What is trade effluent consent, and who needs it?
Trade effluent is any liquid waste from a business process that is discharged to the public sewer, as opposed to ordinary domestic sewage. Under section 118 of the Water Industry Act 1991, you must have consent from your sewerage undertaker before you discharge it, and you must stay within the limits that consent sets for volume and strength.
It applies widely across food and drink, brewing, dairy, manufacturing and processing. The consent is a legal permission with conditions, not a formality, and the water company can monitor, sample and enforce against it.
How is the trade-effluent charge calculated?
Your charge is set by the Mogden formula, the published method UK water companies use. It works out a charge per cubic metre with four parts: reception and conveyance, volumetric and primary treatment, biological oxidation that scales with the chemical oxygen demand (COD) of your effluent, and sludge treatment that scales with its suspended solids. Multiply that by your annual volume and you have the bill.
Because two of the four terms scale with strength, a stronger effluent costs disproportionately more to discharge. You can size your own bill, and see how much of it is strength-driven, with our trade effluent estimator.
Why does strength drive the bill?
The water company has to treat what you send it, and stronger effluent takes more energy and more sludge handling to treat. That is why the COD and suspended-solids terms in the Mogden formula usually account for 60 to 70 percent of a typical trade-effluent bill.
It is also the good news: volume is largely fixed by your process, but strength can often be reduced before discharge. On one site a bill of around GBP 550,000 a year carried roughly GBP 375,000 of avoidable, strength-driven cost.
What happens if you breach consent?
Discharging without consent, or outside its limits, is a criminal offence under the Water Industry Act. Water companies actively prosecute. A summary conviction is capped, but a case taken to the Crown Court carries an unlimited fine.
The fines are material. A food manufacturer was fined GBP 415,000 in 2019 over twenty consent breaches, and a poultry processor was fined GBP 200,000 in 2023. Beyond the fine, a breach is a regulatory record and a reputational risk with customers who audit their supply chain.
How do you bring the bill, and the risk, down?
The lever is strength. Reducing the COD and suspended solids in your effluent before it leaves site cuts the two largest terms in the Mogden formula and widens your headroom against your consent limits at the same time, so cost and compliance improve together.
The aim is to do this without touching food safety or production uptime, and without a new capital civil treatment plant where it can be avoided. The starting point is to size the prize: estimate your bill and its strength-driven share, then confirm what can be reduced per site.