Effects of organic loading on bioelectricity and micro-algal biomass production in microbial fuel cells using synthetic wastewater

This study optimizes the performances of photosynthetic microbial fuel cells (PMFCs) under mixotrophic conditions in a cathode chamber inoculated with Chlorella vulgaris, compared to autotrophic conditions. In mixotrophic cultivation, microalgae in the cathode chamber were provided with organic and inorganic carbon. Different chemical oxygen demand (COD) concentrations of 100, 300, and 500 mg L-1 were added in the cathode chamber of PMFCs. The COD concentration in the anode chambers was maintained at 1000 mg L-1 and 1500 mg L-1 in the Batch 1, and 2, respectively. The mixotrophic PMFC with 100 mg L-1 of COD in the cathode chamber showed a longer power generation period with power densities of 3.93 (+/- 0.74) and 9.07 (+/- 1.40) mW m(-2) in Batch 1 and 2, respectively. In comparison, the PMFC in autotrophic conditions showed lower power generation, and higher internal resistance. However, increasing the COD concentration more than 100 mg L-1, decreased the power generation period due to the favorable conditions for heterotrophic metabolism of microalgae. The algal biomass generation in the cathode chamber was highest at 300 mg L-1 of COD. The highest ammonium nitrogen removal efficiencies (92 % and 82 % in Batches 1 and 2, respectively) were obtained when the cathode chamber was enriched with 300 mg L-1 of COD. This study successfully demonstrated that PMFC performances can be increased in terms of power generation and biomass production under the mixotrophic cultivation of Chlorella vulgaris.