Evaluating sorbents for reducing per- and polyfluoroalkyl substance mobility in biosolids-amended soil columns

Sustainable reuse of biosolids as fertilizers is being threatened by the presence of per- and polyfluoroalkyl substances (PFAS) in our waste stream warranting research on strategies that will minimize PFAS mobility from land-applied biosolids. Here, we evaluated the ability of waste-derived sorbents aluminum chlorohydrate water treatment residuals (ACH-WTRs, 1 wt%) and biosolids-based biochar (1.5 wt%) to reduce mobility of PFAS in columns with 3 wt% biosolids-amended soils with and without sorbent layered on top of soil only and operated under transient unsaturated conditions. Cycles of simulated rain events of approximately three pore volumes distributed over a 4-day period followed by 3 days of drying were imposed for 6 months. Total PFAS concentrations in collected leachates were lower in the sorbent-treated columns compared to the control columns. Biochar outperformed the ACH-WTR with 41% versus 32% lower total PFAS in leachate, respectively, compared to the control. The most significant mitigation effect was observed with PFOS (perfluorooctane sulfonate) with 68% and 62% less PFOS in the leachates from the columns treated with ACH-WTR or biochar compared to the control, respectively. These results provide a first-of-its-kind assessment of the potential benefit of co-applying WTRs or biochar with biosolids to reduce PFAS mobility in biosolids-amended soils.