Full guidance for emissions to drains

3.1 The foul sewer should not be viewed as a disposal route for waste chemicals; in line with the University's 'Zero Hazardous Chemicals to Drains Policy' wherever possible, waste chemicals should be collected in suitable containers for disposal by way of the Hazardous (Chemical) Waste Disposal Service administered by the Health and Safety Office.

3.2 You should check your own building or site's Trade Effluent consent (available on request from your departmental Safety Officer or from the Sustainability Team) for details of what chemicals are explicitly NOT suitable for disposal to foul sewer, however as general guidance the following are typically included on each Trade Effluent Consent:

•    Petroleum spirit and other volatile or flammable organic solvents.
•    Calcium carbide.
•    Cyanide salts.
•    Waste liable to form viscous or solid coatings or deposits on or in any part of the sewerage system through which the trade effluent is to pass.
•    Substances of a nature likely to give rise to fumes or odours injurious to persons working in the sewers through which the trade effluent is to pass.
•    Halogenated hydrocarbons.
•    Halogen substituted phenolic compounds.
•    Thiourea and its derivatives.
•    Ethidium Bromide.

Substances listed in Schedule 1 of the Trade Effluent (Prescribed Processes and Substances) Regulations 1989 Prescribed Substances - Schedule 1, are also banned, i.e.

•    Mercury and its compounds
•    Dichlorvos
•    Cadmium and its compounds
•    1,2-Dichloroethane
•    Gamma-hexachlorocyclohexane
•    Trichlorobenzene
•    DDT
•    Atrazine
•    Pentachlorophenol
•    Simazine
•    Hexachlorobenzene
•    Tributyltin compounds
•    Hexachlorobutadiene
•    Triphenyltin compounds
•    Aldrin
•    Trifluralin
•    Dieldrin
•    Fenithrothion
•    Endrin
•    Azinphos-methyl
•    Carbon Tetrachloride
•    Malathion
•    Polychlorinated Biphenyls
•    Endosulfan

3.3 The Environment Agency are particularly concerned about the discharge of mercury and mercuric compounds from University sites and have included a specific discharge limit of 1 µg/l (1 ppb) for mercury on the trade effluent consents. All procedures using mercury should be notified to the Departmental Safety Officer who will liaise with the Chemical Safety Advisor over correct procedures for the collection and disposal of contaminated waste from the process.

3.4 There are many substances in regular use which contain significant amounts of mercury, that are not readily identifiable from the common or trivial names, e.g. Nesslar's Reagent, Zenker's Solution and Thimerosal. A comprehensive list of some of the more commonly encountered substances is shown in Annex 1. For advice concerning the use and disposal of any of these substances (or other materials that you may suspect contain mercury) please contact the Health and Safety Office.

3.5 Mercury has been widely used throughout the University for many years. Investigations have found that there is widespread contamination of internal and eternal drainage systems due to the presence of metallic mercury from thermometers and manometers that has gained entry to the sewage system and collected in sink traps and joints in pipework, leading to elevated concentrations of mercury in the wastewater discharges. Extensive drain cleaning operations have been carried out by EM to safely remove this contamination to comply with Environment Agency discharge conditions. However, it is important to ensure that any spillage of mercury into the drainage system is immediately notified to the Departmental Safety Officer who will arrange for the cleaning of the drainage system to remove any trapped mercury.

3.6 Wherever possible, departments are encouraged to withdraw the use of mercury thermometers and manometers. Any equipment containing mercury should be used within a containment system (e.g. wide-brimmed tray) to prevent the escape of mercury in the event of spillage or leakage. A typical mercury thermometer contains enough mercury to exceed consent conditions every day for several months.

3.7 All other substances in the Prescribed Substances List are prohibited for discharge, and must not be present in concentrations greater than 'Background Concentration', which is considered to be the concentration contained in the water supplied to the site.

3.8 In addition to the above conditions, certain sites have restrictions on the concentration of heavy metals, e.g. Cadmium, Chromium, Copper, Lead, Mercury, Nickel, Silver, Zinc. Please check the consent for your site to establish the existence of any additional consents pertaining to individual sites: contact the Environment and Energy Section with questions. There are also a series of hazardous substances which may not be discharged to drain.

3.9 For details on which substances can be disposed to foul sewer, for instance by diluting with copious amounts of water, check the Safety Office Disposal of Chemical Waste guidance.

3.10 Environmental Hazards / Risk Phrases of any substance poured down the drain MUST be checked prior to disposal. As a non-exclusive guide, substances with the following risk phrases are NOT suitable for discharge to drain and must be disposed of by way of the Hazardous (Chemical) Waste Disposal Service:
 
•    N Dangerous for the environment. Chemicals that may present an immediate or delayed danger to one or more components of the environment. Characterised by the 'dead tree and fish' symbol
•    R50 Very toxic to aquatic organisms
•    R51 Toxic to aquatic organisms
•    R52 Harmful to aquatic organisms
•    R53 May cause long term adverse effects in the aquatic environment.