Investigation of spent caustic effluent treatment by electro-peroxone process; cost evaluation and kinetic studies

Abstract

Spent caustic is an extremely polluted industrial wastewater with quite complex chemistry and various environmental negative impacts. Conventional wastewater treatment methods are not adequately efficient for the remediation of spent caustic. In the present work, for the first time, the treatment of spent caustic effluent was investigated by the Electro-Peroxone (EP) method as a subdivision of Advanced Oxidation Processes (AOPs). The Central Composite Design (CCD) was employed to optimize the operational parameters, including initial COD, applied current, pH, and ozone flow rate in the removal of COD. The statistical investigations showed an acceptable determination coefficient and a suitable second-order model. The predicted optimal circumstances were as the following: initial COD = 1076 mg. L-1, applied current = 0.79 A, pH = 7.9 and O3 flow rate = 1.68 L.min−1. At optimum points, the predicted and actual COD removal percentages were 96.3 and 95.0 %, respectively. The kinetic investigations showed that the removal of COD followed the first-order kinetic with the half-life and constant reaction rate at 18 min and 0.038 min−1, respectively. The specific energy consumption (SEC) value in the EP process was calculated at 33.96 kWh/Kg COD removal, showing that the combined EP process could be a cost-effective technique for the treatment of spent caustic effluent on an industrial scale.