrial applications.In this paper,the effects of FO membrane materials,process parameters and flow regime of membrane module on performance of HSOB wastewater treatment by FO process were studied with theoretical analysis and experiments.The results may provide support for FO process on HSOB wastewater treatment.Firstly,the performance parameters of polysulfone(PSF)and polyethersulfone(PES)FO membranes were evaluated,including the membrane morphologies,hydrophilicity,surface potential,water flux and reverse salt flux.The results showed that PSF FO membrane had thinner membrane thickness,smaller contact angle,more negative charge on membrane surface and fingerlike pore structure of support layer,while the separation process had smaller mass transfer resistance,better hydropilicity,better anti-pollution performance,higher water flux and lower reverse salt flux.Compared to PES FO membrane,PSF FO membrane was more suitable for HSOB wastewater treatment.Secondly,the artificial HSOB wastewater was prepared in laboratory,and the impacts of draw solution(DS),flow rate,stirring rate,flow pattern and membrane orientation on membrane performances were researched.The results indicated that the FO operation mode was better to achieve a stable water flux of TFC membranes as 29.0 L/m~2·h under 15 cm/s cross-flow rate and 3 mol/L NaCl as the DS,which was 63.20%higher than the water flux in the un-optimized operating conditions.The rejection rate of salt and oil was 98.66%and96.05%,and the pollution recovery rate was 98.58%.Additionally,the effect of different oil concentrations of HSOB wastewater was studied and the results showed that FO performed well to treat HSOB wastewater when the oil concentration was less than 700 mg/L.Finally,spacer placed in membrane module can improve the flow regime,which affects the concentration polarization(CP)and separation efficiency of membrane.Therefore,the effects of spacer position in membrane module,the distance between spacer and membrane,the hole shape and size of spacer on CP were studied to optimize spacer structure and improve treatment efficiency.It was found that the square-hole spacer with 3 mm hole was placed 0.6mm away from membrane in membrane module,which can effectively reduce CP and improve water flux.The water flux increased by 15.98%,the reverse salt flux decreased by 11.54%,and the rejection rates of salt and oil were slightly improved.