a b s t r a c tThe present study investigates the biodegradation of pharmaceutically active compounds (PhACs) by active biomass in activated sludge. Active heterotrophs (X bh ) which are known to govern COD removal are suggested as a determining factor for biological PhAC removal as well. Biodegradation kinetics of five polar PhACs were determined in activated sludge of two wastewater treatment plants which differed in size, layout and sludge retention time (SRT).Results showed that active fractions of the total suspended solids (TSS) differed significantly between the two sludges, indicating that TSS does not reveal information about heterotrophic activity. Furthermore, PhAC removal was significantly faster in the presence of high numbers of heterotrophs and a low SRT. Pseudo first-order kinetics were modified to include X bh and used to describe decreasing PhAC elimination with increasing SRT.

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Neighboring springs draining fractured-rock aquifers can display large differences in water quality and flow regime, depending on local variations of the connectivity and the aperture size distribution of the fracture network. Consequently, because homogeneous equivalent parameters cannot be assumed a priori for the entire regional aquifer, the vulnerability to pollution of such springs has to be studied on a case by case basis. In this paper, a simple lumped-parameter model usually applied to estimate the mean transit time of water (or tracer) is presented. The original exponential piston-flow model was modified to take land-use distribution into account and applied to predict the evolution of atrazine concentration in a series of springs draining a fractured sandstone aquifer in Luxembourg, where despite a nationwide ban in 2005, atrazine concentrations still had not begun to decrease in 2009. This persistence could be explained by exponentially distributed residence times in the aquifer, demonstrating that in some real world cases, models based on the groundwater residence time distribution can be a powerful tool for trend reversal assessments as recommended for instance by current European Union guidelines.

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Diffuse reflectance infrared Fourier transform (DRIFT) spectrometry was applied to a set of sediment samples collected by traps over one and a half years in a mid-mountainous river. Dynamic changes in hydrological and life-cycle conditions generated sediment particles of different C(org) content and organic composition. Periods in the midst of or shortly after flood events left particles poor in C(org) content with spectral features that were enriched in carboxylic and aromatic signals. These are characteristic of terrestrial oxidized vascular plant debris. Low-flow conditions saw the consequent build-up of amide, aliphatic, and polysaccharide moieties as expected for autochthonous biofilm derived material. A peak ratio of two bands representing the alternation of these two types of organic matter showed that flood particle C(org) had a higher affinity for metals than the high C(org) of mature biofilms, probably owing to higher COO- contents in the first. The relative dietary bioavailability of the metals from sediment C(org), which is related to the nutritional value of the substrate, is therefore probably lower in the aftermath of a flood than in prolonged low-flow situations. This needs to be accounted for in future metal speciation and bioavailability modeling approaches.

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