Algae-cathode microbial fuel cell for electricity generation along with nutrient removal in batch and continuous mode operations

다국어 초록 (Multilingual Abstract)

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.

목차 (Table of Contents)

• Chapter 1. Introduction 1
• 1.1 Microbial fuel cell 1
• 1.2 Algae-cathode microbial fuel cell 2
• 1.3 My research on algae-cathode microbial fuel cells 3
• 1.4 References 5
• Chapter 2. Literature review 6
• 2.1 Introduction 6
• 2.2 Algae aeration in the cathode of MFCs for enhanced power generation 9
• 2.2.1 Photosynthetic oxygenation using algae in cathode of MFCs: mechanism and working principle 9
• 2.2.2 Operational parameters influencing the bioelectricity generation 13
• 2.2.3 Recent development in cathode materials for performance improvement in A-MFCs 24
• 2.3 Wastewater treatment by algae growth in the cathode of MFCs 27
• 2.3.1 COD removal by algae growth in the cathode of MFCs 28
• 2.3.2 Nutrient and other pollutants removal by A-MFC 30
• 2.3.3 Heavy metals removal 32
• 2.4 Biofuel and bioproducts generations from algae biomass recovered from the cathode of MFCs in a biorefinery approach 37
• 2.5 Limitations and future perspectives 39
• 2.6 Conclusions 41
• 2.7 References 41
• Chapter 3. Algae cathode microbial fuel cells for electricity generation and nutrient removal from landfill leachate wastewater 59
• 3.1 Introduction 59
• 3.2 Materials and methods 60
• 3.2.1 Wastewater and landfill leachate 60
• 3.2.2 Algae culture 61
• 3.2.3 Microbial fuel cell configuration and operation 62
• 3.2.4 Measurement and analysis 63
• 3.3 Results and discussion 64
• 3.3.1 MFC performance and nutrient removal with 10% leachate 64
• 3.3.2 Voltage generation and DO concentration with various leachate percentages 69
• 3.3.3 COD and nutrient removal with various leachate percentages 71
• 3.3.4 pH and conductivity changes in the MFC operation at different leachate percentages 76
• 3.4 Conclusions 78
• 3.5 References 78
• Chapter 4. Leachate treatment and electricity generation using an algae-cathode microbial fuel cell with continuous flow through the chambers in series 83
• 4.1 Introduction 83
• 4.2 Methods 85
• 4.2.1 Wastewater and landfill leachate 85
• 4.2.2 Algae bioreactor 85
• 4.2.3 MFC construction 86
• 4.2.4 MFC operation 86
• 4.2.5 Measurement and analysis 86
• 4.3 Results and discussion 87
• 4.3.1 Cell voltage, half-cell potential and DO concentration at 20 h HRT 87
• 4.3.2 COD and nutrient removal at 20 h HRT 89
• 4.3.3 Cell voltage, half-cell potential, and DO at various HRTs 92
• 4.3.4 Effect of HRT on COD and nutrient removal 95
• 4.3.5 Bacterial and algal community compositions in the cathode 101
• 4.4 Conclusions 106
• 4.5 References 107
• Chapter 5. Using multiple carbon brush cathode in a novel tubular photosynthetic microbial fuel cell for enhancing bioenergy generation and advanced wastewater treatment 115
• 5.1 Introduction 115
• 5.2 Materials and methods 116
• 5.2.1 PMFC configuration and operation 116
• 5.2.2 Algae bioreactor 119
• 5.2.3 Analytical methods and measurement 119
• 5.3 Results and discussion 120
• 5.3.1 PMFC operation at different HRTs in the anode chamber 120
• 5.3.2 The effect of different cathode HRTs on power generation and DO levels 125
• 5.3.3 The effect of initial COD concentrations of wastewater on power generation of PMFC 127
• 5.3.4 COD and nutrient removal from both chambers of PMFC 129
• 5.4 Supplementary data 133
• 5.5 Conclusions 135
• 5.6 References 135
• Chapter 6. Enhancing electricity generation of algae-cathode microbial fuel cell by using low-cost catalyst on cathode electrode 141
• 6.1 Introduction 141
• 6.2 Materials and methods 142
• 6.2.1 Catalyst preparation and cathode fabrication 142
• 6.2.2 Algae culture 143
• 6.2.3 Microbial fuel cell configuration and operation 143
• 6.2.4 Measurement and Analysis 144
• 6.3 Results and discussion 144
• 6.3.1 Effect of DO on algae-cathode MFC with various cathode electrodes 144
• 6.3.2 Polarization test 145
• 6.3.3 Cyclic voltammetry analysis 147
• 6.4 Conclusions 149
• 6.5 References 149
• Chapter 7. Conclusions 153