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.

Managed Aquifer Recharge (MAR) comprises a wide variety of systems in which water is intentionally introduced into an aquifer and subsequently recovered, e.g. for drinking water or irrigation purposes. The objective is i) to store excess water for times of less water availability and / or ii) to introduce an additional barrier for purification of water from different sources (e.g. surface water, treated waste water) for a specific use. Common MAR techniques in Europe are (Figure 1): river bank filtration (RBF) and artificial groundwater recharge – usually via ponded infiltration (AR). Riverbank filtration (RBF) has a long history as a process for generating safe water for human consumption in Europe. During industrialization in the 19th century drinking water facilities in England, the Netherlands and Germany started using bank filtered water due to the increasing pollution of the rivers. The systematic production of bank filtrates started around 1870-1890 (BMI 1975, 1985). Since then, RBF and in case of insufficient quantity, artificial groundwater recharge (AR) have been generally applied as a first barrier within the drinking water treatment chain. The most common and widely used method for artificial groundwater recharge (AR) are infiltration ponds (Asano, 2007). These simple surface spreading basins provide added benefits of treatment in the vadoze zone and subsequently in the aquifer. Advanced pretreatment of the infiltration water by coagulation, and advanced post-treatment of the recharged water, e.g. with activated carbon or ozonation became necessary in many cases after the 1960’s as the quality of the source water further decreased. Today the water supply of many European cities and densely populated areas relies on riverbank filtration or artificial recharge. Following Castany (1985), in France, the proportion of bank-filtered water reaches approximately 50% of the total drinking water production (Doussan et al., 1997). In the Netherlands 13% of drinking water is produced from infiltration of surface water, such as bank filtration and dune infiltration (Hiemstra et al., 2003). In Germany riverbank filtration and artificial groundwater recharge are used in the valleys of the rivers Rhein, Main, Elbe, Neckar, Ruhr, and in Berlin along the Havel and Spree (Grischek et al., 2002). In Berlin 75% of the drinking water is derived from riverbank filtration and artificially recharged groundwater (Schulze, 1977). Riverbank filtration is also applied in the United States as an efficient and low cost drinking water pre-treatment technology (Ray et al., 2002), also to improve the removal of surface water contaminating protozoa. In most applications, MAR is intended to act as a buffer in terms of water availability (quantity) and water quality. In general, the level of knowledge of natural treatment systems, notably in aquifers, is not as high as in engineered systems, because the biogeochemical environment in aquifers that modify water quality for sure, will vary in space and time (Dillon et al. 2008). The heterogeneity of the system, strengthens its buffer potential on the one hand, but makes it more difficult to describe and control on the other hand. Key parameters that determine the quantitative storage capacity of the system are the specific hydrogeology of the aquifer (e.g. transmissivity and porosity) and the clogging potential at the entry point of the recharge water (infiltration pond, well or river bank). Clogging occurs due to physical, chemical and biochemical processes and needs to be regarded carefully as it may reduce the systems performance substantially. From literature it is known, that increased clogging reduces the oxidation state of the clogging layer. At a bank filtration site at Lake Tegel, Berlin, it was observed that intensity and spatial distribution of clogging strongly depends on the extent and thickness of the unsaturated zone. Geochemical observations suggest, that atmosperic oxygen induces redox processes which lead to a reduction of the clogging layer (Wiese & Nützmann 2008). This is possibly due to the complex interaction of hydrochemical and biological processes within the uppermost centimetres of the aquifer (Hoffmann et al., 2006). If these processes are likewise found in AR system, they may be influenced as to minimize basin-cleaning efforts. This needs to be further investigated. Water quality aspects of MAR are governed by i) the quality of the infiltrated / injected water ii) physical straining of particulate and particle-bound substances, iii) adsorption and desorption, iv) biogeochemical degradation / deactivation processes within the aquifer, iv) the geochemical composition of the aquifer, and v) the quality of the ambient groundwater. The process most important for MAR applications is usually the physical straining of particulate and particlebound substances, lessening the effort for subsequent drinking water treatment. In Berlin, e.g. disinfection of drinking water can usually be avoided due to complete removal of pathogens during underground passage of up to 6 months. Cyanobacterial toxins (e.g. microcystins) that are primarily cell-bound are efficiently removed as well (Grützmacher et al. 2007). On the other hand there is still a lack of understanding under which circumstances microcystins or other cyanobacterial toxins like cylindrospermopsin (currently observed in growing quantities in Germany) are released, thus becoming potentially more mobile in the subsurface. Adsorption to the aquifer matrix contributes to the elimination of organic substances and heavy metals. Although this does not remove the substances completely, peak loads – e.g. from oil spills – are retarded and maximum concentrations reduced. In addition, sorption prolongs the detention time in the aquifer which multiplies the time for biodegradation. Biological degradation in the subsurface is responsible for the elimination of dissolved organic carbon (usually resulting from natural organic matter, NOM) and organic trace substances that occur at varying extent. Investigations have shown that the redox potential in the aquifer is decisive for the degree of elimination (Stuyfzand, 1998; Massmann et al. 2007). Due to increasingly sensitive analytical methods trace organics present in surface waters (e.g. pharmaceutical residues) have been detected in many MAR systems e.g in Berlin and the Netherlands (Massmann et al, 2007, Stuyfzand et al. 2007). Advanced numerical models including reactive flow and transport can simulate the complex interactions between the hydrogeochemical environment and degradation of trace organics (Greskowiak et al. 2006). However, so far this has only been applied for a limited number of compounds at very few sites. Further research is needed to apply these methods for risk assessment. A second method for predicting the removal of organic micropollutants is the more statistically based approach of linking substance properties (molecular weight, number of double bonds, number of aromatic rings, etc.) to biodegradation via quantitative structure-activity relationship (QSAR) type models. This has been applied successfully to other water treatment methods – a transfer to MAR is lacking so far. As MAR is a technology that relies on the interaction of natural processes framework conditions like climate and hydrogeology play an important role. There is a need for testing the transferability from central European conditions to other regions, and for an assessment, how temperature changes affect the system’s elimination capacity. With ongoing climate change, reducing precipitation in some regions of Europe and increasing peak flow events in others, MAR is the ideal technology to act as a buffer for quantity and quality. The European Water Supply and Sanitation Platform (www.wsstp.org) for example has identified MAR as a technology potentially fit for future challenges.

The project “Organic Trace Substances Relevant for Drinking Water – Assessing their Elimination through Bank Filtration (TRACE)” aims at giving an up-to-date overview of the potential risk resulting from the occurrence of chelating agents, perfluorinated compounds (PFCs) and selected pesticides in surface waters and to show if there is a potential for the substances to persist during bank filtration and artificial recharge. During the first phase of the project which is subject of this paper, a literature study was conducted addressing their occurrence (in the Berlin region and elsewhere), amounts produced as well as data on their persistence in the subsurface. This was the basis for a decision on the substance applied in the field scale experiments at the UBAs experimental field during the following project phase. Using freely available databases (e.g. ULIDAT, DIMDI, Tiborder) 1148 references were screened for their relevance to these topics, and 450 of these were classified as relevant. Of these, so far the 223 most important references have been compiled in an ACCESS database which comprises data on the data origin as well as on specific values (e.g. measured concentrations, amounts produced, use, main metabolites, sources, pathways in the environment). The database links this information so that output forms (“fact sheets”) can be created that summarize all data for one specific substance. The regarded substances were subsequently classified according to the criteria: usage / production, occurrence in surface water (if possible also in groundwater and bank filtrate), degradation potential, biological degradability, production of relevant metabolites and toxicity. For the chelating agents three substance groups were examined closely: aminocarboxylates, hydrocarboxylates and phosphonates (all other substance groups were found to be irrelevant due to total biodegradability). The aminocarboxylates are produced in highest numbers and occur most frequently (especially EDTA, PDTA, NTA and DTPA). There are, however, already extensive investigations on this field so that few knowledge gaps were identified. Hydrocarboxylates are produced in lesser amounts and for some ready biological degradability has been shown. For these reasons further investigations were not seen as a priority. Phosphonates produce relevant metabolites (phosphates that enhance eutrophication) and are produced in high amounts (> 1000 t/a). This substance group was therefore recommended for further investigations. Currently a variety of research projects cover the field of perfluorinated compounds (PFCs) that occur in aquatic environments world wide and whose toxicity and persistence is not yet clearly determined. Most investigations aim at the main substances of this group: PFOA and PFOS. These are, however, currently being replaced by shorter chained PFCs on which investigations are lacking. This substance group is therefore also of interest for further investigations. For the pesticides glyphosate and isoproturone high production rates and frequent occurrence in surface and groundwater world wide were determined. Due to this fact and to the presence of relevant metabolites (e.g. AMPA) as well as to limited knowledge on their fate during underground passage these substances were classified as highly interesting for further investigations.