There has been a steady increase in nitrate levels in many ground-water sources. This together with the nitrate standard of 10 mg/l as nitrogen, introduced in the first EU Drinking Water Directive has led to a number of sources being unsuitable for water supply without blending with lower nitrate water, or nitrate removal.

Where a source does have high nitrate levels the first preference is blending. Where this is impractical or expensive then nitrate removal will be required. There are two main options for nitrate removal: ion-exchange or biological treatment. It is also possible to use reverse osmosis or electrodialysis.

The simplest treatment option is ion exchange. Where this is used, a proportion of the flow passes through an ion-exchange unit using resin optimized for nitrate removal. The advantages of ion exchange are simple operation; the process is independent of temperature, can be automated, and is essentially unaffected by varying nitrate concentrations. The drawbacks are the production from regeneration of a saline waste, that may cause disposal problems, and an increase in the corrosiveness of the treated water. The use of ion exchange for nitrate removal normally requires the use of a special resin to be practicable. A conventional resin removes sulfate ions in preference to nitrate ions. Thus where both sulfate and nitrate are present both are removed, reducing the effective capacity of the resin for nitrate, and increasing the regeneration water per unit of nitrate removed. There is a further potential problem associated with the use...