Total Solids (TS) (Total Solids)

Total Solids (TS) is the mass fraction of solid matter remaining in an organic material after all moisture has been removed by oven-drying at 105 degC to constant weight, expressed as a percentage of original wet weight. TS is a foundational characterisation parameter for any anaerobic digestion or composting feedstock because it determines slurry flow behaviour, mixing energy demand, pump selection, and ultimately which digester technology (wet or dry) is viable.

Typical TS values for Indian CBG feedstocks include:

• Fresh cattle dung: 12-18% TS.
• Sugar mill pressmud: 25-35% TS.
• Poultry litter (cage): 25-35% TS; deep litter 40-60% TS.
• Paddy and wheat straw: 85-92% TS.
• Napier grass (green): 18-25% TS.
• Food waste / market waste: 15-30% TS.
• Sewage sludge (thickened): 4-8% TS.

Anaerobic digestion is classified by feed slurry TS at the digester inlet:

• Wet AD: 8-15% TS, pumped continuously, stirred tank reactors (CSTR) — dominant Indian technology.
• Semi-dry AD: 15-25% TS, requires high-shear pumps or screw conveyors.
• Dry AD: 25-40% TS, batch or plug-flow design, no slurry pumping.

Operators dilute high-TS feedstocks with recycled digestate liquor or process water to hit the wet AD target. The trade-off is digester volume versus water management: lower TS means larger digesters per tonne of feed VS but easier mixing and pumping. Higher TS shrinks digester capex but raises mixer power draw, demands specialised slurry pumps, and produces less liquid digestate for irrigation. TS is not the same as Volatile Solids (VS) — VS is the fraction of TS that is organic and biodegradable, typically 70-90% of TS for fresh organic feedstocks. Biogas yield is calculated per kg VS, not per kg TS, so both parameters must be measured to predict plant output accurately.