Effects of drinking water treatment residual amendment to biosolids on per‐ and polyfluoroalkyl substances leachability

Public concerns exist over whether land application of biosolids is a pathway of introducing large amounts of per- and polyfluorinated alkyl substances (PFAS) into terrestrial ecosystems. Ongoing research is investigating a variety of high organic matter (OM) and Al/Fe phases for use as amendments to reduce PFAS leaching from matrices including biosolids. Drinking water treatment residuals (DWTRs) have characteristics (e.g., high OM, oxalate-extractable Al (Alo_x), and/or oxalate-extractable Fe (Fe_Ox) content) linked with PFAS retention and are widely available at low cost. We investigated sorption and desorption of a suite of eight PFAS, including sulfonates and carboxylates varying from C4 to C9, in biosolids amended with Al, Ca, and Fe DWTRs at rates from 2.5% to 10% wt/wt. Three biosolids were used: (1) high OM, low Fe_Ox; (2) high OM, high Fe_Ox; and (3) low OM, high Al_Ox. For all biosolids and DWTRs tested, amendment with 2.5% and 5% DWTR resulted in no significant increase of partition coefficient (Kd) value in sorption for the examined PFAS when compared to controls, and only a few inconsistent significances in desorption. However, at 10% DWTR, significantly increased Kd values were observed in both sorption and desorption in some of the DWTR-treated biosolids, particularly those treated with Al DWTR. These results suggest that DWTRs (especially Al DWTRs) can enhance the retention of PFAS, and that DWTR amendment rate appeared to be more influential on PFAS sorption and desorption than physical characteristics of the DWTRs and biosolids or PFAS properties.