The Apeldoorn wastewater treatment plant (WWTP) is heavily loaded with nitrogen, partly due to return flows from the sludge line. This has drawn increased attention from water authorities, especially regarding the emission of nitrous oxide (N₂O), a greenhouse gas 265 times more potent than carbon dioxide.
THE CHALLENGE
The high nitrogen load made it difficult to maintain stable process performance and consistently meet effluent standards for total nitrogen. A Quick Scan revealed frequent over-aeration, which had a negative impact on both nitrogen removal and energy consumption. This is particularly important since aeration accounts for about half of the plant’s total energy use. The combination of energy inefficiency and elevated N₂O emission risk posed a major operational and environmental challenge.
THE SOLUTION
In 2016, Aqua Suite Pure was commissioned on both lanes of WWTP Apeldoorn, with various controllers including for aeration and internal recirculation. These controls use self-learning algorithms that can be used to make a good estimate of the required base setpoint. As a result, only subtle adjustments need to be made based on the fluctuating actual measured values to achieve the target values.
The big advantage of this is that it anticipates what is to come instead of over-reacting to what is going on in the now. This results in a more optimal and stable operation of the waterline, which improves the functioning of the nitrogen removal process. This can reduce both the total nitrogen in the effluent and the N2O emissions and prevent over-aeration and save a lot of energy. Since the algorithms continue to learn and anticipate, this is a robust solution that also relieves the process operator.
RESULTS
In addition to the tangible results for the three “e’s” (effluent quality, energy saving, and emission reduction), Pure also ensures stable and reliable operation 24/7. This allows the process operator to spend his/her scarce time more effectively. As a self-learning system, Pure can counter the failure of measuring instruments by falling back on the prediction. As a result, the system is secured and controlled with the best alternative setpoint. This minimises manual intervention.
– Frank van de Grootevhee, Process Technologist at Waterschap Vallei & VeluweAqua Suite Pure is a reliable controller, which provides good and stable operations due to accurate DWA predictions. With very limited adjustments, good effluent quality is achieved and N2O emmisions are reduced.
