Trade effluent consent for discharging to sewers

If your business discharges liquid waste (other than domestic sewage) into a public sewer, you need trade effluent consent from your sewerage company. This is a separate requirement from an environmental permit: trade effluent consent covers discharge into the sewer network, while environmental permits cover discharge directly into the environment.

It is a criminal offence under Section 118 of the Water Industry Act 1991 to discharge trade effluent into a public sewer without consent. You could face prosecution, an unlimited fine, and your water company may disconnect your supply.

What counts as trade effluent

Trade effluent is any liquid waste (including particles in suspension) discharged from premises used for a trade or industry. This includes water used in manufacturing processes, food preparation, vehicle washing, cooling, cleaning, and laundry operations. It does not include domestic sewage from toilets, hand basins, or canteens (unless contaminated with trade substances).

Common examples of trade effluent include:

• wash water from food processing, brewing, or dairy operations
• rinse water from metal finishing, electroplating, or printing
• cooling water from industrial processes
• vehicle wash water from garages and transport depots
• waste water from laundries and dry cleaners
• chemical solutions from photographic processing or laboratories
• run-off from contaminated yards or industrial sites

How to apply for trade effluent consent

You apply directly to your sewerage company (the water company responsible for the sewer network in your area), not to the Environment Agency. In England, if you are a non-household customer, your water retailer will coordinate the application with the sewerage undertaker on your behalf.

Prohibited and restricted substances

Certain substances must never be discharged to a public sewer, regardless of consent. These include:

• petrol, diesel, and other petroleum spirits with a flashpoint below 21 degrees Celsius
• calcium carbide (which produces flammable acetylene gas on contact with water)
• substances that could damage the sewer infrastructure or create a health and safety risk to sewer workers

Many other substances are restricted and can only be discharged within concentration limits set in your consent. These include heavy metals, fats oils and grease, sulphates, cyanides, and chlorinated solvents. Your water company will specify limits based on the capacity of the local treatment works and the sensitivity of the receiving watercourse.

Charges

Your water company will charge for receiving and treating your trade effluent. Charges are calculated using the Mogden formula, which takes into account:

• the volume of effluent discharged
• the chemical oxygen demand (COD) or biological oxygen demand (BOD) of the effluent
• the total suspended solids (TSS) content
• a reception and conveyance charge for using the sewer network

Charges are published annually by each water company. They can be significant for high-volume or high-strength discharges. Investing in pre-treatment to reduce pollutant concentrations can lower your ongoing costs.

Monitoring and enforcement

Your water company has the right to:

• sample your discharge at any time without prior notice
• inspect your premises and drainage system
• vary your consent conditions by giving 2 months' notice (you can appeal variations to Ofwat)
• revoke your consent if you repeatedly breach conditions

If you breach your consent conditions, the water company can issue penalty charges, seek an injunction, or prosecute. Repeated or serious breaches can result in consent revocation, leaving you unable to discharge. The Environment Agency may also take action if your discharge harms the environment.

Consent reviews and variations

Your water company can vary the conditions of your consent by giving at least 2 months' written notice. Common reasons for variation include changes to treatment works capacity, tightened environmental standards for the receiving watercourse, or changes to your discharge characteristics. You can appeal any variation to Ofwat under Section 126 of the Water Industry Act 1991.

If your business changes its processes in a way that alters the volume, composition, or nature of your trade effluent, you must notify your water company and may need to apply for a new or amended consent.

Trade effluent consents cannot be transferred. If the premises changes ownership, the new occupier must apply for a new consent before discharging.

What to do next

After securing trade effluent consent, consider whether you also need:

• a water discharge permit from the Environment Agency if any of your discharges go directly to a watercourse or the ground rather than through the sewer
• to register under packaging waste regulations if your business handles packaging that contributes to trade waste
• to review your pollution prevention plan to ensure spills and leaks are contained and do not enter the sewer uncontrolled
• to install monitoring equipment such as flow meters and sampling points if required by your consent