operating cost (opex)

Operating cost (opex) is the recurring annual expenditure required to run a biogas, CBG, or recycling plant once it has been commissioned. It is distinct from capital expenditure (capex) — one-time investments in equipment and infrastructure — and is reported in the project profit-and-loss statement rather than amortised over time. Opex is the single most important variable in the financial viability of small and mid-scale waste-processing projects because revenue is usually fixed by off-take contracts while opex bears the brunt of inflation, feedstock price swings, and energy tariffs.

For a typical 5 TPD CBG plant, opex categories are roughly distributed as follows. Feedstock and feedstock logistics account for 35–50% — this includes purchase price (₹500–2,000 per tonne for agro-residue, often zero or negative for cattle dung), transport, and pre-processing. Energy (electricity for compressors, mixers, separators, and pumps) accounts for 15–20% — a 5 TPD plant typically draws 100–150 kWh per tonne of CBG produced. Labour (plant manager, operators, lab staff, security) accounts for 10–15%. Chemicals and consumables (caustic, iron-oxide media, silica gel, lubricants) account for 5–10%. Maintenance and spares account for 8–12% — typically pegged at 4–6% of capex per year. Compliance and regulatory costs (SPCB monitoring, EPR, FCO testing, insurance) account for 3–5%.

Several opex levers are within plant control. Long-term feedstock supply agreements with FPOs and dairy co-operatives stabilise the largest line item. VFDs on motors cut electricity by 20–30%. Spare parts inventory planning avoids costly emergency procurement. Digestate sale revenue — when achieved at scale through FCO-registered fertiliser branding — can offset 15–25% of opex and is often the difference between a 12% and an 18% IRR. The lesson from Indian CBG operating data is that the plants that hit financial targets are those that secured feedstock contracts, energy efficiency, and digestate off-take before commissioning, not those that tried to optimise these inputs after start-up.