Report No DWI0140

Discreet laboratory analysis and continuous automatic monitoring were investigated for the control of the pilot scale biological denitrification plant at Bucklesham. A major objective of this work was to ascertain whether automated operation was feasibile.

 Discreet laboratory analysis for nitrate, nitrite, methanol, ethanol and acetic acid proved reliable, precise and accurate. The method for methanol did not have sufficiently low limits of detection for reliable monitoring of treated water entering potable supply.

 The EIL continuous monitor for dissolved oxygen (electrode) and temperature proved reliable and required only a low level of maintenance.

 The continuous flow automatic colorimetric analyses for methanol (Technicon Monitor IV) and nitrite (built in-house) proved reliable but required a high level of maintenance (5.5 and 2.5 hrs/week respectively). They were not suited to operation by non-laboratory personnel. As with the discreet analysis , the limit of detection for methanol was not sufficiently low to monitor water entering supply.

 The EIL nitrate monitors proved reliable and had reasonably low maintainance requirements (1.5 hrs/week). They gave an unacceptably large scatter of results when operated on a constant nitrate level solution or when compared to discreet laboratory analyses of the same waters.

 The above results led to the following conclusions:

CONCLUSIONS

1. Automated control of a microbiological nitrate removal plant is not at present possible due to inadequacies in some of the available monitors.
2. Laboratory methods for the analysis of plant samples proved reliable and accurate
3. In order to achieve reliable and economic automated control the following developments will be necessary:

1. A nitrate monitor with considerably improved measurement precision and preferably less maintainence
2. Nitrite and methanol monitors with reduced maintainence requirements
3. A methanol monitor with a lower limit of detection.

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