Total Solids (TS)

Total Solids (TS) is the mass percentage of dry matter in an organic material, calculated as the residual weight after complete water removal at 105 degC divided by original wet weight. It is one of the two primary feedstock characterisation parameters in anaerobic digestion (the other being Volatile Solids), and it dictates digester sizing, technology choice, water management, and slurry handling design for every CBG plant.

The role of TS in plant operation appears in several calculations. Digester volume is sized as: V = Q x HRT, where Q is daily feed slurry volume and HRT is hydraulic retention time. Since feedstocks arrive at very different TS levels — 12% for fresh dung, 30% for pressmud, 90% for straw — operators dilute them to a uniform inlet TS (typically 8-12% for wet AD) before pumping into the digester. This dilution determines water consumption, which in water-stressed Indian regions can be a binding constraint.

Practical implications include:

• Water demand: a 100 TPD plant running at 10% inlet TS needs roughly 100-200 cubic metres of dilution water per day if feedstocks average 30% TS.
• Pump and piping selection: TS above 12% requires positive displacement (progressive cavity or lobe) pumps; carbon steel pipework above DN100 to avoid blockages.
• Mixing energy: viscosity rises exponentially above 8% TS, increasing agitator power demand by 30-50% per 2% TS rise.
• Digestate management: lower inlet TS produces larger volumes of liquid digestate, demanding bigger storage lagoons and irrigation systems.

Operators monitor TS daily through gravimetric oven testing on grab samples, with results trending alongside VS and pH. A typical Indian CBG plant maintains feed TS within +/- 1% of design value to avoid loading instability. The trade-off in TS selection is throughput versus complexity: high-TS dry digestion (25-35% TS) eliminates water demand and shrinks digester volume but needs complex batch-mode operation; low-TS wet digestion is simpler to operate but consumes water and produces large digestate volumes that may exceed what local agriculture can absorb.