Report No DWI0001

Oct 1987



Concern over increasing nitrate concentrations in drinking water and the need for compliance with the EC Drinking Water Directive has necessitated investigation into methods of denitrification for potable water supply. Although a number of denitrification plants exist in Europe, there has as yet been relatively little operating experience and it is considered in the UK that the effects of adopting denitrification have not been fully quantified. Of particular concern is the possibility that, by altering the chemical and microbiological characteristics of the water, the treatment methods employed may have undesirable effects on the distribution system and, as a result, on the quality of water in supply. Effects such as mains corrosion; dissolution or disturbance of previous deposits in mains; organoleptic effects due to bacterial regrowth; and increased risks of leaching of toxic metals, may have an indirect but significant effect on the long term costs of denitrification.

In the light of this, the Department of the Environment commissioned Consultants in Environmental Sciences Ltd to undertake a study of the effects of denitrification on water quality in supply, and of the potential increase in treatment costs associated with any side-effects over and above the costs of the treatment process itself. The study comprised five elements:

  1. A review was undertaken to identify the possible adverse effects of denitrification by both ion exchange (point of entry and point of use) and biological treatment, and to identify correction or control measures which could be applied for amelioration.

  2. Information was collated on existing denitrification plants in Europe and the USA in order to ascertain whether deleterious effects on water quality and the distribution system had been observed, and if so, what measures had been taken in response.

  3. A desk study of the denitrification of three hypothetical groundwater types representative of those from UK aquifers affected by rising nitrate levels was carried out. This served to illustrate the possible changes in the quality of three specific waters caused by nitrate removal and attempted to assess these in terms of the resultant corrosion potential.

  4. Comparative estimates were sought for denitrification plant and correction facilities appropriate to the three representative water types studied. Costs of correction were compared with costs of substituting corrosion resistant fittings. Costs reported for existing denitrification plants were also reviewed.

  5. In addition to the above, a brief appraisal of point-of-use denitrification systems for private supplies was undertaken.

Copies of this report may be available as an Acrobat pdf download under the 'Pre 2000 Reports' heading on the DWI website.