Microalgae cultivation in bio-electrochemical systems

Abstract

Biofuels from algae have the potential to completely replace fossil-based fuels and provide energy security for the future. However, the cost of algae biofuels is still too high for commercial application. In this context, producing algae and electrical energy using photosynthetic microbial fuel cells (PMFCs) is an attractive option. PMFCs utilize the natural process of photosynthesis for algae generation or algae degradation at the anode. In the former system, the process of organic matter degradation complements the process of algae biomass production with concomitant power generation. Electrogenic bacteria oxidize organic matter at the anode anaerobically. The anode transfers the electrons released through oxidation to the cathode, where photosynthetic organisms produce oxygen (O2) as a cathodic electron acceptor. The suitability of bio-electrochemical systems such as microbial fuel cells for algae cultivation can be assessed by comparing them with the conventional method of cultivation, namely open ponds and photobioreactors. PMFCs offer a process that can provide high carbon dioxide concentrations for algal growth, has a mechanism to prevent high inhibitory O2 concentrations and can meet a fraction of the process electricity requirements. The algae biomass can go as high as 4–5 g/L in a PMFC and power output doubles due to activity of algae at the cathode compartment. This chapter discusses the algal growth in bio-electrochemical systems, the factors that influence them and directions for future research.