A Pilot Study On The Treatment Of Nansi Lake Water By UF-NF Membrane Process

Faced with the problem of exceeded organic pollutants and inorganic salts of Nansi Lake water, this paper studied the efficacy of UF-NF membrane process on the treatment of Nansi Lake water. By measureing the Influent and effluent of UF-NF membrane process, we studied the water pollutants removal efficiency of the process. By measuring the effluent water quality and quantity in different operating conditions in the long run, we studied the performance of UF-NF membrane process. By the comparison of two types of NF membranes and two approaches(one-stage or two-stage NF process), we studied the Practical applications of the two NF membranes and the diffirent operating characteristics of two type of NF process. Through the above studies, we can provide technical support for the processes selection of the building of new water supply plants based on Nansi Lake.The contaminant removal by UF-NF process tests showed that, the UF’s removal rates of CODMn and UV254 were 20% and 7% in summer, both were lower than that of 40% and 24% in winter. The CODMn and UV254 concentration in NF product water were lower than 0.6 mg/L and 0.006 cm-1 respectively. The Total Dissolved Solids(TDS) could be removed by more than 88% by Nanofiltration unit(H membrane). The DOC removal rates were 5.8% and 15.29% by coagulation-sedimentation and UF, but the Nanofiltration unit(H membrane) could remove DOC by almost 100%. NF process had a good removal effect of fluorescent substance by more than 80% revomal rates.The evaluation and optimization of NF pretreatment tests showed that, the UF unit can ensure stable product water quality and quantity by taking the low-flux and dead-end filtration mode and conducting a physical backwash per hour. The evaluation and optimization of NF process tests showed that, the NF membrane flux were positively correlated with the operating pressure and water temperature, the higher of pressure and temperature, the more of membrane flux. And the higher of the pressure, the lower of the concentration of conductivity, TDS, water hardness, sulfate, nitrate, fluoride ion and sodium ion in the NF production water. The study of NF’s continuous operation performance as well as the membrane pollution and cleaning tests showed that, without adding scale inhibitors, The NF unit is limited to 20% recovery percent. The NF’s recovery percent could be raised to 34%(one-stage system) or 68%(two-stage system) by adding 7 mg/L PTP-0100 scale inhibitors, and the membrane permeate flux decline was not realy obvious after 21days’ continuous operation. But there still existed more serious pollution on the membrane surface through an analysis of the membrane surface’s contaminants. After chemical cleaning of contaminated NF membrane, the NF flux recoveried by more than 90%.The processing performance comparison of Two NF membranes showed that, The removal effect of G membrane and H membrane were both excellent and had little difference. The sulfate removal rate of G membrane were slightly lower than the H membrane, but which is still higher than 90%. The removal rate of nitrate, fluoride ion and sodium ion of G membrane were 35%, 50% and 20% respectively, while H membrane’s were more than 75%, 79% and 89%. In the same operating condition, the permeate flux of G membrane were higher than H membrane, and with the increase of the pressure and temperature, The G membrane had more obvious adwantages in permeate flux. The G membrane’s power consumption per unit of water was nerely H membrane’s half in the same operating condition. The one-stage and two-stage system comparison study showed that, There was no significant differences in the removal of CODMn, UV254, and divalent ions in the G membrane’s first stage and the second stage produced water. But there indeed existed some differences in TDS, nitrate, fluoride ion and sodium ion in produced water, the second-stage produced water quality was inferior to the first one. The two-stage NF system has more produced water yield by 58% than only one-stage system, which means the two-stage NF system was more energy-saving than one-stage system in the same operating conditions.