A modelling concept is presented that enables a quantitative evaluation of transport and natural attenuation processes during bank filtration. The aim is to identify ranges of degradation rates for which bank filtration is effective or ineffective. Such modelling should accompany experimental work, as otherwise the meaning of determined degradation rates for a field situation remains uncertain. The presented concept is a combination of analytical and numerical methods, solving differential equations directly for the steady state. It is implemented using FEMLABs code and demonstrates a typical idealized situation with a single well near a straight bank boundary. The method can be applied to confined, to unconfined and to partially confined/unconfined aquifers and may be extended for applications in more complex situations, including a clogging layer, galleries of pumping and recharge wells, etc.

In several slow-sand-filter experiments the behaviour of phages during the subsurface passage was measured and modelled. Here the focus is on the effect of the velocity. The observed data show a strong effect of decreasing filter efficiency with increasing velocity. Using a modelling approach, which is based on the transport differential equation, the theoretical influence of velocity on filter efficiency is examined. Finally an extrapolation of the results to large scale filtration units or bank filtration processes is attempted.

In several slow-sand-filter experiments the behaviour of phages during the subsurface passage was measured and modelled. Here the focus is on the effect of the velocity. The observed data show a strong effect of decreasing filter efficiency with increasing velocity. Using a modelling approach, which is based on the transport differential equation, the theoretical influence of velocity on filter efficiency is examined. Finally an extrapolation of the results to large scale filtration units or bank filtration processes is attempted.

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.

Die TU-Forschungsgruppe beschäftigt sich mit dem Verhalten von DOC und organischen Einzelstoffen bei der Uferfiltration. Die Forschung soll Einblick in die Vielzahl von Einflussfaktoren geben, die das Verhalten der Organik in der Bodenpassage beeinflussen. Unterschiedliche Redoxverhältnisse, Aufenthaltszeiten und Bodenbeschaffenheiten beeinflussen den Abbau der Organik. Die Forschung im Rahmen des NASRIProjektes konzentrierte sich in der ersten Phase auf ein umfangreiches Feldmonitoring, welches im Zeitraum Mai 2002August 2005 durchgeführt wurde. Dazu wurden drei Feldstandorte in Berlin ausgewählt, an welchen ein deutlicher Einfluss von behandeltem Abwasser auf das Oberflächenwasser vorliegt. Zusätzlich wurde eine Vielzahl von Experimenten an Bodensäulenanlagen durchgeführt. Neben einem 30 mBodensäulensystem in Berlin- Marienfelde, wurden eine redoxgeregelte Bodensäulenanlage und eine temperaturgeregelte Bodensäulenanlage für die Untersuchungen aufgebaut. Die Feldund Bodensäulenproben wurden mittels DOC, SAK, LC-OCD, differenziertem AOX und Spurenstoffanalytik (HPLC-FLD und HPLC-MS/MS) untersucht. 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 BDOC nur eine einmonatige Bodenpassage notwendig, während es unter anoxisch/anaeroben Verhältnissen aufgrund der langsameren Abbaukinetik bis zu 6 Monate dauern kann. Die Ergebnisse der DOCFraktionierung mittels LC-OCD zeigten, dass die Fraktion der Polysaccharide unter allen Bedingungen sehr schnell abgebaut wurde. Dagegen wurde für die anderen Fraktionen (Huminstoffe, Building Blocks etc.) nur eine partielle Entfernung beobachtet. Bezüglich der Spurenstoffe konnte gezeigt werden, dass das Röntgenkontrastmittel Iopromid in allen Felduntersuchungen schnell entfernt wurde. In den Bodensäulenexperimenten zeigte sich, dass die Entfernung durch Metabolisierung und nicht durch Mineralisierung zustande kam. Das Antibiotikum Sulfamethoxazole wurde unter anoxisch/anaeroben Verhältnissen effektiver entfernt (bis zu 80%), während unter oxischen Bedingungen maximal 50% der Ausgangskonzentration abgebaut wurden.

The aim of the study was to calculate mixing proportions of treated wastewater in the surface water and production wells during bank filtration as well as the travel times to observation and abstraction wells. For this purpose, a variety of tracers such as the stable isotopes deuterium (D) and 18O and several wastewater indicators like chloride, EDTA (ethylenediaminetetraacetic acid), boron and the rare earth element (REE) gadolinium (Gd) are used and compared to each other. Time series measurements in the surface water could be traced back in bank filtrates and raw water. Gd-DTPA was found to be a useful sewage indicator, even though it is biodegradable at favourable conditions at very slow rates. The travel times of the bank filtrates were obtained by the analysis of the peak shift in time-series of the tracer. Most tracers were found to be applicable but best results were obtained with the stable isotopes.

The transect of the bank filtration site at Lake Tegel is characterized with regards to their redox conditions using a Cluster analysis. Four different groups of observation wells could be found, enabling the derivation of a redox zoning with horizontal boundaries, which are moving downward during winter time. At the same site, Regression analysis served to examine influencing variables on the reduction of the pharmaceutical Carbamazepin during bank filtration. Two different regression models for summer and winter time were found, with each of them including the standardized temperature and the travel time as influencing variables. Whereas during winter time the redox conditions seem to have a significant influence on the reduction of Carbamazepin, the same influence could not be found for the reduction of Carbamazepin during summer time.

In the course of the interdisciplinary research project NASRI (natural and artificial systems for recharge and infiltration) many investigations are currently being carried out to assess the risk of break through of persistent organic substances into raw water used for drinking water supply. One part of these studies is the determination of the transport behavior of pharmaceutical residues in test sand filters, so called enclosures, equipped with sampling points at various depths. Breakthrough curves were determined for carbamazepine, primidone (both antiepileptic drugs), clofibric acid (a metabolite of blood lipid lowering agents), diclofenac, ibuprofen (both analgesic drugs) and for chloride, used as a conservative tracer. Retardation coefficients and degradation rates were obtained by using the software Visual CXTFIT. Degradation rates between 0.7 h–1 and 1 h–1 were observed for ibuprofen whereas clofibric acid, primidone, carbamazepine and diclofenac showed no or very little degradation (lambda < 0.06 h–1).

Hydrochemical conditions were evaluated at both bank filtration and artificial recharge sites in Berlin. All bank filtration sites show a strong vertical age stratification. Rather than showing a typical redox zoning with more reducing conditions in greater distance from the surface water, the redox zones are horizontally layered, with more reducing conditions in greater depth. This is believed to be an effect of the strongly alternating groundwaterlevels and by the age stratification. The redox conditions are generally more reducing at the bank filtration sites, mainly as a result of the longer travel times and operational differences. Redox conditions at all sites vary seasonally in particular at the artificial recharge site, which is mainly caused by temperature changes.

The aim of the study was to evaluate the influence of variable redox conditions on a number of pharmaceutically active compounds, namely carbamazepine, phenazone and AMDOPH (1-acetyl-1-methyl-2-dimethyl-oxymoyl2-phenylhydrazide) below an artificial recharge pond in Berlin. The redox conditions change seasonally, mainly as a result of temperature changes of 0 to 24°C in the infiltrate. Aerobic conditions prevail in winter, while manganese reducing conditions are reached below the pond in summer. Phenazone is redox sensitive and was generally fully degraded before reaching the first groundwater well as long as oxygen was present. When conditions turned anaerobic, phenazone was not fully eliminated. AMDOPH (1-acetyl-1-methyl-2-dimethyl-oxymoyl2-phenylhydrazide) and carbamazepine are very persistant drug residues. However, results suggest that AMDOPH may be degradable under certain favourable conditions (i.e. aerobic conditions; relatively high temperatures, low recharge rates), but further studies will need to verify this statement.