Ecological risk assessment of domestic sewage sludge: a case study

Abstract

This study aims to evaluate potential ecological risks and heavy metal pollution in sewage sludge. For these purposes, domestic sewage sludge samples were collected for a period of one year from a wastewater treatment plant in Bursa, Turkey and analyzed for heavy metals. The average heavy metal content of the sewage sludge was wherein decreasing order of Zn>Cu>Ni>Cr>Pb>As>Se>Cd. As a whole, the concentration of heavy metals was below the limit values indicated within the agricultural land application legal standards. Correlation analysis showed a very strong correlation observed between Ni and Cr. Determining to pollution degree and potential ecological risks, some indices such as Enrichment factor (EF), Single-factor pollution index (PI), Geoaccumulation index (Igeo), Nemerow synthetic pollution index (PN), Contamination factor (Cf), Integrated pollution degree (Cd), Pollution Load Index (PLI), Monominal potential ecological risk (ER), Potential ecological risk index (RI), and the Probability of toxicity (mERM-Q) were used in this study. Based on the pollution index calculations, Zn and Se posed the highest contamination while As and Cd posed the lowest contamination. The mERM-Q values indicated that the probability of toxicity varied from 21 to 49%, while ecological indices indicated that ER (2.0-23.7) and RI (67.3-106.2) values were lower than a threshold value for all samples.