Utilization of produced water as a substrate for a microbial electrolysis cell

Produced water (PW) is the main waste stream from offshore oil and gas operations, significantly contributing to the environmental impact factor (EIF). Emerging technologies such as microbial fuel cells (MFC) and microbial electrolysis cells (MEC) are currently being investigated for their potential to
generate electricity and hydrogen while removing oxidizable compounds from domestic and industrial wastewater. The potential of PW as a substrate for a MEC is evaluated in this work through the optimization of different parameters of the setup and two different inocula (marine sediments and domestic wastewater). The Wadden Sea inoculum contains sulfate-reducing bacteria (SRB) that are known exoelectrogens and thrive in oil-rich and PW environments. Both inocula communities were analysed with 16S rRNA amplicon sequencing. The Wadden Sea inoculum showed a high abundance of Marinobacter genus, known for their capacity to degrade hydrocarbons; while the wastewater inoculum was rich in Methanosaeta genus demonstrating potential to convert acetate into methane. A
hydrogen production of 0.105m3H2/m3 of anolyte per day was recorded in Single Chamber configuration with SRB inoculum. However, the low current measurements indicated insufficient bacterial activity, which was also verified with the ATP analysis performed at the termination of the experiment. In future work, bacterial activity may be increased by switching to a continuous operation
supplying fresh substrate and expanding the experiment length, giving enough time for bacteria to acclimatize to the medium. A more representative sample of PW, containing higher concentrations of acetate can also lead to increased hydrogen production.