Microbial carbon-capture cells for wastewater treatment: a step towards environmental sustainability

A light-driven, microbe-based electrochemical system known as the microbial carbon-capture cell, abbreviated as MCCC, is considered a potential device for carbon capture, storage, and utilization. It is the fusion of microbial fuel cell- (MFC-) mediated wastewater treatment with algal cultivation systems. In the standard microbial fuel cells, the chemical energy from organic compounds is converted by microbial-electro-chemical catalysis into electrical energy, by reduction-oxidation reactions occurring at cathode and anode, respectively. Similarly, microbial carbon-capture cells not only treat wastewater but also produce algal biomass, simultaneously producing energy. When the organics in the anodic chamber get oxidized, CO2 is released which gets captured by microalgae, exploited for nutrition, and even fixed photosynthetically into biomass ultimately generating O-2. Many existing problems are efficiently addressed by an integrated system, giving rise to a single entity, combining the microbial carbon-capture cell's strategy with biorefinery, where microbes in the anodic chamber act upon organic matter, degrading them to generate electrons which further reach the cathode completing the circuit by the reduction of oxygen. Such systems have shown to completely remove nitrates and ammonium from the wastewater and organic compounds with an efficiency higher than 90%. This treated wastewater gets allocated to the cathode chamber, through a transition vessel, where the algae grow. The cathodic reaction is self-aided by the O-2 produced during the algal growth, finally retained suspended in the effluent. Several factors like the selected algal strains and their photosynthetic efficiency and effectiveness along with substrate characteristics need to be well understood and optimized for desirable performance of such systems. In this review, we have discussed current developments in the field of MCCCs, associated challenges, and the way forward.