Discharge to the public sewer requires a trade effluent discharge consent from the appropriate company, usually the water company or sewage undertaker. These companies are required by law to accept effluent where it conforms to accepted standards. A charge is levied appropriate to the level of service provided. The company may grant consents unconditionally or subject to certain conditions which the sewerage undertaker thinks fit to impose with respect to:

• The sewer or sewers into which the trade effluent may be discharged
• The nature and composition of the trade effluent which may be discharged
• The maximum quantity of trade effluent which may be discharged on any one day, either generally or into a particular sewer
• The highest rate at which trade effluent may be discharged either generally or into a particular sewer

For information on discharges to sea, surface waters or groundwater – see Discharges to Controlled Waters.

Trade effluent discharge consents will usually state the following conditions:

• The maximum permitted daily flow (m3/day)
• The maximum hourly flow (m3/hour)
• The permitted pH range, typically pH 5-9
• The maximum biochemical oxygen demand (BOD) or chemical oxygen demand (COD) value, expressed in milligrams of oxygen requirement per litre (mg/l)
• The maximum concentration of suspended solids (SS) in mg/l

They may also include stated limits on particular substances such as oil, copper, zinc or organic chemicals such as phenols which could affect treatment facilities or affect the final composition of discharge from sewage works to the environment.

Applications must be made in writing to the local water company or sewerage undertaker.

The relevant water company is required to make a decision on an application for consent within 3 months of receiving the application.

The consent is likely to detail the allowable discharge rate(s) and volume(s), and the periods during which discharges can be made.

The consent is likely to include discharge standards for suspended solids, biochemical oxygen demand (BOD), pH, temperature, oil, fat and grease content, and specific chemicals such as metals, sulphates, nitrates, fluorides, cyanide and organic chemicals.

In addition, the consent will list prohibited substances such as calcium carbide, carbon disulphide, free oil, flammable or explosive materials including petroleum spirit and organo-halogen compounds.

The monitoring/sampling requirements are case specific, but are likely to cover the following:

• Facilities for taking samples
• Meters for measuring or recording the volume and rate of discharges and apparatus for determining the nature, composition and temperature of the discharges
• Recording of sampling and monitoring data (i.e. maintaining a log book)

The consent may require the operator to forward the monitoring results for certain substances to the water company at specified time intervals.

In addition, the water company may visit the site to undertake inspections, measurements, or tests to ensure compliance, or take away and analyse samples of water or effluent or of any land or article.

Inform the local water company or sewerage undertaker (e.g. Scottish Water) immediately.

Discharge of any trade effluent, from any trade premises, without the consent or other authorisation is an offence (Section 118(5)).

Contravention of a trade effluent condition is an offence and the occupier of the premises shall be liable to a fine not exceeding £20,000 and/or imprisonment not exceeding 3 months, on a summary conviction. An unlimited fine or prison sentence of up to two years may be imposed if convicted on indictment.

The Environment Agency has indicated that it intends to introduce a new regime for England and Wales to ‘modernise’ discharge consents. After consultation it is intended to introduce a regime based on Operator Pollution Risk Appraisal (OPRA) and more self monitoring. The new regime dates are yet to be finalised.