Experimental Study On Papermaking Wastewater Advanced Treatment Using Microfiltration And Reverse Osmosis Dual Membrane System

The papermaking wastewater after biochemical treatment has been still difficult to attain the requirements of the relevant work of water, which need advanced treatment. Among advanced treatment after secondary treatment, membrane separation has had a little floor area, simple operation, convenient maintenance, high treatment efficiency, no sludge produced, etc. Amongst membrane separation, microfiltration can intercept macromolecular substances and suspended solids in water, and reverse osmosis can remove soluble inorganic salt and insoluble organics at the same time. According to the quality of papermaking wastewater after biochemical process and separation characteristics of microfiltration and reverse osmosis technology, this paper used "microfiltration and reverse osmosis" double membrane combination technology for papermaking wastewater after biochemical process advanced treatment. With single factor experiment and orthogonal experimental, it studied on the influence of operating pressure, recovery rate, influent inorganic salt concentration, influent pH and influent temperature five factors on removal efficiency, determined the "microfiltration and reverse osmosis" optimum operating conditions of membrane method of double combination process, analyzed influence degree of operating pressure, recovery rate, influent inorganic salt concentration, water pH and influent temperature five factors on membrane fouling and is put forward membrane fouling cleaning solution at last.Single factor and orthogonal test results indicated in the "microfiltration and reverse osmosis" double membrane combination technology advanced treatment of papermaking wastewater after biochemical process, factors affecting the removal rate of CODcr order is influent pH＞influent temperature＞water recovery rate＞influent inorganic salt concentration＞operating pressure. Factors affecting the removal rate of NH3-N order is operating pressure＞influent pH＞water recovery rate＞influent temperature＞influent inorganic salt concentration. The factors affecting the removal rate of Cl-order is water recovery rate＞operating pressure＞influent pH＞influent temperature＞influent inorganic salt concentration. The Factors affecting desalination rate order is influent temperature> influent pH> influent inorganic salt concentration> operating pressure> water recovery rate.Analyzing the comprehensive test results, it determined the optimum operating conditions:operating pressure is0.60Mpa, water recovery rate is69%, influent water conductivity is1109.00us·cm-1, influent pH is8.2, influent temperature is26℃. In real papermaking wastewater biochemical treatment effluent validation experiments, treated effluent CODcr, NH3-N, Cl-and conductivity removal rate reached74.25%,92.88%,94.50%and95.95%, which attained industrial water quality requirements.At the same time, under the orthogonal test it studied the influence factors of membrane fouling about the "microfiltration and reverse osmosis" double membrane combination technology. The ANOVA results show that the order of the factors of membrane fouling is influent temperature> operating pressure> influent inorganic salt concentration> influent pH> water recovery rate, influent temperature and operating pressure have remarkable effect, influent inorganic salt concentration have certain effect, the effect of influent pH and recovery rate is not obvious. When determining the operating condition, the influent temperature and operating pressure should be given priority to, which avoid the operating conditions increasing the chances of membrane pollution. Through the comparison of different cleaning solution, membrane cleaning solution is citric acid (1.5%)+sodium hydroxide (0.1%) of the ratio of combination cleaning fluid, cleaning time for50minutes.