Modern on-line measuring has given many new pieces of information which can reveal so far unknown details about load and process behaviour. This new information is primarily used for control optimisation purposes so that all available unused reserves in the plants during normal operation are used for improving the effluent quality and reducing operation costs. Secondly, the new on-line measurements can also be utilised for identifying the process relations as they are described in: a) software sensors, b) load characterisation and c) capacity of the actual plant.

Because of the 100 times more detailed information we now get from full-scale plant operation, more fundamental development and research can be carried out based on experiments performed directly on full-scale plants and evaluations of the on-line response to identify the model structure and constant dynamics at full scale. In this way it is possible to develop new processes significantly more quickly than before the on-line information was available.

To derive full profit from these improvements the following requirements must be met.

a) Measurement. Before identifying the process design constants it is necessary to compensate for the load applied on the full-scale system. This detailed evaluation is often so tedious that it normally has to be performed on an off-line basis, while the data from on-line measurements are brushed and used for on-line control, consequently the new kind of tools are needed in information handling.

b) The necessary excitations of the processes are always available during alternating operation. A condition for efficient control is controllability of the system; also in this respect the alternating system offers possibilities far more powerful than continuous systems.

c) Third, it is necessary to develop models and strategies which make the new knowledge and control possibilities operational.

The identified models, which are continuously updated, can be used for operational improvements which today give an excellent payback time for investment in on-line measurement and control systems. This is documented by introducing alternating operation which ensures the necessary information richness at plants with capacities down to below 20,000 PE.

This paper discusses the key points in the recommended approach to and structure of the information handling. The efficiency is demonstrated by introducing alternating operation on a conventional recirculating plant.

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