§ Mr. Skeetasked the Secretary of State for the Environment, in the light of the fact that the volume of nitrates in the River Thames has doubled in the past three decades, what methods are now being adopted for nitrate removal; and if he will indicate the position of other United Kingdom rivers and major reservoirs.
§ Mr. Denis HowellHigher nitrate levels in water are mainly confined to Southern England and in particular East Anglia. Other than the Thames, increasing concentrations have also been noted in the rivers Chelmer (Essex), Great Ouse, Hampshire Avon, Medway, Severn and in the reservoirs supplied from these rivers, although the levels vary widely both in maximum values and in monthly average values.
Various methods may be used to reduce nitrate concentrations. The simplest are to blend the water with low nitrate water, where this is available, or to store it in large reservoirs to allow time for natural denitrification. Biological denitrification is practised at a sewage treatment plant on the River Lea, where the treatment process is modified to produce a de-nitrified effluent which is satisfactory for making into drinking water.
For removal of nitrates from raw water, two processes have been developed. One uses an ion-exchange resin (similar in operation to a water softener), the other a bacteriological process. Two ion-exchanging plants of different design have been constructed to evaluate this process and are being tested by the Anglian Water Authority; bacteriological process plants are to be used by the Anglian and Thames water authorities.