The capacity of drinking water wells, i.e. the yield for a given drawdown, is often decreasing after a certain time of operation. This effect is called well ageing and is due to different processes related to the geology and hydrochemistry at any given well site and to the construction and operation of these wells. The Hydrogeology workgroup and partners investigate wells in Berlin and France in terms of their ageing behaviour with the aim to determine suitable measures helping to slow down well ageing processes and optimise strategies for well operation and maintenance. A precondition for well clogging by iron incrustations is the mixing of different groundwaters with incompatible chemical properties in the well and/or within aquifer and is induced by combined hydrochemical and microbiological processes. The assessment of (i) formation of reduced/oxidized groundwater layering in the aquifer, (ii) localization of mixing zones and (iii) mixing ratios within the well was done by field and laboratory studies. The research reveals that redox condition in the well and the surrounding aquifer are subject to short to long-termed variations. These variations are caused by operation intervals of the wells and by seasonal effects. The results permit a characterization of oxygen enrichment and transport dependent on well operation, location and design and further on an input-output balancing and a modeling of incrustation rates.

During WELLMA-DNA, 13 diploma and bachelor theses along with several internships have been completed. A sampling system for biofilm samples as well as a sampling device for water samples have been designed and tested. More than 400 DNA samples of different well sites have been collected and analyzed. Microbiological and molecular methods have been combined to gain a better understanding of the community composition of the ochre forming biofilms inside the wells. Molecular methods included PCR, DGGE, cloning and sequencing. During the project, the bacterial populations of an unprecedented number of wells have been analyzed and several indicator bacteria for iron-related well clogging have been identified. Alongside iron-oxidizing bacteria, iron-reducing bacteria have been found in the wells and their potential for ochre-solubilization was confirmed. Alongside the molecular experiments, microbiological trials included the isolation of pure cultures, microscopic analysis and physiological tests. The morphology of the encountered iron bacteria could be classified into four different groups, which may have an impact on the rigidity of the biofilms on a macroscopic level. We were able to cultivate several of these indicator organisms, which could play an important role in the formation of ochreous deposits in the Berlin wells. During experiments utilizing microscopic flow cells, differences in growth rate and patterns of these ochre-forming bacteria have been observed. For several of the identified indicator bacteria, primers have been calculated. These primers will allow for the first time to quantify the amount of indicator bacteria in a water sample and to derive operational pointers. In addition, several experiments regarding the effect of hydrogen peroxide on ochre forming biofilms have been conducted and the effect of an additional electron donor (ethanol) on the communities has been tested. For future data acquisition and documentation, a guideline for classifying the degree of pump clogging has been developed.

There is a significant potential for optimizing pump systems currently in use in groundwater wells. This potential lies in: (i) the improvement in pump technology, which can yield up to ~5% more efficiency, (ii) the improvement in motor technology, which can yield up to ~3% more efficiency, with further improvements if innovations from aboveground motors are adapted, (iii) the improvement in performance adaptability, which can be very efficient in some cases (~10-50%), but also counterproductive if not adapted to current situation (0% or even efficiency loss), and sometimes not very flexible (impeller trimming); (iv) the improvement of the system maintenance and management which may yield up to ~20% more efficiency, and which, in general, has a shorter payback time than performance adaptability options.The improvement of equipments may induce only moderate additional costs if it is done at the time of scheduled new investments, after amortization of the equipment formerly in use. Unfortunately, these expected savings are influenced by uncertainties, which can be of the same order of magnitude as the savings themselves. For instance, the determination of the optimal operation point of a pump bears uncertainties between 1% and 4% and grows with pump rotation speed (Gülich 2010). Other considerable saving potentials lie within cleaning, maintenance and smart wellfield operation with short to moderate payback times (Table 6). These potentials are however very site-specific, and difficult to estimate on a general basis. Best practices for a “smart” pumping shall include choosing equipment that fits the actual requirements of the system, operating the pumps nearest of their Best Efficiency Point, and operating the motors in an energy-efficient load range. The most obvious energy savings are those associated with improvements in the efficiency of the motor and of the pump (Shiels 1998). Such gains are often worth the added capital expenditure – although often having moderate to long payback times. However, as underlined by (Kaya, Yagmur et al. 2008), that pumps have high efficiency alone is not enough for a pump system to work in maximum efficiency. An improvement of pump technology will yield, even optimistically seen, an efficiency improvement of up to 10%, which is the potential “theoretical limit” (EC 2003). For further improvements, it is necessary to consider solutions that go beyond the pump system, since maximizing efficiency depends not only on a good pump design, but also on a good system design. Even the most efficient pump in a system that has been wrongly designed is going to be inefficient. Moreover, an efficient pump in an inefficient well is pointless. Hence, a global approach of the groundwater abstraction system is required. The optimization potentials highly depend on the site characteristics themselves, on the local demand (what distribution of the demand? what load profile?), and on the operation and maintenance history (e.g., what is the cleaning frequency of the pipes, if any?). Finally, one should not forget the primary objective of water abstraction, which is satisfying a given water demand, thus, the safety of drinking water production prevails over energy efficiency.

In this study the applicability of the microsieve technology together with coagulation and flocculation for advanced phosphorus removal was investigated. A pilot unit including a microsieve with 10 µm mesh size is operated continuously with secondary effluent. By applying a pretreatment of 0.036 – 0.179 mmol/L coagulant and 2 mg/L cationic polymer total phosphorus values below 100 µg/L were easily achieved. Values below 50 µg/L were possible at high metal dosing, but the higher suspended solid load reduced the capacity of the pilot unit. Coagulation with polyalumium chloride (PACl) produced better effluent quality compared to FeCl3 as less suspended solids and less residual coagulant were found in the microsieve effluent. Also the transmission of UV radiation through the water is improved by using PACl. The amount of backwash water was very low (< 3 %). In total, if combined with UV disinfection, microsieving with chemical pretreatment is a viable option for high quality effluent polishing.

In this study the applicability of the microsieve technology together with coagulation and flocculation for advanced phosphorus removal was investigated. A pilot unit including a microsieve with 10 µm mesh size is operated continuously with secondary effluent. By applying a pretreatment of 0.036 – 0.179 mmol/L coagulant and 2 mg/L cationic polymer total phosphorus values below 100 µg/L were easily achieved. Values below 50 µg/L were possible at high metal dosing, but the higher suspended solid load reduced the capacity of the pilot unit. Coagulation with polyalumium chloride (PACl) produced better effluent quality compared to FeCl3 as less suspended solids and less residual coagulant were found in the microsieve effluent. Also the transmission of UV radiation through the water is improved by using PACl. The amount of backwash water was very low (< 3 %). In total, if combined with UV disinfection, microsieving with chemical pretreatment is a viable option for high quality effluent polishing.

Bisherige Analysen des Energieverbrauchs in der Abwasserreinigung beschränken sich oft auf die naheliegende Erfassung des Stromverbrauchs. Im Sinne einer ganzheitlichen Betrachtung sollten aber auch andere Formen der Energie erfasst werden, wie zum Beispiel für die Herstellung von benötigten Chemikalien wie Flockungs- und Flockungshilfsmittel, beim Transport des zu entsorgenden Schlamms oder für zusätzliche Brennstoffe bei der Klärschlammtrocknung. Dafür ist die Erweiterung der Grenzen des zu betrachtenden Systems auf vor- und nachgelagerte Prozesse notwendig, um alle relevanten Beiträge zum Energieverbrauch zu berücksichtigen. Zudem können so auch die verschiedenen Sekundärprodukte der Abwasserreinigung erfasst werden: die Stromproduktion aus Faulgas, die Rückführung von Nährstoffen und Wasser in die Landwirtschaft oder die Substitution von fossilen Brennstoffen in der thermischen Klärschlammentsorgung. Ein geeignetes Instrument für diese Betrachtungsweise ist die Methodik der Ökobilanz nach ISO 14040/44. Mit dieser Methodik lassen sich alle unterschiedlichen Energieformen und Sekundärfunktionen abbilden und in einheitlichen Indikatoren darstellen, ergänzt durch weitere Umweltwirkungen wie den Treibhauseffekt.

In the course of identifying areas of relevance for further research and development the members of the European Water Supply and Sanitation Technology (WssTP) identified Managed Aquifer Recharge (MAR) as an important cross-cutting topic and area relevant for further research. For this reason a Task Force on MAR was initiated with 36 representatives from European research institutes and industry partners with participation of international experts. These task force members developed the basis for a report documenting the state of the art and research needs in the field of MAR that has now been published by the WssTP.

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).

In the city of Berlin regular combined sewer overflows (CSO) lead to acute stress of aquatic organisms in the receiving River Spree and its side channels. Of most concern are oxygen depressions, following the inflow of degradable organic matter via ~180 CSO outlets, along a river stretch of 16 km. For the assessment of the severity of these oxygen depressions, an existing impact-based approach suggested by Lammersen (1997) was combined with information on the local fish fauna. Application of this locally adapted assessment method to seven years of oxygen measurements at a CSO hotspot in the river yielded an annual average of 14 periods with suboptimal conditions for which adverse effects on the fish fauna are expected and 20 periods with critical conditions for which acute fish kills are possible. Further investigation on rain and sewer management data proved that such critical conditions only occurred as a direct result of CSO events, whereas suboptimal conditions are also possible at dry weather and may last up to 32 days (Riechel et al. 2010).