Fig. 2

RDA for chemical analyses of water samples from different cleaning stages at the WWTP Langwiese. Samples were collected between 2012 and 2016. First (horizontal) and second (vertical) axes are shown. The effluent after primary treatment is represented by blue dots (influent), the secondary clarifier by green dots, the “old” effluent with a flocculation/sand filter (without activated carbon) by red dots, the activated carbon stage by violet dots, and the “new” effluent with activated carbon stage and sand filter by black dots. Red arrows depict the investigated endpoints. The length of the arrow indicates the magnitude of effect, and the distance between the arrow and axes indicates their strength of correlation. SAK254: spectral absorption coefficient at 254 nm, a sum parameter giving information about the organic load in water samples. The first axis is primarily determined by the sampling year. Data for 2012 to early 2014 (prior to the WWTP upgrade) are shown on the left side of the figure, those for data from late 2014–2016 (after the WWTP upgrade) on the right side. The second axis allows for distinction between the different treatment stages