Organic micropollutants (OMPs) are widely detected in surface waters. So far, the removal processes of these compounds in situ in river systems are not yet totally revealed. In this study, a combined monitoring and modelling approach was applied to determine the behaviour of 1-H benzotriazole, carbamazepine, diclofenac and galaxolide in a small river system. Sewage treatment plant effluents and the receiving waters of the river Swist were monitored in 9 dry weather sampling campaigns (precipitation < 1 mm on the sampling day itself and <5 mm total precipitation two days before the sampling) during different seasons over a period of 3 years. With the results gained through monitoring, mass balances have been calculated to assess fate in the river. With the DWA Water Quality Model, OMP concentrations in the river were successfully simulated with OMP characteristics gained through literature studies. No removal was determined for 1-H benzotriazole and carbamazepine, whereas diclofenac showed removal that coincided with light intensity. Moreover, modelling based on light sensitivity of diclofenac also suggested relevant degradation at natural light conditions. These two approaches suggest removal by photodegradation. The highest removal in the river was detected for galaxolide, presumably due to volatilisation, sorption and biodegradation. Furthermore, short-term concentration variability in the river was determined, showing that daily concentration patterns are influenced by dynamics of sewage treatment plant effluent volumes and removal processes in the river.

Retention soil filters (RSFs) are vertical flow constructed wetlands. They are mainly used for the treatment of combined sewer overflow or stormwater, and not operated during dry weather conditions. However, RSFs have been successfully tested as continuous post treatment for sewage treatment plant effluents. In this paper we present a new approach, namely dual usage of the retention soil filter. During dry weather the RSF is used for the polishing treatment of sewage treatment plant effluent and during overflow events, the retention soil filter treats the combined sewer overflow. This study was conducted at two pilot RSFs that were fed with sewage treatment effluent for four years. Removal of TOC, DOC, nutrients and 21 organic micropollutants was determined during six months at different sequences of regular effluent and overflow treatment conditions. TOC, DOC and nutrients, appearing in high concentration in combined sewer overflow, were effectively removed, and metformin and caffeine micropollutants showed >99% removal. Residues from this combined sewer treatment that were sorbed on filter material or stored in pore water were washed out directly after treatment when STP effluent infiltration was initiated. This effect declined within 20 h after combined sewer overflow treatment. Dry periods of 18 h between combined sewer and sewage treatment plant effluent feeding counteracted the wash out effects. The highest removal efficiency was found in the beginning of the feeding time of 28 h, indicating that shorter feeding cycles enhance the overall efficiency of the RSF. Finally, the results show that a single RSF system can successfully reduce emissions of TOC, DOC, nutrients and micropollutants to surface waters from two different emission pathways, i.e. from regular treated effluents and storm related sewer overflows. In conclusion, the dual usage of RSF is a promising approach and ready for upscaling and implementation.

Point sources such as wastewater treatment plants (WWTP), combined sewer overflows (CSO) and separate sewer outlets (SSO) are acknowledged to be major pathways for pollutants to enter surface water. As response, retention soil filters (RSF) have been installed among others in the Erft river catchment area over the past two decades to treat outflows of combined sewer systems and rainwater from separate sewer systems. Studies conducted on several of these RSFs have shown that besides reducing solids by filtration, RSFs have good chemical and biological cleaning capacities for a variety of parameters. Concentrations of both nutrients and heavy metals are reduced. Numerous micropollutants such as pharmaceuticals, pesticides and industrial compounds as well as faecal bacteria are eliminated at high rates. With this background a new type of RSF (RSFplus) has been designed for the flexible treatment of WWTP effluent and CSO. The RSFplus treats CSO during rain events. During dry weather periods, the RSFplus is used for polishing WWTP effluent. The RSFplus is divided into three segments which are fed alternately to guarantee aerobic conditions and is equipped with innovative distribution channels to ensure homogeneous feeding. Granulated activated carbon is used as an additive for the filter medium for advanced treatment. The effectiveness of WWTP effluent polishing and reliability of operational parameters have already been tested for 2.5 years on a pilot scale. The first full-scale demonstration site will be built in 2017 at the WWTP Rheinbach in North Rhine-Westphalia (Germany).

Retention soil filters (RSFs) are a specific form of vertical flow constructed wetlands for the treatment of rain water and/or wastewater. We have tested 3 pilot RSFs to investigate removal of dissolved organic carbon (DOC) and 14 different organic micropollutants (OMPs) from the effluent of a large scale sewage treatment plant (STP). Two of them were operated as conventional RSF with material (sand with CaCO3 and organic matter) from two different full-scale RSFs. The third pilot RSF contained filter material (sand with CaCO3) with additional biochar in the upper layer (0–10 cm) and granulated activated carbon (GAC) in the lower layer (60–90 cm). The filters were planted with Phragmites australis. The RSFs were operated and monitored for 3 years, and water samples were taken regularly at inflow, outflows and in 3 depths within the filters. In total 523 samples were taken. In the conventional RSF, best median removal was detected for galaxolide, diclofenac 4-hydroxy, metoprolol and clarithromycin (75–79%). No removal was seen for sulfamethoxazole and carbamazepine. The DOC and OMP removal in the conventional RSFs was best in the upper layer with highest organic matter content, increased in time over the three years of operation and also with extended contact time. In the effluent of the RSF with GAC, 10 out of the 14 OMPs could not be detected; 4 OMPs were detected, but only metformin with removal < 80%, thus showing a more efficient removal than the conventional RSF. A decrease in DOC removal was detected in the GAC layer (>88% to 60%) over the 2.5 years of operation. Biochar was most effective in OMP removal in the first operational year. It can be concluded that the increasing removal efficiency of the conventional RSF material – also present in the RSF with biochar and GAC – might mitigate the reduced efficiency of the sorbent additives biochar and GAC. This enables to extend the operational lifetime of the filters with acceptable removal rates. Finally, our study demonstrates that an RSF with GAC shows an enhanced removal of OMPs, which is a suitable post-treatment step for STPs.

A study was conducted in which the effluent at four small to medium sized sewage treatment plants (STP) in North Rhine-Westphalia, Germany was monitored for three pharmaceutical compounds (carbamazepine, diclofenac, metoprolol) over a period of four years. Grab sampling and auto sampling campaigns were accomplished with respect to various weather conditions in the catchment area. Flow volumes and hydraulic retention times (HRT) from various sampling dates which provide information on processes causing emission changes were additionally taken into account. Monitoring results showed that concentration scattering in the effluent is related to HRT in the sewage treatment plants. Dilution effects following rain events in the catchment area were analysed for the three investigated substances. Short-term emission changes explained by dilution only could be well determined by the mathematical relation between discharge and concentration, and for carbamazepine to be solely determined by the dilution effects at all HRTs. For metoprolol, a clear decrease in concentrations was observed at HRTs above 80 h, and a significant contribution of biodegradation was supported by independent biodegradation tests. For three out of the four STPs, a decrease in concentrations of diclofenac was observed at hydraulic retention times above 80 h, indicating removal, whereas the relationship between concentration and HRT of the other STP could be explained by dilution only. The study shows that emissions can vary with weather conditions, hampering the assessment of emissions and estimation of concentrations in surface waters from generic removal rates only. Furthermore, it illustrates the importance of HRT of rather stable substances in wastewater treatment.

Elevated concentrations of trifluoroacetate (TFA) of more than 100 mu g/L in a major German river led to the occurrence of more than 20 mu g/L TFA in bank filtration based tap waters. Several spatially resolved monitoring programs were conducted and discharges from an industrial company were identified as the point source of TFA contamination. Treatment options for TFA removal were investigated at full-scale waterworks and in laboratory batch tests. Commonly applied techniques like ozonation or granulated activated carbon filtration are inappropriate for TFA removal, whereas TFA was partly removed by ion exchange and completely retained by reverse osmosis. Further investigations identified wastewater treatment plants (WWTPs) as additional TFA dischargers into the aquatic environment. TFA was neither removed by biological wastewater treatment, nor by a retention soil filter used for the treatment of combined sewer overflows. WWTP influents can even bear a TFA formation potential, when appropriate CF3-containing precursors are present. Biological degradation and ozonation batch experiments with chemicals of different classes (flurtamone, fluopyram, tembotrione, fiufenacet, fluoxetine, sitagliptine and 4:2 fluorotelomer sulfonate) proved that there are yet overlooked sources and pathways of TFA, which need to be addressed in the future. (C) 2017 Elsevier Ltd. All rights reserved.

A multidisciplinary research project series has sought to identify and better understand multiple hygienic–microbiological and chemical contaminations from both point sources and diffuse pollution to contribute to the improvement in surface water quality. In the catchment area of the river Swist (Germany), municipal sewage treatment plants were investigated, followed by event-based investigation of combined sewer overflows, rainwater retention basins and diffuse pollution by surface and subsurface run-off as well as drain pipes. Recently, retention soil filters installed between stormwater storage basins and receiving surface waters in order to provide further treatment of combined sewer overflows were investigated. Geographical information system analysis helped to examine the data in their temporal and spatial dimensions. A model for calculating microbial and chemical loads within a catchment area was developed (“Swistbox”) which provides an efficient tool for risk assessment. Nearly two decades of investigation has demonstrated that several elements of the landscape’s water balance account for surface water pollution from both diffuse and point sources. Depending on land cover characteristics, wastewater technology and the proportion of wastewater as compared to total river water flow, a source can vary in its importance for the catchment area. The findings can be applied for sustainable and health-sensitive catchment management in relation to recreational or agricultural water use as well as ecological aspects.

Micropollutant pathways were studied for the Swist river basin (Western Germany). The aim was to verify the effectiveness of a monitoring approach to detect micropollutants entering the river. In a separate sewer system, water was frequently found to be contaminated with micropollutants. Improper connections of sewage canals to the stormwater network seemed to be the cause of pollution. Wastewater treatment plants (WWTPs) exerted the largest influence on micropollutants for the receiving river. During a flu outbreak, antibiotics in the Swist stemming from WWTPs increased remarkably. Elevated levels of pharmaceuticals were measured in discharges from a combined sewer overflow (CSO). The study showed that the pharmaceutical load of a CSO was significantly reduced by advanced treatment with a retention soil filter. Painkillers, an anticonvulsant and beta blockers were the most often detected pharmaceuticals in the sewage of urban areas. Herbicides, flame retardants and industrial compounds were also observed frequently. On cropland, Chloridazon and Terbuthylazine compounds were often found in landscape runoff. Fungicides and insecticides were the most frequent positive findings in runoff from orchards. The paper shows that a coherent approach to collecting valid information regarding micropollutants and to addressing relevant pathways as a basis for appropriate management strategies could be established.