Reservoir water treatment using hybrid coagulation–ultrafiltration

Abstract

A new hybrid coagulation–ultrafiltration process was used to treat reservoir water for drinking purposes. Raw water collected at a local waterworks in Singapore was pretreated under optimized conditions of coagulation pH 5.2 and alum dosing concentration of 5 mg (Al)/L. A hollow-fiber UF membrane module (0.07 m 2) was used to filter the supernatant after pH correction to 7.2. The laboratory-scale UF unit with an automatic control system was used. Different feed flow rates (or membrane fluxes), backwash intervals and water recoveries were studied in the UF operation. The experimental results show that the hybrid coagulation–UF process used could remove turbidity (>99%), NOM in terms of DOC (up to 59.5%) and bacteria (>3 LRV). Turbidity and DOC of the UF permeates were 0.10 NTU max and 2.26 mg/L on average, respectively. Total coliform and total THM were not detectable. The UF membrane used had a high normalized flux of 600–700×10 −5 L m −2 h −1 Pa −1 at 25°C under the conditions of low TMP of 0.013–0.017 MPa and a high water recovery of 99%, and potentially showed low energy consumption for treating the reservoir water. It is concluded that the hybrid coagulation–UF process could be incorporated into existing conventional processes with replacement of dual-media filtration for producing an improved quality of drinking water from reservoir water.