Waste-Made Multisorber: A Solution to PFAS, PPCP, and Heavy Metals in Leachate

Abstract Description: Landfills are a common source of releasing per and polyfluoroalkyl substances (PFAS) into the environment. PFAS removal is very complicated and even if leachate is sent to a municipal wastewater treatment plant (WWTP), it can inhibit WWTP biological processes or accumulate in sludge, preventing its reuse as compost or fertilizer. Pre-treatment is very important not only to reduce the load of PFAS from leachate but also to reduce pharmaceutical and personal care products (PPCP) or heavy metals. Moreover, natural organic matter (NOM) like humic and fulvic acids can pass through the WWTP disinfection system, reducing its efficiency by absorbing UV light.

Adsorbents have been demonstrated to effectively remove heavy metals and organics from leachate, using less chemicals and energy than many competing techniques. Adsorbents made from waste are more sustainable than traditional activated carbon (AC), which is made from coal, a non-renewable resource. Waste-made adsorbents are also typically cheaper since the waste is available at low or no cost. Although adsorbents can effectively remove contaminants from leachate, a single type of absorbent is not effective in removing the variety of heavy metals and organics present. For example, micro- ( < 2 nm) and mesopores (>2 nm & < 50 nm) are favorable for adsorption of short- and long-chain PFAS, respectively. The principal goal of this project is to develop a multiple sorbent mixture “MultiSorb” from readily available waste materials, to cost-effectively remove heavy metals and organics from leachate. Among potential waste materials, Rice Husk (RH) and Sewage Sludge (SS) have great adsorptive capacities and are readily available waste byproducts.

A total of 48 adsorbents were made with both chemicals (3 different chemicals at 3 different temperatures) and physical activation (3 different temperatures, steam). Five controls were tested: unmodified RH, SS, RHA, SSC; commercial AC. Adsorbents were characterized for surface functional groups, surface area, pore size, leaching behavior using SEM, BET, EDS, FT-IR and LEAF. Batch tests were conducted for 48 sorbents and 5 controls to select Presorb (effective for removing Humic and Fulvic Acid) and Multisorb (effective in removing Cu, Fe, PFOA, PFBA, PPCPs). The best sorbents for NOM and metals/PFAS/PPCPs were chosen and mixed to form PreSorb and MultiSorb, respectively, which were tested with real leachate. An overall cost comparison was done with commercial AC.

A total of 6 adsorbents were shortlisted as PreSorb and MultiSorb. BET surface area analysis showed adsorbents to be dominated by mesopores. Use of Presorb prior to Multisorb increased overall adsorption of PFAS, PPCP, and heavy metals. Among shortlisted adsorbents, RH-500-Zn is highly effective in adsorbing PFAS/PPCP, exceeding CAC by a factor of 2 for PFBA and surface area of 634 m2/gm, close to CAC (700 m2/gm). SS-500-Zn is a good adsorber for PFAS, PPCP and heavy metal and SSC-500 was a strong performer for metals. The waste-made adsorbent cost was found to be 22% that of commercial activated carbon (assuming neither is regenerated).