PHOSPHORUS REMOVAL AT THE REGINA WASTE-WATER TREATMENT-PLANT

The City of Regina Wastewater Treatment Plant includes primacy treatme nt followed by aerated lagoons and final clarifiers; alum is added ahe ad of final clarifiers for phosphorus removal. Because of a concern fo r eutrophication of the Qu'Appelle River system, effluent phosphorus l imit has been set at 1 mg/L; however, the plant has not been able to m eet this limit consistently. An analysis of the plant operating data s howed that effluent phosphorus levels were closely related to effluent suspended solids and that erratic chemical dispersal and flocculation may be the problem. A jar testing program was undertaken to determine the effects of different mixing regimes on phosphorus removal efficie ncies. It was found that effluent phosphorus levels less than 1 mg/L c ould be achieved using a 2-5 min rapid mix followed by a 15 min floccu lation period at alum and polymer dosages of approximately 125 and 1 m g/L respectively. The addition of a rapid mix basin ahead of the final clarifier far the proper mixing of alum and polymer was suggested as a solution to maintain effluent levels below 1 mg/L consistently.