This paper is concerned with the performance of a relatively new form of metal-iron coagulant, Polyferric Sulphate (PFS), which has received very little research attention to date. Laboratory experiments have been undertaken in which the coagulation performance of PFS, Ferric sulphate, Aluminium sulphate and Poly aluminium chloride have been studied using ‘model' waters containing single cultures of algae (Anabaenaflos-aquae and Asterionetta formosa) and other ‘model' waters prepared by mixing aquatic humic substances with Asterionella formosa at different concentration ratios. Physico-chemical variables such as colloid charge, floc number concentration and size distribution, DOC concentration and turbidity, have been determined to quantify treatment performance. The performance of PFS was found to be superior to the other coagulants and this was believed to be due to the presence of more highly charged cation species. For all coagulants there was an approximate stoichiometry between coagulant dose and the dissolved organic carbon concentratioa

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