Dead-end ultrafiltration for pretreatment of RO in reclamation of municipal wastewater effluent

A pilot study for pretreatment of RO in reclamation of municipal wastewater effluent has been conducted at Ulu Pandan, Singapore using a ultrafiltration system with the capacity of 150 m(3)/day developed by NORIT The objective of this study was to establish the process of alum injection at the hollow fiber UF plant to achieve a stable operation in dead-end flow mode. Trial runs on various concentrations of alum dosage and water recoveries were conducted. The pilot results showed that the concentration of alum dosage was critical and the optimum concentration was determined at 2.5 mg/L as Al. A stable operation of the plant in dead-end flow has been achieved by optimizing the operating conditions. The pilot plant was operated stably for 4 weeks under the optimum conditions with TMP between 0.22 and 0.26 bar and normalized flux of UF membrane of (200-250) x 10(-5) L m(-2) h(-1) Pat at 20 degreesC. Product water with average SDI of 1.6 and turbidity of 0.13 NTU was produced from the plant at water recovery over 90%. The pilot results also showed that particle (1-15 mum) in the UF permeate was 2 counts/mL. Total coliform was not detectable. Total bacteria was 69 cfu/mL. The total power consumption was 0.194 kWh/m(3). Of which, 0.100 kWh/m(3) was for the operation of UF unit and 0.094 kWh/m(3) was for the submersible pump and the air compressor. The chemical cost was 1.3 cents (US)/m(3) product water at a capacity of 5 m(3)/h. The results demonstrated that the process of alum injection established at the UF plant achieved a stable operation in dead-end mode with low cost and the UF membrane used could be a suitable pre-treatment option prior to RO for producing NEWater from the secondary treated effluent. (C) 2004 Elsevier B.V. All rights reserved.