2.3 Research on High-Efficient Anaerobic Fermentation Technology …
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content reached the highest, being 3079.7 mM and then rapidly decreased. The
contents of other organic acids showed no significant changes in the reaction. The
results showed that the products of anaerobic fermentation of straws pre-treated with
enzymes mainly include acetic acid and ethanol, which belonged to a typical ethanoltype fermentation path. The main fermentation products included ethanol, acetic
acid, CO 2 and H 2 . The changes of production of volatile acids were mainly because
microorganisms in substrates produced VFAs through hydrolysis and acidification of
insoluble particulate organic matter at the beginning of fermentation; after that, in the
late stage of fermentation, methanogens transformed acetic acids and hydrogen into
methane and carbon dioxide, so that the concentration of organic acids decreased.
The content of ethanol in metabolites of the control group reached 3952.7 mM
at 12 h and decreased when hydrogenogenic stage ended. In the methanogenic stage
from 65 to 137 h, the content of ethanol suddenly rose and then rapidly reduced
and finally decreased to the lowest after 305 h. The content of acetic acids slightly
increased at 34 h in the hydrogenogenic stage and then quickly dropped to the lowest. Furthermore, butyric acid slightly rose from 65 to 113 h in the methanogenic
stage, while other volatile acids did no change significantly. According to the main
products of fermentation, the fermentation process of reeds in the control group
mainly belonged to ethanol-type fermentation, accompanying with butyric acid-type
fermentation (Fig. 2.23).
2.3.3.2 DOM
As displayed in Fig. 2.24, by using PARAFAC model, three fluorescent components
are identified in the samples and their values of fluorescence intensity (F max ) in
different stages of anaerobic fermentation are demonstrated in Fig. 2.24. After the
pre-treatment, the values of fluorescence intensity gradually decreased with anaerobic fermentation. The results showed that the reason for the decrease of fluorescence intensity was that macromolecular substances in pre-treated plants were easily
decomposed by microorganisms.
Component 1 shows excitation wavelength (λ Ex ) at 220 and 270 nm and emission
wavelength (λ Em ) at 325 nm and mainly comprises fluorescence of protein, so it
belongs to tyrosine-like fluorescent protein. Owing to protein came from microorganisms in the early stage of fermentation, the component was mainly generated from
metabolic substrates or decay process of microorganisms. In accordance with F max ,
protein-like substances represented by component 1 were the main component in all
samples during anaerobic fermentation. With changing activities of microorganisms,
such as hydrogenogens and methanogens in anaerobic fermentation, fluorescence
intensity of component 1 gradually reduced from the highest value of 10,501.01 mM
to 638 mM. The results demonstrated that in metabolites of anaerobic fermentation
after pre-treatment, protein-like substances were mainly from newly formed DOM
produced by biological or microbial activities.
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content reached the highest, being 3079.7 mM and then rapidly decreased. The
contents of other organic acids showed no significant changes in the reaction. The
results showed that the products of anaerobic fermentation of straws pre-treated with
enzymes mainly include acetic acid and ethanol, which belonged to a typical ethanoltype fermentation path. The main fermentation products included ethanol, acetic
acid, CO 2 and H 2 . The changes of production of volatile acids were mainly because
microorganisms in substrates produced VFAs through hydrolysis and acidification of
insoluble particulate organic matter at the beginning of fermentation; after that, in the
late stage of fermentation, methanogens transformed acetic acids and hydrogen into
methane and carbon dioxide, so that the concentration of organic acids decreased.
The content of ethanol in metabolites of the control group reached 3952.7 mM
at 12 h and decreased when hydrogenogenic stage ended. In the methanogenic stage
from 65 to 137 h, the content of ethanol suddenly rose and then rapidly reduced
and finally decreased to the lowest after 305 h. The content of acetic acids slightly
increased at 34 h in the hydrogenogenic stage and then quickly dropped to the lowest. Furthermore, butyric acid slightly rose from 65 to 113 h in the methanogenic
stage, while other volatile acids did no change significantly. According to the main
products of fermentation, the fermentation process of reeds in the control group
mainly belonged to ethanol-type fermentation, accompanying with butyric acid-type
fermentation (Fig. 2.23).
2.3.3.2 DOM
As displayed in Fig. 2.24, by using PARAFAC model, three fluorescent components
are identified in the samples and their values of fluorescence intensity (F max ) in
different stages of anaerobic fermentation are demonstrated in Fig. 2.24. After the
pre-treatment, the values of fluorescence intensity gradually decreased with anaerobic fermentation. The results showed that the reason for the decrease of fluorescence intensity was that macromolecular substances in pre-treated plants were easily
decomposed by microorganisms.
Component 1 shows excitation wavelength (λ Ex ) at 220 and 270 nm and emission
wavelength (λ Em ) at 325 nm and mainly comprises fluorescence of protein, so it
belongs to tyrosine-like fluorescent protein. Owing to protein came from microorganisms in the early stage of fermentation, the component was mainly generated from
metabolic substrates or decay process of microorganisms. In accordance with F max ,
protein-like substances represented by component 1 were the main component in all
samples during anaerobic fermentation. With changing activities of microorganisms,
such as hydrogenogens and methanogens in anaerobic fermentation, fluorescence
intensity of component 1 gradually reduced from the highest value of 10,501.01 mM
to 638 mM. The results demonstrated that in metabolites of anaerobic fermentation
after pre-treatment, protein-like substances were mainly from newly formed DOM
produced by biological or microbial activities.