Trace Organic Compounds in Urban Water Cycles

Martin Jekel, Dept. of Water Quality Control, Technical University of Berlin, Berlin, Germany

In densely populated areas in and around major agglomerations, the discharge of treated wastewater to the surface waters can be quite significant for the quality of receiving water bodies. The research over the last decades has shown, that the wastewater treatment plants are major sources for a great number or trace organic compounds, TroCs, with the primary sources in households, in medical care, in foodstuffs, in industrial emissions and in run-off. The typical concentrations of TroCs in conventionally treated wastewaters range from a few ng/l up to 100 µg/l. The total number of detected substances overall are in the range of a few thousands, while in a given case, the detected substances are usually above 100. Some are present very frequently and at high concentrations and are good indicators of any human activity in the water collection area.

Some of the TroC are suspected to influence the aquatic life in the receiving water bodies and proposals are in-line for new regulations on relevant compounds, such as Diclofenac or hormones. The findings of these substances have initiated major activities in some countries, like Switzerland and Germany, to study the sources, their fate and the options of advanced wastewater treatment for removal or transformations. We studied these options for the Berlin Water Cycle, which is somewhat special in Germany. The city is discharging wastewater upstream of its own water bodies (rivers and lakes), which are not only natural systems, but serve also for drinking water supply by bank filtration and groundwater recharge (by about 70 % of the volume). Thus, we find a share of about 30 % of wastewater in the lakes and about 20 % in drinking water. 

The technical options for TroC-removal are either oxidative transformations by ozone plus biological post-treatment or physical adsorption on granular or powdered activated carbon. The studies in Berlin within two large cooperative projects, coordinated by us, show the various options to include additional barriers in the local urban water cycle to protect the surface waters and the drinking water. It is shown, that the list of relevant substances for the aquatic life are not identical to the list of substances regulated or proposed for drinking water quality. The conclusions indicate, that we may have to add not only ozonation, but also steps with activated carbon and to improve the biodegradation in our natural underground treatment systems. The large scale tests have started and results will be presented.