12
2 High-Efficient Anaerobic Fermentation Technology of Organic …
microorganisms grow in the pH range of 5–9. Acid-producing bacteria are suitable
in the pH range of 5–8, while methanogens suits for the range of 6.8–7.2 of pH value.
2.1.3.3 Carbon-Nitrogen Ratio
Carbon-nitrogen (C/N) ratio, as a key factor affecting anaerobic fermentation, mainly
influences anabolic process of microorganism itself and oxidation process of organic
matter in organisms and participates in the energy-releasing metabolic process of
bacteria. A too high C/N ratio leads to inadequate nitrogen content and low buffer
ability of fermentation liquids, so that the liquids are easily acidified. A too low C/N
ratio implies the presence of excess carbon content, which easily results in accumulation of ammonia nitrogen, so that anaerobic fermentation process is inhibited. An
appropriate C/N ratio is beneficial for stable operation of anaerobic fermentation. It
is generally considered that the suitable C/N ratio for anaerobic fermentation is in
the range of 20–30, while C/N ratio in the range of 15–20 in the actual operation can
guarantee high-efficient utilization of organic substrates.
2.1.3.4 VFAs and Ammonia Nitrogen
VFAs refer to micromolecular acid substances containing less than six carbon atoms
formed in hydrolytic acidification and they belong to important substrate materials
in the methanogenic process. They mainly include substances, such as acetic acid,
propionic acid, butyric acid and a small amount of pentanoic acid. High-concentration
VFAs can reduce pH, inhibit activity of methanogens and acidify and thus collapse
the system. Ammonia nitrogen produced by decomposing substances, like protein
and amino acids based on catabolism of microorganisms has positive effects on
maintaining stable pH value of fermentation liquids. Ammonium ion (NH 4
+ ) and
free ammonia (NH 3 ) are the dominant forms existing in the transformation of organic
nitrogen, while free ammonia can influence the balance of positive ions in cells
by passing through cytomembrane, thus producing toxicity inhibition in anaerobic
fermentation. VFAs and ammonia nitrogen in the anaerobic fermentation system
can form a buffer system, so that fermentation system has certain buffer ability,
which shows important regulations on long-term and stable operation of anaerobic
fermentation.
2.1.3.5 Microbial Community
The essence of anaerobic fermentation is to decompose organic matter through
the effects of microorganisms and the type, quantity, synergy and antagonism of
2 High-Efficient Anaerobic Fermentation Technology of Organic …
microorganisms grow in the pH range of 5–9. Acid-producing bacteria are suitable
in the pH range of 5–8, while methanogens suits for the range of 6.8–7.2 of pH value.
2.1.3.3 Carbon-Nitrogen Ratio
Carbon-nitrogen (C/N) ratio, as a key factor affecting anaerobic fermentation, mainly
influences anabolic process of microorganism itself and oxidation process of organic
matter in organisms and participates in the energy-releasing metabolic process of
bacteria. A too high C/N ratio leads to inadequate nitrogen content and low buffer
ability of fermentation liquids, so that the liquids are easily acidified. A too low C/N
ratio implies the presence of excess carbon content, which easily results in accumulation of ammonia nitrogen, so that anaerobic fermentation process is inhibited. An
appropriate C/N ratio is beneficial for stable operation of anaerobic fermentation. It
is generally considered that the suitable C/N ratio for anaerobic fermentation is in
the range of 20–30, while C/N ratio in the range of 15–20 in the actual operation can
guarantee high-efficient utilization of organic substrates.
2.1.3.4 VFAs and Ammonia Nitrogen
VFAs refer to micromolecular acid substances containing less than six carbon atoms
formed in hydrolytic acidification and they belong to important substrate materials
in the methanogenic process. They mainly include substances, such as acetic acid,
propionic acid, butyric acid and a small amount of pentanoic acid. High-concentration
VFAs can reduce pH, inhibit activity of methanogens and acidify and thus collapse
the system. Ammonia nitrogen produced by decomposing substances, like protein
and amino acids based on catabolism of microorganisms has positive effects on
maintaining stable pH value of fermentation liquids. Ammonium ion (NH 4
+ ) and
free ammonia (NH 3 ) are the dominant forms existing in the transformation of organic
nitrogen, while free ammonia can influence the balance of positive ions in cells
by passing through cytomembrane, thus producing toxicity inhibition in anaerobic
fermentation. VFAs and ammonia nitrogen in the anaerobic fermentation system
can form a buffer system, so that fermentation system has certain buffer ability,
which shows important regulations on long-term and stable operation of anaerobic
fermentation.
2.1.3.5 Microbial Community
The essence of anaerobic fermentation is to decompose organic matter through
the effects of microorganisms and the type, quantity, synergy and antagonism of