Pilot-scale investigation on the feasibility of simultaneous nitrification and denitrification (SND) in a continuous flow single-stage membrane bioreactor

The aim was to evaluate the effect of three different dissolved oxygen concentration (DO) on membrane fouling and foulants production as well as in the removal of nitrogen and organic matter by Simultaneous Nitrification and Denatrification (SND). For this purpose, a sMBR pilot plant was operated with continuous flow and no separated anoxic zone. Experiments were carried out in three phases, i.e. phase I, II and III, with DO 2.0, 0.8 and 0.4 mg/L, respectively. Under these conditions, a good performance in terms of COD and BOD5,20 was obtained, removals higher than 96% and 97%, respectively. The nitrification was almost complete, even when the dissolved oxygen concentration was the lowest, Phase III. The reduction of DO concentration positively impacted the total nitrogen removal through SND, especially in Phase II, resulting in an average total nitrogen removal of 66%, while in Phase I, the average removal was only 28%. Sludge filterability, membrane performance and total resistance of mixed liquor under SND conditions when the DO was 0.8 +/- 0.1 mgO(2)/L were not significantly affected. Conversely, a significant change was observed when the DO concentration was reduced to 0.4 mg +/- 0.1 mg O-2/L. (AU)