Dynamics of Wastewater Effluent Contributions in Streams and

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Dynamics of wastewater effluent contributions in streams and impacts on drinking water supply via riverbank filtration in Germany – A national reconnaissance Sema Karakurt, Ludwig Schmid, Uwe Huebner, and Jörg E. Drewes Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b07216 • Publication Date (Web): 02 May 2019 Downloaded from http://pubs.acs.org on May 3, 2019

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Environmental Science & Technology

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Dynamics of wastewater effluent contributions in streams and impacts on

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drinking water supply via riverbank filtration in Germany – A national

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reconnaissance

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Sema Karakurt, Ludwig Schmid, Uwe Hübner, Jörg E. Drewes*

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Chair of Urban Water Systems Engineering, Technical University of Munich, Garching, Germany

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Abstract

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The discharge of wastewater effluents to a stream that is subsequently used for drinking

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water abstraction has been previously referred to as de facto water reuse. Where the abstraction

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of surface water for drinking water production occurs via induced bank filtration or aquifer

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additional site-specific factors should be considered to assess the impact of wastewater effluents

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on bank-filtered water. This study represents the first national reconnaissance to quantify

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wastewater effluent contributions in streams across Germany and consequences for indirect

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drinking water abstraction from these streams. An automated assessment using ArcGIS was

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conducted for river basins considering minimum and mean average discharge conditions of

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streams as well as discharge from more than 7,500 wastewater facilities. In urban areas, where

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the natural base discharge is low, wastewater effluent contributions greater than 30-50% were

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determined under mean minimum discharge conditions, which commonly prevail from May to

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September. A conceptual model was proposed to estimate critical bank filtrate shares resulting

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in exceedances of monitoring trigger levels for health-relevant chemicals as a universal

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qualitative assessment regarding the relevance of de facto reuse conditions in surface waters used

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for drinking water abstraction. This approach was validated using chemical monitoring data for

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three case study locations.

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1. Introduction

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Drinking water supply in many countries in central and western Europe heavily relies on

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indirect use of surface water via induced bank filtration (IBF) and aquifer recharge (AR).1,2 In

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Germany, production from IBF and AR accounts on average for 15% of the drinking water

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supplied nationwide3, but at the individual utility level this contribution can be in excess of 70%.4

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While relying on natural treatment processes during IBF and AR, microbial and chemical

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contaminants in surface water can be effectively attenuated during travel through the

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subsurface.1 In highly populated areas and where substantial natural base discharge is lacking,

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the quality of surface water can be highly affected by discharge of effluents of municipal

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wastewater treatment plants (WWTPs), industrial dischargers, as well as contributions from

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various non-point sources (e.g., drainage from agricultural areas, stormwater runoff, urban 1 ACS Paragon Plus Environment


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seepage). Increasing contributions of wastewater effluents to stream discharge will also result in

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an increase of the relative portion of wastewater-derived contaminants, such as pathogens and

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trace organic chemicals (TOrCs) in the water cycle.5–9 This is particularly relevant regarding

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persistent pathogens but also for poorly degradable and polar wastewater-derived chemicals,

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which could potentially make their way into drinking water wells.7,9 This situation will likely

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become more prevalent considering impacts from climate change resulting in more frequent or

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long-lasting low-discharge conditions in streams. Climate change not only adversely affects

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stream discharge and the relative contribution of wastewater effluents, but also impacts IBF

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performance as travel times and redox conditions in the subsurface can change with varying

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discharge conditions and temperatures.10–12

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The discharge of wastewater effluents to a stream that is subsequently used for drinking

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water abstraction has been previously referred to as unintended or de facto water reuse.13,14 In a

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US-wide study, Rice and Westerhoff (2015)13 revealed wastewater effluent impact on half of

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1,210 targeted drinking water treatment plants (DWTP) practicing surface water treatment and

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serving more than 10,000 inhabitants under mean annual discharge (MAD) conditions. The

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effects of mean minimum annual discharge (MMAD) conditions were investigated for an

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additional 80 DWTPs, where 40% of the utilities were characterized by more than 50%

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wastewater effluent in their raw water supply.13 Switzerland engaged in a nationwide study to

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assess the presence of wastewater-derived chemicals in receiving streams, and revealed

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wastewater effluent contributions of more than 10-50% under low discharge conditions,

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particularly in small and medium-sized rivers.15 In order to minimize impacts on aquatic life and

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downstream drinking water abstraction, this situation recently triggered upgrades with either

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activated carbon filtration or ozone for 100 out of 700 conventional WWTPs across

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Switzerland.15,16 A regional study in Catalonia, Spain, analyzed wastewater effluent contributions

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to the River Llobregat, a source of drinking water supply for the metropolitan area of Barcelona,

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and reported between 12 to 25 % wastewater effluent contributions in raw water supplies for

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three different years with varying annual discharges.17 Wang et al. (2017) conducted the first

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assessment on wastewater effluent discharges at 11 gauging stations within the Yangtze River

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watershed, China, supporting more than 1/15th of the world’s population.18 The wastewater

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effluent contributions under low discharge conditions increased from 8% to 14% nearby

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Shanghai between 1998 and 2014 due to an increase in wastewater discharges and decrease in

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streamflow.18 A similar study at regional scale have been reported, which commonly quantify the

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degree of impact from wastewater effluent discharge on stream water quality by simple flow

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balances.19 While these studies point to the need to understanding the relevance of discharge of

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municipal wastewater effluents on drinking water supplies, quantifying what degree of de facto

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reuse actually constitutes a potential threat to human health is lacking. In addition, these studies 2 ACS Paragon Plus Environment

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did not consider the efficacy of water treatment processes employed at a drinking water utility

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or attenuation processes occurring during IBF or AR, where surface water is used indirectly.

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Quantifying the impact of wastewater effluents on streams that are subsequently used indirectly

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via IBF or AR may become complex as it requires a site-specific assessment of stream discharge

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dynamics, relative contributions of augmented groundwater in a production well, and a

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quantitative assessment of attenuation processes in the subsurface. Given these challenges, water

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utilities and health officials are looking for guidance on how indirect drinking water abstraction

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from impaired surface waters via IBF or AR can be adequately managed under shifting climate

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and discharge conditions.

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De facto potable reuse becomes relevant when health relevant chemicals exceed their

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toxicologically relevant values, defined as monitoring trigger levels (MTLs), in bank filtrate where

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subsequent drinking water treatment only utilizes conventional treatment processes (i.e.,

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aeration, filtration, disinfection). We hypothesize that the exceedance of MTLs in bank filtered

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raw water supplies occurs in several river basins in Germany due to high wastewater effluent

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contributions during extended time periods. This nation-wide, comprehensive study is the first

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to quantify the relative contribution of wastewater effluents to streams across Germany under

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varying discharge conditions. It also provides a conceptual impact assessment for downstream

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drinking water abstraction via IBF or AR, validated by three case studies. The developed approach

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can guide water utilities and regulators in assessing the relevance of de facto reuse and identifying

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sites where comprehensive follow-up monitoring programs as well as potential mitigation

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actions are warranted.

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2. Materials and methods

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2.1. Data acquisition and calculation of treated effluent contribution in rivers Modeling approach

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Within the framework of the European Directive 91/271/EEC, the federal states of Germany

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are required to report operational and spatial data of WWTPs with a population equivalent (PE)

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capacity of more than 2,000 to the German Environment Agency (Thru.de), which subsequently

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reports this information to the European Commission’s data base ‘Waterbase – Urban wastewater

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treatment directive (UWWTD)’.20,21 In addition, discharge volumes of WWTPs with a capacity of

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50-2,000 PE were provided by individual federal states including the states of Baden-

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Württemberg, Berlin, Brandenburg, Hesse, North Rhine-Westphalia, Rhineland-Palatinate, and

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Saxony. Year and source of WWTPs discharge data as well as the capacity of WWTPs included for

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different federal states can be found in SI-Table 1. For the federal state of Bavaria, instead of direct

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discharge volumes of WWTPs with capacities of 50-2,000 PE, discharge volumes derived from 3 ACS Paragon Plus Environment


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reported design capacities were considered in this study. For rivers with cross-boundary

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catchments (i.e., Danube, Rhine, Maas, Issel, Elbe and Oder rivers), data from WWTPs >2,000 PE

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of neighboring countries were considered in the model using the Waterbase – UWWTD

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database.21 Through this extensive data collection, a comprehensive database considering

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wastewater contributions from 7,550 WWTPs across Germany was compiled for this study.

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Long-term MAD and MMAD from gauging stations over multiple decades were gathered to

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assess the dynamics of WWTP effluent contributions under MAD and MMAD conditions.22–24

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Discharge data from two years (2003 and 2005) were chosen to illustrate representative dry and

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average years.

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An ArcGIS model (Esri, Kranzberg, Germany) using spatial and operational WWTP data (i.e.,

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location of the WWTP, point and amount of discharge, capacity and level of treatment) and stream

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gauging station runoff data was generated to perform automated assessments of relative

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contributions from treated wastewater effluents to rivers. The locations of WWTP discharge and

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gauging station (i.e. nodes) were spatially linked to hydrological data of the German river network

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at a scale of 1:250,000 (DLM250).25 Flow direction estimation and network analysis for the

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streams were performed using a geometric network. The wastewater effluents upstream of a

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river segment were cumulatively calculated and assigned to a specific gauging station. The

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percentage of wastewater effluent contributions (𝑊𝑊𝑒𝑓𝑓𝑙𝑢𝑒𝑛𝑡 [%]) at each individual gauging

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station was subsequently determined by calculating the ratio of the total discharge rate of

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upstream WWTPs (∑QWW effluent) to the MAD and MMAD data at the respective gauging station

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(Qgauging station) using equation 1, which was coded into GIS using Python scripts. For rivers of

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stream order 1-5 (indicating level of branching in a river stream) with more than two gauging

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stations, the MAD or MMAD along a river were first determined by linear interpolation, and the

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relative wastewater effluent contributions were subsequently calculated for these fictitious

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gauging stations with varying discharge conditions in an automated assessment using equation 1.

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𝑊𝑊𝑒𝑓𝑓𝑙𝑢𝑒𝑛𝑡 [%] =

𝑄 𝑊𝑊 𝑒𝑓𝑓𝑙𝑢𝑒𝑛𝑡 𝑄 𝑔𝑎𝑢𝑔𝑖𝑛𝑔 𝑠𝑡𝑎𝑡𝑖𝑜𝑛

∙ 100%

[1]

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This nationwide study was limited to the arithmetic mean of annual discharges from

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municipal WWTPs and did not include other anthropogenic sources of contamination, such as

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direct discharge of industrial WWTPs, agricultural drainage, and combined sewer and

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stormwater overflows. However, it has to be noted that the vast majority of industrial complexes

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in Germany is included into our study, since they discharge their wastewater after partial

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treatment onsite into a public sewer (indirect industrial discharge), which then is subject to

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municipal wastewater treatment prior to discharge to a stream. An assessment on the relevance

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of direct industrial discharges can be found in the supplementary information. To enable the 4 ACS Paragon Plus Environment

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consideration of the chemical loads (i.e. herbicides) from agricultural drainages, more spatio-

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temporal water quality data as well as models for accurate predictions are needed.26 In addition,

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complete mixing at the point of discharge of the treated wastewater into the receiving river was

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assumed.

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The relative wastewater effluent contributions of the ArcGIS model determined for a given

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gauging station were validated using water quality monitoring data of the wastewater-derived

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conservative indicator chemical for select sites at the river Main (equation 2). Where the

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𝐶𝑟𝑖𝑣𝑒𝑟 𝑖𝑛𝑑𝑖𝑐𝑎𝑡𝑜𝑟 and the 𝐶𝑊𝑊 𝑒𝑓𝑓𝑙𝑢𝑒𝑛𝑡 𝑖𝑛𝑑𝑖𝑐𝑎𝑡𝑜𝑟 are the indicator chemical concentrations at the

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gauging stations and the wastewater effluent, respectively. These sites and indicator chemical

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carbamazepine were chosen for this assessment due to data availability provided by local water

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utilities and regulatory agencies.27

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𝑊𝑊𝑒𝑓𝑓𝑙𝑢𝑒𝑛𝑡 [%] =

𝐶𝑟𝑖𝑣𝑒𝑟 𝑖𝑛𝑑𝑖𝑐𝑎𝑡𝑜𝑟 𝐶𝑊𝑊 𝑒𝑓𝑓𝑙𝑢𝑒𝑛𝑡 𝑖𝑛𝑑𝑖𝑐𝑎𝑡𝑜𝑟

∙ 100%

[2]

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If the secondary effluent is subject to advanced wastewater treatment prior to discharge (i.e.,

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activated carbon or ozone treatment), indicator chemicals may no longer be present at levels

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enabling them to serve as wastewater tracers.28 For this reason, WWTPs employing advanced

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wastewater treatment processes were indicated in the model, to avoid any bias while examining

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the feasibility of our method. As only 24 WWTPs out of 7,550 facilities across Germany are

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currently employing advanced wastewater treatment processes, their discharge did not result in

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a substantial effect on validation of the predicted wastewater contributions.

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Between 2014 and 2016, carbamazepine exhibited consistent average (70-80 ng/L) and

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maximum concentrations (110-140 ng/L) across the entire stretch of the river Main.29 Monitoring

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data of the indicator chemicals, however, represent grab samples from river streams at different

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times of the year. Thus, samples did not hydraulically correspond with wastewater effluent

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samples taken.

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2.2. Determination of the degree of impact on drinking water abstraction

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A nationwide assessment of the impact of wastewater derived compounds on drinking water

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supply is hindered by the fact that national or federal state DWTP databases on the origin and

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quality of the raw water in Germany are lacking. Thus, a conceptual approach to estimate the

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relevance of elevated wastewater effluent contributions in rivers, coupled with the percent bank

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filtrate in raw water was developed. Conservative wastewater-derived chemicals, present at

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elevated concentrations in European wastewater effluents, characterized by a relatively high

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subsurface mobility and exhibiting persistent behavior under aerobic-anoxic conditions, were

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selected as indicator chemicals for this assessment.30,31 Among the conservative wastewater 5 ACS Paragon Plus Environment


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indicator chemicals, potentially health relevant compounds were chosen if their measured

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environmental concentrations (MEC) in wastewater effluent was greater than their MTL32, i.e.

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MEC/MTL>1, (carbamazepine, valsartanic acid and oxypurinol) referring to the concept adopted

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by the State of California for monitoring purpose.33 For wastewater effluent contribution

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scenarios ranging from 0-100%, critical bank filtrate contributions (% 𝐵𝐹𝑐𝑟𝑖𝑡𝑖𝑐𝑎𝑙) in drinking

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water wells (i.e. raw water) were determined where MTLs of indicator chemicals (

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𝑀𝑇𝐿𝑖𝑛𝑑𝑖𝑐𝑎𝑡𝑜𝑟 𝑐ℎ𝑒𝑚𝑖𝑐𝑎𝑙) in raw water could be exceeded using equation 3. The critical bank filtrate

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contribution is assuming that the subsequent DWTP is relying only on conventional treatment

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processes (i.e., subsurface passage followed by aeration and granular media filtration). At

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locations where advanced treatment processes are employed at a DWTP (e.g., ozonation,

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activated carbon filtration), these processes might provide additional barriers to health-relevant

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chemicals and therefore additional margins of safety.

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Min. % 𝐵𝐹𝑐𝑟𝑖𝑡𝑖𝑐𝑎𝑙 =

𝑀𝑇𝐿𝑖𝑛𝑑𝑖𝑐𝑎𝑡𝑜𝑟 𝑐ℎ𝑒𝑚𝑖𝑐𝑎𝑙 % 𝑊𝑊𝑒𝑓𝑓𝑙𝑢𝑒𝑛𝑡 ∗ 𝐶𝑊𝑊 𝑒𝑓𝑓𝑙𝑢𝑒𝑛𝑡 𝑖𝑛𝑑𝑖𝑐𝑎𝑡𝑜𝑟

∗ 100%

[3]

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To validate the proposed approach in order to qualify de facto reuse conditions, this concept

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was applied at three case study locations practicing IBF for drinking water abstraction. The

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selected watersheds of the Havel, Rhine and Main rivers are substantially affected by wastewater

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effluent contributions.

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3. Results and discussion

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3.1. Dynamic of wastewater effluent contributions to rivers during different discharge conditions

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A potential impairment of river stream and bank filtrate quality may occur especially during

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low discharge regimes over a longer period, where the relative contribution from wastewater

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effluents in surface waters increases.18,34 Thus, long-term MMAD and MAD recordings were

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chosen after considering 2,344 gauging stations across Germany to illustrate the effect of

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wastewater effluent contributions during changing discharge conditions on river streams. The

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prevalence of MMAD and MAD scenarios for the Rhine, Main and Neckar rivers were compared

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with daily discharges of years (2003 and 2005) representing typical low and average annual

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rainfall conditions, respectively. These results are depicted in Figure 1 for one representative

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gauging station for each river.

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These results reveal that daily discharges were 63-83% lower than MAD values during both

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dry and average years (2003 and 2005) and reflect MMAD conditions for each of the three gauging

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stations. This comparison illustrates that low discharge conditions prevail for almost six months

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from spring into the summer and fall when water demand is the highest, a situation that may

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become more prevalent in the future considering projected climate change impacts.

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Figure 1: Comparison of MMAD and MAD hydrological characteristic values with daily average discharges

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The ArcGIS model deriving wastewater effluent contributions in the Main river was validated

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by concentrations of the wastewater indicator chemical carbamazepine, determined both in the

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wastewater effluent and along the river. Grab samples were taken at nine gauging stations along

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the Main river during March 201727. Wastewater effluent contributions calculated by

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carbamazepine concentrations more closely follow the distribution of MMAD conditions (average

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MMAD-CBZ= 4%±4%) than MAD conditions (average CBZ-MAD= 15 %±5%) (Figure 2).

during dry (2003) and average (2005) representative years for three gauging stations of the Rhine (at R), Main (at M) and Neckar (at N) rivers.23



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Figure 2: Comparison of wastewater effluent contribution (secondary axis) from GIS model under MMAD

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Given the prevalence of low discharge conditions, wastewater effluent contributions during

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MMAD conditions were determined and depicted for all rivers across Germany (Figure 3-a).

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Based on the results of this study, wastewater effluent contributions of more than 10-20% during

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MMAD conditions dominate in a large number of river basins (Figure 3-b). For more than 40% of

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their gauging stations, the rivers Neckar, Ems, Main, and tributaries of the lower and middle Rhine

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exhibit wastewater effluent contributions of more than 20-30%. During MAD conditions,

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however, the contributions from wastewater effluents vary only between 0-5% for more than

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50% of the gauging stations nationwide, except for the Neckar river basin (Figure 3-c).

(black dots with dashed line) and MAD conditions (black dots with solid line) with dilution calculation using carbamazepine concentrations (grey dots with dashed line). Carbamazepine point samples were measured in wastewater effluents (2010)35 and the Main river (2016)27.

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The impact of wastewater effluent contributions can be considerably less for locations where

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the natural discharge is high. As an example, the tributaries of the Danube river originating from

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the alpine foreland (i.e., Iller: 8-54 m3/s, Lech: 49-113 m3/s, and Isar: 95-174 m3/s under MMAD-

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MAD conditions) dominate the natural discharge of the Danube river and are characterized by

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wastewater effluent contributions of less than 10-20% under MMAD conditions. Thus, the

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confluence of the Iller river results in the dilution of wastewater effluent contributions from 30-

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50% (at gauging station Kirchen-Hausen) to 10-20% (Neu-Ulm) in the river Danube (SI-Figure 1,

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Supplemental Information). Another example is the watershed of the middle and lower Rhine

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river, whose tributaries are dominated by wastewater effluent contributions of more than 50%

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under MMAD conditions. However, wastewater effluent contributions in the receiving middle and 8 ACS Paragon Plus Environment

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lower Rhine river vary only between 10-20% and in the upper Rhine river of less than 5-10% due

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to a high natural discharge (for both MMAD and MAD conditions) of (SI-Figure 2). On the other

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hand, rivers originating in the central uplands and the north German plain (such as Ems, Ruhr,

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Havel, Neckar and Main rivers) are characterized by lower discharges of typically less than 20 to

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90 m3/s for MMAD conditions and 80 to 240 m3/s for MAD conditions, respectively. Furthermore,

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these rivers flow through highly urbanized areas, resulting in more than 30 % and for some in

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more than 50% wastewater effluent contributions during MMAD conditions (SI-Figure 3, Figure

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2 and Figure 3-a).

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The findings of this study reveal a high degree of wastewater impact on streams, which also

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serve as an important source water for drinking water abstraction, industrial usage or irrigation

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purposes, particularly in many urbanized areas across Germany. Moreover, high wastewater

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effluent contributions can impair the ecological and chemical state of surface water due to oxygen

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consumption, discharge of hazardous substances, and elevated amounts of nutrients, which might

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pose a higher risk to aquatic life.



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Figure 3: Map of nationwide wastewater effluent contributions under MMAD conditions (a) and share of gauging stations with relative wastewater effluent contributions for river basins under MMAD (b) and MAD (c) conditions.


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3.2. Relevance of elevated wastewater effluent contributions in streams used for drinking water supply

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The quality of bank filtrate at a given location depends not only on surface water quality, the

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extent of wastewater effluent contributions, and the level of wastewater treatment, but also on a

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large number of site-specific factors. These include location and type of wells, distance between

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the surface water and abstraction wells, relative contributions from landside groundwater, and

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hydro-biogeochemical factors such as hydraulic permeability, sediment conductivity, and

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prevailing redox conditions.36,37 Due to these multiple factors, generating a nationwide

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cumulative estimate of bank filtrate shares (i.e. contributions of bank filtrate to drinking water

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supply) and expected water qualities in drinking water abstraction wells without detailed

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information on the aforementioned factors or local water quality data, was not possible within

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the scope of this study. Further research is essential to generate relevant water quality data per

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catchment area, including the locations of DWTPs and site-specific hydrogeological factors.

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Instead, the conceptual approach to determine critical bank filtrate contributions developed in

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this study (see Section 2.2) was applied for three selected indicator chemicals: oxypurinol (OXY),

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valsartanic acid (VSA), and carbamazepine (CBZ). These compounds are highly persistent in the

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aqueous environment, originate from wastewater effluent, and occur at high concentrations in

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German and European rivers.30,31,38–40 An assessment of their toxicological relevance regarding

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human health protection (MTLs) has been provided by the German Environment Agency.29

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Critical bank filtrate shares in wells, in which the MTL values for each of the three indicator

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chemicals would be exceeded, were calculated for different wastewater effluent contributions

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ranging from 0-100% (Figure 4-left). Based on this conceptual approach, the MTL of oxypurinol

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exhibiting high average wastewater effluent concentrations would be exceeded in a scenario with

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only 5% bank filtrate and 60% wastewater effluent contribution in the stream (Figure 4-left). For

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carbamazepine, which exhibited lower wastewater effluent concentrations, MTL exceedances

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would occur when both the effluent contribution to the stream and the bank filtrate share were

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about 60% (Figure 4-left).

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This assessment using suitable indicator chemicals, known toxicological information, and the

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calculation of critical bank filtrate contributions in drinking water wells provides a universal

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qualitative approach for any location worldwide to qualify possible de facto reuse situations. With

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the assistance of this conceptual approach, possible hot spots of de facto reuse can be identified,

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if the site-specific data on indicator chemical concentrations in wastewater effluent and the

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percent wastewater effluent contribution in a river are known. A proposed workflow building

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upon the results of the ArcGIS model developed during this study (Figure 4-right) can be used by

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water utilities and regulators to identify sites where MTL exceedances could potentially occur, 11 ACS Paragon Plus Environment


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reducing the need for comprehensive monitoring campaigns for a large number of drinking water

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facilities and to engage in site-specific actions to reduce a potential impact on drinking water

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quality.

293 294 295 296

Figure 4: Projected benchmark of MTL exceedances for indicator chemicals OXY (MTL: 300 ng/L),

297 298

1,310 ng/L38 and OXY 9,830 ng/L31) are representing mean values, taken from literature. Guidance for water

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The conceptual approach was validated by site-specific indicator chemical measurements

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(i.e., oxypurinol and carbamazepine) for three different case studies located along the rivers

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Rhine, Havel and Main, which are affected by wastewater effluent contributions of 7 and 17%

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under MAD and 42 % MMAD conditions according to the ArcGIS model, respectively (Table 1).

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Wastewater effluent contributions were determined to be 10% based on locally measured

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chemical data in the river Rhine close to the DWTP-A Düsseldorf, where bank filtered water

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subsequently undergoes ozonation and activated carbon filtration. Contributions of surface water

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in the bank filtrate were determined to be 79% on average and did not result in MTL exceedance

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of carbamazepine. Furthermore, due to subsequent advanced treatment at the DWTP, MTL

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exceedances for indicators even with high wastewater effluent concentrations are not expected

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in the finished drinking water. At case study DWTP-B drinking water is abstracted at Lake Tegel,

310

Berlin via IBF, which serves drinking water with approximately 80% bank filtrate shares to 0.8

311

million inhabitants.4,41,42 MTL exceedances in their lake-impacted drinking water production

312

wells were projected for both carbamazepine (0.3 µg/L) and oxypurinol (1.8 µg/L) according to

313

site-specific measurements (Table 1). Supporting the findings of our conceptual approach, in

314

finished drinking water approximately 13-14% wastewater-derived sources were determined by

315

the Berlin Water Company for DWTP-B in 2016. Subsequently, the finished drinking water,

VSA (MTL: 300 ng/L) and CBZ (MTL: 300 ng/L) under different contributions of wastewater effluent in rivers (%) and bank filtrate in raw water scenarios (%) (left). WWTP effluent concentrations (CBZ 832 ng/L39, VSA utilities and regulators in case of indicator chemical MTL exceedance (right).


Page 13 of 22


316

composed of bank filtrate and landside groundwater, from DWTP-B contained mean valsartanic

317

acid (1 µg/L) and oxypurinol (0.4 µg/L) concentrations, which were above their MTLs (0.3

318

µg/L).41 This situation has triggered actions taken by Berlin Water Company to mitigate the

319

impacts of elevated wastewater contributions in streams in Berlin. The case study area DWTP-C

320

validates a scenario characterized by high wastewater effluent contributions (42 % MMAD) but

321

low bank filtrate shares (11 %), resulting in MTL exceedance of oxypurinol in bank filtrate by 500

322

ng/L as projected by the conceptual approach ().

323 324

Table 1: Validation of conceptual approach for case study areas Rhine, Havel and Main by indicator chemicals measurement data both in surface waters and in bank filtration. 𝑴𝒆𝒂𝒏 River & DWTP

Indicator

WW effluent

𝑪𝑾𝑾 𝒆𝒇𝒇𝒍𝒖𝒆𝒏𝒕

contribution in

IBF shares in wells* [%]

𝑪𝑩𝑭

[ ] 𝒏𝒈 𝑳

𝒏𝒈 ] 𝑳

River (GIS)

River*

CBZ

47835

7.4 (MAD)

9.8

78.7

37

Havel

CBZ

1,80043

32.8

100

300+

DWTP-B

OXY

9,83031

17.3

100

1,800+

OXY

9,83031

45.8

11

500

[ Rhine DWTP-A

Main DWTP-C

17 (MAD)

42 (MMAD)

*Calculations of the bank filtrate shares in wells and bank filtrate concentrations in Rhine-Düsseldorf and Main DWTP-C are based on locally measured confidential data from municipal utility of Düsseldorf and Bavarian Environmental Agency, 2018. Carbamazepine and oxypurinol concentrations from Lake Tegel are taken as 590 ng/L42 and 1,700 ng/L44, respectively. +Mean carbamazepine and oxypurinol concentrations in bank filtrate of DWTP-B, Havel, are based on the data from Hellauer et al. (2018).44

325

The findings of this study might also suggest a potential impact by microbial contaminants

326

(e.g. viruses) on the quality of bank filtered water under the influence of wastewater effluent

327

discharges. Due to lack of monitoring data and in particular information on travel time in the

328

subsurface, no conclusions on occurrence of the microbial contaminants during de facto reuse can

329

be drawn. However, drinking water facilities in Germany are required to comply with a 50-day

330

hydraulic retention time in the subsurface to assure proper inactivation of pathogens, i.e. the

331

microbial safety of raw water. However, where de facto reuse conditions (i.e. exceedance of

332

MTL’s) have been identified, follow-up studies should also include a comprehensive microbial

333

risk assessment.

334

4. Associated Content

335

Supplementary data associated with this article can be found in the online version. 13 ACS Paragon Plus Environment


336

5. Author Information

337

Corresponding Author:

338

*Phone: (+49) 89 289 13701; e-mail: [email protected]

339

Notes: The authors declare no competing financial interest.

340

Page 14 of 22

6. Acknowledgements

341

We would like to thank the German Environment Agency for funding this study (grant

342

number: 91 182) and the German Ministry of Education and Research (grant number:

343

02WAV1404A). Furthermore, we would like to thank Rolf Timmermann, Simone McCurdy and

344

Peter Schätzl (DHI-WASY) and Marian Bachmaier (TUM) for their support during the ArcGIS

345

model implementation.

346

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Figure 1: Comparison of MMAD and MAD hydrological characteristic values with daily average discharges during dry (2003) and average (2005) representative years for three gauging stations of the Rhine (at R), Main (at M) and Neckar (at N) rivers 63x34mm (300 x 300 DPI)

ACS Paragon Plus Environment


Figure 2: Comparison of wastewater effluent contribution (secondary axis) from GIS model under MMAD (black dots with dashed line) and MAD conditions (black dots with solid line) with dilution calculation using carbamazepine concentrations (grey dots with dashed line). Carbamazepine point samples were measured in wastewater effluents (2010)32 and the Main river (2017). 222x127mm (150 x 150 DPI)


Page 20 of 22

Page 21 of 22


Figure 3: Map of nationwide wastewater effluent contributions under MMAD conditions (a) and share of gauging stations with relative wastewater effluent contributions for river basins under MMAD (b) and MAD (c) conditions. 228x155mm (150 x 150 DPI)



Figure 4: Projected benchmark of MTL exceedances for indicator chemicals OXY (MTL: 300 ng/L), VSA (MTL: 300 ng/L) and CBZ (MTL: 300 ng/L) under different contributions of wastewater effluent in rivers (%) and bank filtrate in raw water scenarios (%) (left). WWTP effluent concentrations (CBZ 832 ng/L35, VSA 1,310 ng/L34 and OXY 9,830 ng/L28) are representing mean values, taken from literature. Guidance for water utilities and regulators in case of indicator chemical MTL exceedance (right). 342x153mm (120 x 120 DPI)


Page 22 of 22

Dynamics of Wastewater Effluent Contributions in Streams and

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