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Enhancing the understanding of the fate of wastewater-derived organic micropollutants in rivers is crucialto improve risk assessment, regulatory decision making and river management. Hyporheic exchange andsediment bacterial diversity are two factors gaining increasing importance as drivers for micropollutantdegradation, but are complex to study infield experiments and usually ignored in laboratory tests aimedto estimate environmental half-lives. Flume mesocosms are useful to investigate micropollutantdegradation processes, bridging the gap between thefield and batch experiments. However, few studieshave usedflumes in this context. We present a novel experimental setup using 20 recirculatingflumesand a response surface model to study the influence of hyporheic exchange and sediment bacterialdiversity on half-lives of the anti-epileptic drug carbamazepine (CBZ) and the artificial sweeteneracesulfame (ACS). The effect of bedform-induced hyporheic exchange was tested by three treatmentlevels differing in number of bedforms (0, 3 and 6). Three levels of sediment bacterial diversity wereobtained by diluting sediment from the River Erpe in Berlin, Germany, with sand (1 : 10, 1 : 1000 and1 : 100 000). Our results show that ACS half-lives were significantly influenced by sediment dilution andnumber of bedforms. Half-lives of CBZ were higher than ACS, and were significantly affected only by thesediment dilution variable, and thus by bacterial diversity. Our results show that (1) theflume-setup isa useful tool to study the fate of micropollutants in rivers, and that (2) higher hyporheic exchange andbacterial diversity in the sediment can increase the degradation of micropollutants in rivers.

Enhancing the understanding of the fate of wastewater-derived organic micropollutants in rivers is crucial to improve risk assessment, regulatory decision making and river management. Hyporheic exchange and sediment bacterial diversity are two factors gaining increasing importance as drivers for micropollutant degradation, but are complex to study in field experiments and usually ignored in laboratory tests aimed to estimate environmental half-lives. Flume mesocosms are useful to investigate micropollutant degradation processes, bridging the gap between the field and batch experiments. However, few studies have used flumes in this context. We present a novel experimental setup using 20 recirculating flumes and a response surface model to study the influence of hyporheic exchange and sediment bacterial diversity on half-lives of the anti-epileptic drug carbamazepine (CBZ) and the artificial sweetener acesulfame (ACS). The effect of bedform-induced hyporheic exchange was tested by three treatment levels differing in number of bedforms (0, 3 and 6). Three levels of sediment bacterial diversity were obtained by diluting sediment from the River Erpe in Berlin, Germany, with sand (1 : 10, 1 : 1000 and 1 : 100 000). Our results show that ACS half-lives were significantly influenced by sediment dilution and number of bedforms. Half-lives of CBZ were higher than ACS, and were significantly affected only by the sediment dilution variable, and thus by bacterial diversity. Our results show that (1) the flume-setup is a useful tool to study the fate of micropollutants in rivers, and that (2) higher hyporheic exchange and bacterial diversity in the sediment can increase the degradation of micropollutants in rivers., Environmental Science: Processes & Impacts, 21 (12), ISSN:2050-7887, ISSN:2050-7895

Urban streams receive increasing loads of organic micropollutants from treated wastewaters. A comprehensive understanding of the in-stream fate of micropollutants is thus of high interest for water quality management. Bedforms induce pumping effects considerably contributing to whole stream hyporheic exchange and are hotspots of biogeochemical turnover processes. However, little is known about the transformation of micropollutants in such structures. In the present study, we set up recirculating flumes to examine the transformation of a set of micropollutants along single flowpaths in two triangular bedforms. We sampled porewater from four locations in the bedforms over 78 days and analysed the resulting concentration curves using the results of a hydrodynamic model in combination with a reactive transport model accounting for advection, dispersion, first-order removal and retardation. The four porewater sampling locations were positioned on individual flowpaths with median solute travel times ranging from 11.5 to 43.3 h as shown in a hydrodynamic model previously. Highest stability was estimated for hydrochlorothiazide on all flowpaths. Lowest detectable half-lives were estimated for sotalol (0.7 h) and sitagliptin (0.2 h) along the shortest flowpath. Also, venlafaxine, acesulfame, bezafibrate, irbesartan, valsartan, ibuprofen and naproxen displayed lower half-lives at shorter flowpaths in the first bedform. However, the behavior of many compounds in the second bedform deviated from expectations, where particularly transformation products, e.g. valsartan acid, showed high concentrations. Flowpath-specific behavior as observed for metformin or flume-specific behavior as observed for metoprolol acid, for instance, was attributed to potential small-scale or flume-scale heterogeneity of microbial community compositions, respectively. The results of the study indicate that the shallow hyporheic flow field and the small-scale heterogeneity of the microbial community are major controlling factors for the transformation of relevant micropollutants in river sediments., Scientific Reports, 11 (1), ISSN:2045-2322