Purpose: The transport behavior of human pharmaceuticals in groundwater depends on a multitude of factors such as the physico-chemical conditions in the aquifer and the organic carbon content of the sediment, and, in particular, on the redox conditions in the groundwater. This is of special interest at managed aquifer recharge sites where the occurrence of trace organics is important for drinking water production. The aim of this study was to evaluate the possibility of influencing the redox system of the aquifer in a way that optimizes the potential of managed aquifer recharge systems to reduce the amount of trace organics. Materials and methods: Column studies were performed using natural and thermally treated sediments from an infiltration basin of the Berlin area, Germany. Special emphasis was placed on thermal treatment of the sediments to influence the total organic carbon (TOC) content in the sediment. In one experiment, the sediment was thermally pretreated at 550 °C, in two experiments the sediment was pretreated at 200 °C, and in one the sediment was untreated. Furthermore, the influence of ozonation, a very common disinfectant used in drinking water production, was studied in the experiments. The retardation and degradation parameters for primidone (PMD), carbamazepine (CBZ), and sulfamethoxazole (SMX) under different redox conditions were evaluated. Results and discussion: Oxic conditions were obtained in the experiment with low TOC (0. 06 wt%) in the sediment pre-treated at 550 °C. Anoxic conditions were predominant in two column experiments with a TOC content of 0. 17 wt% in the sediment, irrespective of the mode of treatment (natural or 200 °C). All three pharmaceutical compounds show almost conservative transport behavior with retardation factors between 1. 02 and 1. 25 for PMD, between 1. 06 and 1. 37 for CBZ, and between 1. 00 and 1. 08 for SMX. Differences in the transport behavior were observed depending on the TOC content of the sediment. For CBZ, and to a minor extent for PMD, the higher retardation factors were observed in the sediment with a TOC content of 0. 17 wt% under anoxic conditions. The ozonation of the influent water affects the influent concentrations of PMD, CBZ and SMX. However, it has no influence on the oxygen concentration of the column outflow. Conclusions: CBZ and PMD are retarded in the presence of organic matter in the aquifer. Variations of the TOC content of the sediment have a direct influence on the retardation of CBZ and PMD. The three human pharmaceuticals may be ranked in order of decreasing retardation: CBZ & PMD & SMX. The microbial activity in the experiments was not studied, although it can be assumed that the thermal pretreatment influences the microbial activity in the sediments. In particular, the microbial activity was severely inhibited at 550 °C, resulting in a shift of the redox conditions.

Artificial Recharge (AR) is a method to replenish groundwater in case of insufficient water availability or poor quality. For drinking water production, AR is often used as water purification step to avoid direct surface water abstraction. Besides physical filtration, purification is achieved through chemical processes like precipitation, sorption and (bio-) degradation. These are usually closely linked to redox conditions. It is the activity of micro-organisms and related chemical reactions that change the redox conditions, which in turn control the presence of substances and therefore the water quality. Typical pollutants in surface water that need to be addressed are organic compounds (e.g. pharmaceutical residues or pesticides), pathogens and heavy metals. The purpose of this report is to introduce the theoretical background on redox zoning in infiltration ponds and to review publications in the search for applicable methods capable of controlling redox conditions. This shall serve as basis for further laboratory and technical scale experiments in the course of the OXIRED project. The “optimal redox zonation” for maximum removal of redox-dependent substances is a concept with the aim of defining optimum residence times based on the degradation kinetics of contaminants in the source water: If substances or substance groups that show enhanced removal under anoxic to anaerobic conditions are not present in the source water at drinking water relevant concentrations, anoxic to anaerobic conditions should be avoided in order not to mobilize iron and other inorganic trace elements. Maximum benefit for aerobic subsurface passage is reached after 30 d, for anoxic / anaerobic subsurface passage after 100 d. However, already 15 d of aerobic and 2 d of anoxic / anaerobic passage lead to substantial removal or redox-sensitive substances or substance groups. The main drivers for redox zonation in AR systems are the availability of oxidizing agents (oxygen, nitrate), of reducing agents (organic matter, reduced mineral phases), of nutrients, the biological activity (in infiltration pond and subsurface), and the residence time. These drivers are in turn controlled by many natural, site-specific (exogenous) and design & operation-related (decision) variables. Exogenous variables are e.g. aquifer geochemistry, temperature or natural groundwater recharge whereas the decision variables comprise factors such as pond geometry, distance between pond and well, well depth, pumping rate etc. Theoretically, a wide range of possibilities could be applied to adjust the infiltration pond, the hyporheic zone and the subsurface passage, but only few seem technically feasible. These are e.g. the control of sunlight and temperature in the infiltration pond and upper sediment, the control of water movement in the pond to avoid excessive algal growth while enriching the water with oxygen. For the same reason nutrients could be added or avoided, influencing biomass production. Specific filter material could be used with defined content and characteristic of organic carbon to serve as electron acceptors. Infiltration rates could be controlled by adjusting the hydraulic head in order to enhance the formation of an unsaturated zone. Further downstream the application of redox controlling substances via injection wells could be possible, as well as controlling the residence times by adjusting pumping rates or creating hydraulic barrier wells at different distances from infiltration pond. For newly constructed AR systems the well field design (pond geometry, distance between pond and well, well depth) could be optimized with respect to redox zonation, as long as the other requirements (mainly sufficient production rates) are met. No examples for redox control in infiltration ponds were identified. Therefore, two examples of redox control measures are described: the first serves an artificial reoxidation of a polluted aquifer “BIOXWAND®” and the second provides injection of treated water to influence the redox conditions in the aquifer “Vyridox” and “Nitridox”.

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.

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.

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.

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.