Investigation of the Potential of Monomeric and Polymeric Coagulants in the Treatment of Raw Water used at a Coal-Fired Power Station

Abstract

Abstract-Vast amounts of water are used to operate power stations, such as Grootvlei Power Station. It is essential for the industry to reduce the amount of surface water used due to the scarcity of water in South Africa. The raw water feed to the Grootvlei Power Station is obtained from the Lower Vaal. Surface water commonly have turbidity levels of 20 -200 NTU owing to suspended solids in the water comprising of biological material and undissolved minerals. This study investigates a variety of monomeric and polymeric coagulants and flocculants that can be used to treat the raw water feed to the Grootvlei Power Station. The mechanism of coagulation and flocculation is applicable during the treatment of raw water. The treatment of the raw water is optimized with regard to coagulant and flocculent type, dosage of coagulant and flocculent and mixing conditions. The optimum coagulant is determined as poly-aluminium chloride at 30 mg/L and the flocculent as polyamine at 0.8 mg/L. The optimum jar test conditions were determined as 60 s rapid mixing after the coagulant was added, followed by the addition of the flocculent and a further period of 30 s rapid mixing. The sample was then slowly mixed for 20 min after which it was allowed to settle.