Trade effluent: the overlooked P&L line for commercial laundries

You’ve got machines to keep running, deadlines to hit and customers who need spotless results. Then a water bill lands that’s higher than expected, or a consent warning drops into your inbox. Stress rises.

Trade effluent often sits on the P&L with little attention, yet small process changes can steady both spend and compliance.

What the Mogden formula really means

Trade effluent charges are typically calculated using the Mogden formula or a reasonable variant. The idea is simple:

• How much you send (volume, in cubic metres)
• How dirty it is (strength, based on what’s dissolved or floating in it)

For charging, ‘strength’ is commonly represented by COD and suspended solids, with other parameters controlled via your consent:

• COD (chemical oxygen demand): a test that shows how much “stuff” is in the water that uses up oxygen. Think detergent, soils, oils and dissolved organics.
• Suspended solids: bits that haven’t dissolved e.g. lint, fibres and fine particles.

Higher volume and higher strength mean a higher bill. Your consent will also set limits for temperature, pH and other measures. Breaches can lead to surcharges or enforcement, so control matters.

Why dosing, temperature and pH change what you pay

Dosing

Get the chemistry wrong and costs creep up.

• Over-dosing detergents or coagulants can push COD up and create extra solids.
• Under-dosing leaves soil and fats in the water, which also lifts COD.

What to do: tie dosing to load weight and soil type. Keep simple set points that operators can see and check them regularly. Run quick jar tests with your chemical partner to make sure the mix is doing its job without excess.

Temperature

Many consents cap discharge temperature around the low-40s°C. Hotter flows can damage pipes and are a safety risk, which can trigger action from your water company.

What to do: cool before discharge. A balance tank lets hot and cooler streams mix to a safe level. If you can add heat recovery to pre-warm incoming water, you’ll cool the effluent while saving energy on the wash line.

pH

Most consents set a range (often roughly pH 6 to 10 or 11).Outside that, treatment works less well and corrosion risk rises. pH swings also upset any on-site settlement step, which can raise solids on your samples.

What to do: fit a reliable online pH probe where flows combine, link it to an alarm, and keep spare buffer solution for quick checks. If you dose acid or alkali, add interlocks so the plant pauses if pH drifts out of range.

Make the bill more predictable with a few practical moves

These steps don’t need big projects. They focus on control, evidence and ease for your team.

• Balance the flow

  A simple balance tank evens out peaks in pH, temperature and strength from batch work. That makes samples steadier and bills less jumpy.

• Stop solids early

  Fit a coarse screen on drains and clean lint filters often. Less lint and grit going out means lower suspended solids.

• Keep dosing honest

  Use auto-dosing linked to load weight. Lock the settings and keep a one-page change log so tweaks don’t drift.

• Measure what matters

  Start with three data points: flow (m³), pH and temperature. If you can, add spot checks for COD and suspended solids before and after settlement.

• Know how you’re sampled

  Ask your retailer about composite vs spot sampling, and how averages are set. Align your own checks to that method so you can query any outliers with confidence.

• Train for sampling days

  A short crib sheet helps operators keep the plant in steady mode while a sampler is on site. Consistency brings fairer results.

• Review consent and charging data annually

  If your strength or volume has genuinely reduced, ask your retailer how that will be reflected in sampling, classification, or any consent variation process.

• Ask your retailer

  Are you billed on spot or composite samples?
  Which test is used for strength: COD settled / unsedimented, SS or both?
  What is the temperature and pH limit at point of discharge in your consent?

What “good” looks like

On well-run sites, effluent control feels routine. Operators know the set points. Dosing tracks the load. pH and temperature sit inside limits with live readouts. The lint screen is clean. Samples look similar from week to week. Bills match what the data suggests. Most importantly, managers sleep better because compliance doesn’t hinge on one person’s memory.

Need help with trade effluent or anything water?

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