C ombination of membrane technology and limestone filtration to control drinking water quality

B oth RO and NF are effective for fluoride r emoval from soft, high fluoride groundwater. T he fluoride removals achieved were >95% in R O and 76% in NF. F luoride concentration in the water distrib ution system of the City of Laitila can be m aintained at acceptable levels by treating a p roportion of high fluoride groundwater in the R O/NF plant. Aluminium was also removed in m embrane filtration, and thus its concentration in t he water distribution system can be controlled t ogether with fluoride. L imestone filtration is applicable for alkaliz ation of membrane-filtered water in addition to g roundwater. Free carbon dioxide in water has a m ajor effect on the alkalinity and pH obtained in l imestone filtration. Limestone filtration has e nsured a stable alkalinity and pH in the water d istribution system of the City of Laitila.