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1 Anaerobic Co-digestion as a Smart Approach for Enhanced Biogas Production

availability at a particular location could vary on a daily basis. Moreover, substrate

heterogeneity, seasonal variation, and feasibility of transportation of waste from

source are also to be coordinated. The idea of setting up the AD at the source of

waste generation is a viable option; still the supplies could be erratic or inconsistent.

The opportunity to go for co-digestion not only helps in circumventing the problem

of nonavailability of single substrate but also helps in managing different wastes

generated at source efficiently.

1.2.3

Microbiological Aspects

The emphasis of the role of microbes is well documented in every successful biogas

digester. There is a systematic and sequential breakdown of complex organic waste

into methane carried out by four metabolically distinct bacterial groups:

●hydrolyzing bacteria: complex carbohydrates, fats, and proteins converted to sim-

ple sugars, long-chain fatty acids (LCFAs) and amino acids;

●acidogens: lead to the accumulation of VFAs, alcohols, and carbonic acids;

●acetogens: further degradation results in acetic acid, hydrogen, carbon dioxide

with trace amount of ammonia, H2S, etc.; and

●methanogens: scavenge on H2 and C1 and C2 carbon compounds for energy lead-

ing to production of methane.

Each of the aforementioned groups plays a pivotal role in AD and inactivation

of any one group could possibly lead to accumulation of intermediate compounds

impacting the outcome of the digester performance, while methanogen biomass

ratio is miniscule in comparison to other groups [8]; still their influence is immense

and found to be critical for sustainable biomethanation [9].

1.2.4

Strategies for Inoculum Development

It is highly impossible to define the exact microbial composition of any anaerobic

digester, culturing techniques in coordination with molecular diagnostics can aid

in identification, but never have we deduced the true potential population of AD.

Inoculum for any biogas digester is usually sourced from ruminant fluid, munici-

pal WWTPs, landfill leachate, or sludge collected from any preexisting active biogas

digester. It is primarily important to relate inoculum with its role in biogas digesters,

for example, an inoculum collected from WWTP may have few cellulolytic bacteria

and thus may not lead to a sustainable biomethanation of agricultural wastes. Rumi-

nant intestines harbor a natural population of methanogens, hydrolytic and other

fermentative anaerobes, which cater to efficient biogas production and general suc-

cess only for cattle-dung-based digesters; the same success is difficult to reproduce

when inoculum from cattle-dung-based digester is added to digest poultry waste or

dairy-waste-based digesters. Microbial population may vary even between sample

inoculum and digester, for example, fresh cattle dung is rich in hydrogenotrophs

(93–80%) [10] compared with acetoclastic methanogens (6–20%) [10] (Reasons being

nonavailability of acetates, which are being reabsorbed by ruminant intestines along