Fate of wastewater contaminants in rivers: Using conservative-tracer based transfer functions to assess reactive transport.

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.

Denatonium - A so far unrecognized but ubiquitous water contaminant?

Denatonium is one of the bitterest substances known to man and therefore applied in numerous consumer products to prevent an accidental or intentional consumption. So far no information was available on the occurrence of this compound in the environment. A sensitive targeted method was developed and applied to water samples taken in the federal state of Baden-Württemberg, Germany. Denatonium was detected in 100% of the investigated 22 wastewater treatment plant (WWTP) effluents with a maximum concentration of 341 ng L-1. Additionally, water samples were taken from the Ammer river over a period of one week and all wastewater impacted samples showed denatonium at concentrations up to 195 ng L-1. Retrospective analysis of high-resolution mass spectrometric measurements of WWTP effluents from Italy and Switzerland confirmed and therefore point to an international occurrence of denatonium as anthropogenic contaminant.

A high-precision sampling scheme to assess persistence and transport characteristics of micropollutants in rivers.

Increasing numbers of organic micropollutants are emitted into rivers via municipal wastewaters. Due to their persistence many pollutants pass wastewater treatment plants without substantial removal. Transport and fate of pollutants in receiving waters and export to downstream ecosystems is not well understood. In particular, a better knowledge of processes governing their environmental behavior is needed. Although a lot of data are available concerning the ubiquitous presence of micropollutants in rivers, accurate data on transport and removal rates are lacking. In this paper, a mass balance approach is presented, which is based on the Lagrangian sampling scheme, but extended to account for precise transport velocities and mixing along river stretches. The calculated mass balances allow accurate quantification of pollutants' reactivity along river segments. This is demonstrated for representative members of important groups of micropollutants, e.g. pharmaceuticals, musk fragrances, flame retardants, and pesticides. A model-aided analysis of the measured data series gives insight into the temporal dynamics of removal processes. The occurrence of different removal mechanisms such as photooxidation, microbial degradation, and volatilization is discussed. The results demonstrate, that removal processes are highly variable in time and space and this has to be considered for future studies. The high precision sampling scheme presented could be a powerful tool for quantifying removal processes under different boundary conditions and in river segments with contrasting properties.