Abstract:
The objective of this research was to study the effects of pretreatment using activated carbon and cationic exchange resin on groundwater defluoridation by reverse osmosis membrane. The experiments were operated by using groundwater from the area of Baan-Buakkhang school, Sankamphaeng district, Chiangmai province that has fluoride concentration 11.0 mg/L under the controlled conditions of transmembrane pressure 0.6 MPa and temperature 25.0 oC. It was divided into 2 experiments to compare permeated flux and fluoride rejection efficiency, which were reverse osmosis membrane with pretreatment system and without pretreatment system. Based on the experimental results, the reverse osmosis system using pretreatment has higher fluoride removal than that of the without pretreatment system, which were 97% and 95%, respectively. Fluoride concentration of permeated water were 0.3 and 0.4 mg/L, respectively. Moreover, the reverse osmosis system using pretreatment can produce higher permeated flux than that of the without pretreatment system, which were 1.07 x 10-5 and 9.57 x 10-6 m3/m2.s, respectively.
When synthesized groundwater with Kaolin for study the fluoride rejection efficiency of fouled membrane, the result found that the pretreatment systems efficiency was decreased before another. After chemical cleaning, permeated flux was recovered to 91.9% for pretreatment system, and 80.7% for without pretreatment system. Fluoride concentration in permeated water of both systems were nearly initial results. It was concluded that the pretreatment system was necessary for the reverse osmosis membrane filtration to maintain high fluoride rejection efficiency and prolong water production capacity.