Groundwater defluoridation by ultra low pressure reverse osmosis membrane and nano filtration membrane

Abstract

Grondwater quality of 199 village waterworks in Lamphun province, Thailand was investigated. It was found that groundwater of 53 village waterworks (44.54%) contain fluoride concentration above 0.7mg/L which is the bottled drinking water standard by Ministry of Industry of Thailand. Dental fluorosis investigation in children aged between 13 and 18 were also studied. It was found that the severe cases of dental fluorosis were observed significantly in the high fluoride concentration area. Besides the investigation of groundwater quality and severity of dental fluorosis, the experiments of ULPRO membrane (UTC-70) and NF membrane (UTC-60) for defluoridation of fluorotic groundwater were studied so as to remove excessive amount of fluoride in groundwater for serving as drinkable water. Groundwater from 2 selected sites in fluorotic area in Lamphun province, Thailand, namely, Pra Too Khong Bottled Drinking Water Plant (site A) and San Pa Hiang Membrane Plant (site B) were collected between September 2005 and January 2006. Groundwater from site A containing fluoride concentration in the range of 12.05-16.98 mg/L was defined as very high fluoride concentration site (>5 mg/L) whereas groundwater from site B containing fluoride concentration in the range of 2.84-3.12 mg/L was defined as high fluoride concentration site (1-5 mg/L). It was found that the maximum percent fluoride rejection of UTC-60 membrane in groundwater from site A was about 80% under the operating transmembrane pressure of 0.5 MPa at the feed pH values of natural pH (about 8) while the maximum percent fluoride rejection in groundwater from site B was about 60% at the feed pH value of 7. In the case of UTC-70 membrane, more than 90% of fluoride rejection under OTP of 0.5 MPa at the feed pH value of 7 was achieved in the groundwater from both sites. Thus, it could be stated that the performance of UTC-70 membrane on fluoride removal was higher than the UTC-60 membrane. In addition, based on the membrance experimental results, it was observed that the approximate pH value at an isoelectric point of UTC-60 membrane was 5 while the pH value at an isoelectric point of UTC-70 membrane was 6. Furthermore, it was found that UTC-70 membrane should not be operated at the feed pH value lower than about 4 so as to avoid negative rejection of fluoride.