Mechanistic evaluation of electrocoagulation pre-treatment for reducing calcium–magnesium scaling during non-oily refinery wastewater treatment

by Kanwal Anwar, Muhammad Saqib Nawaz, Sher Jamal Khan, Noreddine Ghaffour, Momina Maheen
Year: 2026 DOI: https://doi.org/10.1016/j.jece.2026.123570

Abstract

Untreated discharge of refinery effluents can cause serious environmental damage. This study focuses on the treatment of the final non-oily wastewater stream originating from an oil refinery and processing site. Pre-treatment using electrocoagulation (EC) and main treatment/water recovery using forward osmosis (FO) is proposed. Firstly, the FO batch experiments were conducted with 0.75 M tetraethyl ammonium bromide (TEAB) as the surfactant draw solution and final non-oily stream as the feed solution. The feed solution cross flow velocity of 8 cm/s with operating temperature of 30 °C achieved the highest permeate flux of 7 L/m2/h, accompanied by a reverse solute flux of 0.19 g/m2/h. The FO membrane remained chemically stable against the contaminants. Carbonates and sulfates of calcium and magnesium were found to be the key contaminants in the membrane surface and were targeted for pre-treatment with EC. The EC process was systematically optimized for the electrode connection, electrode arrangement, current density, reaction time, and electrode material. The preferred configuration for the EC was the MP-P arrangement with aluminum electrodes due to its superior energy efficiency and effective contaminant removal, achieving 88% Mg2+, 42% Ca2+, and 68% SO₄2- removal at 3000 mA for 30 min. The pre-treated stream produced a 35% higher FO flux compared to the untreated stream. The findings of this study could serve a pivotal role in the scale-up applications of EC and FO for water and resource recovery from non-oily effluents.

Keywords

Electrocoagulation pre-treatment Forward osmosis Non-oily refinery wastewater Calcium–magnesium scaling Water and resource recovery