Feedstock

Feedstock is the organic raw material fed into a biogas plant - cattle dung, crop residues, press mud, food and municipal organic waste, and energy grasses. Its type and quality decide how much gas the plant makes, and its reliability decides whether the plant runs at all.

Paddy straw is the stalk left after the rice harvest - abundant across India and often burned, which is a major air-pollution source. It is fibrous and lignocellulosic, so it digests slowly and usually needs size reduction and co-digestion with a nitrogen-rich feed.

Press mud, or filter cake, is the residue left after sugarcane juice is clarified. It yields roughly 140-160 cubic metres of biogas per tonne and, crucially, arrives in bulk at a single site - which removes the aggregation problem that starves plants running on scattered residues.

Yes. Napier, or elephant grass, is a fast-growing energy crop that gives methane-rich biogas - about 63.5% methane as a mono-substrate in one study. It is lignocellulosic, so pretreatment and co-digestion improve yield, and it is water-hungry despite its drought tolerance.

Different feedstocks carry very different volatile-solids content and biogas yield per tonne, so the same plant produces very different gas volumes depending on what is fed. Wet, energy-dense feedstocks such as press mud, food waste and energy grass yield more per tonne than dry dung.

Cattle dung is a stable but modest feedstock, giving roughly 100-140 cubic metres of biogas per tonne, or about 0.20-0.30 cubic metres per kg VS. Much of its energy was already extracted by the animal, so its value is process stability and a nutrient-rich digestate rather than peak yield.

Poultry litter is high in nitrogen and protein, giving relatively high gas yield per tonne - often cited above 60-100 cubic metres. But its C:N ratio of around 10-12:1 makes ammonia inhibition a live risk, so it is normally co-digested with a carbon-rich substrate such as dung or straw.

Yes - segregated food waste and the organic fraction of MSW yield roughly 120-140 cubic metres per tonne, and using them solves a disposal problem at the same time. The hard part is contamination: plastics and grit demand robust pre-sorting, and they push project cost up sharply.

A hammer mill shreds and grinds biomass with rapidly spinning hammers, cutting particle size so microbes can attack more surface area. It is a common first step for fibrous feedstocks such as straw, and it draws real power - on the order of 25 kWh per tonne.

Smaller particles digest faster and more completely because enzymes can reach more surface. Choppers, shredders and hammer mills do that size reduction, and for lignocellulosic feed it is the difference between a digester that keeps up and one that silts up.

Pretreatment reduces particle size and disrupts lignocellulosic structure, exposing more surface to microbes and raising both the rate and the extent of digestion. For fibrous crops such as Napier or straw it is essential, because untreated lignocellulose resists microbial hydrolysis.

Raw biogas carries CO2, water vapour and corrosive, toxic hydrogen sulphide. H2S and moisture must go to protect engines, compressors and pipelines; CO2 is removed to raise energy density. Cleaning is the difference between a corrosive raw gas and a saleable fuel.