Phosphorus Removal from Aerated Lagoons Using Alum, Ferric Chloride and Lime

Abstract

Abstract Laboratory and on-site studies were conducted over a period of 18 months on two wastewater treatment plants. The main objective was the removal of phosphorus. Three coagulants were used: alum, ferric chloride and lime. In the precipitation process, alum was found to react preferentially with polyphosphates, but not with orthophosphates. Seasonal temperature variations in wastewater did not have a detrimental effect on the coagulation and flocculation processes. The molar capacity of alum for precipitating the orthophosphate fraction was greater at the secondary level of treatment than at the primary level. The phosphorus removal efficiency varied between 90 and 95% for all coagulants. For lime, the dosage was relatively high in order to achieve the same degree of dephosphatation, leading to sludge accumulation in the aerated lagoons.