units (measurement units)

Units in biogas and recycling project reports follow a hybrid SI-plus-Indian-industry convention that must be read carefully to avoid order-of-magnitude errors. Gas volumes are reported in Nm³ (normal cubic metres at 0°C and 1 atm), not raw m³, because methane volume varies by 10–15% across the typical 15–45°C operating range. Plant capacity is quoted in TPD (tonnes per day) of feedstock input — never tonnes per year and never tonnes of CBG output — and gross capacity is the design figure while net capacity accounts for moisture and ash.

Composition is reported in kg per tonne or grams per kilogram. Confusion arises because nutrient labels on Indian Fermented Organic Manure bags follow FCO 1985 specs in percentage by weight (e.g. 1% N, 0.5% P, 1.5% K), while lab reports use mg/kg or ppm for trace elements. Soil and digestate salinity is quoted in dS/m (decisiemens per metre, equivalent to mmhos/cm) — values above 4 dS/m indicate salinity stress for most crops, while values above 8 dS/m are reserved for salt-tolerant species.

Currency and pricing units require equal care. CBG sale price under SATAT is quoted ex-plant in ₹ per kg (not per Nm³ or per MMBtu), with a conversion of roughly 1.4 kg of CBG per Nm³ of biogas. EPR credit volumes are expressed in metric tonnes per year, while landfill diversion is reported in tonnes of CO₂-equivalent.

• Nm³ vs m³: a 10% discrepancy at typical operating temperatures — always convert before comparing.
• TPD is feedstock input, not product output — a 100 TPD plant produces only 4–6 tonnes of CBG per day.
• dS/m for salinity, mg/kg for trace nutrients, % for major NPK on FCO labels.
• CBG pricing is ₹/kg ex-plant, with GST and OMC margin added downstream.