Optimization of Forward Osmosis for Oil Refinery Effluent Desalination Using Response Surface Methodology

Abstract

Repurposing usage of oil refinery wastewater with retrofitted desalination technology necessitates the optimization of a forward osmosis (FO) technology. Herein, factors such as draw solution concentration (DS-C) and feed and draw solution flow rates (FS-FR, DS-FR) play significant roles. In this study, the individualistic and interaction effects of these factors were explored to ascertain the FO performance. The effects of these operating factors, DS-C (20-50 g/L), DS-FR (7.5-9.4 L/h), and FS-FR (7.5-9.4 L/h), and their interactive effects on the permeation flux and rejection of Cl^-, SO₄^2- and CO₃^2- from oil refinery effluent, were studied using the Box-Behnken design (BBD) of response surface methodology (RSM). Statistical models were developed to optimize the operating conditions. The analysis of variance and the developed response models were used to evaluate the data at a 95% confidence level. Three confirmatory runs were conducted based on the optimum conditions (FS-FR: 9.2 L/h; DS-FR: 9.4 L/h; DS-C: 32.6 g/L). At a desirability of 81%, average rejections of 94.59 ± 0.32% for CO₃^2- and 100% for SO₄^2- were obtained. Average Cl^- enrichment was 35.5 ± 5.15% and average permeation flux of 3.64 ± 0.13 L/m² h were achieved, suggesting that RSM was a suitable tool for optimizing FO for desalinating the effluent. In addition, the average recovered permeation flux of 86.01 ± 2.66% demonstrated the effectiveness of the FO membrane after cleaning.