Coagulation as Pretreatment of Food Industry Wastewater

Jar-tests, pilot-plant and full-scale experiments on chemical pretreatment of food industry wastewater have been performed. The objectives were to find maximum removal efficiencies, suitable coagulation and flocculation agents, and the optimum process design. The results showed that the wastewater composition greatly influences the maximum removal efficiencies and also the conditions for optimum coagulation and flocculation. Optimum pH depends on the chemical agent and the actual dosage used. With proper pH-adjustment, addition of either 0.10-0.15 mg FeCl₃-6H₂O/mg COD, or about 0.20 mg Al₂(SO₄)₃.18H₂O/mg COD, was sufficient to obtain good removal of organic matter. Maximum removal efficiencies of 67-90 % total COD were achieved, depending on wastewater composition.