Pre-treatment optimisation studies for secondary effluent reclamation with reverse osmosis

Physical-chemical pre-treatment was used for the reverse osmosis unit for reclamation of secondary effluents. The pilot plant was equipped with a variety of tertiary treatment units to prevent fouling and biofouling of the celluloseacetate reverse osmosis membranes used. The optimisation of pre-treatment involved application of various concentrations of lime to raise the pH to 10.3-12.1, and to stabilise the sludge generated, as well as different dosages of ferric chloride (15, 20, and 25 mg/L) for the coagulation and solid-liquid separation. Sodium hypochlorite (8 mg/L) and UV disinfection are used for microbiological control. The water quality obtained, under the optimum conditions (pH = 10.5; FeCl3: 25 mg/L; anionic flocculant: 0.5 mg/L; sodium hypochlorite: 8 mg/L) was high, showing an average conductivity of 66muS/cm and low COD values 4mg O-2/L. The product water is suitable for injection into a groundwater aquifer to counteract seawater intrusion. (C) 2002 Elsevier Science Ltd. All rights reserved.