2.2 Pre-treatment Technologies of Anaerobic Fermentation
25
methanogenic process (1290 mL, 76.1% methane). While after alkali pre-treatment,
the volume fraction of methane was found to be precisely 89.0% in the methanogenic
process during the operation containing two stages.
Based on an overall determination coefficient (R
2 ) of 0.96, the methane production
and cumulative hydrogen on conditions applying different pre-treatments can be
reflected favourably using the modified Gompertz equation for non-linear numerical
estimations (Fig. 2.11). The highest potential of hydrogen production of all these three
pre-treatments in the hydrogenogenic stage was higher than that of the control. The
yield of hydrogen production potential of the PVWs pre-treated with acid was found
to be the maximum of 180 mL, followed by 142 and 19 mL after the pre-treatments
with enzyme and alkali, respectively. The maximum production rates of hydrogen of
the three pre-treatment methods (with acid, alkali and enzyme) were 10.11, 3.64 and
5.65 mL/h, respectively. By contrast, the production rate of hydrogen of the control
was merely 0.16 mL/h. The lag phases of the pre-treatments of PVWs with acid and
alkali changed in a narrow range from 3.88 to 3.61 h and reached to the peak of 4.54 h
for the pre-treatments with enzyme. In comparison, the lag phase for the control was
found to be the minimum (approximately 0.38 h). In the methanogenic stage, the pretreatments with acid and alkali were carried out similarly, during which the highest
potentials of methane production were 851 and 825 mL, separately, while that in
the pre-treatment with enzyme was only 332 mL. Moreover, the highest potential
of methane production was lowest for the control (9 mL). The pre-treatments with
acid, alkali and enzyme were separately found to have the methane production rates
of 4.67, 6.63 and 2.63 mL/h. Likewise, the minimum methane production rate was
observed for the control (0.15 mL/h). Meanwhile, compared with the lag phase
of the control (83.75 h), those for the acid and enzyme pre-treatments were even
longer (146.65 and 147.39 h, respectively). Whereas, the lag phase can be shortened
on conditions that bacteria were enriched by utilizing and pre-adapting to inimical
growth conditions after pre-treatment with alkali in the methanogenic stage. In this
way, it can be seen that the lag time of 87.53 h during the alkali pre-treatment was
similar to that of the control.
2.2.2.3 Impacts of Pre-treatment on TOC and Total Nitrogen
In the CHMP-AF of mixed wastes produced in pedlars’ markets, the changes laws of
COD, TOC and total nitrogen (TN) concentrations in different stages are shown in
the Table 2.2. The research displayed that COD and TOC concentrations of FVWs
increased in the hydrogenogenic stage, mainly because hydrolytic acidification transformed solid materials into soluble ones. In the methanogenic stage, microorganisms
effectively utilized carbon sources, resulting in decrease of COD and TOC concentrations and a low utilization rate of TN in CHMP-AF. This is the main reason
for easy accumulation of ammonia nitrogen and inhibition of biogas production of
microorganisms.
25
methanogenic process (1290 mL, 76.1% methane). While after alkali pre-treatment,
the volume fraction of methane was found to be precisely 89.0% in the methanogenic
process during the operation containing two stages.
Based on an overall determination coefficient (R
2 ) of 0.96, the methane production
and cumulative hydrogen on conditions applying different pre-treatments can be
reflected favourably using the modified Gompertz equation for non-linear numerical
estimations (Fig. 2.11). The highest potential of hydrogen production of all these three
pre-treatments in the hydrogenogenic stage was higher than that of the control. The
yield of hydrogen production potential of the PVWs pre-treated with acid was found
to be the maximum of 180 mL, followed by 142 and 19 mL after the pre-treatments
with enzyme and alkali, respectively. The maximum production rates of hydrogen of
the three pre-treatment methods (with acid, alkali and enzyme) were 10.11, 3.64 and
5.65 mL/h, respectively. By contrast, the production rate of hydrogen of the control
was merely 0.16 mL/h. The lag phases of the pre-treatments of PVWs with acid and
alkali changed in a narrow range from 3.88 to 3.61 h and reached to the peak of 4.54 h
for the pre-treatments with enzyme. In comparison, the lag phase for the control was
found to be the minimum (approximately 0.38 h). In the methanogenic stage, the pretreatments with acid and alkali were carried out similarly, during which the highest
potentials of methane production were 851 and 825 mL, separately, while that in
the pre-treatment with enzyme was only 332 mL. Moreover, the highest potential
of methane production was lowest for the control (9 mL). The pre-treatments with
acid, alkali and enzyme were separately found to have the methane production rates
of 4.67, 6.63 and 2.63 mL/h. Likewise, the minimum methane production rate was
observed for the control (0.15 mL/h). Meanwhile, compared with the lag phase
of the control (83.75 h), those for the acid and enzyme pre-treatments were even
longer (146.65 and 147.39 h, respectively). Whereas, the lag phase can be shortened
on conditions that bacteria were enriched by utilizing and pre-adapting to inimical
growth conditions after pre-treatment with alkali in the methanogenic stage. In this
way, it can be seen that the lag time of 87.53 h during the alkali pre-treatment was
similar to that of the control.
2.2.2.3 Impacts of Pre-treatment on TOC and Total Nitrogen
In the CHMP-AF of mixed wastes produced in pedlars’ markets, the changes laws of
COD, TOC and total nitrogen (TN) concentrations in different stages are shown in
the Table 2.2. The research displayed that COD and TOC concentrations of FVWs
increased in the hydrogenogenic stage, mainly because hydrolytic acidification transformed solid materials into soluble ones. In the methanogenic stage, microorganisms
effectively utilized carbon sources, resulting in decrease of COD and TOC concentrations and a low utilization rate of TN in CHMP-AF. This is the main reason
for easy accumulation of ammonia nitrogen and inhibition of biogas production of
microorganisms.