Katharina Tondera

Survey monitoring results on the reduction of micropollutants, bacteria, bacteriophages and TSS in retention soil filters.

A main source of surface water pollution in Western Europe stems from combined sewer overflow. One of the few technologies available to reduce this pollution is the retention soil filter. In this research project, we evaluated the cleaning efficiency of retention soil filters measuring the concentration ratio of standard wastewater parameters and bacteria according to factors limiting efficiency, such as long dry phases or phases of long-lasting retention. Furthermore, we conducted an initial investigation on how well retention soil filters reduce certain micropollutants on large-scale plants. There was little precipitation during the 1-year sampling phase, which led to fewer samples than expected. Nevertheless, we could verify how efficiently retention soil filters clean total suspended solids. Our results show that retention soil filters are not only able to eliminate bacteria, but also to retain some of the micropollutants investigated here. As the filters were able to reduce diclofenac, bisphenol A and metoprolol by a median rate of almost 75%, we think that further investigations should be made into the reduction processes in the filter. At this point, a higher accuracy in the results could be achieved by conducting bench-scale experiments.

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.

Reducing pathogens in combined sewer overflows using ozonation or UV irradiation

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.

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.

Ecotechnologies for the Treatment of Variable Stormwater and Wastewater Flows

The occurrence of variable stormwater and wastewater flows, mostly precipitation driven, brings with them the challenge of both peak flows and pollutant loads. Wastewater treatment systems can be divided into those that are specifically designed and operated to deal with variable flows, and those that presume more steady-state operation, only coping with peak flows as anomalies for short periods of time. To date, the different types and scales of variability and the impact of this variability on functioning and treatment performance have neither been well characterised nor properly dealt with for the design of suitable treatment systems. In this book, ecotechnologies are defined as processes for the treatment of variable wastewater flows that – harness ecological processes involving microbes, plants, animals, natural soils and media or recycled materials; – have a low reliance on mechanical machinery or external energy sources; and – have a positive impact on the quality and biodiversity of the surrounding environment. K. Tondera (&) Stormwater Research Group, University of the Sunshine Coast, Maroochydore, QLD, Australia e-mail: ktondera@usc.edu.au K. Tondera Institute of Environmental Engineering, RWTH Aachen University, Aachen, Germany C. C. Tanner National Institute of Water and Atmospheric Research, Hamilton, New Zealand e-mail: chris.tanner@niwa.co.nz F. Chazarenc Department of Energy Systems and Environment, Institut Mines Telecom Atlantique, Nantes cedex 3, France e-mail: florent.chazarenc@gmail.com G.-T. Blecken Urban Water Engineering, Luleå University of Technology, Luleå, Sweden e-mail: godble@ltu.se

Emerging Contaminants: Occurrence, Treatment Efficiency and Accumulation Under Varying Flows

Emerging contaminants became a major topic in water treatment when laboratory detection methods for concentrations at a nanogram-scale improved approximately two decades ago. Research on using ecotechnologies to remove emerging contaminants in variable stormwater and wastewater flows has been conducted for more than a decade, but so far, not all removal mechanisms are well understood and only few setups have been investigated. This chapter summarises the current knowledge, focussing on pesticides and emerging contaminants listed on the watch list of the European Union. However, large-scale investigations are still rare and further research will have to be conducted in this field to enable practitioners to provide recommendations for design and maintenance of treatment facilities in the field of ecotechnologies.

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.

Nutrient Removal from Variable Stormwater Flows

When nutrient loads are discharged into surface waters with variable stormwater and wastewater flows, surface water pollution is impaired. Nutrients can lead to oxygen depletion and eutrophication of surface waters, including excessive plant and algae growth. Popular examples of structures harmed by excessive nutrient inflow are the Baltic Sea or the Great Barrier Reef in Australia. Hence, removing nutrients, especially nitrogen and phosphorus compounds, is a major target when variable flows should be treated. This chapter gives an overview of the available removal mechanisms and the potential efficiencies of different treatment facilities. While particle-bound nutrients can be removed via sedimentation processes, dissolved nitrogen and phosphorus compounds cannot as they differ in their biochemical degradation: the adsorption capacity for nitrogen compounds is often renewable, whereas the uptake of phosphorus compounds is limited over time. Hence, treatment facilities need to be able to address the different requirements.

Metals: Occurrence, Treatment Efficiency and Accumulation Under Varying Flows

Metals were the first priority pollutants to be widely investigated in stormwater. In solid phase, they are often attached to very fine particles. The dissolved fraction creates considerable environmental problems as it is the most bioavailable fraction. Hence, removal of both fine and dissolved particles plays a major role in the treatment of polluted runoff. Ecotechnologies specifically designed to remove metals should be able to address different treatment mechanisms. However, the exhaustion of sorption capacity reduces the lifespan of treatment facilities. Additionally, metal concentrations fluctuate extremely—spatially, seasonally and over time—which poses another challenge for further increasing removal efficiencies. While soil- or sand-based systems should be designed in a way that the filter material can be exchanged, newer developments such as Floating Treatment Wetlands show promising removal capacities as the installations bind metals in sludge sediments, which can be removed from time to time. The different treatment mechanisms, aforementioned developments and techniques as well as their removal capacities will be discussed in this chapter.