The UBA’s experimental field on the outskirts of Berlin offers a unique possibility of simulating bank filtration, artificial recharge and slow sand filtration on a technical scale. The site consists of a storage reservoir (pond) with an adjacent artificial aquifer consisting of sand and gravel. Additionally the surface water can be conducted into 4 infiltration basins (two slow sand filters and two aquifer infiltration ponds). Three enclosures as well as large scale columns can be used for shorter and longer term simulation of groundwater transport. The whole site is separated from the surrounding aquifer by a layer of clay. A variety of physico-chemical parameters can be measured continuously and observed online. The travel times for the bank filtration passage determined by tracer experiments range from a few days to a maximum of 3 weeks. In the enclosures, infiltration ponds and large scale columns contact time can be varied between a few hours up to 3 months.

Biofoulingprozesse bereiten in kommunalen und industriellen wasserführenden Leitungssystemen große Probleme. Um dem rechtzeitig entgegenwirken zu können, müssen solche Belagsbildungen frühzeitig erkannt werden. In diesem Zusammenhang wurde eine neuentwickelte optische Messsonde von 3 in Berlin ansässigen Industriepartnern in Zusammenarbeit mit der TU-Berlin auf die praktische Eignung für die Detektion von Biofilmen, und damit hinsichtlich ihres Einsatzpotentials in der Wasserwirtschaft untersucht. Der eingesetzte optische Sensor zeichnet sich dadurch aus, dass gleichzeitig bis zu 4 verschiedene optische Parameter bei bis zu 4 verschiedenen Wellenlängen online erfasst werden können. In den Experimenten wurden Zusammenhänge zwischen den Messsignalen und der Biofilmbildung dokumentiert, durch begleitende chemisch/physikalische und mikrobiologische Untersuchungen verifiziert und erste Ansätze für den Einsatz einer solchen Sonde in wasserführenden Rohrsystemen erarbeitet. Die Versuche wurden in zwei Abschnitten durchgeführt, wobei jeweils ein durchströmter Rohrreakor zum Einsatz kam, der neben der Messsonde mit Referenzsonden ausgestattet war. Dadurch wurden zusätzliche Bewuchsflächen auf identischen optischen Fenstern geschaffen, die über einen längeren Zeitraum begleitend mikrobiologisch analysiert werden konnten. Im ersten Versuchsabschnitt wurde der Reaktor mit dem Ablauf der Kläranlage Ruhleben beschickt, um bei hoher Substratkonzentration in kurzer Zeit Informationen über das Ansprechverhalten der Messsonde zu erhalten und eine erste Abstimmung des optischen Systems vornehmen zu können. Zwischen dem gemessenen TOC und BDOC und der Zellzahlentwicklung (DAPI-Test) resultierten übereinstimmende Tendenzen, zwischen der Biofilmdicke und den optischen Parametern war eine grobe Korrelation erkennbar. In den im zweiten Versuchsabschnitt mit Trinkwasser durchgeführten Experimenten korrelierten die mit dem Fouling-Sensor gemessen optischen Daten gut mit den Zellzahlen, die auf den optischen Fenstern der Referenzsonden gemessen wurden. Ein Vergleich der spektroskopischen Laboruntersuchungen von Ablaufproben des Reaktors mit den Messdaten der optischen Sonde lässt den Schluss zu, dass die dokumentierten optischen Messwerte tatsächlich durch Belagseinflüsse und nicht durch das Freiwasser bedingt sind. Bei differenzierter Betrachtung der Ergebnisse korrelierten die Absorptionsdaten der Messsonde mit der mikrobiologisch gemessenen Zellzahlentwicklung in der Aufwuchsphase sehr gut, während die Streu- und Fluoreszenzparameter ein anderes dynamisches Verhalten zeigten. Schnelle Adsorptionsprozesse durch Wasserinhaltsstoffe wie z.B. Huminstoffe, die neben der relativ langsamen Zellvermehrung in der Aufwuchsphase charakteristisch sind, spiegelten sich besonders in einem relativ starken Anstieg des Fluoreszenzsignals wider. Bei geänderten experimentellen Bedingungen, wie z.B. Temperatur oder Nährstoffangebot, zeigten die optischen Parameter Absorption, Streuung und Fluoreszenz ein unterschiedliches Verhalten, das auch von der gewählten Wellenlänge abhängig ist. Beispielsweise zeigte die Streuung im nahen Infrarotbereich (NIR) im Gegensatz zur bei unterschiedlichen Wellenlängen gemessenen UV-Streuung einen deutlichen Anstieg. Eine Unterbrechung der Nährstoffgabe hatte parallel zu einer leichten Abnahme der Zellzahl auch eine leichte Abnahme der optischen Streuungs- und Absorptionsparameter zur Folge. In den Untersuchungen konnte gezeigt werden, dass der eingesetzte optische Sensor ein großes Potenzial bei der Erfassung von Biofoulingprozessen besitzt, wobei die Messung mehrerer optischer Parameter bei unterschiedlichen Wellenlängen erforderlich ist. Diese ersten Untersuchungen zeigten auch sehr deutlich, dass hinsichtlich der Interpretation der gewonnenen Daten noch nicht alle Möglichkeiten des Sensors ausgeschöpft sind. So lassen die gemessenen Daten vermuten, dass mit den optischen Parametern weitere biochemische Parameter, wie zum Beispiel NAD/NADH, erfasst wurden, womit ein sehr guter Hinweis auf die Stoffwechselaktivität der Zellen im Biofilm gegeben wäre. Um der Wasserwirtschaft ein geeignetes Werkzeug zur Verfügung stellen zu können, müssen die bisherigen Ergebnisse bestätigt werden. Insbesondere ist zu zeigen, inwieweit beginnende und fortgeschrittene Stadien von Foulingprozessen in verschiedenen und komplexen Medien sicher erkannt und dokumentiert werden können. Außerdem müssen Zusammenhänge zwischen den optischen Parametern und den unterschiedlichen Vorgängen während der Biofilmbildung im Detail erfasst werden, um Algorithmen und Kalibrierfunktionen zu entwickeln, die für die Steuerung von Antifoulingmaßnahmen in der praktischen Wasserwirtschaft nutzbar sind.

Access to microbiologically and chemically safe water is limited not only in developing countries, but also in transition Countries and even in remote areas of some developed countries. For these cases, point-of-use (POU) technologies can be promising alternatives to centralized treatment concepts. Membrane-based treatment systems have gained importance for drinking water treatment in the developed countries and can be considered as the dominant technology for new applications at present. Due to the high retention of pathogens and the possibility of downscaling (modular construction) membrane technology seems to be attractive also for application as POU system in developing and transition countries. However, no scientific publications on such systems are available and application is limited. Therefore we conducted an extensive literature and state-of-the art review to evaluate relevance, current use and the research and development needs of membrane-based POU systems in developing and transition countries. POU technologies are widely being used to produce safe and high quality drinking water in rural areas of industrialized countries, where access to centralized supply is not available, or for additional treatment of tap water. However, the cost level of POU systems applied in industrialized countries is in general not acceptable in other cases. Therefore simple low cost systems were developed and applied in developing and transition countries. In a range of case studies, described in literature, these systems show themselves as an appropriate short term solution, but often fail to provide improved access to necessary amounts of safe water. Economical growth of developing and transition countries leads to increasing public concern, affordability and requires long term sustainable solutions of the drinking water problem. Membrane-based POU/POE systems are especially attractive for application in developing and transition countries while they can provide high removal of bacteria, protozoa and viruses, have modular design and can be operated with a range of different energy sources, including mechanical and hydrodynamic energy. But, for their application in developing and transition areas, the cost level is in general not acceptable. Furthermore, the source water quality is often very low and can differ regionally as well as seasonally, and the POU/POE systems should be able to treat this kind of waters. Another critical factor in transition and especially in developing countries is the maintenance and control. Not only the level of education of the local population may be insufficient, but also structural financial means for maintenance and control may be lacking.

As part of the EU-Life ENREM demonstration project the Department of Chemical Engineering, TU Berlin, was appointed to conduct the preliminary pilot trials in a representative site for verification of basic process design and operation criteria of the full-scale MBR demonstration plant. In addition to conception and construction of the pilot plant, this investigation consisted of two successive trial phases with distinct operation conditions. The first one was dedicated to the assessment of the “irregular sludge removal strategy” (the biomass is accumulating in the reactor, which is partly emptied when the sludge concentration reaches a given value). In the second trials phase normal operation conditions with daily sludge wastage were implemented with 28,5d SRT. The major outcome of the trials was that COD removal, enhanced biological phosphorus removal and the post-denitrification performed a similar way under both operational conditions. The denitrification rate was approximately 1 mgN/(h goTS). An influence of the anaerobic sludge loading on the post-denitrification rate was observed with higher rates (up to 4 mgN/(h goTS)) corresponding to higher organic loading. An influence of storage compounds built up in the anaerobic phase is assumed. Nitrification was better in the second phase when 4 mgN/(h goTS) were constantly reached while nitrification was unstable with an average of 2 mgN/(h goTS) in the phase of irregular sludge removal. The aerobic and anoxic reactors were enlarged during the regular sludge withdrawal phase by 23% resulting in 35d SRT. This led to a better COD removal and slightly better nitrogen removal. The enhanced SRT produced possibly a deterioration of biological P removal due to overloaded poly-P storage. A second possible reason is the massive reproduction of sludge worm Tubifex tubifex, which was observed after the plant enlargement. Different strategies to reduce the worm population were attempted. Ammonium dosing had no success. Copper dosing reduced the number of worms significantly but the population grew back after the dosing was stopped. The prolongation of SRT reduced the sludge yield from 0.23 gTS/gCOD at 28.5d to 0.18 gTS/gCOD at 35d.

Two parallel membrane bioreactors (2m³ each) were operated over a period of 2 years. Both pilots were optimised for nitrification, denitrification, and enhanced biological phosphorous elimination, treating identical municipal waste water under comparable operating conditions. The only constructional difference between the pilots was the position of the denitrification zone (pre-denitrification in pilot 1 and post-denitrification in pilot 2). Despite identical modules and conditions, the two MBRs showed different permeabilities and fouling rates. The differences were not related to the denitrification scheme. In order to find an explanation for the different membrane performances, a one-year investigation was initiated and the membrane performance as well as the operating regime and characteristics of the activated sludge were closely studied. MLSS concentrations, solid retention time, loading rates, and filtration flux were found not to be responsible for the different performance of the submerged modules. These parameters were kept identical in the two pilot plants. Instead, the non-settable fraction of the sludges (soluble and colloidal material, i.e. polysaccharides, proteins and organic colloids) was found to impact fouling and to cause the difference in membrane performance between the two MBR. This fraction was analysed by spectrophotometric and size exclusion chromatography (SEC) methods. In a second step, the origin of these substances was investigated. The results point to microbiologically produced substances such as extracellular polymeric substances (EPS) or soluble microbial product.

Bank filtration and artificial recharge provide an important drinking water source to the city of Berlin. Due to the practice of water recycling through a semi-closed urban water cycle, the introduction of effluent organic matter (EfOM) and persistent trace organic pollutants in the drinking water is of potential concern. In the work reported herein, the research objectives are to study the removal of bulk and trace organics at bank filtration and artificial recharge sites and to assess important factors of influence for the Berlin area. The monthly analytical program is comprised of dissolved organic carbon (DOC), UV absorbance (UVA254), liquid chromatography with organic carbon detection (LC-OCD), differentiated adsorbable organic halogens (AOX) and single organic compound analysis of a few model compounds. More than 1 year of monitoring was conducted on observation wells located along the flowpaths of the infiltrating water at two field sites that have different characteristics regarding redox conditions, travel time, and travel distance. Two transects are highlighted: one associated with a bank filtration site dominated by anoxic/anaerobic conditions with a travel time of up to 4–5 months, and another with an artificial recharge site dominated by aerobic conditions with a travel time of up to 50 days. It was found that redox conditions and travel time significantly influence the DOC degradation kinetics and the efficiency of AOX and trace compound removal.

Artificial recharge of groundwater is often used to either purify partially treated wastewater or to enhance the quality of surface water by percolation through a variably saturated zone. In many cases, the most substantial purification process within the infiltration water is the redox-dependent biodegradation of organic substances. The present study was aimed at understanding the spatial and temporal distribution of the redox reactions that develop below an artificial recharge pond near Lake Tegel, Germany. At this site, like at many artificial recharge sites, the hydraulic regime immediately below the pond is characterised by cyclic changes between saturated and unsaturated conditions. These changes, which occur during each operational cycle, result from the repeated formation of a clogging layer at the pond bottom. Regular hydrogeochemical analyses of groundwater and seepage water in combination with continuous hydraulic measurements indicate that NO3 - and Mn-reducing conditions dominate beneath the pond as long as water-saturated conditions prevail. Manganese-, Fe- and SO24 -reducing conditions are confined to a narrow zone directly below the clogging layer and in zones of lower hydraulic conductivity. The formation of the clogging layer leads to a steady decrease of the infiltration rate, which ultimatively causes a shift to unsaturated conditions below the clogging layer. Atmospheric O2 then starts to penetrate from the pond fringes into this region, leading to: (i) the re-oxidation of the previously formed sulphide minerals and (ii) the enhanced mineralisation of sedimentary particulate organic C. The mineralisation of sedimentary particulate organic C leads to an increased H2CO3 production and subsequent dissolution of calcite.