DOI: 10.14457/tu.the.2020.1023
title: Optimization of photosynthetic microbial fuel cell for treating wastewater and simultaneous power generation

description: Microbial fuel cell (MFC) technology is an emerging technology for wastewater treatment, bioenergy generation, and resource recovery. These bio-electrochemical devices can convert the chemical energy stored in organic compounds into electricity using microorganisms. In MFCs, aqueous oxygen is employed as the final electron acceptor in the cathode chamber due to the low cost. Photosynthetic MFCs (P-MFCs) are a relatively new development of MFC technology by incorporating a photosynthetically-aerated cathode chamber. In this system, microalgae or cyanobacteria produce oxygen via photosynthesis. In this study, a P-MFC was investigated to treat wastewater in anode and cathode chambers while generating bioelectricity and microalgal biomass. The performance of the P-MFC was compared with a mechanically aerated MFC system to evaluate the effectiveness of photosynthetic aeration in MFC applications. Photosynthetic aeration under continues light continuous in the cathode chamber showed a maximum power density of 29.55 (± 2.80) mW m-2 which is 40% higher than the mechanical aeration. The internal resistance of 288.6 (± 35.8) Ω in the cell under the mechanical aeration dropped to 249.1 (± 26.2) Ω under the photosynthetic aeration. The higher power generation achieved under the photosynthetic aeration attributed to the higher DO of 10-11 mg L-1 in the cathode chamber compared to the mechanical aeration (8-9 mg L-1).Among two different pure culture strains of Chlorella vulgaris, and Scenedesmus quadricauda, better performance in P-MFC was obtained with Chlorella vulgaris assisted cathode chamber. PMFC was also conducted under photoautotrophic conditions and different mixotrophic conditions to optimize the performances with Chlorella vulgaris. Chlorella vulgaris showed the best performance in terms of power generation under mixotrophic cultivation with 100 mg/L of COD in the cathode chamber. Mixotrophic PMFCs showed higher biomass generation than the photoautotrophic PMFC. The highest biomass generation and ammonium-nitrogen removal efficiency were obtained with 300 mg L-1 of COD in the cathode chamber. These results indicate that the wastewater can be treated efficiently for NH4+ in a PMFC by Chlorella vulgaris if supplemented with the appropriate organic carbon concentration in the cathode chamber while simultaneously reducing the organic carbon under mixotrophic conditions. Circulating 5-day treated anode chamber effluent to the cathode chamber resulted in lower COD removal efficiencies. Increasing the retention time to 10 d in the anode chamber, and subsequent 10 d in the cathode chamber resulted in higher power generation with approximately 70% of a total COD removal efficiency in both chambers. Increasing the retention time to 20 d in the anode chamber resulted in inadequate nutrients available for the microalgae growth in the cathode chamber due to the higher treatment efficiencies achieved in the anode chamber. Circulation of the anode chamber effluent to the cathode chamber for further treatment provides a promising sustainable solution to wastewater treatment with simultaneous organic and nutrient removal.