Artificial groundwater recharge (AR) is used as semi-natural pre-treatment for drinking water production in Berlin and many other sites world-wide. Earlier research has focussed on the degradation of organic substances in these recharge systems (NASRI final reports 1 – 6), and has improved our knowledge of AR in the specific sites in Berlin. Nevertheless, a process understanding which might enable a transfer to other sites and boundary conditions is still lacking. Since biodegradation – which is assumed to be the main removal process of organic compounds – depends on the presence and activity of microorganisms, characterisation experiments with respect to biological activity will help to interpret results from soil column experiments simulating AR. In this stage of the OXIRED project, it will be of interest to link biological activity to degradation patterns in soil columns. Therefore, the following questions related to microorganisms could be necessary to answer: 1) How many are there? 2) How active are they? 3) Who is living there? A review of published literature yielded that in general, soils and sediments contain great numbers of microorganisms. Whereas in surface soils concentrations of culturable microorganisms can be found in the range of 108 per gram of dry soil, the number of culturable organisms in the subsurface are dependent on depth and are generally lower. In order to analyse them, adapted sampling methods and a sound sampling strategy are necessary for a reliable overview of microbial life. Another important aspect of microbial investigations is the detachment of organisms from biofilms for which enzymatic based methods have proven to be very useful. Different microbiological and biomolecular methods were described and assessed with respect to their suitability: 1) Cultivation: Since less than 1% of the microorganisms in natural environments can be cultured they will not be useful when one aims to get more insight into the microbial community. 2) Nucleic acid based techniques: Whereas DNA based primers can be used to detect specific species, general primers can be used to get a broad overview of the microbial life within a sample. Furthermore, active organisms can be detected by the use of RNA based primers. 3) Physiological technique: Microbial activity can be estimated indirectly based on AOC or BDOC measurements. To assess the micro-organisms present in soil columns and their activity the following methods are recommended: (i) Substrate degradation assessments by BDOC (or AOC) measurements (normally done in column studies) (ii) Direct counts (DAPI/ Acridine Orange) of direct extracted organisms and organisms present on buried slides. (iii) DGGE with universal primers (iv) qPCR (v) Direct counts with LIFE/DEAD staining and (vi) CTC redox dye o Clone libraries constructed from DGGE bands In addition to an extensive literature database of references for further details the results are summarized in a table with an overview of methods for detection, quantification and activity assessments of microbial communities in soils and sediments.

The project OXIRED 2 started in January 2010 as a continuation of OXIRED 1. The project is guided by KompetenzZentrum Wasser Berlin (project leader Dr. G. Grützmacher); it is sponsored by Berliner Wasserbetriebe (BWB) and VEOLIA Eau. WP3 (Redox Control and Optimization at AR Ponds) consists of two main parts: (I) Laboratory column experiments with special emphasis on sediment characteristics (by TUB) and (II) Numerical modeling of the results of the TUB column experiments (by UIT). The present report belongs to Part II of WP3. In Berlin, around 70 % of abstracted groundwater originates from riverbank filtration and artificial recharge (AR). During percolation and subsurface passage the quality of the infiltrated water improves due to physical filtration, sorption and biodegradation. Biodegradation is a major driver for redox zonation and so it is highly influenced by redox conditions, too. The main purpose of WP3 is to investigate these processes in column experiments including its numerical simulation.

In the 2nd phase of the project (OXIRED 2), trials at lab and technical scale were conducted to validate the results for trace organic and DOC removal from OXIRED 1 and to gain a more reliable knowledge about oxidation by-product formation for surface water from Berlin. To assess the stability of the process, a pilot unit was operated at Lake Tegel. Moreover the effect of oxidation + MAR on toxicological parameters was investigated (s. D 1.1). To prepare a field study three sites in Germany were evaluated regarding their suitability including parameters such as aquifer depth and composition, source water quality and possibility of authorization (s. D 2.1). The results were that none of the sites (Hobrechtsfelde, Braunschweig WWTP or artificial recharge site in Görlitz) was identified as suitable. The current state-of-the-art for influencing the redox zonation in the subsurface was reviewed (D 3.1) and the options to assess the quantity, composition and activity of the microbial population in the soil samples were summarized (D 2.2). To investigate the dynamic of redox processes, short term column tests were conducted (D 3.2). On the basis of these results reactive flow and transport modelling was carried out (D 3.2 and 3.3). The aim of this report is to give a summary of the main results from OXIRED 2 and to identify promising opportunities for further experiments and transfer to field scale.

Cyanobacteria of the order Nostocales – native species as well as alien species from tropical regions – were found to increase in many Brandenburg lakes while the formerly dominating microcystin (MC) producing cyanobacteria (Microcystis and Planktothrix) occurred less often and in lower amounts. As a consequence, lower MC concentrations were observed while the toxin cylindrospermopsin (CYN) that is produced by Nostocales was found to be widely distributed and to exceed sometimes the recommended guideline value for drinking-water of 1 µg L-1. Recent data on the occurrence of further neurotoxins (paralytic shellfish poisoningtoxin, PSP and anatoxin, ATX) produced by cyanobacteria of the order Nostocales did not exist. Nostocales are superior competitors under conditions of high light intensity and nitrogen depletion because they can fix molecular nitrogen. Their germination is regulated by temperature and the temporal starting point of the pelagic population determines the population size (the earlier the larger). Therefore, the following working hypothesis has been put forward: Combined effects of declining trophic state and global warming favor the development of Nostocales and cause a shift in the species composition as well as in the occurrences of cyanobacterial toxins. The NOSTOTOX project aimed to determine the present occurrence and future development of Nostocales and their toxins in waterbodies. Special emphasis was paid to answer the question, which Nostocales species and which toxins can be expected under conditions of a proceeding decline in trophic state and increasing water temperature. The outcome of the project aims to contribute to developing recommendations and guidelines for the management of inland waters and drinking water supplies.

The redox environment is of utmost importance for the removal of organic compounds during artificial recharge. Within the research project OXIRED-2 five laboratory sand column experiments with natural sediments from the Lake Tegel infiltration pond and with microsieved surface water from Lake Tegel (Berlin) were performed to study the possibility to control the redox environment. Special emphasis was given to the sediments, the set-up of the column experiments, and the contact time within the column. The sediment was used either untreated or heated to 200°C or 550°C to study the effect of activation of organic carbon at 200°C and the effect of at least partial removal of natural organic carbon at 550°C. Additionally, an artificially produced iron coated sand was used for a two-layer experiment to increase the residence time of compounds susceptible to sorption within a given redox zone. Results reveal an immediate decrease of oxygen content at the outflow of the column in every experiment. Likewise, the redox potential also dropped significantly and immediately after the experiments started. However, the redox potential was significantly lower (approximately – 200 mV) in the experiments with the untreated or slightly heated sediments, and higher (about + 300 mV) for the experiment with the sediment heated up to 550°C. The redox zones known in natural environments developed also within the experiments even down to sulfate reduction at experiment No. 2. Ozonation of the influent water did not change the redox environment at the outflow of the column indicating a high reduction capacity of the natural sediment in the column within the duration of the experiments of up to 19 days. A constant input of ozone and an extended duration of the experiments might lead to a depletion of organic carbon in the sand column which could increase the redox potential. However, a complete depletion of organic carbon is very unlikely for managed aquifer recharge systems. The two-layer experiment with natural sand and artificially produced iron coated sands revealed that the iron coated sands had no influence on the redox system and only slight effect on the transport of ions. However, combining layers with different functionality might show great opportunities for designing and controlling redox systems especially with specific residence times in different redox zones for certain compounds in mind.

Natürliche und künstliche Systeme zur Infiltration von Wasser (im Englischen: Managed Aquifer Recharge) werden weltweit genutzt, um Grundwasserressourcen quantitativ oder qualitativ zu verbessern. Dies erfolgt beispielsweise bei der Uferfiltration oder künstlichen Grundwasseranreicherung zur Trinkwassergewinnung, bei der Klarwasserverregnung zur weiteren Abwasserreinigung und -nutzung oder bei der Injektion von Süßwasser als hydraulische Barriere in Salzwasserintrusionsgefährdete Grundwasserleiter. Dabei nutzt man nicht nur den mengenmäßigen Ausgleich von überbeanspruchten Grundwasserressourcen, sondern auch die Reinigungsleistung des Untergrundes für eine naturnahe und meist auch kostengünstige Wasseraufbereitung. In Berlin, wo seit über 150 Jahren Trinkwasser mittels Uferfiltration gewonnen wird, wurden in Zusammenarbeit mit den Berliner Universitäten in der Vergangenheit umfangreiche Untersuchungen zur Stoffelimination bei der Untergrundpassage durchgeführt. Diese zeigten, dass auch die Konzentrationen von organischen Spurenstoffen häufig bei der Infiltration oder weiteren Grundwasserleiterpassage zurückgehen. Eine statistische Auswertung von Beobachtungen an verschiedenen Standorten ergab, dass die Mehrheit der untersuchten Substanzen wie beispielsweise Clofibrinsäure, Diclofenac und Phenazon bevorzugt unter oxischen Bedingungen abgebaut werden oder generell eine gute Entfernung erfahren. Einige wie z.B. Carbamazipin oder Sulfamethoxazol werden vor allem unter anoxisch- bis anaeroben Bedingungen entfernt. Aus diesen Beobachtungen ergab sich die Frage, ob ein optimaler Redoxzustand bzw. eine optimal Redoxabfolge für Systeme wie Infiltrationsbecken definiert werden könnte. Erste theoretische Studien erfolgten auf der Basis verfügbarer Abbaukinetiken und unter Einbeziehung weiterer Redox-sensitiver Wasserinhaltsstoffe wie Nitrat und Eisen. Diese ergaben, dass eine Aufenthaltszeit von 30 Tagen im aeroben Milieu und 100 Tagen im anoxischen Milieu während der Untergrundpassage zu einer optimalen Entfernung Redox-sensitiver Problemstoffe führt. Jedoch können bereits 15 Tage aerobe und 2 Tage anoxische / anaerobe Untergrundaufenthalt zu einem deutlichen Rückgang dieser Stoffe führen. Generell sollte jedoch berücksichtigt werden, dass unter anoxischen bis anaeroben Bedingungen mit einer Mobilisierung geogener Spurenelemente wie Eisen und Mangan zu rechnen ist. Obwohl theoretisch eine Vielzahl an Möglichkeiten existiert, den Infiltrationsbereich, die hyporheische Zone und die Untergrundpassage im Hinblick auf eine optimierte Redoxzonierung zu modifizieren oder gar zu steuern, sind nur wenige technisch tatsächlich machbar. Weitere Untersuchungen sollen nun diejenigen Möglichkeiten identifizieren, die in die Praxis übertragbar sind und zu einer Optimierung der künstlichen und natürlichen Systeme zur Infiltration beitragen könnten.

It was the aim of the EU funded research project TECHNEAU to investigate the relevance and feasibility of bank filtration (BF) plus post-treatment for newly industrialised and developing countries. Field studies at BF sites in Delhi (India) were supplemented by literature studies and modelling in order to investigate if this natural drinking water (pre-) treatment is a sustainable option to provide safe drinking water for countries like India. The results showed that especially for those substances that are of relevance in newly industrialised and developing countries subsurface passage can represent an efficient barrier. However, certain limiting factors for BF application also need to be considered: high ammonium levels in surface water, usually associated with high shares of poorly or un-treated sewage, will not be mitigated during subsurface passage and require extensive post-treatment. In order to support decision makers in the difficult task of assessing the feasibility of BF systems at a certain site a simple decision support system was developed. This simple tool enables to assess a range of abstraction rates and well locations for a specific field site that could fit with their needs (e.g. minimum required travel time or share of BF).

This paper presents the results of an evaluation of the environmental footprint of the Braunschweig wastewater scheme with Life Cycle Assessment. All relevant inputs and outputs of the system are quantified in a substance flow model and evaluated with a set of environmental indicators for cumulative energy demand, carbon footprint, acidification, eutrophication, and human and ecotoxicity. The analysis shows that energy demand and carbon footprint of the Braunschweig system are to a large extent offset by credits accounted for valuable products such as electricity from biogas production, nutrients and irrigation water. The eutrophication of surface waters via nutrient emissions is reduced in comparison to a conventional system discharging all effluent directly into the river, because some nutrients are diverted to agriculture. For human and ecotoxicity, a close monitoring of pollutant concentrations in soil is recommended to prevent negative effects on human health and ecosystems. Normalised indicators indicate the importance of the primary function of the wastewater system (= protection of surface waters) before optimisation of secondary environmental impacts such as energy demand and carbon footprint. A further decrease of the energy-related environmentalfootprint can be reached by applying optimisation measures such as the addition of grass as co-substrate into the digestor, thermal hydrolysis of excess sludge, or nutrient recovery from sludge liquors.

Triggered by climate change, local freshwater scarcity and rising public awareness towards ecological issues, environmental aspects are becoming key decision criteria for planning of urban water management infrastructure. Simultaneously, the implementation of measures according to the EU Water Framework Directive requires huge investments in the coming years for both upgrading of existing infrastructure and the construction of sewer networks or treatment plants. Among existing tools for environmental impact assessment, LCA offers the most accepted and comprehensive method to support decision makers with information on the environmental profile of new investments or upgrading of existing infrastructure. This paper describes on-going case studies using LCA for systems of urban water management and raises potential difficulties while applying LCA in the water sector.

This study presents the use of Life Cycle Assessment as a tool to quantify the environmental impacts of processes for wastewater treatment. In a case study, the sludge treatment line of a large sewage treatment plant is analysed in energy demand and the emission of greenhouse gases. Results show that the existing process is positive in energy balance (+166 MJ/PECODa) and GHG emissions (+19 kg CO2-eq/PECODa) by supplying secondary products such as electricity from biogas production and substituting fossil fuels in incineration. However, disposal routes for stabilised sludge differ considerably in their environmental impacts. In total, LCA proves to be a suitable tool to support future investment decisions with information of environmental relevance on the impact of WWTPs, but also larger urban water systems.