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Vertical-flow constructed wetlands remove pollutants from combined sewer overflows (CSOs) and have been in operation for approximately 20 years in Germany. More than 150 sites are currently operated in the state of North-Rhine Westphalia, with most of them constructed according to the same guidelines. This number provides an adequate statistical population to evaluate the treatment efficiency of this design; however, most available data have not been collected in a standardized way. This study presents the results from a survey amongst operators of these plants, who provided long-term data for 24 sites. It also describes a statistical approach to harmonizing the data and evaluating the removal efficiencies of wastewater pollutants while considering errors and uncertainties with a Monte Carlo simulation. This method makes it possible to harmonize data from surveys and to draw generalized conclusions on the treatment efficiency of large-scale facilities. In this study, the evaluation could be adapted for the removal efficiencies of chemical oxygen demand, total suspended solids and total phosphorus. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Fecal contamination of water resources is a major public health concern in densely populated areas since these water bodies are used for drinking water production or recreational purposes. A main source of this contamination originates from combined sewer overflows (CSOs) in regions with combined sewer systems. Thus, the treatment of CSO discharges is urgent. In this study, we explored whether ozonation or UV irradiation can efficiently reduce pathogenic bacteria, viruses, and protozoan parasites in CSOs. Experiments were carried out in parallel settings at the outflow of a stormwater settling tank in the Ruhr area, Germany. The results showed that both techniques reduce most hygienically relevant bacteria, parasites and viruses. Under the conditions tested, ozonation yielded lower outflow values for the majority of the tested parameters. [ABSTRACT FROM AUTHOR]