Fate and Spatial–Temporal Variation of 23 Elements at 7 Wastewater Treatment Plants in Southeast City of China

Abstract

Rapid urbanization has caused an increase in the discharge of inorganic elements into the environment; however, the knowledge about the fate and annual variations of multiple elements in wastewater treatment plants (WWTPs) is limited. To understand the distribution and change of those elements, we collected and analyzed wastewater and sludge samples from seven WWTPs in a southeast city of China. Results revealed the elemental concentration ranging from 0.06 μg·L−1 (Tl) to 221.90 μg·L−1 (Mn) in the influent, below the detection limit (Er), to 206.40 μg·L−1 (Mn) in the effluent, and 0.58 mg·kg−1 (Tl) to 309.30 mg·kg−1 (Zn) in the sludge. The removal analysis revealed that rare earth elements (REEs) were removed well from the wastewater with removal efficiencies ranging from 88.03% (Tm) to 97.37% (Sm), while heavy metals were poor, with removal efficiencies ranging from 10.71% (Mn) to 89.17% (Pb). The elemental flux analysis highlighted that activated sludge served as a major temporary storage site for 23 elements, while excess sludge acted as the major sink for REEs. Significant spatial variations were detected among different WWTPs. On the contrary, the temporal variations were insignificant based on the monitoring data from 2010 to 2020, indicating the satisfactory implementation of current environmental regulations.