Infectious rain? Evaluation of human pathogen concentrations in stormwater in separate sewer systems.

Separate sewer systems collect and discharge rainwater directly into surface water bodies. In residential areas covering moderate traffic load these are alternative drainage routes to avoid combined sewer overflow discharge and to keep rivers clean as required by the EU Water Framework Directive. This overflow's microbial quality, however, needs to be evaluated, since stormwater run-offs are potential pathways for pathogens into river systems. Between 2010 and 2016, two separate sewer systems in North Rhine-Westphalia (Germany) were investigated. The stormwater outflow was sampled during discharge events and microbiologically analysed. The results showed high concentrations of Escherichia coli (1,100-1,100,000 CFU/100 mL) and Clostridium perfringens (20-13,000 CFU/100 mL). Campylobacter and Salmonella were detected in 97% and 43% of the samples. Giardia cysts were more often detected (31.6%) than Cryptosporidium oocysts (10.5%). The sources of human pathogens in rainwater run-off are heterogeneous. While roads have already been declared as chemical polluters via rainwater run-off, our study detected supplementary pollution of mainly faecal microorganisms. Presumably, failed connections in the sewer system itself are important sources of human pathogens. We suggest treatment of stormwater run-offs before being discharged into the river system.

Retention soil filter as post-treatment step to remove micropollutants from sewage treatment plant effluent.

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.

Pharmaceutical concentration variability at sewage treatment plant outlets dominated by hydrology and other factors.

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.

Decision support for water quality management of contaminants of emerging concern.

Water authorities and drinking water companies are challenged with the question if, where and how to abate contaminants of emerging concern in the urban water cycle. The most effective strategy under given conditions is often unclear to these stakeholders as it requires insight into several aspects of the contaminants such as sources, properties, and mitigation options. Furthermore the various parties in the urban water cycle are not always aware of each other's requirements and priorities. Processes to set priorities and come to agreements are lacking, hampering the articulation and implementation of possible solutions. To support decision makers with this task, a decision support system was developed to serve as a point of departure for getting the relevant stakeholders together and finding common ground. The decision support system was iteratively developed in stages. Stakeholders were interviewed and a decision support system prototype developed. Subsequently, this prototype was evaluated by the stakeholders and adjusted accordingly. The iterative process lead to a final system focused on the management of contaminants of emerging concern within the urban water cycle, from wastewater, surface water and groundwater to drinking water, that suggests mitigation methods beyond technical solutions. Possible wastewater and drinking water treatment techniques in combination with decentralised and non-technical methods were taken into account in an integrated way. The system contains background information on contaminants of emerging concern such as physical/chemical characteristics, toxicity and legislative frameworks, water cycle entrance pathways and a database with associated possible mitigation methods. Monitoring data can be uploaded to assess environmental and human health risks in a specific water system. The developed system was received with great interest by potential users, and implemented in an international water cycle network.

Monitoring micropollutants in the Swist river basin.

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.

The emission potential of different land use patterns for the occurrence of coliphages in surface water.

Different land use patterns were investigated for their potential as non-point sources of coliphage emissions into surface waters. Water samples were taken regularly at five locations in the upper reaches of the river Swist, Germany. Samples of surface and subsurface run-off were taken within the same catchment area after rainfall events using a newly developed device that made it possible to collect current concentrations of the effluent compounds. The water quality was examined for the occurrence of somatic coliphages and F(+)-specific RNA-bacteriophages as well as for various bacteria over the period of a hydrological year. The potential of various bacteria as indicators for the occurrence of phages was evaluated using statistical correlations. The load of coliphages varied depending on the land use type, but it did not differ as much as the bacterial parameters. River sections in intensively used areas turned out to be more contaminated than in less intensively used regions. The concentrations of phages from surface and subsurface run-off in most samples were quite low for all land use types and did not show conspicuous variations of surface and subsurface run-off within one land use type. Therefore, high concentrations of phages in river water cannot be explained only by non-point effluent from open ground. Following consideration of the statistical results, conventional indicator bacteria seem not to be reliable indicator organisms for coliphages and subsequently for human pathogen viruses. The detected concentrations of coliphages in several water samples of river sections surrounded by intensively used areas underpin an existing health risk in the use of river water for e.g. recreational activities or irrigation.