( 1 ) Temperature
Temperature affects the rate of hydrogen production metabolism of biological fermentation bacteria, and there is a big difference in the temperature of hydrogen production of hydrogen-producing bacteria. The results show that most of the hydrogen-producing bacteria belong to thermophilic bacteria, and there is no report on hydrogen-producing bacteria at room temperature. There are few reports on high-temperature fermentation hydrogen-producing bacteria. When the highest temperature is 55 °C, a better hydrogen production effect can be achieved.
( 2 ) pH value
The pH value of the solution is one of the important parameters affecting the hydrogen production process of biological fermentation. The reason is that the pH value will affect the metabolism of bacterial microorganisms, directly affecting the activity of hydrogenase in the hydrogen-producing microbial cells, the redox potential of the cells, the types and forms of metabolites, and the utilization of the substrate. Most of the studies have shown that biological fermentation microorganisms can usually exert high hydrogen production efficiency under weak acidic conditions. The pH value directly affects the metabolites. When the pH value is high, the fermentation metabolites are mainly acids. When the pH value is low, the fermentation metabolites are mainly ketones and alcohols. The pH value of hydrogen production by ethanol fermentation was 4.2 ~ 4.5, and the pH value of hydrogen production by butyric acid fermentation was 6.0 ~ 6.5.
( 3 ) Substrate
The effect of substrates on the efficiency of hydrogen production by biological fermentation is obvious. The substrates used in theoretical research are usually glucose, sucrose, starch, cellulose, etc., and the molecular structure of these carbohydrates is relatively simple. The biological fermentation of hydrogen production with organic waste as a substrate becomes very complicated. The source of wastewater is different, and the composition of the substrate will vary widely. For the use of organic waste for bio-fermentation hydrogen production, these waste with complex components are first pretreated ; the organic matter in the waste can be used or easily used by hydrogen-producing microorganisms. There are five common pretreatment methods, namely ultrasonic vibration treatment, acid treatment, sterilization treatment, freeze-thaw treatment and addition of methane bacteria inhibitors. The results showed that the hydrogen production effect of freeze-thaw and acid treatment was good, followed by sterilization treatment. The inorganic nutrient elements in the substrate are necessary for the production of fermentative hydrogen-producing bacteria cells. The addition of inorganic nutrient elements can directly affect the process of bio-fermentation hydrogen production. For example, Fe, as an important part of the center of gravity of intracellular enzyme activity, can maintain the stability of biological macromolecules and cell structure. The activity of hydrogenase decreases with the consumption of iron. Iron is also an important component of iron redox proteins.
( 4 ) Water conservancy residence time
If the continuous fermentation hydrogen production device is adopted, the hydraulic retention time becomes a very important influencing factor. Due to the different types of fermentation hydrogen production reactors, the hydraulic retention time will be different. Usually, the hydraulic retention time is 2 ~ 24h.