Initial project plan
State of the art and preliminary work
Wastewater treatment plants serve to minimise the pollution of aquatic systems by losing the matter cycles in terrestrial urban catchments, aiming at an efficient elimination of nutrients and harmful substances. However, the treated wastewater often contains dissolved substances and soils of biotic and abiotic origins that are either not eliminated during the process or are even added during the treatment process. Discharging these residual substances into natural urban water bodies will strongly interact with their interfaces. Phosphorus (P) being the key nutrient for the eutrophication is often eliminated in treatment plants (Sabelfeld & Geissen 2011) by using metal salts containing sulphate as an anion and which are discharged in large quantities into surface waters. For example, sulphate load originating from the surface water treatment plant (OWA) at Lake Tegel, Berlin, amounted to 70% of the total sulphate load (Kleeberg 2012). It is well known that high and increasing sulphate concentrations stimulate P release across the sediment water interface due to the formation of immobile iron sulphides (Zak et al. 2006, Baldwin & Mitchell 2012), thus diminishing the P retention capacity of lakes. Therefore, the efficiency of expensive P load reduction seems to be partly reduced by internal lake processes induced by the way in which of wastewater is treated and P is eliminated. The controversial debate about the need for nitrogen elimination reveals the fact that we do not fully understand the linkages between technical and natural components of the urban water systems (Petzoldt & Uhlmann 2006). On the one hand, an increasing number of studies has shown that nitrogen rather than P can temporarily limit primary production and can influence the phytoplankton composition (e.g. Sterner 2008, Dolman et al. 2012). On the other hand, the nitrate in the water overlying iron-rich sediments can suppress the redox-controlled P release from the sediments as long as nitrate is available (Petzoldt & Uhlmann 2006, Cabezas et al. 2013). Aquatic systems are able to eliminate nitrogen in substantial quantities by denitrifying bacteria. This “service function” of lake ecosystems could be reduced when primary production is lowered due to measures taken to reduce eutrophication (Mengis 1996). This simple example shows that successful and cost-intensive management measures for reducing eutrophication can influence ecosystem service functions and requires new technical approaches. Thus, the success and efficiency of the management of urban lakes are crucical for the understanding of the processes of all parts of the managed system, as well as their interactions.
Aims and work steps
The adverse effects of technical purification process on urban surface waters will be analysed on the basis of case studies, available data for mass balance calculations, and laboratory experiments. An interface model will be developed which connects existing wastewater treatment and surface water quality models as a basis for an improved Integrated Water Resources Management (IWRM). The Matlab®/Simulink™ based SIMBA® simulation system will be chosen to model the wastewater treatment by the IWA ASM models. The ASM models need to be extended for different P species and sulphate. The wastewater treatment plant modelling will be connected with the surface water model HMS (Simons et al. 2014, see N7 and T3) and a sediment model based on SPIEL (Schauser et al. 2006) by the configuration of the interfaces. The different temporal resolutions of the models and their accuracies must be considered. The Lake Tegel, Wannsee and Teltow channel will be used as a model region to validate the models and to calculate different scenarios based on different phosphorus and nitrogen effluent loads discharged by the wastewater treatment plants. By considering the impacts on receiving water bodies, an optimal strategy to meet good water quality standards according to EU Water Framework Directive will be identified.
Connections to interfaces and other doctoral theses
This doctoral thesis will be carried out in close collaboration with N5, N6 and N3 which are focused on the sediment water interface in aquatic ecosystems and with N4 on metabolism. T1 and T2 will provide data on the sulphur input of the wastewater treatment plant. Modelling approaches will be developed in cooperation with N7 and T3.
Baldwin,D.S. & Mitchell,A. (2012): Impact of sulphate pollution on anaerobic biogeochemical cycles in a wetland sediment. Water Research 46, 4: 965-974
Cabezas,A., Gelbrecht,J. & Zak,D. (2013): The effect of rewetting drained fens with nitratepolluted water on dissolved organic carbon and phosphorus release. Ecologica Engineering 53: 79-88
Dolman,A.M., Ruecker,J, Pick,F.R., Fastner,J., Rohrlack,T. & Mischke,U. (2012): Cyanobacteria and Cyanotoxins: The Influence of Nitrogen versus Phosphorus. PLOS ONE 7, 6: DOI:10.1371/journal.pone.0038757
Kleeberg,A. (2012): Eintrag und Wirkung von Sulfat in Oberflächengewässern. In: Hupfer,M., Calmano,W., Klapper,H., Wilken,R.D. (Eds.): Handbuch Angewandte Limnologie
Mengis,M. (1996): Nitrogen elimination in lakes by N2 and N2O emission. Dissertation, ETHZürich, Zürich
Petzoldt,T., Uhlmann,D. (2006): Nitrogen emissions into freshwater ecosystems: Is there a need for nitrate elimination in all wastewater treatment plants? Acta hydrochimica et hydrobiologica, 34, 305-324
Sabelfeld,M. & Geißen,S.-U. (2011): Verfahren zur Eliminierung und Rückgewinnung von Phosphor aus Abwasser. Chemie Ingenieur Technik 83: 6, 782-795
Schauser,I.,Hupfer,M., & Brüggemann,R. (2006): Process analysis with a phosphorus diagenesis model (SPIEL). Ecological Modelling 190: 87-98
Simons,F., Hou,J., Özgen,I., Busse,T., & Hinkelmann,R. (2014): A model for overland flow and associated processes within the Hydroinformatics Modelling System. Journal of Hydroinformatics, 16 (2), 375-391, DOI:10.2166/hydro.2013.173
Sterner,R.W. (2008): Review Paper: On the phosphorus limitation paradigm for lakes. Published online in Wiley-VCH, Internat. Rev. Hydrobiol., 93 (4-5), 433-445
Zak,D., Kleeberg,A. & Hupfer,M. (2006): Sulphate-mediated phosphorus mobilization in riverine sediments at increasing sulphate concentration, River Spree, NE Germany. Biogeochemistry, 80 (2), 109-119