Abstract:

Laboratory-scale experiments were conducted with two different commercial types of the nanofiltration (NF) membranes (DL and DK) to soften one brackish water in the Huanghuai region of China. The influences of feed pH (3-10), feed total dissolved solids (1317-5926 mg·L^-1) and total organic carbon (2.72-12.24 mg·L^-1) on both selected NF membranes separating efficiencies were evaluated. The experimental results indicated that with the increase of feed pH, both DL and DK nanofiltration membrane specific fluxes firstly increased, then decreased, and finally slowly declined. But it decreased all the time with the increase of feed TOC and TDS. The divalent ions (Mg²⁺ and Ca²⁺) rejection rates for candidate NF membranes were on the rise during the testing scope. DL nanofiltration membrane was selected to continue to carry out the long-term stability test. When the operating time was running to 267 h, the membrane specific flux decreased by more than 10%, and chemical cleaning was adopted immediately. After chemical acid cleaning, the membrane specific flux recovery rate reached 85.05%; and after the coupling acid cleaning and alkali cleaning, the value is as high as 97.2%. Combined with scanning electron microscope and atomic force microscope characterization images, it was clearly showed that the chemical cleaning has good removal effect for membrane fouling.

Key words: nanofiltration, separation, fouling, feed water quality, long-term operation

摘要：

针对黄淮地区苦咸水，构建了小试级别的纳滤膜法软化系统，并开展了包括pH、总溶解固体含盐量（TDS）和总有机碳（TOC）等进水水质对DL、DK型纳滤膜的软化分离实验。结果表明，pH为3~10、TDS为1317~5926 mg·L^-1和TOC为2.72~12.24 mg·L^-1的进水条件下，DL和DK纳滤膜比通量随pH的增加分别呈先上升后下降和缓慢下降的趋势，随进水TDS和TOC的增加呈整体下降趋势，而纳滤膜对硬度离子（Mg²⁺和Ca²⁺）的截留率均呈明显的上升趋势。DL膜运行至267 h时，膜比通量下降幅度超过10%，进行化学清洗，酸洗后膜比通量恢复率达到85.05%，酸洗加碱洗后该值高达97.2%，结合扫描电子显微镜和原子力显微镜表征结果，可知化学清洗对膜面污染有较好的去除效果。

关键词: 纳滤, 分离, 结垢, 进水水质, 长期运行