Moisture Content (water content)

Moisture content is the mass of water in a sample expressed as a percentage of either total fresh weight (wet basis, w.b.) or oven-dry weight (dry basis, d.b.). The two conventions give very different numbers for the same sample — a feedstock at 80% w.b. moisture is 400% on a dry basis — so the basis must always be stated. Determination follows IS 1350 or ASTM E871: a known mass is dried in a hot-air oven at 105°C until constant weight, and the lost mass is reported as water.

Moisture content directly governs four operational decisions across CBG, rubber processing and tyre pyrolysis. First, it sets the digestion mode: feedstocks below 10% total solids run wet anaerobic digestion in CSTR or lagoon designs; 10-20% solids run semi-dry; above 20% require dry batch or plug-flow digesters. Second, it controls calorific value — moisture is dead weight that must be evaporated before combustion, consuming roughly 2.26 MJ per kg of water removed. Tyre crumb above 1% moisture causes vapour explosions in pyrolysis reactors. Third, it determines storage behaviour: agricultural residues above 20% moisture self-heat, ferment and lose dry matter at 1-2% per month, while sub-15% material stores stably for a year. Fourth, it affects transport economics — paying freight to move water cuts effective tonne-kilometre rates by half for slurry-like feedstocks.

Typical Indian ranges include cattle dung at 80-85% w.b., press mud at 65-75%, food waste at 70-80%, paddy straw at 10-15% after field drying, and rubber crumb at 0.5-1% after sun-drying. For digester sizing the dry-matter calculation is decisive: a plant rated for 100 TPD of fresh cow dung is actually processing only 15-20 TPD of volatile solids, and the digester must be sized on the latter figure to avoid undersizing the gas plant.