Abstract
Interpreting the fate of wastewater contaminants in streams is difficult because their inputs vary in time and several processes synchronously affect reactive transport. We present a method to disentangle the various influences by performing a conservative-tracer test while sampling a stream section at various locations for chemical analysis of micropollutants. By comparing the outflow concentrations of contaminants with the tracer signal convoluted by the inflow time series, we estimated reaction rate coefficients and calculated the contaminant removal along a river section. The method was tested at River Steinlach, Germany, where 38 contaminants were monitored. Comparing day-time and night-time experiments allowed distinguishing photo-dependent degradation from other elimination processes. While photo-dependent degradation showed to be highly efficient for the removal of metroprolol, bisoprolol, and venlafaxine, its impact on contaminant removal was on a similar scale to the photo-independent processes when averaged over 24 h. For a selection of compounds analyzed in the present study, bio- and photodegradation were higher than in previous field studies. In the Steinlach study, we observed extraordinarily effective removal processes that may be due to the higher proportion of treated wastewater, temperature, DOC and nitrate concentrations, but also a higher surface to volume ratio from low flow conditions that favorizes photodegradation through the shallow water column and a larger transient storage than observed in comparable studies.
Highlights
IntroductionThe persistence of wastewater contaminants has mainly been studied in the laboratory to assess their respective susceptibilities to natural attenuation processes (Andreozzi et al, 2002; Durán-Álvarez et al, 2015; Lindström et al, 2002; Yamamoto et al, 2009)
Wastewater treatment plants (WWTP) are primary sources of contaminants in streams, the persistence of which determines how far they spread within the river network, raising concerns regarding the extent of their environmental impact.The persistence of wastewater contaminants has mainly been studied in the laboratory to assess their respective susceptibilities to natural attenuation processes (Andreozzi et al, 2002; Durán-Álvarez et al, 2015; Lindström et al, 2002; Yamamoto et al, 2009)
We present a method to disentangle the various influences by performing a conservative-tracer test while sampling a stream section at various locations for chemical analysis of micropollutants
Summary
The persistence of wastewater contaminants has mainly been studied in the laboratory to assess their respective susceptibilities to natural attenuation processes (Andreozzi et al, 2002; Durán-Álvarez et al, 2015; Lindström et al, 2002; Yamamoto et al, 2009). The complexity of natural environments, makes it difficult to transfer laboratory results to the field, where many environmental influences can either hinder or foster the elimination of contaminants in a river (Andreozzi et al, 2002; Kunkel and Radke, 2011; Li et al, 2016; Nödler et al, 2014; Rühmland et al, 2015). This calls for improved field assessment methods to identify key environmental parameters of contaminant elimination in streams
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