Whole Effluent Assessment of urban discharges

The European Water Framework Directive and the Environmental Quality Standards Directive lay down a framework for maintaining or obtaining good ecological and chemical status of European surface and coastal water bodies by the year 2015. The aim of this work was through Whole Effluent Assessment (WEA) to identify problematic urban discharges, e.g. stormwater, municipal wastewater, combined sewer overflow (CSO), industrial wastewater.

Samples from around Copenhagen were therefore tested in the Larval Development Ratio (LDR) test using the marine crustacean Acartia tonsa. The number of non-hatched eggs, nauplii and copepodites was determined in controls as well as in samples and the effect was calculated as the ratio between the number of copepodites and the sum of the numbers of nauplii and copepodites.

Ratios below or above 1 significantly (t-test) differing from the control group are considered inhibited or stimulated, respectively, both indicating an effect of the stressor. Except for the stormwater, which did not show any effects at a concentration of 72%, all samples need to be diluted to more than 72%.

Compared with the control group, the CSO from Belvedere needs to be diluted between 1,000 (P=0.001) and 10,000 (P=0.1736) times, the concentrate from the PP needs to be diluted around 1,000 (P=0.126) times and the outlet from the WWTP Damhusåen needs to be diluted at least 200 (P=0.001) times before the development of the organisms are comparable with the control group.