Conditioning treatments mitigate the levels of fecal pollution indicators in soil during land-application of sewage sludge

Abstract

Sewage sludge is a major source of fecal pathogens in the environment, and its application to land can result in a significant release of these pathogens into the soil. While conditioning treatments are crucial for improving the dewatering process of sludge, their impact on the presence and behavior of fecal pathogens in soil remains unclear. This study aims to assess four extraction methods for recovering fecal pollution indicators from soil amended with unconditioned and conditioned sludge. The indicators include Escherichia coli (EC), human-specific HF183 Bacteroides (HF183), human adenovirus (HAdV), human BK polyomavirus (BKPyV), human JC polyomavirus (JCPyV), and cross-assembly phage (crAssphage). This study also examines how soil moisture content affects the decay of these fecal pollution indicators in soil amended with raw sludge and investigates the influence of conditioning treatments with cationic polyacrylamide (PAM), Fenton’s reagents, Fe[III]/CaO on their persistence in soil. The results indicated that the direct extraction method was the most effective and unbiased for recovering fecal pollution indicators from sludge-amended soil compared with the three elution-concentration methods. All fecal pollution indicators, except HAdV, remained stable under dry soil conditions, while high soil moisture content (48.39%–53.14%) slowed the decay rates of these indicators. During the application of sludge to soil, effective control of fecal pollution indicators was observed, with JCPyV and HAdV becoming undetectable within a short period. The log reduction values of HF183, BKPyV, and crAssphage ranged from 0.1 to 2.8 logs after 30 d of cultivation. The application of conditioned sludge, especially Fenton’s reagent-conditioned sludge, resulted in a reduction in human fecal contamination in the receiving soil. Therefore, implementing appropriate conditioning methods, such as using Fenton’s reagent, can effectively mitigate the health risks associated with fecal pathogens.