An integrated system of fuel cell and microorganisms offers a sustainable means to extract electrons for power generation. The biocatalyst oxidizes the substrate and generated electrons are transferred from anode to cathode through an external circuit. The electrons combine with electron acceptor at cathode thus generating electricity. Among all the available substrates, algal biomass is the most cost effective as it requires low energy for cultivation. Algae can be utilized at anode and/or cathode. If combined with the waste water treatment, many gram negative bacteria (present in waste water) such as Pseudomonas aeruginosa, Shewanella sp. etc., can degrade algal biomass in the anode chamber generating electrons. On the other hand, algae can be solely used at anode for electron generation through water splitting- the first step of photosynthesis. The viability of this system mainly depends on the light harvesting efficiency of photosystem II. Algae usage at cathode is associated with availability of oxygen to undergo reduction and producing water. In most cases it is done by growing the algae inside the cathode chamber. The beauty lies here is that algae can be grown simply in water with light exposure. Alternatively, oxygen may be supplied to the cathode through a channel which is connected to a photobioreactor carrying algae cultivation. The use of algal cathodes reduces the operational cost by replacing the need of mechanical air supply. It also captures the CO2 emissions released from the anodic bacterial respiration. Other benefits include low cost of biomass generation, utilization of algal biomass for biofuels and other chemicals and nutrient recovery (such as nitrogen and phosphorus) for use as fertilizers.
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