Microbial capacitive desalination for integrated organic matter and salt removal and energy production from unconventional natural gas produced water

Abstract

The rapid development of unconventional oil and gas generates a large amount of contaminated produced water. The treatment and reuse of such water generally require multiple treatment processes to remove different constituents from the waste, such as salts and organic matter. This study characterized the performance of a new microbial capacitive desalination technology for simultaneous removal of organic pollutants and salts from shale gas produced water as well as its energy production during the process. The microbial capacitive desalination cell (MCDC) was able to remove total dissolved solids (TDS) at a rate of 2760 mg of TDS per liter per hour and chemical oxygen demand (COD) at a combined rate of 170 mg of COD per liter per hour, which was 18 times and 5 times faster than the traditional microbial desalination cell (MDC), respectively. The MCDC had a coulombic efficiency of 21.3%, and during capacitive deionization regeneration, 1789 mJ g⁻¹ activated carbon cloth (ACC) was harvested. One advantage of MCDC is that all three chambers could be used to remove both organic and inorganic contaminants. The reactor removed greater than 65% of the TDS and 85% of the COD in 4 hours of operation in the desalination chamber, and more than 98% of the salts and 75% of the organics were recovered during the regeneration process. This technology provides a new integrated process to complement current systems for organic matter and salt removal as well as energy recovery from real produced water.