Investigating the Result of Current Density, Temperature, and Electrolyte Concentration on COD: Subtraction of Petroleum Refinery Wastewater Using Response Surface Methodology

Sharon Chakawa,Mujahid Aziz

doi:10.3390/w13060835

Abstract

Electrochemical oxidation (EO) investigated chemical oxygen demand (COD) subtraction from petroleum refinery wastewater (PRW) as a capable remediation process. Titanium substrates coated with iridium–tantalum oxide mixtures (Ti/IrO2–Ta2O5) were used as the dimensional stable anode (DSA). The Box-Behnken Design (BBD), a statistical experimental design and response surface methodology (RSM), was used to matrix the current density, temperature, and electrolyte (NaCl) concentration variables, with COD removal efficiency as the response factor. A second-order verifiable relationship between the response and independent variables was derived where the analysis of variance displayed a high coefficient of determination value (R2 = 0.9799). The predicted values calculated with the model equations were very close to the experimental values where the model was highly significant. Based on the BBD for current density, the optimum process conditions, temperature and electrolyte (NaCl) concentration were 7.5 mA/cm2, 42 °C and 4.5 g/L, respectively. They were resulting in a COD removal efficiency of 99.83% after a 12-hour EO period.

Highlights

Introduction and Alexandros IStefanakisGlobal demand for petroleum products is increasing rapidly; our environment is exposed to rising hazardous impacts
The results indicated that a maximum chemical oxygen demand (COD) removal of 91.7% was achieved at temperature, NaCl concentration and current density of 40 ◦ C, 4 g/L and 7.5 mA/cm2, respectively
The data attained from 16 experimental runs were fitted into a second-order polynomial model equation to determine the relationship between the coded factors and the response, as shown in Equation (2)

Summary

Introduction

Introduction and Alexandros IStefanakisGlobal demand for petroleum products is increasing rapidly; our environment is exposed to rising hazardous impacts. South Africa produces approximately 115 million litres of oil a day through six refineries by consuming 177 million litres of freshwater and generating about 137 million wastewater [3] These high water demands and consumption have resulted in water becoming increasingly scarce and reducing groundwater levels, increasing water shortages in many areas [4]. Effluents from petroleum refinery are significant pollution sources that exhibit high concentrations of organic and inorganic pollutants and are characterised by high concentrations of chemical oxygen demand, fats, oil and grease, and phenol [2] These pollutants have various adverse impacts on the surrounding environment. Before discharging the wastewater into the environment, the amounts of these contaminants must be lowered to acceptable levels [6,7]

Objectives

Results

Conclusion