Concurrent Desalination and Hydrogen Generation Using Microbial Electrolysis and Desalination Cells

Abstract

The versatility of bioelectrochemical systems (BESs) makes them promising for various applications, and good combinations could make the system more applicable and economically effective. An integrated BES called microbial electrolysis and desalination cell (MEDC) was developed to concurrently desalinate salt water, produce hydrogen gas, and potentially treat wastewater. The reactor is divided into three chambers by inserting a pair of ion exchange membranes, with each chamber serving one of the three functions. With an added voltage of 0.8 V, lab scale batch study shows the MEDC achieved the highest H(2) production rate of 1.5 m(3)/m(3) d (1.6 mL/h) from the cathode chamber, while also removing 98.8% of the 10 g/L NaCl from the middle chamber. The anode recirculation alleviated pH and high salinity inhibition on bacterial activity and further increased system current density from 87.2 to 140 A/m(3), leading to an improved desalination rate by 80% and H(2) production by 30%. Compared to slight changes in desalination, H(2) production was more significantly affected by the applied voltage and cathode buffer capacity, suggesting cathode reactions were likely affected by the external power supply in addition to the anode microbial activity.

Mathematical Model of Dynamic Behavior of Microbial Desalination Cells for Simultaneous Wastewater Treatment and Water Desalination

“…Therefore, it holds great promise to significantly reduce energy consumption in desalination processes. MDC research is still in an early stage, and studies have been carried out to improve the understanding of MDCs by investigating the key factors, such as the anode organic loading rates, 5 salt loading rates, 6,7 external resistance, 8,9 hydraulic retention time, 9 new functions, 10,11 membrane fouling, 12,13 intermembrane distance, 14 and system configuration. 15 Given complex desalination processes and strong interactions between biological, electrochemical, and engineering factors in MDCs, a proper mathematic model will be essential for the optimization and the scaling up of MDCs.…”

Bioelectricity inhibits back diffusion from the anolyte into the desalinated stream in microbial desalination cells

“…The desalination can be enhanced through stacked cells (Chen et al, 2011;Kim and Logan, 2011), electrolyte recirculation (Chen et al, 2012a;Qu et al, 2012), applying small external voltage (Ge et al, 2014), incorporating forward osmosis membrane in situ (Zhang and He, 2012) or ex situ (Yuan et al, 2015), adding ion exchange resin , or integrating capacitive adsorption (Forrestal et al, 2012). Hydrogen and other chemicals can be produced by combining electrolysis with an MDC (Chen et al, 2012b;Luo et al, 2011). The scale of MDCs has been advanced from milliliters to over 100 L (Zhang and He, 2015).…”

Microbial electrosynthesis of biochemicals : innovations on biocatalysts, electrodes and ion-exchange for CO2 supply, chemicals production and separation

“…The middle compartment is partitioned by an anion exchange membrane (AEM) towards the anode and a cation exchange membrane (CEM) towards the cathode. Bacteria on the anode oxidize biodegradable substrates and generate electrons and protons; the electrons are externally transferred to cathode whereas the anions (e.g., SO 4 2-, Cl ) in the desalination compartment migrate to the anode and the cations (e.g., K + , Na + ) are transferred to the cathode to maintain charge neutrality, thereby, desalination of the middle chamber solution occurs [10,113,114]. In MDC, the migration of ions from the saline water in the middle chamber towards the anode and cathode increases the conductivity of the anolyte and catholyte.…”

“…Jacobson et al [115] compared RO systems that use 2.2 kWh energy to desalinate 1 m 3 of seawater with MDCs, that can produce 1.8 kWh of electric energy, with a net benefit of 4 kWh by treating 1 m 3 of seawater. When an MDC is operated in electrolysis mode for hydrogen production at the cathode, 180-231% surplus energy than the input electricity can be recovered as H 2, with the added advantage of water desalination [114,116].…”