Variability of zinc, copper and lead contents in sludge of the municipal stormwater treatment plant

Several years of observations enabled us to assess the extent and variability of heavy metal contamination (Zn, Cu and Pb) of the sludge of the municipal stormwater treatment plant (the town of Puławy, Poland). In terms of size (high capacity) and innovation, it is the only facility of this kind in the country. It collects rainwater run-offs from two catchments (separate inlets) with a total area of about 500 ha. The concentration of the analysed metals is characterised by a large spatial and temporal diversity. The reason for this may be differences in the manner and intensity of use of drained surfaces and different hydraulic conditions (of sedimentation) prevailing in the particular treatment devices. The highest pollution was found in sediments in the grit chamber and in the part of the settler from the side of the interceptor supplying sewage, i.e. from the main traffic route of the town (heavy traffic and developed technical infrastructure). The best-quality sludge was retained in the pond for treated wastewater. In the pool of analysed components, the largest share is Zn, which amounts to about 85%. The content of heavy metals limits the possibility of the natural use of sludge from the municipal stormwater treatment plant. In chemical terms, they should be seen as a potentially dangerous waste and undergo remediation.