A study of the optimisation of the process chain of flocculation — flotation — filtration was performed at Lackarebäck treatment plant in Gothenburg. The Göta River water is a high quality supply of low turbidity and moderate TOC. In winter time the water is generally cold.
Chemistry (coagulant type and pH) affected organics removal. Overall, ferric sulphate produced higher UV and TOC removals than alum. Physical design and operating variables like flocculation time, flocculation mixers, flotation and filtration rates did not affect removals of TOC across the plant, i.e., raw versus filtered waters. Excellent DAF and filter performance were found in treating the cold river water with 5 minutes flocculation and with high flotation and filter rates. Dual media filter performed better than monomedia sand filters, and no benefit was observed for trimedia filters.