3.2. Effect of organic loading on gas production and
composition in anaerobic UASB reactor
Fig. 6 shows the effect of organic loading on the gas production
and composition. It can be suggested that the acidogenesis
is dominant at high organic loading rates while
the rate of methanogenesis decreased. This results in low
methane gas production rates. A 70, 60 and 20% methane
percentages were observed at loading rates of 6, 15 and
20 kgCODm−3 per day. A decrease in methane gas production
was accompanied by increases in TVFA/bicarbonate
alkalinity (B/A) ratio (See Fig. 6). Increases in TVFA/BA
ratio in UASB effluent samples indicate the activity of acid
producing bacteria and TVFA accumulation. The reactor is
stable when the TVFA/BA ratio is lower than 0.4 [24]. If
the TVFA/BA ratio is lower than 0.8, the reactor system is
moderately stable or unstable as reported by Behling et al.
[24]. As shown in Fig. 6 this ratio varied between 0.5 and
0.8, indicating the high TVFA concentrations at high organic
loading because of high COD and dye concentrations
in the reactor. As a result, the intermediates and anaerobic
degradation products could not be converted to methane and
the reactor was unstable at shock organic loading as high as
20–25 kgCODm−3 per day. In other words, although shock
organic loads cause decreases in COD removal efficiencies,
no negative effect was observed in color removal. This can
be explained by color removal due to acidogenic bacteria
together with methanogens as reported by Chinwekitvanich
et al. [25].
3.2. Effect of organic loading on gas production and
composition in anaerobic UASB reactor
Fig. 6 shows the effect of organic loading on the gas production
and composition. It can be suggested that the acidogenesis
is dominant at high organic loading rates while
the rate of methanogenesis decreased. This results in low
methane gas production rates. A 70, 60 and 20% methane
percentages were observed at loading rates of 6, 15 and
20 kgCODm−3 per day. A decrease in methane gas production
was accompanied by increases in TVFA/bicarbonate
alkalinity (B/A) ratio (See Fig. 6). Increases in TVFA/BA
ratio in UASB effluent samples indicate the activity of acid
producing bacteria and TVFA accumulation. The reactor is
stable when the TVFA/BA ratio is lower than 0.4 [24]. If
the TVFA/BA ratio is lower than 0.8, the reactor system is
moderately stable or unstable as reported by Behling et al.
[24]. As shown in Fig. 6 this ratio varied between 0.5 and
0.8, indicating the high TVFA concentrations at high organic
loading because of high COD and dye concentrations
in the reactor. As a result, the intermediates and anaerobic
degradation products could not be converted to methane and
the reactor was unstable at shock organic loading as high as
20–25 kgCODm−3 per day. In other words, although shock
organic loads cause decreases in COD removal efficiencies,
no negative effect was observed in color removal. This can
be explained by color removal due to acidogenic bacteria
together with methanogens as reported by Chinwekitvanich
et al. [25].
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