Major reservoirs are a key element for public water supply in many countries. In Europe over 800 major reservoirs serve primarily this purpose. Eutrophication affects significant numbers of lakes and reservoirs, and is the well-known issue currently impacting drinking water supply reservoirs. In most cases, phosphorus is the principal cause of eutrophication, and therefore has been studied intensively. The presence of micro pollutants (e.g. pesticides, pharmaceutically active compounds - PhaCs) is not systematically monitored but some substances are very mobile and tend to resist degradation. Such contaminants have been detected in numerous surface water bodies (lakes, reservoirs and rivers). As agriculture is intensifying and land use is changing in many areas, the impact of diffuse pollution on water quality is expected to be more pervasive in the future. The project Aquisafe proposes to investigate the topic in a multi-step approach which will include: i) an analysis of the nature, occurrence and risk of surface water contamination, ii) a modelling approach to quantify the contaminants origin, load and repartition to assess the effects of adapted controlled measures, and iii) the development, adaptation or optimisation of the design and operation of mitigation zones (riparian corridors and small scale wetlands) to reduce downstream loads of pollutants. Thus, Aquisafe is a first step to establish the state-of-the-knowledge on current existing solutions, identify emerging issues and assess the feasibility of using models for the evaluation of mitigation zones for contaminants removal. Within the Aquisafe project it will expected: i) a recommendation on potential key substances to be targeted, also for further investigations, ii) an identification of drinking water source vulnerability to emerging contaminants using a coupled modelling approaches, and iii) an analysis of existing mitigation methods and scientific background for the construction of riparian corridors and/or constructed wetlands in order to mitigate trace contaminants entering the surface water.

The KompetenzZentrum Wasser Berlin (KWB) is a private research and development center, created in 2000, with a status of public interest, and mainly supported by Veolia Water and Berliner Wasser Betriebe. This is where I did a six month-training period as part of my studies at the French AgroParisTech ENGREF engineering school. Within the department “Point and non-point source pollution control”, the KWB initiated a program called Aquisafe. The aim is to investigate the mitigation of trace contaminants from diffuse sources in rural and semi-rural areas to improve water quality of surface water bodies. The sustainable way of addressing pollution control is that the selected mitigation metods are natural or nature-based: namely constructed wetlands and riparian1 corridors. To develop knowledge and tools about these mitigation zones, an innovative approach was chosen when conducting the project: - The first part aims at a background study about surface water and pollutions from diffuse sources, leading to a progressive focus on key pollutants for the future of the project. The second part investigates modelling tools as diagnosis tools for the repartition and load of contaminants in a watershed. The third part contains field experiments and uses results from previous parts. The final purpose is to assess the mitigation efficiency of the systems and to optimize their design in the perspective of improving surface water quality. In charge of the first part, I did set the context of the project by reviewing background information on surface waters in Europe and associated pollutions, that move to water via soil surface run-off or subsurface run-off. After using criteria related to the Aquisafe context, the main pollutant families of interest for the rest of the screening process are pesticides used in agriculture, pollutants coming from the spreading of animal waste on land, pollutants coming from the spreading of sludge from wastewater treatment plants, pollutants from natural and extensive areas, and pollutants from transportation networks. During the study it appeared that in a rural or semi-rural area, the land use of the watershed plays a key role in the selection and assessment of priority pollutants coming from diffuse sources and entering surface waters. The importance of this factor should always be kept in mind as the project goes on. The work is still in progress concerning the review of pollutant families, and will lead to the final screening at the molecule level, providing a list of key contaminants for the other parts of the Aquisafe project. Finally the results of Aquisafe will tell if such sustainable mitigation zones can be used as a real innovative management tool of diffuse pollution in a watershed.

Urban water courses are considerably degraded in terms of their hydrology, riparian and channel morphology, substrate heterogeneity and habitat features as well as water and sediment quality. In addition, the combined sewer overflows and the ecotoxicological impacts of its components lead to a change of the physical-chemical and microbial mass balance affecting the biocenoses of higher trophic levels. Combined sewer overflows are therefore an additional stress to the ecological status of the urban course of the River Spree and of its channels, which is damaged already by both preload and background load of the aquatic environment. With regard to the assessment of the ecological water status, the European Water Framework Directives gives priority to the aquatic biocenoses in their capacity as ecological quality parameters. Against this background, an immission-oriented approach for the assessment of combined sewer overflows has to describe also their impacts on the biocenoses of the macrozoobenthos, the fish fauna, the macrophytes and the phytoplancton. These biocenoses are protected against the harmful impacts resulting from CSO only if the modification of their physical and chemical environment is avoided or reduced to an ecologically tolerable level respectively. In case that unfavourable impacts cannot be completely eliminated, the degree of impairment and the number of damaging CSO discharge events, which appear to be acceptable, should be defined. The present study is based on the bibliographic study „ Impact of urban use on the mass balance and the biocoenosis of lowland rivers under special consideration of combined sewer overflows” and deals with the assessment of CSO impacts on the ecological situation of the urban Spree and the channels (Cyprinid water bodies). In general, the immissionoriented assessment of CSO impact on the biocenoses (macrozoobenthos, fish fauna) requires the observation of the intensity, duration and frequency of occurrence of the individual events based on the assumption that, due to the background pollution, top priority is currently given to the acute CSO impacts. Requirements for the protection of aquatic biocenoses are developed with regard to the target parameters oxygen and ammonium/ammoniac and ecological tolerances of the biocenotic subjects of protection, which are strongest influenced by CSO. Initially, it is discussed to what extent the already existing results from laboratory investigations can be transferred to field situations. Next to the commonly accepted threshold values for oxygen concentrations during continuous persistent loads, particular requirements for the oxygen balance in case of peak loads are formulated.

The objective of the studies performed in the scope of the Integrated Sewage Management (ISM) project on combined sewer overflows in Berlin, Germany was to develop methods that would make it possible to assess wastewater management measures performed under the city’s water management permit as well as more sophisticated strategies (e.g., global real time control) through the application of water body-related criteria. For this purpose, a preliminary study was first performed to characterize the underlying water body-specific processes and hydraulic, physical, chemical and ecological parameters relevant to the status of Berlin’s surface waters (LESZINSKI et al., 2007a). The second step involved the development of a method for water quality-oriented assessment of wastewater management measures (LESZINSKI ET AL., 2007b). In addition to the already recognized thresholds for dissolved oxygen concentration during continuous, long-term water load conditions, particular focus was placed on formulating requirements for oxygen demand under peak load conditions. Ammonia toxicity due to sewage input, another important stress factor for aquatic ecosystems, was also analyzed and threshold values for both chronic and acute peak ammonia loads were defined. The results of the third phase of this research are described in this report. Two numerical simulation models (for urban drainage networks and surface waters) were combined and the feasibility of the developed method was evaluated based on the case of a combined sewer overflow event documented by the surface water monitoring. The simulations were performed using InfoWorksTM CS hydrological/hydrodynamic urban drainage network modeling software (ISM model) and the GERRIS/HYDRAX/Qsim unsteady ecosystem modeling system. The latter model was developed by the Federal Institute of Hydrology in Koblenz and is used by the Senate Department of Health, Environment and Consumer Protection (SenGesUmV). The present report describes the theoretical principles of the utilized models, the base of data available for analysis of the selected event, and the assumptions made in cases of missing input data for hydraulic modeling as well as for the water quality simulations. The one-dimensional hydraulic modeling results for the branched surface water system of the reach Berlin-Charlottenburg demonstrated that the hydraulic conditions can be simulated with satisfactory accuracy using the current data. In the case of water temperature, it was also possible to achieve a high degree of agreement between the measured and computed values in spite of the lack of highresolution temporal input data from the tributaries (Landwehr Canal, Panke River, BerlinSpandau Ship Canal). However, this was not the case for dissolved oxygen concentration, the main parameter used for evaluation of combined water treatment. The DOC simulations computed using input data based on a monthly sampling interval did not show satisfactory agreement with the online measurements in the water system. Dry-weather biological processes, which were associated with high-level, short-term oxygen enrichment or consumption, could not be depicted in the simulations. After completion of the water quality simulations, the effect of variation of individual input parameters was assessed. This analysis showed that no significant improvement of agreement with the measured values could be achieved by adjusting the assumptions for individual parameters (chlorophyll-a and BSB5). In the case of ammonia, the second most important parameter, the available sampling data from the tributaries in the investigated water system were collected only once a month, if at all. Therefore, it cannot be expected that the temporal distribution of this parameter was correctly reflected by the model. The number of validation measurements taken within the water system was also insufficient. Summarizing the results of the study of the linked urban drainage/surface water quality model, which was tested for the first time, it can be concluded that InfoWorks CS and GERRIS/HYRDRAX/Qsim provide problem-oriented simulation tools for reaching the objective of ISM study of assessing various scenarios for reduction of impacts from combined sewer overflows. By contrast, the available data are deficient and do not allow to adjust and calibrate the models to meet the specific needs of this task, particularly in light of the fact that short-term effects of combined sewer overflows are to be analyzed.

Two membrane bioreactors were operated with biological phosphorus removal, carbon degradation and denitrification to check how comparable and representative they were compared to full-scale plants. One was fed with synthetic municipal wastewater and was switched from pre- to post-denitrification without carbon dosing. The influent of the second plant was drawn from a separate sewer. This plant worked the whole time with post-denitrification without carbon dosing. The synthetic wastewater was designed to achieve a realistic COD:TN:TP ratio and tested for long time biodegradability. The eliminations were >94% (COD) and >97% (TP) for both plants. This was within the range of commercial plants, as well as the TN elimination for the pre-denitrification of plant I (>75%). The eliminations of TN for post-denitrification were above 80% for both plants despite the high influent concentrations and the missing carbon source for post-DN. A calculation of the nitrification rates gave values similar to those found in literature (1–6 mgN/(gMLVSS h)). A comparison of the denitrification showed expected rates for pre-denitrification (7.5 mgN/(gMLVSS h)) for plant I. The values (on average 1.8 mgN/(gMLVSS h)) for post-denitrification in plant II were higher than endogenous denitrification rates which are commonly reported as 0.2–0.8 mgN/(gMLVSS h). The rates for post-denitrification in plant I were only slightly higher than endogenous ones (0.9 mgN/(gMLVSS h)).

The widespread application of the membrane-assisted activated sludge process is restricted by membrane fouling, which increases investment and operating costs. Soluble microbial products (SMPs) are currently considered as the major cause of membrane fouling in membrane bioreactors (MBRs). This study aims at elucidating and quantifying the effects of varying environmental conditions on SMP elimination and rejection based on findings in a pilot MBR and in well-defined lab trials. Several factors are thought to influence the concentration ofSMP and their fouling propensity in one way or the other, but findings are often inconsistent or even contradictory. Here, SMP loading rate was found to have the greatest effect on SMP elimination and thus on concentration in the MBR. The degree of elimination decreased at very lowDO and low nitrate concentrations. On average, 75% of influent SMP were eliminated in both pilot and lab trials, with the elimination of polysaccharides (PS) mostly above 80%. Rejection of SMP components by the used membrane (PAN, 37nm) ranged mainly from 20% to 70% for proteins and from 75% to 100% for PS. Especially protein rejection decreased at higher temperatures and higher nitrification activity. The increased fouling rates at lower temperatures might therefore partly be explained by this increased rejection. Apparently, mainly the nitrite-oxidising community is responsible for the formation for smaller SMP molecules that can pass the membrane.

Fouling still is one of the major issues of membrane bioreactor (MBR) research. Most attention is currently paid to extracellular polymeric substances (EPS) in either bound or soluble/colloidal (soluble microbial products, SMP) form. While several trends or correlations were reported, the comparability of results is still limited by the numerous differences in plant set-up and analytical methods. The aim of this study is to compare polysaccharide concentrations and their respective fouling potential in different MBR operated under different conditions using the same analytical and evaluation tools and considering all relevant differences. Results are also compared to literature findings in an attempt to come to more generally valid conclusions. Results indicate that SMP influence fouling only under certain conditions such as low sludge age and large pore size.