The removal of organic waste matter from secondary sewage effluents by chemical coagulation

The removal of organic waste matter was investigated: a) On both a maturation pond effluent and a secondary clarifier effluent, collected from the same municipal sewage-treatment plant, and b) On a maturation pond effluent collected from a different municipal sewage-treatment plant. The inorganic coagulants alum, ferric chloride and lime as well as organic polyelectrolytes were tested for their ability to remove the organic waste matter from the above effluents under various conditions of pH and coagulant concentration. The tests were on laboratory scale and were conducted under constant room temperature, mixing and stirring conditions. A standard laboratory technique was employed which approximately simulates the large scale operation. Removal was evaluated in terms of Chemical Oxygen Demand (COD) of the wastewater. It was found that, among the inorganic coagulants tested, ferric chloride was, in all cases, the most effective coagulant for COD removal. In general, the final COD achieved with ferric chloride was between 10 and 40 milligrams per litre, depending on the initial COD level of the raw effluent