Riverbank filtration (RBF) denotes the process whereby river water is induced to infiltrate into a groundwater system by well operation adjacent to banks. In Central Europe, RBF has been common practice for 100 years to produce drinking water. Due to the easy implementation and little maintenance necessary, BF has been suggested to be a useful drinking water treatment for developing and newly-industrialised countries. Experience from Europe has demonstrated that RBF is suitable to remove a range of organic and inorganic contaminants while an exhaustion of cleaning capacity has not been observed. RBF systems can mitigate shock loads and are particularly known for the efficient removal of pathogens, suspended solids and algal toxins from surface water, all being water quality parameters of high relevance in developing and newly-industrialised countries. Another benefit of RBF operation is the storage capacity which may help to balance freshwater availability in areas experiencing high variations of precipitation and run-off. This report aims at evaluating the relevance and opportunities of RBF systems to provide safe water to these countries. In order to evaluate the relevance and opportunities of RBF systems to developing and newly-industrialised countries, the report is structured to address key considerations and (i) identify prerequisites for successful RBF operation based on the experience in Central Europe and the United States, (ii) assess the removal potential of RBF for various water contaminants based on available literature, the TECHNEAU investigations in India and NASRI data from Berlin and (iii) evaluate the sustainability and relevance of RBF operation with regard to the particular needs in developing and newly-industrialised countries.

While climate change is an emerging hazard to water supply, literature on the vulnerability of bank filtration (BF), a proven technique of drinking water production in Central Europe and North America, is yet scarce. The Intergovernmental Panel of Climate Change (2007) has projected a global temperature increase between 1.1 and 6.4 °C by 2100. This will affect vital factors for water supply such as precipitation regime, groundwater recharge, run-off, river discharge and raw water quality. Projections on climate change and the implications are difficult because of the uncertainties associated with climate scenarios and modelling. However, in Europe and North America where BF is in operation, the projected increase in seasonal floods and droughts has already been experienced. In addition, site-specific considerations (e.g. land use, demographic trends) are to be taken into account to evaluate the potential impacts on water supply. To fill the current gap in literature, this report provides a first overview on how changing environmental conditions may affect BF operation.

The use of groundwater for public water supply and irrigation has many benefits for water suppliers as well as for consumers. Over the last decades availability and consumption of this valuable resource has increased worldwide along with technical progress, but it has often been ignored that any abstraction of groundwater is an intervention in the balance of the natural water cycle. Managed aquifer recharge (MAR) present the double interest : 1. to be a possible technical answer to over-exploitation of groundwater reservoirs and can contribute to water resource preservation and possibly reuse 2. to provide a natural cleaning step to pre-treat surface water for drinking water supply, and therefore could contribute to reduce the need for highly sophisticated treatment methods which are cost intensive in installation and also in maintenance. In many parts of the world, such as low income countries, MAR offers the possibility to profit from the storage and purification capacity of natural soil/rock and to guarantee a sustainable management of groundwater. River bank filtration is an ancient and widely used method that currently provides water to a large number of population in EU (45% of Hungarian water supply, 16% of German water supply, 5% of The Netherland water supply). River bank filtration relies on natural conditions to operate efficiently and allow to produce a quality of water which, in some cases, doesn't required further treatment before distribution (such as in Berlin). There are now many evidences that global environmental conditions are progressively changing and may impact existing water supply scheme by bank filtration. The extensive study of bank filtration systems in different environmental settings (such as in India with higher temperature, different surface water quality, systems subject to monsoons and flooding …) will allow apprehending the limitation that current bank filtration systems may face, and highlight the possible need for adaptive strategies. The aim of this report is to document work performed within the first 6 months since the start of WP 5.2 of TECHNEAU integrated project and to give an overview of the results and future planning. This includes detailed regional investigations, field studies and laboratory work performed in collaboration between the KompetenzZentrum Wasser Berlin gGmbH (KWB), the Indian Institute of Technology in Delhi (IIT) and the Freie Universität Berlin (FUB). Preliminary studies at potential sites in different parts of the world were performed prior to the TECHNEAU Project with the aim to investigate their suitability for RBF and thus to allow for deeper investigation within TECHNEAU. These preliminary studies were carried out in the cities Kaliningrad (Russia), Recife (Brazil) and New Dehli (India), and were funded by Veolia Water. In Recife (Brazil), the investigation performed by the FUB showed that both hydrogelogical data and model results indicate that the area is not suitable for the production of drinking water by RBF in sufficient amounts due an unfavorable hydrogeological conditions (too low transmissivity of the target aquifer because of the low content of sand in the samples and the scarce distribution of sandy sediments). At this point further investigations were stopped since no alternative field site area was found. In Kalingrad, water quality data that was gained in the preliminary study from the field site and will be compared with the data gained from investigations in Delhi and Berlin. In Delhi, India, the appropriate conditions, as well as the establishment of a valuable collaboration with the IIT, has lead to the implementation of three different field sites (in three different conditions). The activity performed within the techneau framework and included (i) the integration of existing information and literature on local climate, geology and water supply system, (ii) the detailed investigation about the local hydrogeology and ground and surface water quality and (iii) the development of a GIS (Geo Information System). In agreement with local authorities, three different field sites were selected in the territory of Delhi, representing distinctly different environmental conditions within the district. According to local conditions, a net of 17 groundwater observation points (piezometers) has been designed and installed on each of the field sites. A description of local geology, including stratigraphical charts has been elaborated, based on the evaluation of information obtained during the drilling and from analysis of sediment samples. A strategy for monitoring of water level and water sampling analysis has been developed, and monthly field campaigns have been carried out. Water samples have been analyzed, considering a broad variety of parameters including major chemical contents, trace substances and pathogens. Hydraulic tests have been conducted to obtain aquifer properties in order to estimate travel velocities during underground passage.

Im Oktober 2006 wurde das NASRI (Natural and Artificial Systems for Recharge and Infiltration) Projekt, ein Vorhaben der Kompetenzzentrum Wasser Berlin gGmbH, endgültig mit einer öffentlichen Präsentation der wichtigsten Ergebnisse abgeschlossen. In fast vier Jahren interdisziplinäre Forschungstätigkeit untersuchten mehr als 40 Wissenschaftler aus mehreren Berliner Universitäten und dem Umweltbundesland, gemeinsam mit den Berliner Wasserbetrieben die Prozesse während der Uferfiltration und künstlichen Grundwasseranreicherung. Es war ein Hauptziel des Projektes ein umfassendes Prozessverständnis zu entwickeln, um so die nachhaltige Nutzung der Uferfiltration und künstlichen Grundwasseranreicherung unter Berücksichtigung zukünftiger Anforderungen und Bedrohungen langfristig sicherzustellen.

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.

The redox conditions below an artificial recharge pond in Berlin were largely dependent on seasonal temperature changes of 0-24 °C in the infiltrate. Aerobic conditions prevailed in winter, when temperatures were low, while anaerobic conditions were reached below the pond when temperatures exceeded 14 °C. In contrast to temperature changes, cyclic changes between saturated or unsaturated conditions below the pond had only a minor effect on the redox conditions. However, the intrusion of gaseous oxygen during unsaturated conditions caused a temporary reinforced increase in oxidation of particulate organic matter. The effect of variable redox conditions on the behaviour of a number of pharmaceutically active compounds, namely carbamazepine, phenazone and several phenazone-type PhACs, was investigated. 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. 1-Acetyl-1-methyl-2-dimethyl-oxymoyl-2-phenylhydrazide (AMDOPH) and carbamazepine are very persistent drug residues. However, results suggest that AMDOPH may be slightly degradable under aerobic conditions too, but further studies will be needed to verify this statement.

Reactive multicomponent transport modeling was used to investigate and quantify the factors that affect redox zonation and the fate of the pharmaceutical residue phenazone during artificial recharge of groundwater at an infiltration site in Berlin, Germany. The calibrated model and the corresponding sensitivity analysis demonstrated that temporal and spatial redox zonation at the study site was driven by seasonally changing, temperature-dependent organic matter degradation rates. Breakthrough of phenazone at monitoring wells occurred primarily during the warmer summer months, when anaerobic conditions developed. Assuming a redoxsensitive phenazone degradation behavior the model results provided an excellent agreement between simulated and measured phenazone concentrations. Therefore, the fate of phenazone was shown to be indirectly controlled by the infiltration water temperature through its effect on the aquifer’s redox conditions. Other factors such as variable residence times appeared to be of less importance.