A critical review of per- and polyfluoroalkyl substances (PFAS) in wastewater biosolids and sludge

Biosolids derived from wastewater treatment plants are commonly used as agricultural soil amendments. However, long-chain PFAS species tend to accumulate in these biosolids, raising environmental and human health concerns. USEPA risk assessment reveals that land application of sewage sludge containing 1 ppb PFOA or PFOS presents human health risk that is beyond the agency’s acceptable threshold for non-carcinogenic and carcinogenic effects. Therefore, this review systematically examines the literature published on the occurrence, quantification, treatment, and management of PFAS in wastewater sludge and biosolids, utilizing science mapping and bibliometric analysis approaches. PFAS have been detected in sludge and biosolids across all inhabited continents, with the exception of South America where no studies have been published. PFOS is the most widely detected compound in biosolids whereas the concentration of 6:2 FTCA reached up to 22000 ng/g (dry weight) in an industrial wastewater sludge. This review also discusses PFAS treatment methods in biosolids and their operating conditions and degradation/removal mechanisms. Pyrolysis and hydrothermal treatments were the most widely studied. This is because they can remove PFAS from the solid residues while producing added-value products such as biochar/hydrochar. Additionally, mitigation approaches to minimize PFAS mobilization in the environment, including desorption from biosolids, enrichment, and stabilization techniques are discussed. Overall, significant advancements in PFAS management in sludge and biosolids were highlighted, along with the identification of challenges, limitations, and areas requiring further research to raise awareness about this topic, and to guide researchers in identifying future directions for enhanced PFAS treatment in wastewater biosolids. • Science mapping and bibliometric analysis were conducted to review PFAS in biosolids. • Long-chain PFAS, especially PFOS, dominate in biosolids. • Pyrolysis and hydrothermal treatment are common for PFAS removal in biosolids. • Stabilization shows promise in preventing PFAS mobilization in the environment. • Research gaps and recommendations for future works were highlighted.