Treatment of petroleum refinery sulfidic spent caustic wastes by electrocoagulation

In order to protect environment and to recover caustic soda solution, electrocoagulation technology was used to remove sulfide and organics from refinery spent caustic wastes. The performance of elctrocoagulation in the removal efficiency of sulfide and organic compounds was investigated. Several working parameters, such as solution pH, current density and electrode nature were studied in an attempt to achieve a higher removal capacity. The optimum electrocoagulation time, initial pH, current density were found to be 30 min, pH 9 and 21.2 mA cm(-2) for initial sulfide concentration of 34,517 mg L-1 and COD of 72,450 mg L-1 respectively. Under the optimum conditions established, removal efficiency of sulfide and organics expressed as COD was greater than 80%. Furthermore, successive electrocoagulation technique (dual EC units) yields a very effective (>95%) removal of residual compounds and heavy metals in basic aqueous medium. The method was found to be highly efficient and relatively fast compared to conventional existing techniques such as chemical oxidation, precipitation or by neutralisation. (C) 2013 Elsevier B.V. All rights reserved.