Aerated lagoons are used in developing and developed countries to treat domestic and industrial wastewater especially from small communities. They represent a reliable method of biological treatment capable of producing satisfactory effluent throughout the year. They are preferred to several other treatment processes like the activated sludge because of the simplicity of the overall system, less need for trained operator assistance and very competitive overall cost of wastewater treatment. In Québec where there are some 1400 small municipalities this method of treatment is found to perform satisfactorily, notwithstanding the extreme temperature variations. The objective of the present study is to evaluate the performance of this method of waste stabilization from the point of view of organic removal, retention time, power requirement and nutrient removal without chemical coagulation. An existing treatment plant with aerated lagoons was used for the study. The results show that a summer retention time of about 8 days can produce an effluent having 20-25 mg/L of BOD, 20 mg/L of SS and 2-3 mg/L of total phosphates without coagulant addition.

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