Changes in Speciation and Bioavailability of Trace Elements in Sewage Sludge after the Ozonation Process

This work aimed to detect changes in trace element chemical speciation in sewage sludge (SS) after the ozonation process. The modified Community Bureau of Reference (BCR) sequential extraction procedure was performed to determine the chemical speciation of trace elements in SS after the ozonation process. To assess potential soil contamination with trace elements from sewage sludge after the ozonation process, the risk assessment code (RAC) coefficient was used. The bioaccumulation factor (BAF) and translocation factor (TF) values were also calculated to characterize the efficiency of trace element accumulation in the studied plant species from soil fertilized with sludges after the ozonation process. Generally, the mean concentration of total trace elements in the SS after the ozonation process was higher, but the differences were statistically significant only in the case of Mn, Cu, Pb, and Cd. The dominant fraction of Fe, Cr, Pb, and Cd was the residual fraction F4, while the extractable/exchangeable fraction F1 was present in the smallest amount. Therefore, in the case of Mn, Zn, and Ni, the ozonation process had a significant impact on the increase in the content of these elements in the F1 fraction. The application of the SS stabilized by ozonation process for maize and wheat fertilization did not significantly affect the bioaccumulation of most of the analyzed metals in aboveground biomass. Higher values of BAF coefficients after the application of ozonated SS were found only in the case of Cu and Ni. In turn, the determined TF coefficients were lower than 1 in most cases. The obtained results showed that the slight change in the concentration of Zn, Mn, and Ni in fraction F1 causes a specific risk of their mobility in the soil environment. It should be noted that due to the variable composition of sewage sludge, an analysis of the content of individual trace elements in chemical fractions should be carried out to assess its actual impact on the environment. This can help to indicate further actions that should be undertaken to limit their negative impact on the environment.