Influence of a Zagreb Central Wastewater Treatment Plant on a Geochemical Characteristic of Sava River Sediment

Field sampling of water and sediments from Sava river in Zagreb, in a total length of 36, 73 km was collected in March 2019, with the goal to determine the geochemical characteristic of sediment in the vicinity of discharge at main outlet of a Zagreb central wastewater treatment plant. Samples were collected under the Jankomir bridge (a), Bridge of Youth (b), a zone of outlet (c) and in Rugvica (d) (Fig. 1). In all water sample pH and electrical conductivity (EC) were measured. Results are similar for 3 of 4 locations (pH around 8, and EC around 430 μs). The sample from location c shows an increase in electrical conductivity (844 μs) and decrease of pH value (7, 65). All sediment samples were dry to constant weight and divided into the two sub-samples. The first one was used for bulk analysis, while the second one was sieved and fraction < 0, 063 mm was collected for further analysis. The qualitative mineral phase omposition was performed, to determine the mineral phases by the Philips X’pert powder diffractometer with CuKα radiation from the tube operating at 40 kV and 45 mA. An X-ray diffraction data set was collected from 4° to 63° 2Ɵ. All analysed bulk samples have a similar composition, with the quartz as the main phase, calcite, dolomite, muscovite and kaolinite as phases presented in smaller amount. In the fraction < 0, 063 mm quartz was also determined as main mineral phase and all phases from bulk are present with adition phases, albite and magnesium calcite. The amount of carbonate component was also determined by the Austrian standard methods ÖNORM L1084 using Scheibler calcimeter. Amount of carbonate component decrease downstream, but all bulk samples have a high amount of a CaCO3 components, from 36% to 29, 5%. Qualitative and quantitative chemical analysis of metals in sediment and water as well as sequential extraction chemical analysis by BCR protocol was performed and results will be presented at the poster, due to the additional data processing which must be performed.