Abstract
Since the more stringent new french standard of the 3 rd of January 1992 relating to water and embracing Urban Run Off Water Discharges during wet weather, some research works have been carried out to treat run off water. In particular, processes based on lamellae settler have been studied. The study presented in this paper describes optimal conditions achieved on a lamellae settler prototype and the results obtained. Parameters investigated were as follow: – injection of coagulant (ferric chloride) controlled by the Suspended Solids (SS) flow feeding the lamellae settler – energy input in the flocculator to improve flocs polymerisation – sludge scraped in the thickened area – optimum adjustment of extracted sludge. Sludge recirculation combined with on line monitoring of Suspended Solids in the flocculator allowed the maximum sludge loading to be established. Those optimisations were applied with an hydraulic load of 150 m.h −1 . Removal efficiency were 70% for Suspended Solids and 60% for Chemical Oxygen Demand (COD). The concentration of extracted sludge was 30 g.l −1 .
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