Produced water treatment using microbial desalination cells
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Globally, 250 million barrels of produced water is generated daily for extracting 80 million barrels of oil. Having a highly variable composition and no economic value, produced water presents serious environmental problems. While the treatment of produced water is of paramount concern, existing desalination technologies are highly expensive and energy-intensive leading to great investments by oil industries. Microbial desalination cells (MDC) provide a promising alternative through their potential for negligible energy input, use of low-cost resources, low waste production, and electricity generation. However, MDC is a relatively new technology and its application in industries is limited by its low desalination efficiency and pH instability. This research investigates the effect of various factors on the performance of MDC employing Saccharomyces cerevisiae yeast as electron generating microorganisms. Two mediators, methylene blue, and menadione are used as electron promoters to shuttle the electrons from the yeast cells to the anode electrode. In particular, a two-level partial factorial design is implemented where, MDC desalination efficiency is investigated at two (low/high) levels of three input factors: aeration in anolyte (aerobic/ anaerobic), hydrophilic mediator concentration (0.5– 2 mM), and concentration of Total Dissolved Solids (TDS) in produced water (20– 40 g/l). Acquired experimental data are statistically analyzed using single effect and interaction plots. In addition, several other operating parameters and configurations are investigated in order to achieve optimum conditions for best performance. These include aeration rates in the anode and cathode chambers, the concentration of lipophilic and hydrophilic mediators, the pH of the anolyte solution, the use of activated carbon granules, and the repeated batch operation. Moreover, an MDC unit is operated at the optimized conditions where it resulted in 36% desalination after 72 hours. The study revealed that the operation of repeated batch cycles was the most effective among other parameters in improving desalination efficiency of MDCs. Furthermore, the factorial design study concluded that produced water TDS has the highest single effect on MDC performance and that there is a significant interaction between all three input factors employed in the factorial design.