A comparative study on optimizing electrocoagulation for organic contaminant removal in shale gas fracturing wastewater

Abstract

Shale gas fracturing wastewater (FW) exhibits high total dissolved solids (TDS) content, averaging 13 g L⁻¹, along with an average total suspended solids (TSS) content of 676 mg L⁻¹ and an average chemical oxygen demand (COD) content of 1370 mg L⁻¹. Chemical coagulation processes are effective in removing suspended solids but perform poorly in removing organic contaminants. Consequently, the electrocoagulation (EC) process was employed to enhance the COD removal efficiency from shale gas FW. The EC process performance was assessed by examining various operational parameters such as pretreatment methods, current density levels, pH values, and reaction times. It was found that chemical coagulation achieved a COD removal efficiency of 43.1% at a dosage of 500 mg L⁻¹. Compared to chemical coagulants at the same concentration, the EC process demonstrated a higher COD removal efficiency and was nearly one-fifth of the cost. When the FW samples were treated directly by the EC process, the optimal COD removal efficiency of up to 85% was achieved under the conditions of 70 A m⁻² current density, a pH of 7, and a reaction time of 20 minutes. However, after aeration pretreatment for 30 minutes, the optimum removal efficiency of 88.3% occurred at a current density of 50 A m⁻² and a reaction time of 15 minutes. The pseudo first-order model was found to be more suitable for simulating both COD and DOC removal in the EC process with significant coefficients (R² > 0.89). The results confirmed that the EC process combined with aeration pretreatment is an innovative alternative for real-scale shale gas FW treatment.