Wastewater as a driver of heavy metal pollution in river catchments – A study of possible scenarios

Heavy metals can enter rivers i.a. from point sources such as wastewater treatment plants (WWTPs) and industrial plants with inadequately-treated wastewater. The present article examines (i) the impact of WWTPs and industrial facilities on the pollution of the Pilica River, (ii) heavy metal loads along its continuum, and (iii) the identification of common pollution patterns in wastewater and river water, and the effect of their physicochemical properties. A novel aspect of this study is the use of two distinct data calculation approaches: Variant 1 -values below the quantification limit (LOQ) were replaced with LOQ/2, Variant 2- LOQ replaced with zero. Analyses have shown that pollution scenarios differ depending on the calculation method used. Nevertheless, regardless of the calculation method, the general conclusions that can be drawn are: i) among WWTPs, the highest heavy metal concentrations are generated by the smallest plants, ii) the highest loads by the largest ones, which is related i.a. to the size of their flow, iii) industrial plants are significant sources of point pollution of rivers, with arsenic, tin, zinc, cobalt, copper, molybdenum, nickel, lead, chromium, mercury and barium being detected in wastewater. The most common heavy metal in the Pilica was found to be Barium, with the highest loads observed in winter (66.29-216.98 kg/day), and depending on the season, arsenic, copper and nickel were also detected. The innovative aspect of the work is an example of modification of the sedimentation-biofiltration system as a sustainable solution for removing heavy metals from treated wastewater.