Study Of The Membrane Fouling In Advanced Treating Vitamin C Secondary Effluent By Membrane Technology

In China, the production of vitamin C ranks first, and it discharges huge amount of wastewater. Vitamin C wastewater as a typical high concentration organic wastewater, has the characteristics of high color, high salinity and high concentration of organic matter, with great reuse value. Membrane fouling is still an important factor restricting its development. The paper studied the nanofiltration and reverse osmosis advanced treatment on Vitamin C wastewater, and experiment the the factors (water quality, membrane properties, operating conditions) affecting the membrane fouling.First, analysis the inorganic and organic matter of the Vitamin C wastewater. Vitamin C wastewater has high concentrations of inorganic salts, high conductivity of18.0-18.9mS/cm, including calcium ion concentration of251mg/L, magnesium ion concentration of55.3mg/L. The organics of Vitamin C wastewater has the following characteristics:high levels, TOC reached16.7-19.6mg/L; with high content of the hydrophobic substance, representing64.89%; Mostly small organic molecules, most organics<2kDa, the500-1000Da organics representing63.44%; mainly organic humic acid, fulvic acids by three-dimensional fluorescence analysis. Use NFW, HNF90, HPA2, NFX, SW1for vitamin C wastewater filtration test. Experimental results show that pressure, temperature, feed flow rate, and other factors affect permeate flux. The increase of the permeate flux is with the increase of pressure, temperature, and feed flow rate, and the retention of contaminants is stable. Experiments show that the NFW, HNF90and HPA2membranes have a higher flux and rejection for treatment of vitamin C wastewater.By RSM, the models obtained by ANOVA were used to optimize the operating conditions to simultaneously maximize the permeate flux and minimize the fouling index. For an overall desirability of0.571, HNF90permeate fluxes of32.51L/m2h and fouling index of21.27were estimated with the worst operating variables (P=1.29MPa, T=23℃, and Q=326L/h). For an overall desirability of0.756, HPA2permeate fluxes of30.51L/m2h and fouling index of17.85were estimated with the worst operating variables (P=1.39MPa, T=21℃, and Q=228L/h). For an overall desirability of0.638, NFW permeate fluxes of95.31L/m2h and fouling indexof21.82were estimated with the worst operating variables (P=0.966MPa, T=24℃, and Q=456L/h). From the experiments, the fitting results match the experimental results primarily, and lengthening the period of pollution, the optimum operating conditions still had advantages compared with the worst conditions.The NFW^HNF90and HPA2clean membranes have the following characteristics:form the infrared spectroscopy and XPS elemental analysis, NFW, HNF90, HPA2membranes are typical polyamide membrane; Chargeability:HPA2> HNF90> NFW; hydrophility:HPA2> HNF90> NFW; smoothness:NFW> HPA2> HNF90.Membrane fouling includes not only organic and inorganic pollution, also including divalent ions complexed with organic matter. Known by the XPS elemental analysis, NFW has the worst organic pollution, divalent ion fouling:HPA2> NFW> HNF90. Known by the infrared spectrum, membrane fouling layer mainly contains hydroxyl groups and carbonyl groups. Known by membrane surface morphology, the fouling layer of HNF2is close to HPA90, which were denser and smoother than NFW. Known by the membrane resistance analysis, the three membranes fouling is reversible, and the order of resistance:HNF90> HPA2> NFW. The best cleaning agent of HNF90and HPA2is NaOH, and the best cleaning agents of NFW are NaOH and NaClO.By comparison of the five membranes, the most appropriate membrane in the treatment of the vitamin C wastewater is HPA2membrane, and membrane should be under the condition of pressure P of1.55MPa, temperature T of30℃, flow rate Q of228L/h. The best cleaning agents of HPA2is NaOH for removing organic membrane fouling.