Removal of Pb2+, Cu2+, and Cd2+ Ions from a Saline Wastewater Using Emulsion Liquid Membrane: Applying Response Surface Methodology for Optimization and Data Analysis

Remote and mobile refineries are designed to utilize local groundwater (if abundantly available) to meet their industrial applications and inner uses. However, groundwater usually suffers hardness and salinity. Therefore, reverse osmosis (RO) technology is applied to treat the groundwater before use. The RO concentrate water stream is mixed with other refinery wastewater effluents resulting in a high saline wastewater. Upon discharging the refinery wastewater in constructed or natural lagoons, organic and non-organic pollutants permeate to groundwater reservoirs (aquifers) causing groundwater contamination build-up. The present study adopted the response surface methodology (RSM) to evaluate and optimize the simultaneous extraction of Pb2+, Cu2+, and Cd2+ ions from a refinery saline wastewater using emulsion liquid membrane (ELM). The experimental results were compared with those obtained from a previous study conducted for a simulated synthetic wastewater. Lower removal efficiencies of Pb2+, Cu2+, and Cd2+ ions were noticed for the refinery (real) wastewater due to possible interactions between dissolved salts of salinity, and metal ions. The lower removal efficiencies are due to the potential chemical complexation of the heavy metal ions with the petroleum organic and inorganic anions during the cations/carrier complexation at the wastewater/membrane interface which hinders the free migration of the metal ions. Also higher breakage was observed to cause lower stability of the ELM system in comparison with the simulated synthetic wastewater system. The impacts of the feed pH (2-6), homogenizer speed (5700-19,700 rpm), surfactant concentration (2-6%v/v), and carrier concentration (2-6%v/v) on the removal efficiencies of the Pb2+, Cu2+, and Cd2+ ions were investigated. The results of the regression analysis showed that experimental data could be fitted to quadratic models with values of determination coefficients (R-2) equal to 91.18%, 88.91%, and 91.16% for Pb2+, Cu2+, and Cd2+ respectively. Maximum removal efficiencies of 92.33%, 88.98%, and 76.29% for Pb2+, Cu2+, and Cd2+ ions respectively were obtained at the optimum operating conditions of feed pH of 5.15, homogenizer speed of 5700 rpm, surfactant concentration of 3.97% v/v, and carrier concentration of 6% v/v.