Aeration control for simultaneous nitrification-denitrification in a biological aerated filter using internal model approach.

Experience has shown that simultaneous nitrification/denitrification in a biological aerated filter is possible. However these systems react very sensitively to the aeration control strategies applied. Poorly adapted control strategies induce a strong decrease in treatment efficiency. A new control strategy for simultaneous N/DN is developed. The strategy proposed makes use of ammonia measurements and the inlet and outlet: a Feedback/Feedforward block. Passing by a calculation of the load to be eliminated, an estimation of the air flow velocity to be applied is carried out dynamically. A retroactive loop corrects this prediction in order to reach exactly the desired set point. This control approach has been implemented and tested at pilot plant scale for a period of 18 months. The pilot plant consists of two coupled BAF cells, reflecting closely industrial scale situations. Comparative studies reveal clearly the improved performance of the developed FF/FB control strategy compared to classical controllers. The benefits include 5% increase in nitrogen removal performance and a reduction of 15 to 20% in air requirement, offering a rapid return of investment costs.