Insights into the adsorption of perfluoroalkyl substances (PFASs) on excess sludge from an on-site leachate treatment plant

Abstract

The disposal and reduction of excess sludge is one of the most challenging aspects of wastewater treatment. Recycling excess sludge as functional materials is an innovative approach that has garnered broad attention, as it can address environmental concerns and reduce the consumption of valuable materials. However, this approach is still challenging due to the low mixed liquor suspended solids in sewage treatment plants and the high synthesis costs involved. In this study, we proposed the application of excess sludge from an on-site leachate treatment plant for the efficient removal of perfluoroalkyl substances (PFASs) from wastewater. A simple thermal treatment was conducted and the obtained sludge-based adsorbents enable effective PFASs removal. Through the use of low field nuclear magnetic resonance and structural characterizations, results demonstrated that denitrifying sludge had higher hydrophobicity and specific surface area (30.85 m2/g) than nitrifying sludge, resulting in enhanced PFASs adsorption capacity and initial adsorption rates. Kinetic and isotherm simulations indicated that the adsorption was efficient and controlled by surface and intraparticle diffusion. Characterization and regulation results showed that the adsorption was dominated by hydrophobic and electrostatic interactions. These findings suggest a promising recycling approach of excess sludge while elucidating the dominant mechanisms involved.