GaN-based ultraviolet-C (UVeC) light emitting diodes (LEDs) are of great interest for water disinfection. They offer significant advantages compared to conventional mercury lamps due to their compact form factor, low power requirements, high efficiency, non-toxicity, and overall robustness. However, despite the significant progress in the performance of semiconductor based UV LEDs that has been achieved in recent years, these devices still suffer from low emission power and relatively short lifetimes. Even the best UV LEDs exhibit external quantum efficiencies of only 1e2%. The objective of this study was to investigate the suitability of GaN-based UV LEDs for water disinfection. The investigation included the evaluation of the performance characteristics of UV LEDs at different operating conditions as well as the design of a UV LED module in view of the requirements for water treatment applications. Bioanalytical testing was conducted using Bacillus subtilis spores as test organism and UV LED modules with emission wavelengths of 269 nm and 282 nm. The results demonstrate the functionality of the developed UV LED disinfection modules. GaN-based UV LEDs effectively inactivated B. subtilis spores during static and flow-through tests applying varying water qualities. The 269 nm LEDs reached a higher level of inactivation than the 282 nm LEDs for the same applied fluence. The lower inactivation achieved by the 282 nm LEDs was compensated by their higher photon flux. First flow-through tests indicate a linear correlation between inactivation and fluence, demonstrating a well designed flow-through reactor. With improved light output and reduced costs, GaN-based UV LEDs can provide a promising alternative for decentralised and mobile water disinfection systems.

Berlin’s drinking water is produced from groundwater replenished by 60 % from surface water from the city’s abundant rivers or lakes using bank fi ltration or artifi cial groundwater recharge. Compared to other bank fi ltration 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 are attenuated during subsurface passage to a varying degree. Substances that were found to be poorly removed under oxic conditions or even persistent include carbamazepine, 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 fi nished drinking water due to low initial concentrations in the surface water or additional removal during post-treatment (aeration and fi ltration for iron and manganese removal).

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.

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.

The impact of a pre-treatment by pre-ozonation (2-10 mg O3/L) and subsequent coagulation (FeCl3: 2-6 mg Fe3+/L) on the performance of a polymeric ultrafiltration membrane was studied. No free dissolved ozone was in contact with the membrane. Lab tests were performed using Amicon test cells fed with secondary effluent and the flux decline during filtration tests was measured. Flux decline was reduced with increasing coagulant concentration as well as with increasing ozone dosage. This effect was confirmed by a reduction in the amount of biopolymers measured with size exclusion chromatography by organic carbon detection (LC-OCD). Conducted multi filtration cycles revealed a significant increase in irreversible fouling after pre-ozonation that might be caused by increasing colloidal iron concentrations. Phosphorus in the permeate was successfully reduced to concentrations < 60 µg/L

Managed aquifer recharge provides efficient removal for many organic water constituents but it is a difficult task to quantify removal under field conditions: Observed concentrations often scatter and may be biased by subsurface mixing of different waters. Removal efficiency is affected by different environmental parameters, such as redox potential, travel times, threshold values, and also field site specifics. In addition, it is crucial to know the corresponding surface water concentration for all samples. We developed a method, which overcomes these difficulties, quantifies the efficiency and removal kinetics and is applicable to extensive databases. It combines both, statistical and graphical evaluation which allows the determination of precise values and also interpretation based on expert knowledge. The database of this study was collected within the NASRI project between 2002 and 2005 at two bank filtration sites (Tegel BF, Wannsee BF) and one basin aquifer recharge site (Tegel AR) in Berlin. In total, 38 organic constituents were analysed (Table 1).

Die EU-Wasserrahmenrichtlinie (2000) verlangt bis zum Jahre 2015 für alle europäischen Gewässer die Wiederherstellung eines „guten ökologischen Zustands“. In Berlin muss zur Erfüllung dieses Ziels insbesondere der Phosphoreintrag aus Kläranlagen minimiert werden, da Phosphor als limitierender Nährstoff für die Eutrophierung der Gewässer hauptverantwortlich ist. Vor diesem Hintergrund wird die Einführung einer Membranfiltrationsstufe mit vorgeschalteter Phosphatfällung in der Berliner Kläranlage Ruhleben diskutiert (Gnirß 2008). Das Jahresmittel der Phosphorkonzentration im Ablauf der Kläranlage Ruhleben beträgt 0,3 - 0,4 mg P/L. Der Zielwert für die weitergehende Behandlung des Klarlaufes wurde mit 0,05 - 0,1 mg P/L festgelegt. Die Filtration von Klärwerksabläufen mit Niederdruckmembranen bietet in Kombination mit einer Flockungsstufe eine wirkungsvolle Möglichkeit für das Erreichen niedriger Phosphorkonzentrationen und einer zusätzlichen Entfernung von Pathogenen. Das Hauptproblem beim Betrieb von Niederdruckmembranen stellt jedoch nach wie vor der durch Fouling auftretende Verlust der Filtrationsleistung dar. Dieser entsteht durch das Verblocken der Membranporen mit organischem Material sowie Kuchenbildung auf der Membranoberfläche und schlägt sich entweder in der Verringerung des transmembranen Fluxes oder im Anstieg der transmembranen Druckdifferenz mit der Zeit nieder. Als Folge des Foulings müssen die Membranen regelmäßig physikalisch bzw. chemisch gereinigt werden, was zu einer Verringerung ihrer Standzeit führt. Lediglich 10 % der im Klarlauf enthaltenen organischen Substanzen leisten dabei einen Beitrag zum Fouling (Laabs 2004). Diese Substanzen eluieren bei einer Größenausschlusschromatographie im sogenannten Biopolymer-Peak, der sowohl Polysaccharide als auch organische Kolloide und Proteine umfasst. In Studien zum Fouling von Niederdruckmembranen wurden Biopolymere (BP) in Form von Proteinen und Polysacchariden sowie Partikel und Kolloide in der Größenordnung von 10 bis 450 nm als Hauptverursacher des Membranfoulings ermittelt (Zheng 2009, Poele 2006). Im Rahmen des Projekts „Oxeram“ (Technische Universität Berlin, KompetenzZentrum Wasser Berlin, Berliner Wasserbetriebe) wird untersucht, ob durch eine Ozonierung vor der Flockungsstufe das Fouling der nachgeschalteten Membran reduziert und somit die Leistungsfähigkeit der Membranfiltration verbessert werden kann und ob sich aus deKombination dieser Prozesse synergetische Effekte ergeben. Eine Ozonierung kann bei einem Einsatz von geringen Ozondosen (1 - 2 mg/O3/L) in Kombination mit einer Flockung aufgrund des Mikroflockeneffekts zu größeren, stabileren und robusteren Flocken führen. Diese können sich bei einer nachgeschalteten Membranfiltration positiv auf die Filtrationsleistung auswirken. Höhere Ozondosen (10 - 12 mg O3/L) dienen der Oxidation von organischen Wasserinhaltsstoffen und Spurenstoffen. Die hier dargestellten Ergebnisse beziehen sich auf Versuche, die in AmiconTestzellen im Labormaßstab durchgeführt wurden. Ziel war es zunächst, eine optimale Kombination von Ozoneintrag und Flockungsmittelkonzentration zu ermitteln.

Advances in the analysis of organic trace compounds revealed that many of the in high amounts prescribed pharmaceutical active components as well as diagnostic agents are not removed by conventional waste water treatment techniques and that some of them can accumulate in the aquatic environment. Because most of the compounds applied in medicine are excreted via urine the emission into the aquatic environment could be reduced if the urine is separated at the source and treated by a specific process. In the project PharmaTreat it was studied if the reductive treatment with zero-valent iron is a suitable, simple and low cost process for the treatment of urine. The results show that the selected antibiotics (Ciprofloxacine, Piperacillin, Cefuroxime), cytostatic drugs (Ifosfamide and Methotrexate) and iodinated X-ray contrast media (Iopromide and Diatrizoate) are transformed by the treatment with zero-valent iron. The reaction rate constant depends highly on the pH. Under acidic conditions the mechanism of the transformation is most probably the reaction with adsorbed atomic hydrogen which is produced on the iron surface. The increase of the pH-value from 3 to 7, which might happen if the solution is discharged into the waste water system, leads to the precipitation of the dissolved iron resulting in a strong removal of the transformation products out of the solution by co-precipitation. The toxicity of the remaining transformation products was determined using the growth inhibition test (DIN 38412-37). It could be demonstrated that the biological impact of the pharmaceuticals is reduced by the transformation with zero-valent iron. By using the Zahn-Wellens-Test (DIN EN ISO 9888) it could be shown that the transformation products are better biodegradable in contrast to the original compounds, except for the iodinated Xraycontrast media. The treatment of one cubic meter urine costs 9.88 Euro. The cost estimation is based on conditions with the lowest material consumption and not on the reaction time. According to the calculated price for on cubic meter the treatment of about 6,525 m3 urine (the amount of urine produced in all hospitals of Berlin) costs ca. 64,500 Euro/a. By accelerating the reaction the treatment time can be shorten but the specific material consumption is higher whereas the energy costs are lower. In dependence of the actual prices for iron, acid and electricity the costs can be optimized for the treatment.