Bioenergy for water desalination using advanced carbon materials as anode and cathode electrodes

Current desalination technologies require high energy input, being reverse osmosis (RO) the most-widely used technology for seawater desalination with an energy consumption of at least 3 kWh/m3. In this context, MIDES project... [ view full abstract ]

Current desalination technologies require high energy input, being reverse osmosis (RO) the most-widely used technology for seawater desalination with an energy consumption of at least 3 kWh/m³. In this context, MIDES project aims to revolutionize desalination by developing a low-energy sustainable process called Microbial Desalination Cell (MDC) as a pretreatment for RO. The integration of MDC technology with commercial RO allows seawater desalination with an energy consumption below 0.5 kWh/m³. MDC treat simultaneously wastewater and perform desalination using the energy contained in the wastewater. In fact, MDC can produce around 1.8 kWh of bioelectricity from energy contained in 1 m³ of wastewater. This energy is directly used to lower salt content in seawater from 35 to 5 g/L (brackish water) without external energy input. The performance of anode and cathode electrode is a parameter that must be optimized using advanced materials to obtain a high desalination rate. Here, the properties, the developments and the characterizations of anode and cathode electrodes based on carbon materials are presented.

Carbon materials are perfect material to use as anode material because are nontoxic and biocompatible with microorganisms, have resistance to corrosion, good electrical conductivity, adjustable surface morphology and chemistry and economic fabrication. The performance of more than 20 carbon materials was evaluated as anode electrode by monitoring the inoculation process kinetics through electrochemical techniques. Results demonstrate that carbon fibers and carbon felts materials are suitable as anode materials as these materials could be efficiently inoculated in less than 20 days, achieving proper current outputs.

Carbon materials also are employed as cathode electrode. Here, oxygen reaction reduction (ORR) is one of main bottlenecks to use these materials for air-cathode electrodes. In this study, air cathodes based on carbon nanofibers (CNFs), acting as a support matrix for metal nanoparticles (Co and Fe) that act as catalysts, were developed. Air cathode materials were fabricated using electrospinning technique followed by a thermal treatment. ORR were characterized electrochemically in an abiotic cell. Results indicate that CNFs doped with Fe and Co nanoparticles have proper ORR performance to be use as air-cathode electrodes, with higher performance than Fe doped CNF.