(565f) Electricity Generation from Hydraulic Fracturing Wastewater Using a Reverse Electrodialysis Stack

Hydraulic fracturing (HF) wastewater is produced during the fracking process for oil and gas production. Due to the high salinity of produced wastewater, it is an environmental challenge with potentially severe impacts on soil and water resources. In this study, electricity generation from HF wastewater was examined by using a reverse electrodialysis (RED) stack. A 10-cell RED stack was used that contained pairs of cation exchange membranes (CEMs) and anion exchange membranes (AEMs). Different synthetic salt solutions (NaCl+CaCl₂, NaCl, CaCl₂, Na₂SO₄, NaCl+Na₂SO₄) and a real HF wastewater were employed to assess the effect of different divalent and monovalent ions on power production. Due to the temperature gradient between produced HF wastewater and feed solution, the effect of the temperature gradient between concentrated and diluted streams was also assessed. Membrane characterizations, including permselectivity and electrical resistance, were analyzed in the presence of the synthetic salt solutions and the HF wastewater over a temperature range of 25- 60 ⁰C. Based on the results, the presence of calcium and sulfate ions drops the permselectivity of CEMs and AEMs by 50% and 35%, respectively. Results of electrochemical impedance spectroscopy (EIS) revealed a sharp reduction in the electrical residence of both AEMs and CEMs with increased temperature. Based on polarization data a maximum gross power density of 2.6 W.m^-2 was achieved when HF wastewater was used in a RED stack. Applying a temperature gradient further increased the power density to 3.7 W.m^-2 which is among the highest power densities reported for a RED stack with a waste stream.