The Application Study Of An Effective Hollow Fiber Membrane In Oily Waste Water Separation

Membrane technology for oil-water separation has great potential advantages, including simpler system, good effluent quality, high and stable removal efficiency, etc. However, the deterioration of membrane separation performance due to concentration polarization and membrane fouling has shielded many of these advantages and limited its more widespread applications of membrane separation technology in oily water treatment. Therefore, utilizing a membrane with excellent anti-oil ability to treat oily wastewater is desirable.In this study, we investigated the performance of a novel hollow fiber membrane prepared from polyvinylidene fluoride (PVDF) as the base material and a modified PVDF copolymer with hydrophilic and oleophobic segments as the additive for oil-water separation and examined its structure, wettability, mechanical property and surface charge of the prepared membrane samples. Permeate flux and oil rejection efficiency during the filtration of oil-containing water were monitored and the operation conditions were optimized through the orthogonal experimental design. The fouling resistance was also analyzed and a prediction model was established to describ the permeate flux during the filtration process. It was found that the prepared membrane had a dense layer on the support layer with finger-like macrovoids. The surface of the prepared membrane showed both hydrophilic and oleophobic property, and was negatively charged. The membrane also showed good resistance to high chemical corrosion and oxidation.With hexadecane as a model oil compound, the permeate flux and oil rejection efficiency of the membrane during the filtration process were evaluated and the results were found as follows:the temperature had a positive effect on the permeate flux; initial permeate flux increased and the flux decayed became faster with the increase of the trans-membrane pressure (TMP); the sustained permeate flux was greater and the flux decay rate was smaller with the increase of the concentrated stream recirculation.TOC in the filtrate can be as low as1～4mg/L when TOC in the influent was at the range of300to400mg/L, achieving a high removal oil efficiency of99.0%.or above. The flux decayed during the filtration process could be fully recovered by water flush cleaning, and its recovery rate can be maintained at above95.0%after many cycles of filtration and flush cleaning.The orthogonal experiments with four factors and three levels were carried out to optimize the process performance, such as permeation flux, the flux decay rate, and the permeate TOC concentration. The optimum operation conditions were found to be: TMP at0.06MPa, temperature at35℃, the feed oil concentration at400mg/L and the retentate flux at106.0L/h.Different types of fouling resistances were analyzed with a series of resistance model. The results demonstrated that the membrane resistance was the main resistance, which accounted for about86.0～94.0%of the total resistance for the prepared membrane. The flux decay of the filtration process was dominated by the concentration polarization resistance and the reversible fouling resistance, which were effectively removed by simple physical water flush cleaning.Based on the above investigation, the prepared membrane for treatment of real samples of palm oily waste water and mechanical cutting oil waste water, respectively. For the palm oily wastewater treatment, the removal rate of COD and turbidity reached58.3%and97.2%, respectively, and the decay of the permeate flux was only4.1%for an influent COD at12820mg/L. For the mechanical cutting oil wastewater treatment, the demulsification and the oil removal were achieved effectively with the removal rate of COD and TOC at as high as89.0%and97.2%, respectively, and the decay of the permeate flux at7.2%only. A permeate flux model was established on the basis of the data obtained from treating hexadecane emulsion water sample. The model was found to satisfactorily predict the permeate flux change in the filtration process of the actual waste water samples with the prepared membranes.