Municipal solid waste incineration (MSWI) ash co-disposal: Influence on per- and polyfluoroalkyl substances (PFAS) concentration in landfill leachate

Municipal solid waste incineration (MSWI) ash is often managed through co-disposal with unburned wastes in landfills, a practice previously reported to result in enhanced leaching of pollutants (e.g., heavy metals) in landfill leachate. The objective of this study was to evaluate the effect of co-disposed unburned wastes on perand polyfluoroalkyl substances (PFAS) in MSWI ash landfill leachate. Leachate was collected from four landfills containing MSWI ash, either as a sole waste stream or co-disposed of with sewage sludge and MSW screenings. Samples of ash and unburned materials were collected and assessed separately for leachable PFAS in the laboratory. All samples were analyzed for 26 PFAS. Results showed that greater ash content was associated with lower leachate PFAS concentrations. The pure ash monofill exhibited the lowest PFAS in landfill leachate (290 ng L-1) while the landfill contained a large amount of unburned waste had the highest PFAS (11,000 ng L-1). For laboratory leaching tests, average n-ary sumation 26PFAS concentration in lab ash leachate (310 ng L-1) was 10 and 24 times lower than observed in lab sewage sludge leachate (3,200 ng L-1) and lab MSW screenings leachate (7,500 ng L-1), respectively. Leachate from the ash-only landfill had n-ary sumation 26PFAS concentration similar to what was measured in the ash itself. On the contrary, n-ary sumation 26PFAS concentration in co-disposal landfill leachates were similar to those in PFAS-rich unburned waste itself, regardless of the percentages of landfilled unburned wastes. We hypothesize that leachate generated in co-disposal scenarios preferentially flows through PFAS-rich unburned materials and that biotransformation of precursors enhanced by unburned waste degradation further contributes to higher concentrations of terminal PFAS in ash co-disposal sites. Landfill operators should expect PFAS in leachates to be higher when PFAS-rich unburned wastes are disposed of alongside MSWI ash, even if the unburned fraction is small.