494

32 Microbiology of Biogas Production from Food Waste: Current Status, Challenges, and Future Needs

Thermophilic

Fermicutes

Clostridia,

Synergestetes

Plant biomass

Firmicutes,

Bacteriodetes,

Proteobacteria,

Actinobacteria,

Chloreflexi,

Spirochaetes,

Thermotogae,

Gemmatimonadetes,

Deinococcus-Themus

Methanobateriales,

Methsnimicrobilaes,

Methanosarcinales

Hydrolysis-amino acids,

sugars, alcohol, fatty

acids

Fermicutes

Clostridia,

Synergestetes

Firmicutes,

Bacteriodetes,

Proteobacteria,

Actinobacteria,

Chloreflexi,

Spirochaetes,

Thermotogae

Mesophilic

Methanobateriales,

Methsnimicrobilaes,

Methanosarcinales,

Methanosaetacea

Acidogenesis-

acetate + CO2 + H2

Methanogenesis-

CH4 + CO2

Figure 32.1

Microorganisms in anaerobic digestion of plant biomass under mesophilic

and thermophilic condition.

hemicellulose, and cellulose), proteins and fats to sugars, amino acids, and

long-chain fatty acids (LCFA) along with various other end products. Lipolytic

enzymes produced by Clostridia and Micrococci convert lipids to LCFAs which

is further degraded by ß-oxidation to produce acetyl CoA. The proteases pro-

duced by Clostridium, Bacteroides, Fusobacterium, Butyrivibrio, Streptococcus, and

Selenomonas hydrolyze proteins to amino acids. Campylobacter, Peptococcus,

Clostridium, Bacteroides, and Selenomonas degrade the amino acids to acetate,

propionate, and ammonia.

The plant cell wall polysaccharide present in the biomass feedstock is hydrolyzed

by enzymes produced by hydrolytic bacteria of Firmicutes and Proteobacteria as indi-

cated in Figure 32.1. Hexose metabolism in anaerobic bacteria results in pyruvate

and Nicotinamide adenine dinucleotide (NADH) via Emden-Meyerhof-Parnas path-

way (EMP). Further fermentation of pyruvate generates lactate, propionate, acetate,

and ethanol. However, sugars and amino acids also undergo acidogenic fermen-

tation to produce low-concentration acetate and H2. Hydrolyzing bacteria are the

significant microbiome in degradation of plant-based feedstock [3] (Table 32.1).

32.4.2

Acetogenesis

During the process of biogas production, hydrogen-producing acetogenic bacteria

are capable of producing acetate and H2 from higher fatty acids which is a high

free-energy-consuming process. H2 generated during acetogenesis is known to

inhibit the isolation and growth of acetogenic bacteria. Syntrophobacter wolinii and

Syntrophomonas wolfei are, respectively, the propionate and butyrate decomposing