Ecological risk assessment of sewage sludge from municipal wastewater treatment plants: a case study

Abstract

The aim of this study was to characterize sewage sludge from mechanical-biological wastewater treatment plants (WWTPs) in terms of total concentrations of heavy metals (HMs) and their distribution. Moreover, HM mobility, stability and ecological risk were assessed by calculating the mobility factor (MF), the reduced partition index (I_r) and the ecological risk index (ERI). Hierarchical cluster analysis (CA) was used to group the HMs in the sludges on the basis of their MF, I_r and ERI. The concentration of HMs decreased in the following order: Zn > Cu > Ni > Pb > Cd. HM mobility, as indicated by the MF values, was as follows: 18.7%–30.6% (Zn), 8.1%–36.4% (Ni), 6.8%–11.1% (Cu), 3.2%–32.2% (Pb) and 0% (Cd). Based on the average I_r values, the stability of the metals in the sludge increased in this order: Zn (0.23)=Pb (0.23)<Cd (0.45)=Cu (0.45)<Ni (0.69). Despite the high mobility of some metals, each sewage sludge had low environmental risk, as indicated by the ERI (ERI ≪ 150). The HMs were more similar in terms of their mobility (two clusters) than in terms of their ecological risk (three clusters).

Keywords:

• Sewage sludge
• heavy metals
• mobility
• stability
• environmental risk

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The study was supported by the Ministry of Science and Higher Education in Poland (Statutory Research, 528-0809-0801).