纳滤膜在给水中污染分析及清洗研究

Pollution analysis and cleaning of nanofiltration membrane in feed water

纳滤膜作为第三代给水处理工艺,可以保证出水水质稳定优于饮用水标准,相较于传统混凝沉淀+消毒和臭氧活性炭工艺,其对水中含量超标的硝酸盐、亚硝酸盐、硫酸盐等均有较高的去除率,确保了饮用水的安全性,近些年来纳滤工艺也逐渐受到政府和市场的认可。以福建省某纳滤供水厂为研究对象,记录了纳滤工艺运行状况,并对膜污染物进行了针对性的分析和溯源,此后又采用不同的清洗方式对膜恢复情况进行研究,结果表明,影响纳滤膜污染速度的关键因子是SDI值,在SDI值≤3时,纳滤膜的污染速率比较慢,而当SDI值>5时污染速度是成倍增长。影响SDI值主要由前端无阀滤池水质波动导致的,通过对膜污染物的分析,其中无机污染物主要成分有铝、硅、铁等胶体和颗粒物,其含量占比为92.1%;通过对清洗工艺的研究,采用先酸洗(2%柠檬酸)后碱洗(1%EDTA+0.1%NaOH),清洗恢复率可达90%。为了延缓纳滤膜的污染速率,工程建议采用精度更高的超滤膜来替代砂滤池来作为纳滤的预处理或者采用多级PP棉和其他精细过滤器。

As the third generation water supply treatment process, nanofiltration membrane can ensure that the effluent quality is stable and better than the drinking water standard. Compared with the traditional coagulation sedimentation + disinfection and ozone activated carbon process, it has a higher removal rate of nitrate, nitrite and sulfate in the water, ensuring the safety of drinking water, In recent years, nanofiltration technology has been gradually recognized by the government and the market. Taking a nanofiltration water supply plant in Fujian Province as the research object, the operation status of nanofiltration process is recorded, and the membrane pollutants are analyzed and traced. After that, different cleaning methods are used to study the membrane recovery. The results show that the key factor affecting the pollution rate of nanofiltration membrane is SDI value. When SDI value ≤ 3, the pollution rate of nanofiltration membrane is relatively slow. When SDI value > 5, the pollution rate increases exponentially. The influence on SDI value is mainly caused by the water quality fluctuation of the front-end valveless filter. Through the analysis of membrane pollutants, the main components of inorganic pollutants are colloids and particles such as aluminum, silicon and iron, accounting for 92.1%. Through the research on the cleaning process, the cleaning recovery rate can reach 90% by first pickling(2% citric acid) and then alkali washing(1% EDTA + 0.1% NaOH). In order to delay the pollution rate of nanofiltration membrane, it is recommended to use higher precision ultrafiltration membrane instead of sand filter as nanofiltration pretreatment, or multi-stage PP cotton and other fine filters.