| Content:Environmental pollution has become the bottleneck of the development of sweet potato starch production because the wastewater has the characteristics of containing high concentration of organic substance, concentrated of discharging time and difficult to be treated. The new treat technique is expected and which fit for Chinese middle and small starch fabrication enterprise. The sweet potato starch has a rich source of protein, however, they have to be discharged in the wastewater because of lacking of effective separation technology, so large amount of protein resources are wasted and the environment is polluted. The object of this paper is extracted protein from wastewater of sweet potato starch production. The optimum conditions are determined of spinning conditions of hollow fiber membrane with polyvinyl chloride (PVC).The influences of dope solutions composition, Pore-forming agent and modifier on properties of such modified ultra filtration membrane are investigated through the methods of preparing hollow fiber membrane, Pretreatment and field experiment evaluation. The mechanism of membrane modification was discussed. The anti-fouling and high efficiency hollow fiber membrane modules with polyvinyl chloride (PVC) are prepared by phase-inversion. The pretreatment of sweet potato starch production wastewater has been filtered out. The extraction parameters were determined through combing membrane separation technology. The effect for protein retention and contamination removal are evaluated though pilot test.The experimental results show that a new anti-pollution that nanometer powder was added into PVC hollow fiber ultrafiltration membrane was developed. The optimum membrane formula is determined. The PVC, DMAc, content were16,80wt%, the best coagulant bath temperature is25℃, the best pre-evaporation time is30s.At the same time, the optimal conditions for preparing the hollow fiber membrane spinning is core liquid flow rate20ml/min, speed of metering pump42r/min, the winding speed of wire machine20r/min, coagulant bath temperature20℃. The membrane performance is significantly improved because of the modifier moderately to be added in the casting solution of PVC hollow fiber UF membrane. The specific surface area of modifier was large, the adsorption was produced between hydroxyl groups and PVC molecular chain, mechanical stability and hydrophily were increased because of large molecular network structure was formed,were the main mechanisms of modification. It was shown that the modified membranes expressed better anti-fouling ability in the ultrafiltration. When the moderate modifier concentration was added, membrane flux and the rejection of the modification effect is best. The pressure increased from0.04MPa to0.2MPa, the membrane flux increases and rejection is stable with the increases of pressure. So we choose0.18MPa as the working pressure of PVC hollow fiber ultrafiltration membrane. Then, the processes of hydrolysis acidification precipitation, cold storage, centrifugal, chemical flocculation and biological flocculation were studied as pretreatment methods for sweet potato starch production wastewater. The best pretreatment process was screened out through comparison. Sweet potato production wastewater was treated by the best pretreatment method and UF process, and the optimum process parameters and processing was obtained. Finally, pilot scale treatment device is designed and assembled for treating actual production wastewater from enterprises, operating parameters, the combined process treatment effect and protein retention effect were further evaluated.The protein from wastewater of sweet potato production was recoved with modified PVC hollow fiber ultrafiltration membrane. The membrane flux recovery rate is92.5%,and retention of protein is83.2%。The modified ultrafiltration membrane increased by more5.8%and2%compared with that of unmodified membrane. Experiments show that the optimal pretreatment is hydrolysis acidification precipitation. Wastewater was pre-treated by hydrolysis acidification precipitation, after that, Effluent was treated by ultrafiltration. The removal rate of COD and soluble protein is14.2%and95.7%. The inside-out hollow fiber ultrafiltration equipment was made by modification of PVC hollow fiber membranes. Wastewater from starch factory in Weihai was treated by this equipment. Equipment operated continuous period (10days),10hours of work per cycle. The average removal rate of COD is15.3%when Ultrafiltration equipment run10hours. The average removal rate of COD and soluble protein is20.8%and83.6%. The average removal rate of total nitrogen and total phosphorus is21.2%and8%.when ultrafiltration equipment continuous operated10days.The test results show that, the soluble protein in wastewater can be efficient intercepted by ultrafiltration equipment of modified PVC hollow fiber membrane. |
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