Rain water runoff is the largest untreated source of potentially high loads of micro pollutants to urban surface waters. Given first findings it can be expected that new rainwater based micro pollutants will be included in future lists of priority substances of the EU Water Framework Directive (WFD). Knowledge of the type and amount of micro pollutants is (therefore) pivotal for enabling good management. Pollutant concentrations depend heavily on rain event characteristics such as rain depth, mean rain rate, intensity, duration and dry-weather-period. As rainfall is usually reported to fall in events and is separated by rainless intervals of a certain duration, the minimum interevent time (MIT) plays a major role within the criteria for defining such rain events. Surprisingly little attention has been paid to the importance of rain event definitions in similar published works, which limits the significance of the results and their comparability to other researches. That is why this work aims to identify independent rain events from a pluviograph record with the help of further hydraulic data. It is also the goal to examine rainfall characteristics of (5) sub-catchments within in the larger catchment Berlin and their sensibility through the variation of rain event definitions, like the very important Minimum-Inter-event Time Definition (MITD). Several rain gauges close-by as well as sensors to measure the water level and the flow inside a storm water sewer of a separated sewage system supply the necessary data. Additionally a number of criteria, found in literature, help to identify the most stable definition of a rain event for these catchments. It is also the intention to set the basis for further analysis (within the project this thesis is realized in) in order to generate the most adequate concentration data of micro pollutants in Berlin’s urban rain water runoff, as this definition will play a major role for further project analysis. Moreover this work intents to emphasize the relevance of the selection and documentation of rain event criteria in studies that apply event-based data analysis.

Urban stormwater runoff is a potential entrance pathway for a wide range of anthropogenic trace pollutants, like biocides, plasticizers, heavy metals or flame retardants, to urban lakes and rivers. However, little is known on dependencies of the occurrence of these trace pollutants on rain event characteristics and climate or seasonal influences. Furthermore, the importance of such dependencies for the calculation of loads and the uncertainties involved are unclear. This thesis evaluates possible correlations between trace pollutant concentrations in urban stormwater runoff and rain event characteristics together with further climate and seasonal influences, based on a large set of measurements from the project “Trace organics in Berlin stormwater runoff (OgRe)”. Here, samples were taken in a one-year monitoring program for five stormwater catchments representing specific urban structure types. Additionally, this thesis investigates whether the consideration of those correlations is necessary for the calculation of loads or whether the use of a mean concentration is sufficient. A method for the correlation analysis is developed and applied to the data, under the requirement to use just one influencing factor (predictor) per correlation and to keep the models simple. Regression models are fitted with regard to normal and log-normal error distributions. The models are evaluated regarding their goodness of fit using the Nash-Sutcliffe efficiency, the log-likelihood ratio, and the prediction coefficient of determination. For 45 out of 48 of the considered substances at least one correlation (i.e. in one of the five catchments) with rain or climate predictors is found. In addition, it is demonstrated that seasonal influences have an effect on substance concentrations for 25 out of 48 substances. Thus, the selected predictor values prove useful to explain the measured concentrations. Only 11 substances show the same correlation with a rain/climate predictor in four catchments and none in all five catchments. So, while concentrations for single events in one catchment can be well explained by the correlations, overall concentration patterns seem to be strongly influenced by the catchment, i.e. its urban structure type. Furthermore, it is shown that the assumption of a normally distributed error does not represent the data adequately in most cases. Consideration of a log-normal error distribution improves most regression models significantly. Regarding single substances, the correlation analysis helps to explain observed patterns. For instance, terbuthylazine, an agricultural pesticide, was only detected during typical application months of May and June, with the same observation in all five catchments. Accordingly, atmospheric deposition from the agricultural surroundings seems a reasonable explanation. In a second example, nicotine was found at very high concentrations in four catchments for low rain event durations, showing a strong decrease with increasing duration. This behavior can be explained by the fast elution of nicotine from cigarette butts within the first minutes of a rain event, followed by dilution during longer rain events. An exemplary load estimation based on a 30-year rain series for Berlin using a Monte Carlo simulation demonstrates that the use of regression models versus mean concentrations can lead to very different results. The reason lies in the selection of sampled rain events which are not distributed according their contribution to the total runoff volume (there should be more small to medium rain events, which contribute more to the total runoff volume). In conclusion, errors in the load estimation can result from i) using a mean concentration instead of a valid correlation, but also from ii) using a non-valid correlation. This underlines the importance of performing a correlation analysis before load calculations, but also the importance of a critical evaluation of the sample data and the correlations. For the latter, a combined evaluation along several goodness-of-fit metrics is suggested, together with plausibility checks of the correlation and of the considered range of values within which the regression model is applied.

In recent years several ways of recovering phosphorous from municipal wastewater have been developed. Depending on the applied technology the recovered products vary significantly concerning the concentrations of heavy metals and organic residues. Within the boundaries of data quality and present uncertainties a comparative risk assessment of seven secondary phosphorus fertilizers, sewage sludge, raw ash and triple super phosphate has been conducted for PCDD/Fs, PCBs, PAHs, As, Cd, Cr, Cu, Hg, Ni, Pb and Zn. Local exposure assessment was done using the kinetic model of the European Union’s Technical Guidance Document for all substances accounting for both fertilization and average atmospheric deposition. For substances of concern (Cd and Zn) the exposure was additionally refined using a solute transport model (HYDRUS-1D) and a precipitation model (Visual MINTEQ-software). An annual fertilizer amount equivalent to 60 kg P2O5/ ha × year by these products is assumed. In order to account for potential accumulation a time span of 100 years is modelled. Results indicate that out of the selected 11 (groups of) chemicals only cadmium and zinc are of concern. Regarding soil organisms, zinc is of concern for sludge, raw ash and one of the seven secondary phosphate fertilizers in case of soil-pH above pH 6.0. Regarding groundwater, cadmium and zinc are of concern below pH 6.0 since mobilization at this pH level increase significantly. No risk is expected regarding the endpoint humans. Among the investigated products struvites have shown the lowest phosphorus-specific heavy metal contents. For ash related products more data from full scale operations are needed to reduce still existing uncertainties like the influence of raw wastewater quality and WWTP operation on the final product.

Dieser Beitrag vermittelt einen Überblick über die im Rahmen des EU Projektes P-REX erzielten Ergebnisse und Schlussfolgerungen. Neben der Bewertung von praxisrelevanten Verfahren zur Phosphorrückgewinnung aus dem Abwasserpfad und den jeweiligen Recyclaten geht es vor allem auch um Aspekte zur flächendeckenden Implementierung und Marktentwicklung. Vor allem integrative Ansätze, die auf eine bessere Ausnutzung der bereits vorhandenen Infrastruktur zur Optimierung des Phosphorrecyclings abzielen, bieten vielversprechende und vor allem kurzfristig umsetzbare Lösungen. Um jedoch Anreize für deren Umsetzung zu schaffen, bedarf es Entscheidungen und verlässlicher politischer Weichenstellungen. Für den Fall des Phosphorrecycling haben Goethes Worte „Wissen ist nicht genug, wir müssen auch anwenden! Wollen ist nicht genug, wir müssen auch tun!“ höchste Aktualität.

In recent years several ways of recovering phosphorous from municipal wastewater have been developed. Depending on the applied technology the recovered products as well as the quality of sewage sludge vary significantly concerning the concentrations of heavy metals and organic residues. Within WA 4 “environmental, economic and risk assessment of P recovery options” of the P-REX project a quantitative risk assessment of substances in phosphorus products for humans and environment is intended. In this deliverable risk assessment is done as a relative risk ranking for PCDD/F, dl-PCB, PAH, As, Cd, Cr, Cu, Hg, Ni, Pb and Zn between seven secondary phosphate fertilizers from wastewater stream, sewage sludge, mono-incinerated ash from sewage treatment and conventional phosphorus fertilizers.

The recovery of phosphorus (P) from sewage sludge, sludge liquor, or ash from monoincineration can be realized with different processes which have been developed, tested or already realized in full-scale in recent years. However, these pathways and processes differ in their amount of P that can be recovered in relation to the total P content in sludge, in the quality of the recovered P product, and in their efforts in energy, chemicals, fuels, and infrastructure required for P recovery. This study analyses selected processes for P recovery from sludge, liquor, or ash in their potential environmental impacts, following the method of Life Cycle Assessment (LCA, ISO 14040/44). Based on available process data from technology providers and end users, these processes are implemented in a hypothetical reference system for sludge digestion, dewatering and disposal in mono-incineration, including potential side-effects on mainstream wastewater treatment with the return load from sludge dewatering. Recovered products (e.g. P or N fertilizer, electricity, district heating) are accounted as credits for substituting equivalent industrial products. Depending on the maturity of the investigated process, collected process data of process efficiency, product quality, and energy and material demand originates from full-scale plants, pilot trials, or prospective modeling (status in 2014). This data is validated with the technology providers, transferred to the reference system and evaluated with a set of environmental indicators for energy demand, global warming, acidification, abiotic resource depletion, eutrophication, and human and ecotoxicity. Results show that pathways and processes for P recovery differ heavily in their amount of recovered P, but also in energy and related environmental impacts (e.g. greenhouse gas emissions). As direct struvite precipitation in sludge or liquor relies on the dissolved amount of P in digested sludge, these processes are only applicable in wastewater treatment plants with biological P removal. Here, they can recover 4-18% of total P in sludge with a relatively low effort in energy and chemicals, reducing return load to the mainstream process and eventually improving sludge dewaterability in case of direct precipitation in sludge. Acidic leaching of P from digested sludge can yield up to 48% of P for recovery, but requires a significant amount of chemicals for control of pH (leaching and precipitation) and for minimizing heavy metal transfer into the product. The quality of products from sludge and liquor is good with low content on heavy metals, leading to a low potential toxicity for humans and ecosystems. Leaching of monoincineration ash with sulphuric acid yields 70% P with moderate chemical demand, but the leached ash and co-precipitated materials have to be disposed, and the product contains some heavy metals. Complete digestion of ash in phosphoric acid and multi-stage cleaning with ion exchangers yields high recovery of 97% P in a high-quality product (H3PO4) and several coproducts, having an overall low environmental impact. Thermo-chemical treatment of ash can recover up to 98% P with moderate energy input in case of integration into an existing monoincineration facility, but the product still contains high amounts of selected heavy metals (Cu, Zn). Metallurgic treatment of dried sludge or ash can also recover up to 81% of P, but the process has still to be tested in continuous pilot trials to validate product quality, energy demand, and energy recovery options. Sensitivity analysis shows that other pathways of sludge disposal (e.g. co-incineration combined with upstream P extraction, direct application in agriculture) may also be reasonable from an environmental point of view depending on local boundary conditions and political targets. In general, the use of life-cycle based tools is strongly recommended to evaluate and select suitable strategies for regional or national concepts of P recovery from sewage sludge.

Food production in Europe is dependent on imported phosphorus (P) fertilizers, but P use is inefficient and losses to the environment high. Here, we discuss possible solutions by changes in P management. We argue that not only the use of P fertilizers and P additives in feed could be reduced by fine-tuning fertilization and feeding to actual nutrient requirements, but also P from waste has to be completely recovered and recycled in order to close the P balance of Europe regionally and become less dependent on the availability of P-rock reserves. Finally, climatesmart P management measures are needed, to reduce the expected deterioration of surface water quality resulting from climate-change-induced P loss.

Germany’s municipal sewage treatment plants generate some two million tons of dry sewage sludge annually, with the proportion of thermally treated sewage sludge increasing from 31.5 per cent in 2004 to more than 54 % in 2011. Sludge, which is usually incinerated or used as agricultural fertilizer, contains a whole series of harmful substances that complicate the task of sludge management. But sludge also contains a number of nutrients such as phosphorus, nitrogen and potassium. Hence the goal of sewage sludge management is to remove sludge pollutants while retaining sludge nutrients. Sewage sludge undergoes thermal recycling at facilities such as sewage sludge mono-incineration plants, cement plants and coal fired power plants. Sewage sludge utilization for farming purposes has plateaued of late (2006 to 2011) at around 29 %, an evolution attributable to more stringent quality standards for sewage sludge. However, sewage sludge is set to take on greater importance as a raw material, mainly due to the increased concentrations of phosphorous it contains. This pamphlet discusses the potential offered by sewage sludge and the ways it can be used sustainably. The pamphlet also describes the current status of sewage sludge management in Germany, with particular emphasis on the extent to which sludge use as a fertilizer can be reduced without foregoing phosphorous and other sludge nutrients. Over the next one to two decades, Germany needs to wean itself away from using sewage sludge for farming and at the same time efficiently leveraging the potential for using sewage sludge as a low cost fertilizer.

Im Rahmen des Forschungsprojekts SEMA ist die Prognosequalität eines Alterungsmodells anhand der TV-Inspektionsdaten der Stadt Braunschweig geprüft worden. Die Qualität der Prognose wurde auf der Grundlage einer Probe von 35.826 Inspektionen bewertet. Die Inspektionen wurden mittels eines substanzbasierten Modells klassifiziert. In einem zweiten Schritt wurde das statistische Modell KANEW-Z angewandt, um die Kanalalterung zu simulieren. Der Vergleich der Inspektions- mit den Simulationsergebnissen zeigt, dass das Modell in der Lage ist, die Zustandsverteilung des Systems ziemlich genau wiederzugeben. Die Ergebnisse sind auch ermutigend auf individueller Haltungsebene. Im Allgemeinen zeigt das Alterungsmodell viel bessere Ergebnisse als ein einfaches lineares Alterungsmodell. Schlussfolgernd unterstreichen die Ergebnisse das Interesse und den potentiellen Nutzen der Anwendung von Alterungsmodellen zur Unterstützung von Asset-Management-Strategien.