Remediation of PFAS-impacted agricultural soil with destructive methods (soil washing, excavation, incineration, chemical oxidation) is challenging because of the diffuse character of the pollution. Furthermore, these destructive approaches will impair soil ecosystem services and cause carbon emissions. In-situ methods such as phytoremediation and sorbent amendment are less intrusive, more cost-effective, and align with the concept of nature-based solutions. Biochar from biomass combustion in the absence of air (pyrolysis), has been proposed as a sustainable sorbent material, due to its benefits in terms of carbon sequestration, nutrient recycling / waste handling, energy generation and contaminant immobilization. This is particularly the case if the biochar is made from contaminated biosolids, as pyrolysis can mineralize the PFAS. Pyrolyzing the contaminated biomass additionally alleviates the constraints of biomass disposal. Amendment with 1% sludge biochar or (activated) high-temperature (> 800 °C) wood biochar reduced PFOS leaching from contaminated soil by up to 92-99%, with notably better effectiveness for long-, than for short-chain (C4 and C5) PFAS (40-70%). A high potential for terrestrial and aquatic plant bioaccumulation of PFAS has been shown for ultra-short chain and short-chain perfluoroalkyl acids (PFAA). Most studies were performed with crop species (e.g. corn, wheat, rapeseed) and rarely tested in field conditions. The main challenges for phytoremediation include not only high variabilities between the plant uptake potential of different PFAS (chain length, charge), but also high variations between plant species and field conditions, making it hard to predict removal efficiencies. With the suggested solution, we create a virtuous cycle when combining phytoremediation to accumulate short-chain PFAS in plant biomass, destroying of accumulated PFAS by pyrolytic treatment, and applying the resulting biochar to immobilize long-chain PFAS in agricultural top-soils.
