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Aerzen’s iAir BioProcess Control System (iAirBP) is an integrated solution for controlling the dissolved oxygen (DO) concentration in the activated sludge treatment process. The iAirBP system is able to maintain DO concentrations at their set points independent of influent biochemical oxygen demand (BOD) and ammonia loading. Typically, DO is controlled using a PI feedback controller. The problem with a PI control is that the proportional (P) and integral (I) gains have to be tuned to a certain operating condition. If the loading (i.e. the oxygen uptake rate (OUR)) deviates significantly from the standard condition, the control loop becomes unstable and the actual DO oscillates around the setpoint. Additionally, the PI controller does not control the blower. Blowers are operated at a constant pressure, so whenever additional air is needed, it is communicated via a drop in pressure (or vice versa). This causes a time lag in the system response and can lead to a second oscillating loop. The whole system can “hunt” around a stable operating point.

iAirBP control is based on an activated sludge aeration model. Utilizing plant specific model equations, AirBP determines the OUR in real time and calculates the total airflow required (production side) as well as the exact airflow required in each aeration zone (distribution side) to maintain the DO at the setpoint. iAirBP then quickly and accurately adjusts the valves to distribute the airflow as required. iAirBP also measures the DO in each control basin, and in a cascaded control loop fine tunes the valve setting for each individual aeration zone to achieve the desired DO profile. The iAirBP-Plus utilizes additional information from an ammonia analyzer to calculate loading for the precise determination of OUR based on the Activated Sludge Model (ASM) and the current operating conditions for feed-forward control, in addition to the iAir control.

In either version, iAirBP provides precise DO control and a fast, accurate response to changing conditions without hunting or over-shooting.