In Berlin – wie auch in anderen Regionen Deutschlands – wird ein Großteil des Trinkwassers durch Uferfiltration gewonnen. Durch eine Untergrundpassage mit einer Dauer von meist mehreren Wochen erhält es eine Aufreinigung, die den Aufwand der konventionellen Trinkwasseraufbereitung verringert und eine zusätzliche Barriere gegenüber Schadstoffen darstellt (Kühn 2001). Das Ziel eines interdisziplinären Forschungsvorhabens mit dem Titel NASRI (Natural and Artificial Systems for Recharge and Infiltration) war, die Reinigungsprozesse für verschiedenste Substanzen zu ermitteln und Empfehlungen für das zukünftige Wassermanagement in Berlin abzuleiten (Fritz 2003). Aufgabe der Arbeitsgruppe des Umweltbundesamtes war dabei zu klären, wie wirksam Microcystinen (MCYST) als wichtigste Gruppe der Cyanobakterientoxine durch die Bodenpassage eliminiert werden. Im Folgenden werden einige Schlüsselergebnisse berichtet. Für eine ausführliche Ergebnisdarstellung siehe Grützmacher et al. (2006). MCYST sind in der Regel überwiegend (> 90 %) zellgebunden, so dass die physikalische Filtration der Zellen an der Sedimentoberfläche als Eliminationsprozess im Vordergrund steht (Grützmacher et al. 2003). Das extrazelluläre MCYST wird dagegen überwiegend biologisch abgebaut (Lahti et al. 1998, Grützmacher et al. 2005a). Um unter naturnahen Bedingungen Extremfälle für den biologischen Abbau zu simulieren, wurden i) Freilandversuche unter variierenden Redoxbedingungen und ii) Laborsäulenversuche bei unterschiedlichen Temperaturen durchgeführt. Ferner wurde die Freisetzung von MCYST aus sedimentierten Zellen untersucht.

Redox processes during bank filtration were evaluated in Berlin, where bank filtered water is abstracted for drinking water production. The investigations included the mapping of the infiltration zone, a column study and hydrochemical analyses of the groundwater sampled between lake and production well. The organic carbon content increased and the permeability of the lake sediments decreased with distance from the shoreline. The most important changes with regard to the redox state of the infiltrate occurred within the first metre of flow. Infiltration was mostly anoxic, as oxygen was rapidly consumed within the organic rich sediments. The infiltration zone revealed a vertical redox stratification with hydrochemical conditions becoming more reducing with depth rather than with distance from the lake. The redox zones were found to be very narrow below the lake and wider towards the production wells, suggesting that other than differing flow paths, reaeration after infiltration may also occur and possible mechanisms are presented. Redox conditions were influenced by strong annual temperature variations of the surface water affecting the microbial activity. Aerobic infiltration only took place close to the shore in winter.

The spatial distribution of confining layers within a system of two aquifers strongly affects the hydraulics and sensitivity to pollution. The test site is located close to a well field. Wells are switched with short intervals and hydraulic heads are recorded in several observation wells. Because the absolute levels of simulated hydraulic heads do not always coincide with the measurements, the model is calibrated with short term head variations. The characteristic shape of the hydraulic heads at each observation wells contains sensitive information about the structure of the aquifer. A numerical technique is developed which enables to simulate the spatial distribution of the confining layer. The method comprises the use of pilot points and regularisation technique. Cross validation is carried out in order to show the results are physically based. The method is shown to provide significant results even under non optimal conditions.

Berlin relies on induced bank filtration from a broad-scale, lake-type surface water system. because the hydraulic conductivity of the lake sediments is low, infiltration only occurs close to the more permeable shore zones. Using multiple environmental tracer methods, a strong vertical age stratification of the bank filtrate could be shown. travel times are generally long and vary throughout the upper aquifers from a few months near the ground surface to several decades in greater depth. infiltration is mostly anoxic and redox zones were found to be vertically stratified too, becoming more reducing with depth. because berlin’s watercourses contain a proportion of treated municipal sewage a number of wastewater residues, e. g. pharmaceutical residues, were detected in surface water and groundwater. While the majority of the pharmaceutical residues studied were efficiently removed during underground passage, some substances (aMDOPh, primidone and carbamazepine) were found to be very persistent.

Eine Forschungsgruppe derTechnischen Universität Berlin beschäftigt sich mit dem Verhalten von gelöstem organischen Kohlenstoff, DOC und organischen Einzelstoffen beider Uferfiltration. Die Ergebnisse zeigten, dass sowohl oxische als auch anoxisch/anaerobe Infiltrationsbedingungen zu einem ähnlich niedrigen DOC führen können. Unter oxischen Verhältnissen ist zur Mineralisierung des bioverfügbaren DOC (BDOC) nur eine einmonatige Bodenpassage notwendig, während es unter anoxisch/anaeroben Verhältnissen aufgrund der langsameren Abbauklnetik bis zu sechs Monate dauern kann. Bezüglich der Spurenstoffe konnte gezeigt werden, dass das Röntgenkontrastmittel lopromid in allen Felduntersuchr./ngen schnell entfernt wurde. Das Antibiotikum Sulfamethoxazol wurde unter anoxisch/anaeroben Verhältnissen effektiver entfernt (bis zu 80%), während unter oxischen Bedingungen maximal 50% der Ausgangskonzentration abgebaut wurden. Zusammenfassend kann die Uferfiltration als eine durchaus sehr.wirksame Stufe zur Entfernung von Organika bewertet werden.

Berlin relies on induced bank filtration from a broad-scale, lake-type surface water system. Because the surface water contains treated sewage, wastewater residues are present in surface water and groundwater. Multiple environmental tracers, including tritium and helium isotopes (3H, 3He, 4He), stable isotopes (d18O and d2H) and a number of persistent sewage indicators, such as chloride, boron and a selection of pharmaceutical residues (phenazone-type analgesics and their metabolites, carbamazepine and anthropogenic gadolinium, Gdexcess), were used to estimate travel times from the surface water to individual production and observation wells at two sites. The study revealed a strong vertical age stratification throughout the upper aquifer, with travel times varying from a few months to several decades in greater depth. Whereas the shallow bank filtrate is characterized by the reflection of the time-variant tracer input concentrations and young 3H/3He ages, the deeper, older bank filtrate displays no tracer seasonality, 3H/3He ages of a few years to decades and strongly deviating concentrations of several pharmaceutical residues, reflecting concentrations of the source surface water over time. The phenazone-type pharmaceuticals persist in the aquatic environments for decades. Bank filtration in Berlin is only possible at the sandy lakeshores. In greater water depth, impermeable lacustrine sapropels inhibit infiltration. The young bank filtrate originates from the nearest shore, whereas the older bank filtrate infiltrates at more distant shores. This paper illustrates the importance of using multiple tracer methods, capable of resolving a broad range of residence times, to gain a comprehensive understanding of time-scales and infiltration characteristics in a bank filtration system.

Cyanobacterial toxins are toxic substances produced by cyanobacteria or blue-green-algae. The can occur in surface waters wordwide and have to be removed sufficiently when using infested surface waters as drinking water source. Bank filtration has been used since 150 years for drinking water (pre-)treatment and utilizes natural elimination processes like sorption and degardation in the sub-surface. During several research projects the German Federal Environmental Agency (Umweltbundesamt, UBA) carried out field investigations and experiments in different scales in order to assess under which conditions secure elimination of microcystins (the most common group of cyanobacterial toxins) takes place. Filtration of cells on the sediment surface is the most prominent process for eliminating the primarily cell-bound toxins. Middle to coarsly grained sands eliminated more than 99.9 % of intracellular toxins within the first 10 centimeters. Elimination of extracellular microcystin during underground passage is mainly due to biodegradation. Reversible adsorption processes do not reduce the total load but lead to longer contact times for extended biodegradation. Laboratory experiments showed that high clay and silt content is crucial for maximum adsorption. However, redox conditions play an important role for degradation rates: under aerobic conditions half lives of less than one day occured frequently whereas anoxic conditions resulted in lag phases of one day and more as well as in half lives of up to 25 days. Field experiments could show that temperature is crucial for degradation velocity under natural conditions.

The behaviour of residues of phenazone-type pharmaceuticals during bank filtration was investigated at a field site in Berlin, Germany, where bankfiltered water is used for drinking water production. The concentrations of the pharmaceutical residues in the shallow, young bank filtrate (travel times < 1 month) were correlated to the prevailing hydrochemical conditions at the field site. In addition, their behaviour in an undisturbed sediment core from the lake base at the site (clogging layer) was evaluated in the laboratory. Phenazone, 4-acetylaminoantipyrin (AAA), 4formylaminoantipyrin (FAA) and 1,5-dimethyl-1,2- dehydro-3pyrazolone (DP) were eliminated more efficiently under oxic conditions, while 1-acetyl-1-methyl-2-dimethyloxamoyl-2phenylhydrazide (AMDOPH) was not eliminated at all. The redox conditions and the elimination of the respective pharmaceutical residues displayed strong seasonal variations. Oxic conditions were only encountered close to the shore in winter, when temperatures were low. The column study showed that the elimination is restricted to the uppermost decimetres of the lake base, where oxygen is present. While phenazone elimination is almost complete during aerobic rapid sand filtration in the waterworks, the compounds were found to be more persistent under anoxic field conditions.

Within the scope of the interdisciplinary NASRI research project (Natural and Artificial Systems for Recharge and Infiltration) dealing with river bank filtration processes at Berlin water works, a semi-technical column experiment is ongoing since January 2003 to simulate river bank filtration. Here a 30 m long ensemble of 6 soil columns is operated by surface water sampled from Lake Tegel (Berlin, Germany). In April 2004, oxic conditions in the column ensemble were forced to change in anoxic by gassing the flushing solution supply with nitrogen gas. The objective of reactive transport modelling was to (i) identify the main biogeochemical processes and the governing redox conditions within the soil column system during flushing as a conceptual model for river bank filtration and to (ii) verify the observed hydrochemistry of the pore water.

Cyanobacterial toxins are substances produced by cyanobacteria that occur in surface waters world wide. The most common group of cyanobacterial toxins is the group of structurally similar microcystins (MCYST). Sand passage as used in slow sand filtration, artificial recharge and bank filtration has shown to be effective in eliminating microcystins in many cases. For secure drinking water production from surface waters infested by microcystins removal has to be ensured in a wide variety of cases met in the field. It was therefore the aim of experiments in technical and semitechnical scale on the UBA’s experimental field in Berlin to test some worst case scenarios for the reliability of microcystin elimination during sand passage. Experiments were conducted with virgin sand (no previous contact to MCYST) and high filtration rates as well as under anaerobic conditions. The results show that the greatest problem for MCYST elimination can be found under anaerobic conditions as degradation is not complete and may lead to harmful residual concentrations.