[Influence of co-existing chloride on fluoride removal from drinking water by nanofiltration membrane]

The influence of co-existing chloride to defluoridation of groundwater using nanofiltration membrane and membrane fouling were studied. The results show that nanofiltration has retention effect to all co-existing anion. When influent fluoride concentration was less than 6 mg/L, the fluoride concentration in permeated water was less than 1.2 mg/L which could reach the drinking water standard in rural area. The fluoride retention rate decreases with the increase of influent fluoride concentration or co-existing chloride concentration. The decreasing percentage of fluoride retention rate is the same when Cl- concentration increased 1 mol or F- concentration increased 0.1 mol. The fluoride retention rate increased when influent chloride concentration exceeded 220 mg/L. But the variation had no significant change. Environmental scanning electron microscope (ESEM) and its energetic chart analysis apparatus, X-ray diffration (XRD) analysis showed that the main fouling component was CaCO3. The fouling membrane could be recovered flux using citric acid and ammonia cleaning method.