Vol. 533 No. 6
313 Mr. Gormley asked the Minister for the Environment and Local Government the relevant advantages of tertiary sewerage treatment over secondary treatment; and his views on whether secondary sewerage treatment of municipal sewerage and landfill leachate is acceptable prior to discharge into a salmonoid-rated river. [9808/01]
The term secondary treatment of waste water, prior to its discharge to waters, generally means biological treatment to improve the quality of the discharge by reducing the biochemical oxygen demand, the chemical oxygen demand and the level of total suspended solids. Secondary treatment reduces the impact of a discharge on the receiving waters below that of a discharge which is either untreated or subject only to primary treatment. Tertiary treatment further reduces the impact of a discharge by providing for additional treatment more stringent than secondary treatment, including, for example, for the removal of either or both of the nutrients nitrogen and phosphorus.
The impact of any discharge is partly determined by the extent of dilution available. Accordingly, where secondary treatment has been applied to a sewage discharge, this would be satisfactory to protect salmonid waters if there is adequate dilution available to reduce phosphorus levels sufficiently to prevent eutrophication. This would have to be assessed on a case by case basis. The standards which apply to designated salmonid waters are set out in the European Communities (Quality of Salmonid Waters) Regulations, 1988 (S.I. No. 293 of 1988). It is primarily a matter for the relevant local authority, where necessary, to adopt an action programme comprising appropriate measures to reduce pollution and ensure that the standards are complied with in relation to any designated salmonid waters in its functional area.
Landfill leachate is not discharged directly to waters but is usually collected and tankered to a sewage treatment plant where it is mixed with sewage before treatment. Landfill leachate is, therefore, generally, subject to the same treatment and discharge requirements as sewage. The operation of a landfill is subject to licensing by the Environment Protection Agency under the Waste Management Act, 1996.
