Adaptive control of external carbon flow rate in an activated sludge process

In this study an adaptive carbon flow rate controller is applied to a pre-denitrifying pilot-scale plant. The goal of the control strategy is to maintain a low nitrate concentration in the anoxic zone by controlling the external flow rate of the carbon source. Results from practical experiments show that the control strategy works well and the nitrate concentration could be kept close to a desired set-point (reference value). The used nitrate sensor needed, however, frequent maintenance. During the experiment the carbon flow rate was automatically varied to keep the nitrate concentration at a constant low level. We conclude that a low effluent nitrate concentration without an excessive carbon flow rate is hard to achieve without an automatic control strategy.