Work package WP 5.2 “Combination of Managed Aquifer Recharge (MAR) and adjusted conventional treatment processes for an Integrated Water Resources Management“ within the European Project TECHNEAU (“Technology enabled universal access to safe water”) investigates bank filtration (BF) + post-treatment as a MAR technique to provide sustainable and safe drinking water supply to developing and newly industrialised countries. One of the tasks within this work package is to assess the costefficiency of BF systems. For this a comparative cost analysis (CCA) between groundwater waterworks using BF as natural pre-treatment step and surface water treatment plants (SWTPs) is performed. The CCA yielded that, under the assumption of equally low surface water quality, BF systems are more cost-efficient than SWTPs. This result is in line with the general water source priority of water suppliers, which prefer resources with the best water quality and security under the constraint of guaranteeing sufficient water availability. Furthermore the sensitivity analysis confirmed that the natural boundary condition 'pumping rate per production well' has a major impact on the specific total costs of BF systems. Lower pumping rates lead to increasing capital costs for the additional production wells, which are not fully compensated through pumping cost savings and thus lead to increasing total costs. In addition the result of the monitoring scenario clearly confirmed that for this aspect groundwater waterworks have a structural disadvantage compared to surface waterworks. Subsequently, if monitoring costs are taken into account, a higher critical pumping rate per production well is required to exceed the break-even-point. In a nutshell the CCA shall support water supply managers in the complex process of making rational investment decisions. However, since within this analysis only water abstraction and treatment process costs are considered, the CCA does not cover the total cost structure of a waterworks (e.g. costs of building sites). Thus the application of the CCA is only valid if both (i) neglected costs and (ii) benefits are in the same order of magnitude for all alternatives (exception: most cost-efficient alternative provides excess benefits). In case that the above stated prerequisites are not fulfilled, the CCA is only a first step in the economic assessment and more powerful evaluation methods (e.g. cost-benefit analysis) are needed.

Brunnen werden seit Jahrtausenden zur Wassergewinnung genutzt. Doch erst seit wenigen Jahren spielt neben der Ergiebigkeit auch die Nachhaltigkeit von Brunnen eine Rolle, da Neubaugenehmigungen immer schwieriger und langwieriger zu erhalten sind. Durch optimale Auslegung des Brunnens und die Wahl des richtigen Standorts wird versucht, eine möglichst lange Betriebszeit zu erreichen. Trotz bester Voraussetzungen nimmt die Förderleistung von Brunnen im Laufe ihres Betriebes ab, das als Brunnenalterung bezeichnet wird. Die Alterungsrate ist abhängig von den geologischen und hydrochemischen Bedingungen, dem Brunnenausbau und dem Betrieb. Mithilfe vorbeugender oder reaktiver Instandhaltungsmaßnahmen wird versucht, die Leistung eines Brunnens möglichst lange zu erhalten oder wiederherzustellen. Die Wirtschaftlichkeit von Instandhaltungsmaßnahmen lässt zum „Lebensende“ eines Brunnens jedoch nach. Dann sollte der Ersatz des Brunnens geplant werden. Die vorliegende Arbeit ist Teil des durch das vom Kompetenzzentrum Wasser Berlin (KWB) durchgeführten Forschungsprojektes WELLMA, welches sich mit dem Betrieb und der Pflege von Trinkwasserbrunnen zur Optimierung der Leistung und der Wasserqualität beschäftigt. Hierfür sollte eine Methode getestet werden, die die Wirtschaftlichkeit von Regenerierungen eines Trinkwasserbrunnens mittels eines Vergleiches der Steigung der alterungsbedingten Betriebskosten und der Umlage des Gebrauchswertes bewertet. Ist die Steigung der Gebrauchswertumlage größer als die der alterungsbedingten Betriebskosten, lohnt sich eine weitere Regenerierung. Im gegenteiligen Fall wäre es wirtschaftlicher, den betroffenen Brunnen neu zu bauen. Außerdem sollte das wirtschaftliche Minimum der alterungsbedingten Betriebskosten prognostiziert werden, um daraus die Dauer der anstehenden Betriebsperiode ableiten zu können. Die Berechnung des methodischen Ansatzes erfolgte am Beispiel vier ausgewählter Brunnen der Berliner Wasserbetriebe. Zwei der vier Referenzbrunnen wurden aufgrund ihrer regelmäßigen präventiven Instandhaltung mit Wasserstoffperoxid (H2O2) ausgewählt, um zusätzlich deren Auswirkung auf die Wirtschaftlichkeit von Regeneriermaßnahmen beurteilen zu können. Die Berechnung der Referenzbrunnen bestätigte die Praxistauglichkeit des gewählten Verfahrens. Ausschlaggebende Parameter für die Kalkulation sind u.a. die spezifische Ergiebigkeit, die Anzahl der Betriebsstunden sowie die jährliche Abnahme der Fördermenge. Zudem bestätigte sich, dass durch den Einsatz von H2O2 eine Steigerung der spezifischen Ergiebigkeit erzielt wurde, in dessen Folge die Wahrscheinlichkeit auf eine weitere wirtschaftliche Regenerierung erhöht wird.

Berlin’s drinking water is produced from groundwater replenished by up to 60 % of surface water from the city’s abundant rivers or lakes using bank filtration or artificial groundwater recharge. Currently 700 production wells, located along the banks produce more than 200 Mio m³/a of drinking water, which is treated only for iron and manganese removal before distribution. This is due to the fact that different natural treatment processes (e.g. straining of particles, adsorption or biodegradation) occur during subsurface passage so that post-treatment effort is reduced. Compared to other bank filtration sites world wide, the situation in Berlin is characterized by low hydraulic conductivities but nevertheless high capacities. Interdisciplinary research projects have shown that travel times and redox conditions during subsurface passage are highly transient due to seasonal effects and discontinuous pump operation. Trace organics like pharmaceuticals and x-ray contrast media that occur in Berlin’s surface waters due to relevant shares of treated waste water are attenuated during subsurface passage to varying degree. Substances that were found to be poorly attenuated under oxic conditions or even persistent include carbamazipine, primidone, sulfamethoxazole, 1,5 NDSA, MTBE and EDTA. Under anoxic to anaerobic conditions others like phenazone and diclofenac show little removal. However, none of these substances occur at relevant concentrations in the finished drinking water due to low initial concentrations or additional removal during post-treatment. Research is currently focussing on hybrid systems combining subsurface passage with advanced drinking water treatment in order to be prepared in case higher source concentrations occur.

Bank filtration, i.e. the abstraction of groundwater from wells along a river or lake, thus inducing infiltration has a long history as (pre-) treatment step for drinking water production in Europe. The goal of this study is to assess whether groundwater waterworks using BF have a cost advantage compared to SWTPs if both, water abstraction and treatment processes are considered.

The herbicide Glyphosate was detected in River Havel (Berlin, Germany) in concentrations between 0.1 and 2 µg/L (single maximum outlier: 5 µg/L). As the river indirectly acts as drinking water source for the city's 3.4 Mio inhabitants potential risks for drinking water production needed to be assessed. For this reason laboratory (sorption and degradation studies) and technical scale investigations (bank filtration and slow sand filter experiments) were carried out. Batch adsorption experiments with Glyphosate yielded a low KF of 1.89 (1/n = 0.48) for concentrations between 0.1 and 100 mg/L. Degradation experiments at 8 °C with oxygen limitation resulted in a decrease of Glyphosate concentrations in the liquid phase probably due to slow adsorption (half life: 30 days).During technical scale slow sand filter (SSF) experiments Glyphosate attenuation was 70-80% for constant inlet concentrations of 0.7, 3.5 and 11.6 µg/L, respectively. Relevant retardation of Glyphosate breakthrough was observed despite the low adsorption potential of the sandy filter substrate and the relatively high flow velocity. The VisualCXTFit model was applied with data from typical Berlin bank filtration sites to extrapolate the results to a realistic field setting and yielded sufficient attenuation within a few days of travel time. Experiments on an SSF planted with Phragmites australis and an unplanted SSF with mainly vertical flow conditions to which Glyphosate was continuously dosed showed that in the planted SSF Glyphosate retardation exceeds 54% compared to 14% retardation in the unplanted SSF. The results show that saturated subsurface passage has the potential to efficiently attenuate glyphosate, favorably with aerobic conditions, long travel times and the presence of planted riparian boundary buffer strips.

Subsurface passage as utilized during bank filtration and artificial groundwater recharge has shown to be an effective barrier for multiple substances present in surface waters during drinking water production. Additionally it is widely used as polishing step after wastewater treatment. However, there are limitations concerning the removal of DOC and specific trace organics. The project ”OXIRED“ aims at assessing possibilities to overcome these limitations by combining subsurface passage with oxidation by ozone. Results from the first phase of the project have demonstrated that oxidation with ozone is a suitable method to reduce the concentrations of several relevant trace organic compounds (e.g. carbamazepine, sulfamethoxazole) and to significantly enhance biodegradation of DOC during subsequent soil passage. For efficient removal of DOC in the soil columns, specific ozone consumptions of 0.6 to 0.7 mgO3/DOC0 were sufficient. Project objectives in OXIRED-2 were to i) verify results from laboratory scale experiments at a larger scale with longer retention times, ii) study feasibility under field conditions with seasonal variations by operating a pilot unit, iii) evaluate the formation of oxidation by-products and their persistence during subsurface passage and iv) propose a standardized test protocol to analyse benefits of ozonation and artificial groundwater recharge at different sites. To investigate effects of ozonation on groundwater recharge with longer retention times, a technical scale column system with a length of 30 m and a hydraulic retention time of approximately six weeks was operated at the UBA’s experimental site in Berlin Marienfelde. Pilot studies were conducted at Lake Tegel using an ozone unit from ITT-Wedeco with a 4 g/h generator and subsequent slow sand filtration. Reduction of bromate was assessed in laboratory scale soil columns under different redox conditions. In addition, anoxic reduction of bromate was evaluated in a diploma thesis at TU Berlin. To analyse effects of DOC removal after ozonation, a standardized test protocol using recirculating columns was proposed and tested. Results from the different experiments confirmed the conclusions of the first phase of the project. Removal of surface water DOC during infiltration significantly increased with preozonation. In pilot studies, effluent DOC of approximately 4.7 mg/L after 1 d of retention time was measured, which is comparable to residual DOC from artificial groundwater recharge in Berlin Tegel after 30 days retention time [1]. In addition, strong effects of temperature on DOC removal were observed. During experiments with ozonation, overall DOC reduction decreased from approximately 40% in October to about 30% in the end of November. Biological testing of slow sand filter effluent revealed no genotoxic or cytotoxic effects in the water prior to further infiltration into the aquifer. Many persistent trace compounds were efficiently transformed during ozonation with specific ozone doses of 0.8 mg O3/mg DOC0. For example, realistic surface water concentrations of carbamazepine, sulfamethoxazole, phenazone and bentazone were reduced below the limits of quantification (LOQ). Primidone was only partly transformed during ozonation (70%). Since primidone is persistent during infiltration, a breakthrough in combined ozonation and artificial recharge can be expected. Also the substances MTBE and ETBE, the pesticide atrazine and some metabolites detected in Lake Tegel persist partially during treatment with ozone and subsequent groundwater recharge. For efficient transformation of these substances, higher ozone doses or an optimisation of the oxidation process, for example as advanced oxidation process (AOP), should be considered. Efficient reduction of the concentration of adsorbable organic iodine (AOI), an indicator for x-ray contrast media, during ozonation or infiltration was not observed. In contrast, adsorbable organic bromine decreased by 70 - 80 % during ozonation. Formation of the oxidation by-product bromate during ozonation of Lake Tegel water with a specific ozone consumption of up to 1.0 mg O3/mg DOC0 was below the limit of the German drinking water directive. Removal during subsurface passage was observed under anoxic conditions in presence of biodegradable organic carbon. Since artificial recharge after ozonation is likely aerobic, no significant reduction of bromate can be expected. Thus, formation of bromate needs to be controlled during surface water ozonation. Formation of nitrosamines was monitored in batch experiments with a specific ozone consumption of up to 1.15 mg O3/mg DOC0. No formation of nitrosamines including NDMA (LOQ: 5 ng/L) was observed. Operating a preceding bank filtration step will reduce ozone demand for efficient DOC removal. In addition, problems with particles from source water can be minimised. However, additional energy consumption for operation of extraction wells has to be taken into account. Overall, the presented results confirm that the objectives of enhanced removal of trace organics and DOC by combining ozonation and subsurface passage are well met. Further investigations need to focus on seasonal variations in long-term pilot studies and the formation, retention and toxicity of transformation products.

The present study aimed at developing a universal method for the localization of critical source areas (CSAs) of diffuse nitrate (NO3-) pollution in rural catchments with low data availability. Based on existing methods, land use, soil, slope, riparian buffer strips and distance to surface waters were identified as the most relevant indicator parameters for diffuse agricultural NO3- parameters were averaged in a GIS-overlay to localize areas with low, medium and high risk of NO3- pollution. The five parameters were averaged in a GIS-overlay to localize areas with low, medium and high risk of NO3- pollution. A first application of the GIS approach to the Ic catchment in France, showed that identified CSAs were in good agreement with results from river monitoring and numerical modelling. Additionally, the GIS approach showed low sensitivity to single parameters, which makes it robust to varying data availability. As a result, the tested GIS-approach provides a promising, easy-to-use CSA identification concept, applicable for a wide range of rural catchments.

Rural watersheds often face diffuse pollution problems due to agricultural activities. In the Ic watershed in Brittany (France), nitrate concentrations in rivers frequently exceed the EUthreshold of 50 mg-NO3 L-1, despite various actions to reduce the impact from agriculture. As a result, other solutions are considered, such as mitigation systems that can prevent transfer of agricultural pollutants from cropland to the streams. Constructed wetlands have been shown to fit this aim, because they can reach significant N removal for water residence times above ~12 hours, can be implemented decentrally within rural watersheds, while meeting cost and policy requirements. However, constructed wetlands require space, which is particularly scarce and costly in intensively used agricultural watersheds. As a consequence, it was decided to test a more area-effective solution in three pilot systems. On the one hand land-use itself was optimized (i) at site 1 by placing two wetlands with same inflow and dimension on an area of minor agricultural value adjacent to a stream (one surface and one subsurface-flow, both 20 x 10 meters) and (ii) at site 2 by building an elongated infiltration wetland (45 x 2 meters) directly in an existing drainage ditch, thus preventing any use of agricultural surface. In both cases farmers agreed to the placement of the wetlands free of charge. On the other hand it was attempted to raise the areal removal efficiency, with a focus on denitrification, since nitrate is of most concern with inflow concentrations to the sites ranging between 30 and 66 mg-NO3 L-1. This increase in denitrification is attempted (a) by increasing the range of anoxic zones within the wetlands and (b) by adding carbon sources. For (a) one wetland at each site is filled with gravel with bottom outlets to enforce underground passage. Moreover saturation level within the infiltration wetlands and thus hydraulic retention time, can be controlled at drain outlets. For (b) organically rich soil is added to both wetlands at site 1 and carbon sources are mixed with the gravel at site 2. The three wetlands have been constructed in 2010 and are currently monitored for flow and water quality at inlets, as well as at surface and subsurface outlets. The monitoring will allow the calculation of substance mass balances for the entire rain season, expected from December 2010 to May 2011.