Circular economy in wastewater treatment plants: Treatment of contaminants of emerging concerns (CECs) in effluent using sludge-based activated carbon

Abstract

Contaminants of Emerging Concern (CECs), including polycyclic aromatic hydrocarbons (PAHs), polybrominated diphenyl ethers (PBDEs), and poly and perfluoroalkyl substances (PFASs), have been frequently detected at high concentrations in discharged wastewater effluents and biosolids. This study investigates the occurrence and removal of various PAHs, PFASs, and PBDEs from the final discharge effluent of a major Canadian wastewater treatment plant. We evaluated two seasons of the year (warm and cold) (effluents A and B) using sludge-based activated carbon (SBAC) samples synthesised from thickened waste secondary sludge and biosolids, named TS-SBAC and BioSBAC, respectively. The average removal efficiency of BioSBAC (at concentrations of 1 and 10 g SBAC in 1-L effluent) for PAHs and alkyl-PAHs in effluent A was 88–100% (residual concentrations below the reporting limit [RL] at 16.7 ng/L), and that of TS-SBAC (concentration of 1 g SBAC in 1-L effluent) in effluent B (below RL, at 20.8 ng/L) was 68–100%. The average removal efficiency of BioSBAC for PBDEs was 88–100% for effluent A (below RL, at 1.26 ng/L), and that of TS-SBAC for effluent B (below RL, at 1.14 ng/L) was 52–100%. The average BioSBAC removal range of PFASs from effluent B (below RL, at 5.37 ng/L) was 30–100%, with significant removal of long-chain (>C7) PFASs. These findings indicate that producing an efficient adsorbent (i.e., SBAC) from sewage sludge is a sustainable integrated circular economy solution for stabilising CECs, including PAHs, PFASs, and PBDEs, to improve the quality of wastewater effluents in a closed-loop system, with no waste being generated.