Optimised particle separation in the primary step of wastewater treatment

Since the pollutants in wastewater to such a large extent are associated with particles, enhanced particle separation in the primary step of wastewater treatment should be aimed at. Space restrictions demand pretreatment options will a small "foot-print". In this paper it is shown that coagulation with metal salts is very efficient but leads to excessive sludge production. It is demonstrated how the use of cationic polymers may reduce the sludge production considerably without ruining the SS-removal efficiency and also how improved flocculation, either chemically, by the addition of flocculants or physically, by improvement of settling tank design, may lead to better particle separation as well as smaller "foot-print" of the plant. As an alternative to primary settling, primary filtration in coarse, floating filters are discussed as well. (C) 1998. Published by Elsevier Science Ltd. All rights reserved