Evaluating biochar and fungi for the remediation of PFAS in landfill leachates.

Abstract

Per- and polyfluoroalkyl substances (PFAS) have become widespread environmental contaminants, often detected in various ecosystems, including waterways, and found in numerous products such as cosmetics. In New Zealand, PFAS contamination poses a significant risk to both environmental and human health. This study works towards developing an innovative PFAS removal technology utilizing biochar to adsorb PFAS and fungi to degrade PFAS. The work was broken into several stages, the first finding suitable growing conditions for fungi on biochar and attempting to quantify the growth, the second examining biochar adsorption properties, first with humic acid and the second with PFAS. Three different types of fungi, Oyster, Shiitake, and Pekepeke (native to New Zealand), were cultivated on biochar and substrates made from woodchips and other organic materials. Growth was best on a combination of biochar and woodchip. The chloroform fumigation method showed that the oyster/biochar culture had a growth of 17.6 mg/g/day, while shitake/biochar was 14.6 mg/g/day and the oyster/biochar/woodchip had a growth of 20.7 mg/g/day. Biochar had a low adsorption capacity (5 mg/g) and affinity for humic acid. The Freundlich isotherm gave a marginally better fit to adsorption data than the Langmuir and SIPS isotherms. The low adsorption was due to both humic acid and biochar having predominantly negative charges, biochar had a surface charge of 0.824 mM -ve charges/g biochar, six times that of dry soil which has a surface charge of 0.125 mM/g soil. Biochar was tested for its ability to adsorb three species of PFAS (PFBSA, PFHexA, PHHepA). Under the environmentally relevant PFAS concentration ranges tested, biochar adsorbed all of the PFAS, resulting in no PFAS being able to be detected in solution. PFAS adsorption to the biochar is predominantly by hydrogen bonding