pH Buffering: Maintaining the Microorganisms' "Comfort Zone"
During dark fermentation, the continuous production of organic acids leads to a continuous decrease in the pH value (a measure of acidity) of the fermentation environment, making it increasingly acidic. Most hydrogen-producing microorganisms are very sensitive to acidic environments, and excessively low pH can severely affect their physiological activity.
Biochar, especially biochar made from certain raw materials (such as mineral-rich straw), contains some alkaline substances (such as potassium carbonate and calcium carbonate). These substances can neutralize the acids produced during fermentation, acting as a pH buffer, resisting drastic changes in pH and striving to maintain the fermentation environment within a pH range that is relatively friendly to microorganisms. This is crucial for maintaining microbial activity.
Tip: pH is a measure of acidity and alkalinity; 7 is neutral, below 7 is acidic, and above 7 is alkaline. Buffering refers to the ability to maintain a relatively stable pH.
Adsorption of Inhibitors: Removing "Harmful Waste"
The porous structure and large specific surface area of biochar give it excellent adsorption capabilities. Like activated carbon, it can adsorb metabolic byproducts that accumulate in the fermentation broth and are toxic to microorganisms (such as excessive organic acids and ethanol) onto its surface and pores.
In this way, biochar can effectively reduce the free concentration of these inhibitors in the fermentation broth, thereby reducing their direct toxicity to microorganisms and alleviating product inhibition effects.
Tip: Adsorption refers to the phenomenon of a substance (such as an inhibitor) attaching to the surface of another substance (such as biochar).
Microbial Immobilization: Providing "Settlement Sites"
In addition to adsorption, the rough and porous surface of biochar is an ideal attachment site for microorganisms. Microorganisms can "settle" on the biochar, forming a biofilm. Compared to microorganisms "drifting" in the liquid, biofilm communities formed by attached growth usually have stronger organization and tolerance to external environmental stresses (such as high concentrations of inhibitors).
By providing these "settlement sites," biochar helps microorganisms better adapt to and resist unfavorable environments, maintaining higher biomass and activity, thereby promoting the stable progress of the hydrogen production process. This is called microbial immobilization or cell colonization.
