The use of flow predictions and on-line nutrient sensors in BNR plants has given the basis for introduction of radical operational changes. Because of the detailed monitoring, the control actions are allowed to go closer to critical process limits while balancing between hydraulic and biological capacities.

One of the new modes of operation, settling in the aeration tanks as an active control, is documented below. This new operation, Aeration Tank Settling (ATS) has been tested at full scale and shows a great potential for storm water control. With ATS control the hydraulic capacity is increased 25–75% on existing plants without reducing the organic capacity in periods ranging from 2 hours to 2 weeks.

ATS control can be initiated directly by raising the inlet flow to the treatment plant, but even better by 1/2 - 1 hour prediction of the inlet flow. These predictions of flow are achieved from statistical grey-box handling of data from on-line rain gauges and measured inlet flow pattern during normal and stormwater conditions.

Hourly predictions of concentrations in the inlet to the plant and selected points in the sewer system during dry weather and storm situations will improve the combined system control efficiency radically.

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