Cost Per Bin or Cost Per Tonne: Which Number Should You Budget On?

Two managers can look at the same solidification programme and reach opposite conclusions, because one is counting currency per bin and the other is counting currency per tonne. Neither is wrong. They answer different questions, and the confusion between them is where most business cases fall apart in front of a finance team.

Why per-bin pricing hides the weight

Collection is usually quoted per lift. A 240-litre bin at 14 currency units per lift is easy to budget and impossible to compare, because the same 14 units buys 40 kg at one site and 65 kg at another. Solidifier makes this worse in a helpful way: the same bin now carries more mass in the same volume, so the per-bin cost per kilo falls even though the invoice has not moved.

That is the real argument for solidifying on a per-bin contract. If your lift price is fixed and your bins were previously under-filled because they were wet and half-empty of usable volume, you are now getting more waste into each lift. Sites typically gain 10 to 20 percent effective capacity, which is a quiet saving that never appears on any invoice line.

Building the per-tonne view

Per-tonne costing is what you need for benchmarking and for arguing with procurement. Three inputs: total tonnes collected per year, total collection cost, total polymer cost. Then add the invisible ones — washdowns, liner upgrades, staff time, rejected loads.

Worked example. A restaurant produces 60 kg of food waste a day, six days a week, so about 18.7 tonnes a year. Collection on three lifts a week with 240-litre bins, two bins per lift, at 14 per lift, comes to 4,368 a year, or 234 per tonne. Polymer at 10 g/kg is 187 kg a year; at 2.50 per kg that is 468, or 25 per tonne. Add 200 for heavier liners and 300 for the washdowns you no longer do, and the net position is roughly 259 per tonne with solidifier against 234 without — except the site has moved from five lifts a week to three, which is where the 1,456 saving sits.

Run the same numbers on a per-bin basis and the polymer looks like 1.25 per bin. That is the number a kitchen manager can hold in their head. It is also the number that gets dismissed as trivial by a finance director who is looking at the annual line.

Use both, for different audiences

Give the site manager cost per bin, because that is what they control and what they can influence by dosing properly. Give the finance team cost per tonne and cost per lift, because that is where the contract decision lives. Never present one without the other — the first looks like rounding, the second looks unmanageable.

Watch the trap in per-tonne figures: if you reduce lifts, your tonnes do not change but your cost per tonne falls sharply, which flatters the case. If you increase dose to survive a longer sit, tonnes stay flat and cost rises. Both movements are real, but they mean different things, and a business case that mixes them proves nothing.

Limits worth stating up front. Per-tonne comparisons only work if you have weighbridge tickets; estimated weights from bin counts are usually 15 to 25 percent out. And no cost model survives a menu change, a seasonal peak or a hauler who re-prices mid-contract, so rebuild the numbers twice a year rather than once.

Anchor the polymer side on real specification rather than a placeholder price — the SAP powder product range lists grades by absorption rate, and the cheaper grade is not always the lower cost per tonne once dose is accounted for.