Fate and Ecological Risk Assessment of Nutrients and Metals in Sewage Sludge from Ten Wastewater Treatment Plants in Wuxi City, China

The concentrations of nutrients (total nitrogen, total phosphorus and organic matter) and metals (Cu, Pb, Zn, Ni, Cd, Cr, As and Hg) in sewage sludge samples were determined to evaluate the level of contamination. Sewage sludge samples were collected from ten wastewater treatment plants from 2016 to 2018 in Wuxi city, China. All the studied sewage sludge samples displayed high fertility properties due to their richness. Total concentrations of metals in the sewage sludge samples were within the regulation of the Chinese legislation. The levels of the eight metals temporally varied. Sewage sludge pollution assessment was undertaken using pollution index, geo-accumulation index, potential ecological risk index and aggregative toxicity index. Multivariate statistical analysis indicated that Pb, Cr, As and Hg may have similar transport behavior and derive from anthropogenic sources. Ecological risk assessment revealed that Hg contamination is the major concern for human health, since the treated sewage sludge is used for agricultural purposes.