TREATMENT OF ACRYLONITRILE PLANT WASTE-WATER

Wastewater from an acrylonitrile manufacturing plant, with a chemical oxygen demand (COD) of 120,000 mg l(-1) and containing acrylonitrile (1330 mg l(-1)) and acetonitrile (480 mg l(-1)), was treated by a three-step treatment process. The wastewater was first wet air oxidized and the resulting effluent was diluted (four times) and subjected to activated sludge treatment in a sequential batch reactor (SBR). The effluent obtained after SBR treatment needed activated carbon treatment in order to remove colour, one of the non-biodegradable components present in the wastewater. The kinetics of wet air oxidation (WAO) and activated sludge treatment were investigated. The WAO reaction was first order with respect to COD and zero order with respect to oxygen concentration in the temperature range of 150 to 250 degrees C and oxygen partial pressure range of 0.69 to 1.38 MPa. The value of energy of activation for the reaction was 9.49 kcal mol(-1). For activated sludge treatment in the SBR, the values of yield coefficient, decay coefficient, half velocity constant and maximum specific growth rates were found to be 0.68 d(-1), 0.029, 8840 mg l(-1) and 0.34 d(-1) respectively. The final effluent was colourless and had a COD of 40 mg l(-1).