EXPERIENCE WITH THE UPGRADING OF 14 TREATMENT PLANTS TO N-AND-P REMOVAL IN THE MUNICIPALITY OF AARHUS

The experience with the upgrading of 14 treatment plants to N and P re moval is presented. For all plants it has been possible to fulfil the effluent standards. Through process optimization it has been possible to achieve a stable biological P-removal. The introduction of control systems based on on-line sensors for ammonia, nitrate and phosphate ha s resulted in a more stable effluent quality and an increased capacity . The experience also shows that it can be very difficult to predict a nd control the changes in the industrial load From this it is conclude d that instead of spending a lot of time on fine-tuning the design cri teria in the design phase, it may be better to incorporate a considera ble flexibility into the design, allowing the processes to be adjusted to the changing operational conditions during time. (C) 1998 IAWQ. Pu blished by Elsevier Science Ltd