Study On Nanofiltration And Reverse Osmosis Technolgy Used In Reuse Of Salt Chemical Wastewater

The secondary effluent of salt chemical wastewater containing high salt, direct emissions would result in the pollutions of rivers and other freshwater resources, and the advanced treatments of salt chemical wastewater for industrial cooling water is an important way to prevent water pollution and solve the problems of water shortage.In this paper, pretreatment+NF+RO process was proposed for treatments of salt chemical wastewater, focusing on the influences of operational factors on separation performance of the nanofiltration membrane, finding the appropriate operating conditions of the nanofiltration membrane by orthogonal experiments.The effluent of the nanofiltration membrane was as the influent of the reverse osmosis membrane, and the influences of operating factors on the reverse osmosis membrane were investigated,and the appropriate operating conditions were finded, finally, the controls of the nanofiltration membrane fouling and the reverse osmosis membrane fouling were studied.Single-factor experiments of the nanofiltration membrane were conducted, the factors influencing separation performance of the nanofiltration membrane were operating pressure, temperature, influent flux, and pH. The experimental results showed that with the increasing of operating pressure, the rejections of salt ions were increasing, and effluent flux, effluent recovery rate were linearly increasing; the overall trend was that the rejections of the salt ions decreased with increasing temperature,but the effluent flux and the effluent recovery rate was increasing; improving of influent flux resulted in the increasing of the rejections of salt ions and the efluent flux;low pH was conducive to the rejections of the salt ions.Orthogonal experiments of the nanofiltration membrane showed that the influences of temperature,operating pressure,influent flux on the effluent recovery rate were highly significant,while the influences of pH on the effluent recovery rate were not so significant,the order of the effect factors on the recovery rate was operating pressure> temperature> influent flux> pH,the appropriate operating conditions for high recovery rate were when temperature was30℃, pH was5, the operating pressure was1.0MPa, influent flux was8L/min;the influences of temperature and operating pressure on the effluent flux were highly significant, whlie the influences of pH and influent flux on the effluent flux were not significant,the order of the effect factors on the effluent flux was operating pressure> temperature> influent flux> pH,the appropriate operating conditions for high effluent flux were when temperature was30℃, pH was4, the operating pressure was1.0MPa, influent flux was12L/min;the influences of temperature and operating pressure on desalination were highly significant, and the influence of pH on desalination was significant, while the influence of influent flux on desalination was not significant, the order of the effect factors on desalination was operating pressure> temperature> pH> influent flux, the appropriate operating conditions for high desalination were when temperature was10℃, pH was4, the operating pressure was1.0MPa, influent flux was16L/min;the influences of temperature, pH and operating pressure on Ca2+rejections were highly significant, while the influences of influent flux on Ca2+rejections were not significant, the order of the effect factors on Ca2+rejections was operating pressure> temperature> pH> influent flux, the appropriate operating conditions for high Ca2+rejections were when temperature was15℃, pH was4, the operating pressure was1.0MPa, influent flux was16L/min.single-factor experiments of the reverse osmosis membrane showed that the appropriate operating conditions were when the operating pressure was4.0MPa, influent flux was13L/min.When the fouled nanofiltration membrane and the fouled nanofiltration membrane were cleaned firstly by the2.0%citric acid solution secondly by the2.0%STPP and0.8%EDTA-Na solution, the membrane flux were up to98.2%and98.6%of the original flux, pretreatment+NF+RO process for advanced treatment of secondary effluent of salt chemical wastewater is technically feasible.