Microbial fuel cells (MFCs) are an innovative and environmentally friendly bioenergy technology, having great potential towards electricity generation with simultaneous wastewater treatment. MFCs operation with oxygenation by algae growth in the catho...
Microbial fuel cells (MFCs) are an innovative and environmentally friendly bioenergy technology, having great potential towards electricity generation with simultaneous wastewater treatment. MFCs operation with oxygenation by algae growth in the cathode chamber called algae-cathode MFCs have drawn considerable attention in the last decade due to the wastewater treatment, electricity generation, CO2 sequestration and many valuable bioproducts generation from algal biorefinery. In the first study, algae-cathode MFCs were first operated to treat leachate (nutrients) by algae growth in the cathode and simultaneously supply oxygen to the cathode for high bio-electricity generation. Optimum leachate dilutions were investigated to obtain high nutrient (nitrogen and phosphorus) removal and electricity generation with algae growth in the cathode chamber. Landfill leachate at different percentages (5- 40%) was fed to algae cathode microbial fuel cells (MFCs) for electricity generation along with chemical oxygen demand (COD) and nutrient removal. Maximum cell voltage of 300 ± 11 mV was obtained with 5% leachate, but the cell voltage decreased with an increase in leachate percentage. The maximum dissolved oxygen (DO) was 19.57 mg/L with 5% leachate. The COD in the anode chamber was almost completely removed (97%) with all leachate percentages, while the maximum COD removal was 52% with 10% leachate in the cathode chamber. Enhanced nitrogen and phosphorus removal were observed with leachate percentages less than 10%, but nitrogen removal efficiency was significantly reduced, and even more phosphorus was observed with leachates higher than 25% (NH4+-N = 651mg/L). This study suggests that leachate can be treated at an appropriate dilution with simultaneous electricity generation in algae cathode MFC.
In the second study, algae-cathode microbial fuel cells (MFCs) with various hydraulic retention times (HRTs) were investigated for electricity generation, and chemical oxygen demand (COD) and nutrient removal from diluted landfill leachate (15% v/v). The cell voltage and dissolved oxygen (DO) in the cathode were considerably affected by the HRT. The highest cell voltage was 303 mV at 20-h HRT and DO concentration of 5.3 mg/L was only observed at 60-h HRT. Nutrient removal increased with increasing HRTs, and the maximum removal efficiency was 76.4% and 86.3% at 60-h HRT for ammonium and phosphorus, respectively. The highest COD removal of 26% was observed at 60-h HRT. The dominant phyla in the cathode were Proteobacteria, Cyanobacteria, Bacteroidetes, and Chlorophyta, which could have contributed to electricity generation and nutrient removal. This study suggests that an algae-cathode MFC with an appropriate HRT can continuously generate electricity and simultaneously remove nutrients from real leachate wastewater in field applications.
In the third study, a novel tubular-type photosynthetic microbial fuel cell (PMFC) was operated with algae growth and multiple electrodes in the cathode chamber. The PMFC operations were initially conducted at various hydraulic retention times (HRTs; 2, 6, 12, and 24 h) of an individual chamber to determine the optimum HRTs for high electricity generation and nutrient removal. At fixed 24-h HRT in the cathode chamber, cell voltage with domestic wastewater (acetate addition) in the anode chamber and BBM in the cathode chamber gradually increased with a decrease in HRT of the anode, but it quickly dropped at 2-h HRT. The highest cell voltage of 315 mV was obtained at 6h HRT with average DO concentration of 10.31 ± 2.60 mg/L. The maximum efficiency of wastewater treatment in the anode chamber was obtained at longer HRT (24 h), with the COD removal was 40.0 ± 7.8% and nutrient removals of 65.6 ± 4.6% TN and 98.7 ± 0.3% TP. However, the HRT changes in the cathode chamber did not affect much the cell voltage generation although the sharp decrease in cell voltage was observed at 2-h HRT. With domestic wastewater passed through both chambers of PMFC (total HRT=19.3h; 6-h at anode and 13.3-h at cathode), the cell voltage increased proportionally with the increase of initial COD concentration up to 300 mg/L, and then it decreased with higher COD loading. The highest cell voltage was 161 ± 6 mV with 300 mg/L of COD concentration, and the DO concentration was 4.42 ± 0.65 mg/L in the cathode. The maximum COD and phosphorus removals were 98.1 ± 3.4% and 49 ± 1.7%, respectively, with 300 mg/L COD, and for nitrogen, the maximum value was 79.2 ± 2.4% with 400 mg/L COD. This study demonstrates that PMFC with multiple electrodes in algae cathode chamber can efficiently treat wastewater without external aeration with sustainable electricity generation.
Lastly, the typical double chamber cubic MFC was carried out with the Ni-Fe3O4 as a non-noble and facile catalyst on the carbon cloth cathode electrode to investigate the improvement of electricity generation from algae-cathode MFC. The performance of an algae-cathode MFC equipped with the catalyst at different DO concentrations in the cathode chamber improved compared to plain carbon electrode by enhancing the oxygen reduction reaction. Additionally, polarization test and cyclic voltammetry (CV) were carried out to determine the electrochemical performance of an algae-cathode MFC equipped with various cathode electrodes at different DO concentrations.