The robustness of the control strategies developed in the COST 624 benchmark have been tested against the sophistication of the model describing the hydraulic behaviour of the biological reactor of a wastewater treatment plant by activated sludge. In such a large biological reactor of the channel type, hydrodynamics are intermediate between plug flow and well-mixed and are function of the liquid flow rate and the aeration intensity. No large effect of these hydrodynamics could be observed in the various tested scenarios, suggesting that the actual benchmark is indeed a good tool for a first assessment of the efficiency of control schemes.