502

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

Table 32.2

Direction of process occurring in a bioreactor and simultaneously indicating

possible process problems.

Indicator

Trend of graph

pH

CH4

CO2

Alkalinity

Volume

pH

Down

—

Down

—

—

—

CH4%

Down

Down

—

Up

Down

Up

CO2%

Up

—

Down

—

—

—

Alkalinity

Down

Down

—

—

—

—

Volatile acids

Up

—

Down

—

—

—

bonding. The furfurals produced during caramelization of sugarcane are found to be

toxic to methanogenic bacteria. The bacteria can tolerate between 50 and 100 mg/l

of soluble sulfide with little effect [6].

32.8

Application of Metagenomics

Anaerobic digestion is associated with intricate microbial diversity. Isolation

of certain microflora in biogas digester through cultural techniques cannot be

accomplished owing to the presence of non-culturable microbes. Hence, molecular

characterization and metagenomic tools can aid in the insight of anaerobic digester

microbiome. Such advanced techniques can identify the pathway and microbiome

needed for transformation of feedstock to biogas. High-throughput sequencing data

along with bioinformatics analysis play a crucial role in characterization of micro-

bial metagenome. This in combination with artificial neural network is anticipated

in a big-data-based precision fermentation with enhanced biogas yield [12].

Molecular biology techniques applied to explore the relationship between micro-

bial diversity and biogas generation included DNA extraction and quantification,

polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE),

analysis of DGGE profiles, PCR amplification for illumina next-generation

sequencing (NGS), and its data analysis. The prevalent phyla were Bacteroidetes,

Firmicutes, Proteobacteria, and Actinobacteria. Fruit waste being rich in carbohy-

drates hydrolyzed rapidly with acid formation and generates CO2 as it lacks the

microflora essential for methanogenesis. The DGGE and NGS data revealed the

presence of Actinobacteria in cow dung. The genus Syntrophomonas capable of

hydrolyzing long-chain organic acids to acetate and propionate was dominant in

co-digestion. Firmicutes in cow dung and food waste plays a key role in degradation

of cellulosic material. The PCR-DGGE results indicated maximum microbial

diversity in co-digestion as compared with mono-digestion of cow dung and food

waste with predominance of methanogens (Methanosaeta and Methanosarcina).

The functionality of microflora in AD is imperative for enhanced generation of

biogas from the feedstock [4] (Table 32.3).