Title Page
Contents
ABSTRACT 12
1. INTRODUCTION 15
1.1. Research background 15
1.2. Research objectives and scope 16
2. LITERTURE REVIEW 18
2.1. Background and current scenario of biogas 18
2.2. Anaerobic digestion and biogas characteristics 19
2.3. Limitation of biogas and upgrading technologies 21
2.3.1. Physical and Chemical methods 22
2.3.2. Biological methods 23
2.4. CH₄ loss recovery through H₂ injection in AHPD 27
2.5. Dark fermentation (DF) + Anaerobic digestion 28
3. UPFLOW ANAEROBIC SLUDGE BLANKET REACTOR OPERATION UNDER HIGH PRESSURE FOR ENERGY-RICH BIOGAS PRODUCTION 30
Abstract 30
3.1. Introduction 30
3.2. Materials and methods 32
3.2.1. Inoculum and substrate 32
3.2.2. Experimental setup and operation 32
3.2.3. Analytical methods 33
3.3. Results and Discussion 34
3.3.1. UASB performance 34
3.3.2. Granule characteristics 38
3.3.3. EPS and EEM 40
3.3.4. Microbial community and gene analysis 41
3.4. Conclusions 44
4. HIGH-CALORIFIC BIOHYDROGEN UNDER HIGH PRESSURE: Ca²⁺ ADDITION, THEORETICAL PREDICTION, AND CONTINUOUS OPERATION 45
Abstract 45
4.1. Introduction 45
4.2. Materials and Methods 47
4.2.1. Inoculum preparation and substrate 47
4.2.2. Batch operation 47
4.2.3. Continuous operation 48
4.2.4. Analytical methods 49
4.3. Results and Discussion 50
4.3.1. Batch performance 50
4.3.2. Theoretical approaches 53
4.3.3. Continuous operation 57
4.3.4. Microbial community and gene analysis 62
4.5. Conclusions 66
5. ENHANCED H₂ CONVERSION TO CH₄ BY ELECTRICAL VOLTAGE APPLICATION 68
Abstract 68
5.1. Introduction 68
5.2. Materials and methods 70
5.2.1. Inoculum and substrate 70
5.2.2. Experimental setup and operation 70
5.2.3. Analytical methods 71
5.3. Results and discussion 71
5.3.1. CSTRs performance 71
5.4. Conclusions 75
6. TWO-STAGE ANAEROBIC DIGESTION FOR HIGH CALORIFIC BIOGAS PRODUCTION UNDER HIGH PRESSURE 76
Abstract 76
6.1. Introduction 76
6.2. Materials and methods 78
6.2.1. Inoculum and substrate 78
6.2.2. Experimental setup and operation 78
6.2.3. Analytical methods 79
6.3. Results and discussion 79
6.3.1. UASB performance 79
6.3.2. Microbial community 83
6.4. Conclusions 85
7. SUMMARY OF THE WORK 87
8. FUTURE WORK 89
REFERENCES 90
Table 2.1. General characteristics of biogas. 21
Table 2.2. Features of different biogas upgrading technologies. 27
Table 3.1. EPS characteristics of granules at different pressure conditions. 40
Table 4.1. Batch reactors performance for H₂ content and yield. 52
Table 4.2. Comparison of theoretical and measured H₂ production in the UASB reactor at different pressure conditions. 62
Table 6.1. CH₄ content and CH₄ yield at different pressure. 83
Fig. 2.1. global biogas demand for direct use, 2018-2040. 19
Fig. 3.1. (a) Daily performance of upflow anaerobic sludge blanket reactor (UASB) under different organic loading rates (OLR) and pressure conditions, and (b) COD removal efficiency... 35
Fig. 3.2. COD balance and CH4 content at different pressure conditions. 37
Fig. 3.3. A comparison between size and settling velocity of the granules at different pressure conditions. 39
Fig. 3.4. Relative abundance of archaeal community adapted at different pressure conditions. 41
Fig. 3.5. Gene expression for archaea (a) V-type ATPase, and (b) carbonic anhydrase at different pressure conditions. 43
Fig. 4.1. (a) pressure change, (b) hydrogen (H₂) content, (c) change in pH, and (d) cumulative H₂ production under different conditions in the batch reactors (Control and Ca²⁺ added) with time. 51
Fig. 4.2. COD balance of batch reactors at different pressures. 53
Fig. 4.3. Theoretical calculation for (a) H₂ content and (b) pH before and after the addition of sodium bicarbonate (NaHCO₃) and Calcium ion (Ca²⁺). 56
Fig. 4.4. (a) Daily performance of upflow anaerobic sludge blanket reactor (UASB) at different pressure conditions, and (b) glucose removal efficiency and pH. 58
Fig. 4.5. COD balance of UASB reactor at different pressures. 59
Fig. 4.6. Relative abundance of bacterial community (a) batch reactors, and (b) UASB reactors at different pressure conditions. 63
Fig. 4.7. Relative abundance of gene expressions (a) for batch reactors, and (b) UASB reactor at different pressure conditions. 65
Fig. 5.1. CH4 production from the control and EEI. 72
Fig. 5.2. Biogas composition for CH4, H2 and CO₂ from the control and EEI. 73
Fig. 5.3. Acetate concentration and pH for the control and EEI. 74
Fig. 6.1. (a) Daily performance of UASB reactor, (b) COD removal efficiency and pH under different OLR and pressures. 81
Fig. 6.2. COD balance and CH4 content at different pressure conditions. 82
Fig. 6.3. Relative abundance of (a) archaea and (b) bacteria. 85