Treatment and reuse of shale gas wastewater: Electrocoagulation system for enhanced removal of organic contamination and scale causing divalent cations
Abstract
The present study explores the feasibility of using the electrocoagulation (EC) process for the treatment and reuse of wastewater produced during shale gas recovery by hydraulic fracturing. The electrocoagulation process has been evaluated for the removal of suspended solids, total organic carbon (TOC) and scale (hardness) causing divalent cations, which, if untreated, can clog the gas well. Experiments were performed with actual shale gas wastewater (ASWW), synthetic shale gas wastewater prepared with low concentration of dissolved salts (SSWW – LDS) and synthetic shale gas wastewater prepared with a high concentration of dissolved salts (SSWW – HDS). EC is found to be effective for removing TOC and hardness from both the actual and synthetic shale gas wastewaters. The electric energy required per unit mass (EEM) for removal of TOC for ASWW, SSWW – LDS and SSWW – HDS are 243, 102 and 70 kWh/kg respectively. The EEM for removal of hardness for ASWW, SSWW – LDS and SSWW – HDS are 303, 104 and 25 kWh/kg respectively. The high conductivity of SSWW – HDS helps in achieving higher currents and hence the lower reported EEM values for SSWW – HDS. Also, under alkaline conditions, the performance of EC increases significantly. Combination of aeration with EC is also found to increase the performance of EC, especially for wastewater containing high concentrations of chloride ions.