In combined sewer systems domestic, trade and industrial waste water and in case of rainfall events significant volumes of storm water are collected and transported to wastewater treatment plants (wwtp). In the frame of this study a literature review on the impact of combined water inflow on wastewater treatment and the identification of critical system processes and parameters has been carried out. The objective of this work was to study the possibilities of an optimal charging of wwtps during rain and to analyse in how far those concepts could be transferred to Berlin plants. When the inflow of combined sewage to the wwtp increases, screening waste increases, too. However, this is no problem if the screening capacity is sufficient. In the primary settler the formation of primary sludge increases due to the higher inflow load. Concerning dissolved substances there can be an adverse effect when the highly concentrated content of the primary settler is pushed into the biological tanks. To ensure a reliable separation of the primary sludge a hydraulic residence time of 30 minutes is recommended. In literature, the processes of nitrification, biological P removal and the separation of the activated sludge in the final clarifier have been identified as being most critical during combined water inflow. Usually, effluent concentrations of the critical parameters increase only at the beginning of a rain event. Due to the dilution effect that typically can be observed after a maximum duration of 2 hours the concentrations then keep constant again. The process of biological P elimination can be supplemented by chemical P precipitation to avoid critical effluent concentrations during combined water inflow. In the aerated zone the oxygen content can be regulated to improve P incorporation. In the past, in Germany combined water inflow to the wwtp was limited to 2*Qwastewater+Qinfiltration (according to the standard ATV-A 131, 1991). However, the treatment capacity of wwtps that have been designed according to ATV-A 131 (1991) may exceed this value. According to the standard ATV-DVWK-A 198 an inflow of 3-6 times the average dry weather flow may be possible. In literature it can be found that factors of 3 to max. 4 have been realized successfully. Hence, in praxis the peak factor for combined water inflow is rather in the lower range given in ATV-DVWK-A 198. In Berlin the approach given in ATV-DVWK-A 198 will not be applicable. Since wastewater transport is realised via long pressure mains the dilution by stormwater reaches the wwtps only after 5-10 hours. In contrary to wwtps that are directly connected to a gravity sewer system, this Berlin situation leads to long-lasting disturbances of the processes in the activated sludge tanks and in the final clarifiers. However, it must be mentioned that only few information was available on the behavior of the Berlin wwtps during combined water inflow (mainly inflow data). At some wwtps (Stahnsdorf and Ruhleben) an adapted sporadic increase of the inflow rates during rain may be possible. The “bypass process” and an adapted oxygen regulation may be further interesting options for the management of combined water at the wwtp. However, the “bypassprocess” has not yet been tested in situations with long-lasting (5-10 hours) high load situations. The most important options for the reduction of combined water overflows in Berlin will still be the unsealing of currently impervious surfaces, the reconfiguration of the combined sewer system into a modified system (preventing stormwater to enter the combined sewer), the prevention of stormwater inflow into the sanitary sewers of the separate system and the construction and (real-time) control of storage capacities within the combined sewer system. In the future it would be desirable to charge the Berlin wwtps in accordance to their actual capacities based on measurement information. Thus, an optimisation between combined water treatment (reduction of combined water overflows) and the capacity and resilience of the plant could be realised. Therefore, a system for the assessment of the actual capacity of a wwtp (nitrification, final clarification) would be needed.

Ein wichtiges Teilgebiet der Siedlungswasserwirtschaft ist die Entwässerung urbaner Gebiete. Zum Ableiten von anfallendem häuslichen Abwasser wurden im Laufe der Jahrhunderte Kanalisationen entwickelt, die für bessere hygienische Verhältnisse in besiedelten Gebieten sorgen sollten. Dies waren zumeist offene Gerinne zwischen Fahrbahn und Bürgersteig, in denen sich das Brauch- und Regenwasser mit dem Unrat der Straße vermischte und in ein nahe gelegenes Gewässer eingeleitet wurde. Dies führte zu starken Verschmutzungen der Gewässer. Heutzutage werden Kanalisationen unterirdisch gebaut. Das Abwasser wird zur Reinigung einer Kläranlage zugeführt und von dort aus einem Oberflächengewässer zugeführt. Durch das Einleiten von Niederschlagswasser, den Einträgen aus der Industrie, den Einleitungen aus kommunalen Kläranlagen sowie Einleitungen aus diffusen Quellen wird das Gewässer sowohl hydraulisch als auch stofflich stark belastet. Herkömmliche Maßnahmen für den Rückhalt von Mischwasser sind der Bau von Speicherbecken. Da ein Neubau meist sehr kostenintensiv ist und viel Platz in Anspruch nimmt, der in Großstädten meist nicht zur Verfügung steht, kann die Bewirtschaftung von vorhandenem Kanalraum als eine Alternative angesehen werden. Durch den Bau von Regenrückhaltebecken und die Regenwasserbewirtschaftung ist ein Rückgang der Mischwassereinträge und dadurch eine Verringerung der Gewässerbelastung zu verzeichnen. Trotzdem ist der Verschmutzungsgrad der meisten Gewässer weiterhin bedenklich. Auf Grund der Tatsache, dass die Trink- und Abwasserentsorgung Berlins innerhalb der Stadtgrenzen betrieben wird, ist es wichtig, einen umfassenden Gewässerschutz zu betreiben. Mit der Einführung der Wasserrahmenrichtlinie (WRRL, 2000) hat man sich auf europäischer Ebene darauf geeinigt, dass alle europäischen natürlichen Oberflächengewässer bis zum Jahr 2015 einen „guten ökologischen und guten chemischen Zustand“ erlangen sollen (Art. 4.2 WRRL). Ein Ansatz zur Umsetzung dieser Vorgaben ist die Reduzierung der Mischwasserüberläufe während Regen. Dies kann z.B. unter Zuhilfenahme einer Verbundsteuerung umgesetzt werden. Ziel dieser Diplomarbeit ist es, einen bewertenden Vergleich zwischen einer Verbundsteuerung und der momentanen Berliner Steuerungsstrategie (lokale Steuerung) an ausgesuchten Abwasserpumpwerken durchzuführen. Dabei soll festgestellt werden, ob und in wie weit, eine übergeordnete Verbundsteuerung zur Reduktion von Mischwasserüberläufen beitragen kann. Zu diesem Zweck sollen Simulationen durchgeführt werden. Dabei soll einerseits mittels Langzeitsimulationen das Potential einer Verbundsteuerung im Gegensatz zur derzeitigen Steuerung (Kap. 2.3.2) theoretisch bestimmt werden. Auf der anderen Seite werden auf der Basis gemessener Daten (Fördermengen und Wasserstände) Einzelsimulationen für ausgewählte Regenereignisse (Kap. 7.2) durchgeführt. Diese dienen der Überprüfung des eventuell theoretisch vorhandenen Steuerungspotentials.

Well biofouling is a complex and yet not sufficiently understood process. Water wells represent a unique habitat, since they create a link between the anaerobic ground water, containing Fe(II) and the aerobic surface. These special conditions set ideal conditions for the growth of iron bacteria (Stuetz and McLaughlan, 2004). Some of these bacteria are known to be responsible for well clogging by precipitation of iron hydroxides (Cullimore, 1999). The consistency of the ochres can range from soft and bulky to solid and compact. The type of deposit strongly depends on the dominant species of bacteria at the well screen and inside the gravel pack. Within this project (WellMa) a sampling system was created, which allowed the collection of unaffected biofilm samples from inside the wells. The samples were microscopically examined, DNA was extracted and community profiles were created.

Bacterial induced well clogging is a common problem in water wells. The well represents a unique habitat by creating a link between the anaerobic ground water, containing Fe(II) and the aerobic surface. The presence of trace amounts of free oxygen in the well screens, sets ideal conditions for the growth of iron bacteria (Stuetz and McLaughlan, 2004). These bacteria precipitate iron hydroxides (Cullimore, 1999), that not only block the filter area, but also the adjacent gravel pack or even parts of the aquifer and result in a steady decrease of well performance. Each well has it’s own distinct chemical conditions, which impact the type of bacterial community that forms in the gravel pack. Within this project a novel sampling system was developed, which allowed the collection of intact biofilm samples from a selected range of Berlin water wells. The resulting biofilms were microscopically examined to gain a first rough overview of the different sampling sites. Subsequently, the bacterial DNA was extracted and used for a population comparison utilizing denaturing gradient gel electrophoresis, cloning and sequencing.

A continuous monitoring, using UV-VIS spectrometers, was carried out in Berlin from 2010 to 2012. It combined (i) continuous measurements of the quality and flow rates of combined sewer overflows (CSO) at one main CSO outlet downstream of the overflow structure and (ii) continuous measurements of water quality parameters at five sites within the urban stretch of the receiving River Spree. Locally, the collection of data aims at (i) characterizing CSO emissions, (ii) assessing the local dynamics and intensity of CSO impacts on the river and (iii) calibrating sewer and river water quality models being part of a planning tool for future CSO management in Berlin (Riechel et al., 2011). UV-VIS spectrometers are in-situ probes, which measure absorbance spectra ranging from UV to visual wavelengths. Concentrations, such as chemical oxygen demand (COD), are calculated from these spectra. Due to the varying composition of waste and river water a local calibration is required to enhance the measurement quality. According to Gamerith et al. (2011), manufacturer global calibration can lead to systematic error up to 50% for COD measurements.

The MBR technology is able to fulfil similar or even higher standard for nutrients removal than conventional activated sludge processes. This paper presents the results of a scheme constructed in a remote and yet unsewered area of Berlin requiring high quality wastewater treatment, and consisting of one containerised MBR unit together with a low pressure sewer. The process includes enhanced biological phosphorus removal and post-denitrification. In order to flatten out the hydraulic and load profile, and therefore to reduce the size of the biological reactor and the membrane surface, a buffer tank was installed before the MBR-plant. The full-scale MBR demonstration plant in Berlin-Margaretenhöhe or 250 p.e.(person equivalent) could be operated continuously by remote control and could fulfil high quality treatment for both disinfection and enhanced biological phosphorus and nitrogen removal, matching under design load conditions the effluent criteria of TP < 0.1 mgP/L and TN < 10 mgN/L ( 99% P- and 90% N-elimination).

Two membrane bioreactor (MBR) plants were operated with a process which combines enhanced biological phosphorus removal (EBPR) and post-denitrification without external carbon dosing in the anoxic zone. An enhanced post-denitrification with denitrification rates (DNR) twice as high as the expected endogenous rate was observed. Batch tests revealed a linear correlation between the anaerobic acetate loading and the postDNR which is remarkable since the aerobic phase was located in-between the anaerobic and anoxic phase. An anaerobic build up of a carbon storage compound which can outlast the aerobic phase is postulated. Measurements showed that neither polyhydroxyalkanoates (PHAs) nor glycogen are used as carbon source for the enhanced post-denitrification. A carbon mass balance in the anaerobic phase strongly indicates the formation of a different so far unknown storage compound. This assumption is supported by literature data which show carbon recovery ratios of known storage compounds (PHAs and glycogen) in the anaerobic phase of EBPR systems often below 1 down to 0.3, in particular for trials performed with real wastewater. The potential of enhanced post-denitrification in conventional UCT systems is also demonstrated in full-scale non-MBR wastewater plants. When implemented in MBR process, enhanced nutrients elimination could be biologically achieved with 99% TP-removal and 90% TN-removal. A small full-scale unit is in operation in Berlin since March 2006 to demonstrate the process in real operation conditions with domestic wastewater.