2.1 Overview
11
recovery process. The research demonstrates that by taking glucose as an example, when acetic acid is the only intermediate metabolite, the maximum theoretical
hydrogen production rate of 1 mol of glucose is 4 mol. However, the actual hydrogen
production rate is far smaller than the theoretical value, generally being 0.5–2.5 mol
and the intermediate metabolite is generally a mixture containing volatile fatty acid
(VFA) and alcohol, while they are the best substrate of methanogens. The highest theoretical energy recovery efficiency of hydrogen production in biochemical reaction
is only 33.5% through anaerobic fermentation, which is lower than 83.2% of that of
methane production via anaerobic fermentation. Furthermore, the theoretical energy
recovery efficiency in the combined production of hydrogen and methane via anaerobic fermentation (CHMP-AF) can reach 89%. Therefore, coupling the CHMP-AF
process under phase separation can obtain two energies, i.e. hydrogen and methane.
This effectively improves energy recovery rate of organic wastes through anaerobic
fermentation and overcomes feedback inhibition of acidic metabolite and hydrogen
partial pressure in traditional processes, which is favorable for long-term and stable
operation of the process.
2.1.3 Influence Factors of Anaerobic Fermentation
2.1.3.1 Temperature
Temperature is an important factor influencing biogas production efficiency in anaerobic fermentation. The temperature mainly affects hydrolysis degree of materials,
enzyme activity and structure and function of microbial population in the fermentation. According to the influences of temperature on microbial activity, the anaerobic fermentation can be divided into four temperature ranges, i.e. low-temperature
fermentation at 15–20 °C, moderate-temperature fermentation at 30–35 °C, hightemperature fermentation at 50–55 °C and ultra-high-temperature fermentation above
70 °C. Of them, anaerobic fermentation at moderate and high temperature is mainly
studied, because too low temperature can slow down metabolic rate of microorganisms, while too high temperature can inactivate protease in cells. Both of the two
conditions probably reduce biogas production efficiency.
2.1.3.2 pH Value
pH value is an important factor for measuring stable operation of the anaerobic
fermentation system. It mainly affects the changes of enzyme activity in metabolic
process. Through the changes of membrane charge, it has effects on transmission
of substances on the two sides of cytomembrane of microorganisms and adsorption
of nutrients. Moreover, different pH ranges correspond to different fermentation
types for hydrogen production, thus affecting biogas production efficiency. It shows
impacts on succession of structure of microbial community. The vast majority of
11
recovery process. The research demonstrates that by taking glucose as an example, when acetic acid is the only intermediate metabolite, the maximum theoretical
hydrogen production rate of 1 mol of glucose is 4 mol. However, the actual hydrogen
production rate is far smaller than the theoretical value, generally being 0.5–2.5 mol
and the intermediate metabolite is generally a mixture containing volatile fatty acid
(VFA) and alcohol, while they are the best substrate of methanogens. The highest theoretical energy recovery efficiency of hydrogen production in biochemical reaction
is only 33.5% through anaerobic fermentation, which is lower than 83.2% of that of
methane production via anaerobic fermentation. Furthermore, the theoretical energy
recovery efficiency in the combined production of hydrogen and methane via anaerobic fermentation (CHMP-AF) can reach 89%. Therefore, coupling the CHMP-AF
process under phase separation can obtain two energies, i.e. hydrogen and methane.
This effectively improves energy recovery rate of organic wastes through anaerobic
fermentation and overcomes feedback inhibition of acidic metabolite and hydrogen
partial pressure in traditional processes, which is favorable for long-term and stable
operation of the process.
2.1.3 Influence Factors of Anaerobic Fermentation
2.1.3.1 Temperature
Temperature is an important factor influencing biogas production efficiency in anaerobic fermentation. The temperature mainly affects hydrolysis degree of materials,
enzyme activity and structure and function of microbial population in the fermentation. According to the influences of temperature on microbial activity, the anaerobic fermentation can be divided into four temperature ranges, i.e. low-temperature
fermentation at 15–20 °C, moderate-temperature fermentation at 30–35 °C, hightemperature fermentation at 50–55 °C and ultra-high-temperature fermentation above
70 °C. Of them, anaerobic fermentation at moderate and high temperature is mainly
studied, because too low temperature can slow down metabolic rate of microorganisms, while too high temperature can inactivate protease in cells. Both of the two
conditions probably reduce biogas production efficiency.
2.1.3.2 pH Value
pH value is an important factor for measuring stable operation of the anaerobic
fermentation system. It mainly affects the changes of enzyme activity in metabolic
process. Through the changes of membrane charge, it has effects on transmission
of substances on the two sides of cytomembrane of microorganisms and adsorption
of nutrients. Moreover, different pH ranges correspond to different fermentation
types for hydrogen production, thus affecting biogas production efficiency. It shows
impacts on succession of structure of microbial community. The vast majority of