Report No DWI0280

Nov 1991

Nitrate removal treatment processes will be needed at many sites within the next few years to achieve drinking water quality standards. Biological denitrification processes have been demonstrated to be feasible at full-scale for this application. However, means of controlling nitrite production and carbon source residual concentration are needed to maintain satisfactory treated water quality.

The objectives of this work were to establish reliable monitoring techniques for the carbon sources used in biological denitrification, and recommendations for operating conditions to minimise nitrite concentrations in the treated water.

A volatile organics monitor developed by WRc, and a gas chromatography technique using head-space vapour injection, have been shown to be capable of achieving the desired detection limits for methanol and ethanol, but not for acetic acid. Biosensor techniques also show promise for monitoring and control of carbon source residual concentrations, but costly development work would be needed to produce a prototype system for further investigation.

Control of nitrite residual can be achieved through overdosing of carbon source to establish nitrate limited operation. Excess carbon source can be removed by the development of biological activity in post-denitrification conventional water treatment processes.

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