On-site treatment of hospital wastewater in a full-scale treatment plant in Germany: SARS-CoV-2 and treatment performance.

The separate, advanced treatment of hospital wastewater might be a promising approach to prevent the dissemination of residual compounds of high environmental concern, like pharmaceuticals, viruses and pathogenic microorganisms. This study investigates the performance of a full-scale, on-site treatment plant, consisting of a membrane bioreactor and a subsequent ozonation, at a German hospital. We analysed the elimination of pharmaceutical residues, microbiological parameters and SARS-CoV-2 RNA fragments. Additionally, we conducted an orienting study on the practicability of implementing targeted wastewater monitoring at a hospital. Our results demonstrate that after 10 years of stable operation, the treatment plant works highly efficiently regarding the elimination of pharmaceuticals and bacterial indicators. Elimination rates for pharmaceutical substances were above 90%, and log reductions of up to 6 log10 units for microbiological parameters were achieved. SARS-CoV-2 RNA could be detected and quantified in the influent but not in the effluent. The RNA load in the raw wastewater showed good correspondence with COVID-19 case numbers in the hospital. We showed that the full-scale on-site treatment of hospital wastewater is technically feasible and contributes to sustainable hospital effluent management and that monitoring biological markers on the building level might be a useful complementary tool for disease surveillance.

Implementation of a Pilot-Scale Biotrickling Filtration Process for Biogas Desulfurization under Anoxic Conditions Using Agricultural Digestate as Trickling Liquid.

A pilot-scale biotrickling filter (BTF) was operated in counter-current flow mode under anoxic conditions, using diluted agricultural digestate as inoculum and as the recirculation medium for the nutrient source. The process was tested on-site at an agricultural fermentation plant, where real biogas was used. The pilot plant was therefore exposed to real process-related fluctuations. The purpose of this research was to attest the validity of the filtration process for use at an industrial-scale by operating the pilot plant under realistic conditions. Neither the use of agricultural digestate as trickling liquid and nor a BTF of this scale have previously been reported in the literature. The pilot plant was operated for 149 days. The highest inlet load was 8.5 gS-H2Sm-3h-1 with a corresponding removal efficiency of 99.2%. The pH remained between 7.5 and 4.6 without any regulation throughout the complete experimental phase. The analysis of the microbial community showed that both anaerobic and anoxic bacteria can adapt to the fluctuating operating conditions and coexist simultaneously, thus contributing to the robustness of the process. The operation of an anoxic BTF with agricultural digestate as the trickling liquid proved to be viable for industrial-scale use.

Improvement of wastewater and water quality via a full-scale ozonation plant? - A comprehensive analysis of the endocrine potential using effect-based methods.

Micropollutants (MPs), especially endocrine disrupting compounds (EDCs), are mainly released from WWTPs into surface water bodies and can subsequently lead to adverse effects in biota. Treatment with ozone proved to be a suitable method for eliminating such MPs. This method was implemented at the WWTP Aachen-Soers by commissioning the largest full-scale ozonation plant in Europe at the moment. Recently, effect-based methods (EBMs) have been successfully proved for compliance monitoring, e.g. estrogenic compounds. Therefore, the impact of ozone treatment on endocrine potential (agonistic and antagonistic) of treated wastewater was investigated using the ERα- and AR CALUX assays. Additionally, the impact on the receiving stream and a potential preload of the water body was assessed. Therefore, the current study could deal as a case study for small rivers being highly impacted by WWTPs. The estrogenic potential was nearly fully eliminated after ozone treatment. Contrary, the antagonistic (anti-estrogenic and anti-androgenic) potential did not show a clear elimination pattern after ozone treatment independent of the applied ozone dosage and control system. Therefore, further investigations are required regarding the antagonistic potential. Additionally, preloading of the receiving stream was found during the study period. One significant impact is a rain overflow basin (ROB) located upstream of the WWTP effluent. The highest endocrine potential was found after a ROB overflow (2.7 ng EEQ/L, 2.4 µg TMX-EQ/L, 104 µg FLU-EQ/L), suggesting that such runoff events after a heavy rainfall may act as a driver of endocrine loading to the water body. This manuscript contributes significantly to the basic understanding of the efficiency of eliminating the endocrine potential of ozone treatment by, e.g., showing that there is a further need for improving the removal efficiency of antagonistic potential. Moreover, it highlights the need to include other point sources, such as ROBs, to assess polluted surface waters comprehensively.

Spatial multicriteria approach to support water resources management with multiple sources in semi-arid areas in Brazil.

Semi-arid regions often face severe drought events that reduce agricultural and livestock production. In recent years, some international studies have used multicriteria decision analysis (MCDA) approaches combined with geographic information systems (GIS-MCDA) to support decision-makers in assessing the suitability of agricultural land for irrigation in semi-arid regions. Unlike previous studies, which have only considered a single source of water for crop irrigation, this study proposes a GIS-MCDA approach that considers all potentially available local water sources (e.g., groundwater, surface water, and wastewater) as possible alternatives for better multisource water resource management (MWRM) in regions facing water shortages. The geospatial multicriteria evaluation implemented in this study considers a series of technical, environmental, and agricultural productivity criteria using the analytical hierarchy process (AHP) method. Three independent baseline maps were generated, showing the spatial distribution of suitable areas for crop irrigation for each considered water source in the studied area. Surface water, groundwater, and wastewater offered suitable crop irrigation for 83%, 70%, and 26% of the study area, respectively. Overlapping these areas produced a final map showing all the feasible areas for each crop irrigation alternative at the same time. The MWRM approach considering all water sources increased the coverage of suitable areas to be irrigated in the study area by 2.2%, 20.4%, and more than 225% compared to considering surface water, groundwater, and wastewater, respectively, independently. The GIS-MCDA framework proposed in this study provides better support for decision-makers and stakeholders, favouring a reduction in possible conflicts over water scarcity, the diversification of irrigated crops, and an improvement in the quality-quantitative management of water resources in semi-arid regions.

Removal of pharmaceuticals from wastewater of health care facilities.

Health care facilities can represent point sources for pharmaceutical residues in public sewer systems. Compared to general hospitals, more specialized health care facilities might also have a different pattern of medication. Therefore, the on-site treatment of wastewater from such facilities could be an effective strategy to reduce emissions into water bodies and was the aim of this study. Wastewater from three health care facilities (nursing home, clinic with orthopaedic focus, and psychiatric clinic) was treated in lab-scale and semi-industrial trials. Biological treatment was performed via an ultrafiltration membrane bioreactor (UF-MBR), after which adsorption onto granular activated carbon (using rapid-small-scale column tests GAC-RSSCT), ozonation and a UV/H2O2 advanced oxidation process (AOP) were tested and compared. The removal of 17 pharmaceutical compounds and drug metabolites from 9 drug classes (e.g. analgesics, antibiotics, anticonvulsants) was evaluated. Most of the measured OMP were detected with concentrations between 1,000 and 30,000 ng L-1 in the influent of the MBR. The UF-MBR provided an effective mechanical-biological cleaning of the wastewater, with micropollutant removal efficiencies between 0 and > 95%, making further treatment necessary to remove the micropollutants. Each combination of the UF-MBR with one of the three further treatments achieved removal efficiencies above 80% for most of the investigated substances, reducing many to below the quantification limit of 10 ng L-1. The results show the general suitability of combining the UF-MBR with either GAC-adsorption, ozonation or AOP for eliminating pharmaceutical residues. However, the AOP process has a significantly higher energy demand than the other two processes. Moreover, specific settings and dosages depend on the respective wastewater matrix.

Tool for selecting indicator substances to evaluate the impact of wastewater treatment plants on receiving water bodies.

The elimination of organic micropollutants (OMPs) from wastewater could in future become mandatory for operators of wastewater treatment plants (WWTPs). Indicator substances are a great help and a cost-efficient way in monitoring the pollution of water bodies with OMPs caused by the discharge of WWTPs. However, with the still increasing number of OMPs in our environment, the selection of suitable indicator substances presents a challenge. A concept was developed to help identify representative indicator substances. The derived indicator substances are not only used to assess water pollution, but can also be used to calculate elimination efficiencies of WWTPs. In the present investigations, the indicator substances were used to evaluate the reduction of OMPs in the water body on the basis of the expansion of a WWTP with an ozonation plant. The transferability of the tool was verified with a second WWTP. Furthermore, the impact of the number of measurements was analysed via statistical combinatorics. With the tool, 36 substances were classified, leading to the identification of 9 suggested indicator substances. Among them ibuprofen and diclofenac attracted attention due to their ecotoxicological relevance. Detailed data analyses were carried out using principal component analysis (PCA) and loads.

Assessing the role of microbial communities in the performance of constructed wetlands used to treat combined sewer overflows.

Combined sewer overflows are contaminated with various micropollutants which pose risk to both environmental and human health. Some micropollutants, such as carbamazepine and sulfamethoxazole, are very persistent and difficult to remove from wastewater. Event loaded vertical-flow constructed wetlands (retention soil filters; RSFs) have proven to be effective in the treatment of combined sewer overflows for a wide range of pollutants. However, little is known about how microbial communities contribute to the treatment efficiency, specifically to the reduction of micropollutants. To the best of our knowledge, this is the first study attempting to close this gap. Microbial communities in pilot-scale RSFs were investigated, which showed explicit grouping of metabolic activity at different filter depths with some differential abundance of identified genera. The highest microbial activity was found in the top layer of 0.75 m deep filters, whereas homogeneous activity dominated in a 0.50 m deep filter, indicating oxygen availability to be a limiting factor of the metabolic activity in RSFs. The removal efficiencies of all investigated organic trace substances were correlated to the utilization of specific carbon sources. Most notable is the correlation between the carbon source glucose-1-phosphate and the removal of metoprolol. The strongest correlations for other substances were the removal of diclofenac to the utilization of the carbohydrate i-erythritole; bisphenol A to carbohydrate α-d-lactose, and 1-H-benzotriazole to carbonic acid D-galacturonic acid. Those results are supported by positive correlations of specific microbial genera with both the utilization of the above mentioned carbon sources and the removal efficiency for the respective micropollutants. Most notable is correlation of Tetrasphaera and the removal of benzotriazole and diclofenac.

Elimination of micropollutants in four test-scale constructed wetlands treating combined sewer overflow: Influence of filtration layer height and feeding regime.

Municipal wastewater can contain large amounts of organic micropollutants. Some of these substances are harmful to the environment, even at low concentrations, e.g. when being discharged untreated into surface water bodies in case of combined sewer overflows (CSOs) during or after heavy rainfall events. Constructed wetlands can be very effective in treating CSOs. To date, there have only been few investigations about the retention of micropollutants using retention soil filters (RSFs), which basically are vertical flow constructed wetlands with an additional retention area. Thus, focus of this study was set on the interaction between dry periods, loading events, filter operation time, and the resulting removal of micropollutants originating from CSOs. The removal of 1-H-benzotriazole, carbamazepine, diclofenac, metoprolol, sulfamethoxazole and bisphenol A was examined in four test-scale RSFs. Removal efficiencies of approximately 70% were found for metoprolol. 1-H-benzotriazole, diclofenac and bisphenol A were removed moderately between 30 and 40%. For carbamazepine and sulfamethoxazole, negative retention rates were found. No significant correlations were found between removal efficiencies and the length of the antecedent dry period and/or filter operation time. However, the study showed that removal efficiencies depend strongly on respective inflow concentrations. Thickness of the filter layer seems to have an influence as well; does not lead to uniform results, though.

Combination of In Situ Feeding Rate Experiments and Chemical Body Burden Analysis to Assess the Influence of Micropollutants in Wastewater on Gammarus pulex.

Wastewater discharge is one of the main sources of micropollutants within the aquatic environment. To reduce the risks for the aquatic environment, the reduction of the chemical load of wastewater treatment plant effluent is critical. Based on this need, additional treatment methods, such as ozonation, are currently being tested in several wastewater treatment plants (WWTPs). In the present study, effects were investigated using in situ feeding experiments with Gammarus pulex and body burden analyses of frequently detected micropollutants which used a Quick Easy Cheap Effective Rugged and Safe (QuEChERS) multi-residue method to quantify internal concentrations in collected gammarids. Information obtained from these experiments complemented data from the chemical analysis of water samples and bioassays, which predominantly cover hydrophilic substances. When comparing up- and downstream feeding rates of Gammarus pulex for seven days, relative to the WWTPs, no significant acute effects were detected, although a slight trend of increased feeding rate downstream of the WWTP Aachen-Soers was observed. The chemical load released by the WWTP or at other points, or by diffuse sources, might be too low to lead to clear acute effects on G. pulex. However, some compounds found in wastewater are able to alter the microbial community on its leaves, leading to an increase in the feeding rate of G. pulex. Chemical analysis of internal concentrations of pollutants in the tissues of collected gammarids suggests a potential risk for chronic effects with the chemicals imidacloprid, thiacloprid, carbendazim, and 1H-benzotriazole when exceeding the critical toxic unit value of -3. This study has demonstrated that a combination of acute testing and measurement of the internal concentration of micropollutants that might lead to chronic effects is an efficient tool for investigating river systems, assuming all relevant factors (e.g., species or season) are taken into account.

Redox potential as a method to evaluate the performance of retention soil filters treating combined sewer overflows.

Retention soil filters (RSFs) protect water bodies from pollutant loads originating from combined sewer overflows (CSOs) by filtering the wastewater through a filter layer having a depth of 0.75 to 1 m. The microbiological processes in the filter material are influenced by the redox potential (Eh). This potential is a strong indicator of the prevailing environmental conditions and the possible type of microbial activity. Previous investigations of filter bodies have been confined to constructed wetlands (CWs) with regular intermittent wastewater inflow. Compared to CWs, RSFs are characterized by higher oxygen availability due to alternating operating and dry periods. This study aimed to determine the Eh in RSFs and investigate its influence on the removal efficiency for different substances. We established a conceptual model for the standard Eh curve following a loading event, and the variations to this standard in two depths and between treatments. Correlations were determined with a canonical correlation analysis between the pollutant removal of COD, ammonium, phosphorous, E. coli, somatic coliphages and diclofenac and the Eh. Although the removal efficiency is influenced by several additional operating factors such as the preceding dry period, filter age and the respective inflow concentrations, our results show that the Eh is an adequate approach to assess the removal efficiency of RSFs for these substances.

Reduction of micropollutants and bacteria in a constructed wetland for combined sewer overflow treatment after 7 and 10 years of operation.

Repeated investigations on constructed wetlands for the treatment of combined sewer overflows, also named bioretention filters or retention soil filters, are necessary to provide information on their long-term performance. In this study, a sampling campaign was conducted on micropollutants, indicator microorganisms and standard parameters ten years after such filters were in operation and three years after the first investigation; it revealed that the filters lost capacity to remove chemical substances with no or only slow biological degradability. This was the case e.g. for phosphate (decrease from 29 to 11%), diclofenac (67 to 34%) and TCPP (34% to negative reduction). They continued to remove easily degradable parameters such as COD (stable around 75%) stably. The indicator microorganisms Escherichia coli (1.1/0.8 log10), intestinal enterococci (1.3/0.8 log10) and somatic coliphages (0.6/1.0 log10) showed comparably low process variations given the difficulties in sampling and analysing microbial parameters representatively as well as given natural variations in microbial behaviour and growth. Additionally, for bisphenol A, we found a temperature-related difference of removal efficiencies: while in the cold months (winter), the removal was only 53% on average, it increased to 90% in the warm months (summer). As for the long-term prospective of retention soil filters, decision-makers need to identify the most important pollutants in a specific catchment area and adapt the filter design accordingly. If pollutants are targeted that lead to an exhausted filtration capacity, post treatment or the exchange of charged filter material is necessary. However, for easily biologically degradable substances, so far, there is no limit in their use.

Ozonation of valsartan: Structural elucidation and environmental properties of transformation products.

The pharmaceutical valsartan is classified as a trace organic compound and is released into wastewater from human consumption. Trace organic compounds are not completely removed during conventional wastewater treatment. In order to prevent their release into the aquatic environment, advanced wastewater treatment technologies such as ozonation are currently implemented. Ozonation leads to the formation of transformation products (TPs), which then enter the receiving waters. In the present work, laboratory-scale ozonation experiments of valsartan solutions were performed. The resulting TPs were analyzed by HPLC-MS and searched for using a non-targeted approach. Of the 51 compounds detected, 27 have tentative structural suggestions based on MS/MS experiments. Ozonation of valsartan does not lead to the formation of TPs with higher toxicity towards A. fischeri than the parent compound. According to QSAR-based environmental behavior estimations, most TPs reveal lower lipophilicity, increased biodegradability as well as decreased acute and chronic toxicities concerning fish, daphnia and algae compared to their parent compound valsartan.

Ozonation of nursing home wastewater pretreated in a membrane bioreactor.

Nursing home (NH) wastewater was pretreated in an ultrafiltration membrane bioreactor (MBR) and subsequently ozonated in a pilot plant in order to evaluate the elimination of pharmaceutically active compounds (PhACs). Dosing of the pre-treated wastewater with 5 mg ozone (O3) L-1 led to the elimination of >50% for nearly all investigated PhACs in the ozonation plant, whereas dosing 10 mg O3 L-1 increased elimination to >80%. A total hydraulic retention time of 12.8 min proved sufficient for PhAC elimination. Specific ozone consumption and influent dissolved organic carbon (DOC) (8.2-9.5 mg L-1) were in similar ranges for all three performed trials. Combining the MBR with subsequent ozonation at a dosage of 5 mg O3 L-1 achieved elimination of >90% and effluent concentrations below 250 ng L-1 for nearly all the investigated PhACs. Influent concentrations of the MBR were comparable to those found in municipal wastewater. Thus, the recommended dosage for PhAC elimination of 5 mg O3 L-1 (i.e. a specific consumption of 0.6 g O3*(g DOC)-1) is in the same range as for municipal wastewater. However, due to a smaller plant size, the specific costs for treating NH wastewater would significantly exceed those of treating municipal wastewater.

Reduction of bacteria and somatic coliphages in constructed wetlands for the treatment of combined sewer overflow (retention soil filters).

Combined sewer overflows (CSOs) introduce numerous pathogens from fecal contamination, such as bacteria and viruses, into surface waters, thus endangering human health. In Germany, retention soil filters (RSFs) treat CSOs at sensitive discharge points and can contribute to reducing these hygienically relevant microorganisms. In this study, we evaluated the extent of how dry period, series connection and filter layer thickness influence the reduction efficiency of RSFs for Escherichia coli (E. coli), intestinal enterococci (I. E.) and somatic coliphages. To accomplish this, we had four pilot scale RSFs built on a test field at the wastewater treatment plant Aachen-Soers. While two filters were replicates, the other two filters were installed in a series connection. Moreover, one filter had a thinner filtration layer than the other three. Between April 2015 and December 2016, the RSFs were loaded in 37 trials with pre-conditioned CSO after dry periods ranging from 4 to 40 days. During 17 trials, samples for microbial analysis were taken and analyzed. The series connection of two filters showed that the removal increases when two systems with a filter layer of the same height are operated in series. Since the microorganisms are exposed twice to the environmental conditions on the filter surface and in the upper filter layers, there is a greater chance for abiotic adsorption increase. The same effect could be shown when filters with different depths were compared: the removal efficiency increases as filter thickness increases. This study provides new evidence that regardless of seasonal effects and dry period, RSFs can improve hygienic situation significantly.

Performance of granular activated carbon to remove micropollutants from municipal wastewater-A meta-analysis of pilot- and large-scale studies.

For reducing organic micropollutants (MP) in municipal wastewater effluents, granular activated carbon (GAC) has been tested in various studies. We did systematic literature research and found 44 studies dealing with the adsorption of MPs (carbamazepine, diclofenac, sulfamethoxazole) from municipal wastewater on GAC in pilot- and large-scale plants. Within our meta-analysis we plot the bed volumes (BV [m3water/m3GAC]) until the breakthrough criterion of MP-BV20% was reached, dependent on potential relevant parameters (empty bed contact time EBCT, influent DOC DOC0 and manufacturing method). Moreover, we performed statistical tests (ANOVAs) to check the results for significance. Single adsorbers operating time differs i.e. by 2500% until breakthrough of diclofenac-BV20% was reached (800-20,000 BV). There was still elimination of the "very well/well" adsorbable MPs such as carbamazepine and diclofenac even when the equilibrium of DOC had already been reached. No strong statistical significance of EBCT and DOC0 on MP-BV20% could be found due to lack of data and the high heterogeneity of the studies using GAC of different qualities. In further studies, adsorbers should be operated ≫20,000 BV for exact calculation of breakthrough curves, and the following parameters should be recorded: selected MPs; DOC0; UVA254; EBCT; product name, manufacturing method and raw material of GAC; suspended solids (TSS); backwash interval; backwash program and pressure drop within adsorber. Based on our investigations we generally recommend using reactivated GAC to reduce the environmental impact and to carry out tests on pilot scale to collect reliable data for process design.

Improving the microbiological quality of the Ruhr River near Essen: comparing costs and effects for the reduction of Escherichia coli and intestinal enterococci.

After rain events in densely populated areas, combined sewer overflows (CSOs) can have severe health-related effects upon surface water quality, as well as diffuse overland runoff and wastewater treatment plants (WWTPs). All of these sources emit pathogens and fecal indicator bacteria into the surface water, which the EU Bathing Water Directive addresses by giving threshold values for the indicators Escherichia coli and intestinal enterococci. This study presents a comparison between 21 scenarios of costs for processes that reduce the load of Escherichia coli and intestinal enterococci into the Ruhr River during and shortly after rain events. The methods examined include UV irradiation for WWTPs, integrated sewer management and treatment of CSOs with vertical flow constructed wetlands or performic acid. For pollution by diffuse overland flow, we evaluated organizational measures. The treatment of only diffuse pollution shows merely a slight effect on intestinal enterococci, but none on Escherichia coli and hence, was not considered further. Combining all three CSO reduction methods with the irradiation of WWTP effluent provides the best simulation results in terms of reducing both indicator bacteria.

Energy demand for elimination of organic micropollutants in municipal wastewater treatment plants.

Organic micropollutants (OMP), e.g. pharmaceuticals and household/industrial chemicals, are not fully eliminated in state-of-the-art municipal wastewater treatment plants and can potentially harm the aquatic environment. Therefore, several pilot and large-scale investigations on the elimination of organic micropollutants have taken place in recent years. Based on the present findings, the most efficient treatment steps to eliminate organic micropollutants have proven to be ozonation, adsorption on powdered activated carbon (PAC), or filtration through granular activated carbon (GAC). Yet a further treatment step implies an increase in energy demand of the wastewater treatment plant, which has to be considered along with OMP elimination. To this aim, data on energy demand of ten large-scale municipal wastewater treatment plants (WWTP) with processes for OMP elimination was collected and analyzed. Moreover, calculations on energy demand beyond the WWTP for production and transport of ancillary materials were performed to assess the cumulative energy demand of the processes. An assessment of the greenhouse gas emissions of the processes was achieved, which shall facilitate future life cycle analyses. The results show that energy demand of ozonation at the wastewater treatment plant is dependent upon the ozone dosage and is significantly higher than energy demand of PAC addition or GAC filtration (2 to 4 times higher without consideration of delivery heads). Despite uncertainties regarding the energy demand for production of activated carbon, it could be shown that the cumulative energy demand of adsorption steps is significantly higher than the energy demand at the WWTP. Using reactivated GAC can lead to energy and greenhouse gas emissions savings compared to using fresh GAC/PAC. Moreover, energy demand is always plant-specific and depends on different factors (delivery heads, existing filtration or post-treatment etc.). Since processes for elimination of organic micropollutants are still in a developing phase, future optimization steps shall minimize their energy demand.

Reducing pathogens in combined sewer overflows using performic acid.

Combined sewer overflows contribute significantly to pathogen loads in surface water. Some chemical disinfectants such as chlorine have proved to reduce the levels of microorganisms even in complex matrices such as wastewater in combined sewer systems; however, some of them release toxic by-products into water bodies and increase costs of plant maintenance and repair. In this study, we determined if performic acid (PFA) disinfection units can be operated at decentralized treatment facilities and reduce bacteria, viruses, and protozoan parasites in combined sewer overflows (CSOs). The PFA dosing unit at the inflow of a CSO storage tank dosed a fixed flow volume into the inflowing stormwater and, thus, concentrations varied between approximately 12-24mgl-1. The results showed a reduction of most hygienically relevant bacteria with mean removal efficiencies of 1.8log10 for Aeromonas spp. and 3.1log10 for E. coli. For viruses, however, reduction was only observed for somatic coliphages with 2.7log10. In this setting, PFA does not seem to be suitable to remove e.g. protozoan parasites such as Giardia lamblia. In terms of operation, dosing the substance is uncritical in decentralized facilities, but the PFA needs too much time to react with pathogens after being dosed into the overflow of CSO storage tanks and before dilution with surface water in most facilities.

Developing an easy-to-apply model for identifying relevant pathogen pathways into surface waters used for recreational purposes.

Swimming in inner-city surface waters is popular in the warm season, but can have negative consequences such as gastro-intestinal, ear and skin infections. The pathogens causing these infections commonly enter surface waters via several point source discharges such as the effluents from wastewater treatment plants and sewer overflows, as well as through diffuse non-point sources such as surface runoff. Nonetheless, the recreational use of surface waters is attractive for residents. In order to save financial and organizational resources, local authorities need to estimate the most relevant pathways of pathogens into surface waters. In particular, when detailed data on a local scale are missing, this is quite difficult to achieve. For this reason, we have developed an easy-to-apply model using the example of Escherichia coli and intestinal enterococci as a first approach to the local situation, where missing data can be replaced by data from literature. The model was developed based on a case study of a river arm monitored in western Germany and will be generalized for future applications. Although the limits of the EU Bathing Water Directive are already fulfilled during dry weather days, we showed that the effluent of wastewater treatment plants and overland flow had the most relevant impact on the microbial surface water quality. On rainy weather days, combined sewer overflows are responsible for the highest microbial pollution loads. The results obtained in this study can help decision makers to focus on reducing the relevant pathogen sources within a catchment area.