Electrocoagulation Modeling in Gas Refineries Oily Wastewater by Response Surface Methodology for COD reduction

The effluents’ COD of an oil and gas refinery is quite high (~16500 mg/L) - so is their turbidity - and the demulsifier which is presently used for oil-in-water emulsion breakdown requires to be used in large quantities and is of poor performance. Consequently, the treated effluents do not meet the local environmental standards for being discharged into the sea and an alternative replacement for treatment seems to be inevitable. In this research the possibility of electrocoagulation as a replacement was investigated. For this approach the Design of Experiments (DoE) was selected based on the Central Composite Design (CCD) and was developed by using the Response Surface Methodology (RSM). Three process variables that have a major role in the electrocoagulation process were found to be: pH of the effluent (2-9), current density (20-50 mA/cm2), and duration of operation (10-120 min). The removal of chemical oxygen demand (COD) and turbidity were selected as the response process. Based on analysis of variance (ANOVA) results, the first-order effects of all three variables and their second-order effects showed to be greatest on COD and turbidity removal. The maximum removal of COD with an efficiency of 93% and turbidity of 94% was observed both under the conditions of pH of 5.5-7, current density of 50 mA/cm2 in operation duration of 65 minutes. Also, the amount of turbidity removed in this range was 94%.

Keywords:

Oily Wastewater , Electrocoagulation , Response Surface Methodology