32.7 Factors Influencing Biogas Production

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silage digester liquid during the first 30 days of digestion was Alphaproteobac-

teria, Betaproteobacteria, Gammaproteobacteria, Firmicutes, Actinobacteria, and

Chloroflexi. The leaf biomass feedstock floats due to the adhering biogas bubbles

resulting in drying, ununiform distribution of bacteria and decreased decomposi-

tion rate which can be overcome in plug-flow-like digesters. The plant feedstock

in an anaerobic digester undergoes degradation of pectin by Proteobacteria first

followed by hemicellulose and cellulose degradation by Firmicutes. The initial VFA

flux created during anaerobic digestion of biomass feedstock limits the enhanced

conversion of VFA and thereby colonization by methanogens which needs to be

prevented by innovative technologies [3].

32.7

Factors Influencing Biogas Production

The physico-chemical aspects of significance in the microbial process of biogas pro-

duction are pH, temperature, feedstock composition, and microbiological factors

such as inoculum, phages, etc.

32.7.1

Temperature

Both mesophilic and thermophilic temperatures prevail during anaerobic digestion.

The microbial enzymes are significantly influenced by minor temperature fluctua-

tion resulting in activation or denaturation of the enzyme. Gradual start up proce-

dures and precautions to prevent heat loss in the mesophilic reactor are the limiting

aspects. This can be overcome by extending the residence time to facilitate the max-

imum feedstock decomposition and use of solar enabled digester to warm the water

used for mixing animal-based food stock [3].

A slow increase or decrease in temperature (±1 ^∘C/day) is suggested to be ideal

for the microbial adaptation. In thermophilic condition, it is noted that the shift is

higher toward ammonia generation which has an inhibitory effect on biogas pro-

duction [5].

Under thermophilic conditions, the methane production rate is about 25–50%

higher than psychrophilic conditions, while the net sludge growth is about 50%

lower. Thermophilic bacteria are more sensitive to temperature shocks than

mesophilic bacteria. Temperature changes greater than 2

∘will reduce methane

former activity, while acids are still forming. This results in losing the buffering

capacity and possibly incapacitating the reactor. The best bacterial activity will

occur in reactors operating at a constant temperature somewhere between 36 and

40 ^∘C. Once the best temperature for the individual reactor is found, based on the

highest gas production and ability to hold the pH near 7.0, that temperature should

be held within ±1 ^∘C [6].

32.7.2

pH

Fluctuation in feedstock can significantly influence the activity of microbial enzyme

activity. The optimum pH range for the functioning of methanogenic bacteria was