, 2010) and activated sludge performance (Straub, 2009; testing limited to COD removal only). The positioning of the high OC-only dosing period in the middle of the pandemic scenario (i.e. dosing of OC and antibiotics) meant that we were not able to completely differentiate the causes of the perturbation to community structure and function; however, it is clear from this study that WWTPs may experience reduced

efficiency during an influenza pandemic owing to the high concentrations of bioactive pharmaceuticals, such as antivirals and antibiotics. The SBR chosen for this study had a relatively long history of stable EBPR performance (>6 months). EBPR failure has previously been shown to occur as a result of competition with glycogen-accumulating organisms (Bond et al., 1999) and from bacteriophage infection (Barr et al., 2010; Barr STA-9090 chemical structure et al., 2010); hence, the loss in reactor function in this study might not be due to pharmaceutical exposure. However, as quantitative FISH analyses did not demonstrate a decrease in the relative abundance of Candidatus‘Accumulibacter phosphatis’, as would be expected if bacterial competition or bacteriophage predation was to blame, it was concluded that pharmaceutical exposure was the more likely cause. As the SBR was operated as a granular (rather than floccular) sludge, it remains untested whether floccular sludge

would respond differently to such exposure. Granular sludge systems do have some operational differences to floccular systems, such as longer sludge ages, higher mixed liquor SS and lower available surface click here Erythromycin area, all of which might affect sludge–pharmaceutical interactions. It was only after dosing high concentrations of antibiotics and OC that effects on EBPR performance were

noticed. Therefore, it may be that it is only under severe pandemic scenarios that disruption to WWTPs is of concern. Nonetheless, this research highlights the reality of this chemical risk to WWTP function and the need for additional mixed-pharmaceutical dosing studies in WWTP systems. These will be important for optimizing WWTP operation to contend with threats to WWTP function, and for understanding and modelling the release of pharmaceuticals into the environment. We thank F. Hoffman-La Roche Ltd for the kind donation of OC and Michael Poole for assistance with Fig. S1. This work was funded by a UQ New Staff Research Start-up Grant awarded to F.R.S. and the Natural Environment Research Council – Knowledge Transfer Initiative (PREPARE) contract no. NE/F009216/1 awarded to A.C.S. We thank two anonymous reviewers for their comments on the text. Fig. S1. Simulated effluent OC concentrations based on measured influent OC concentrations and four SBR draw and fill occurrences per day, each with a volumetric exchange ratio of 1:4, and assuming no sorption or biological transformation (i.e.