Study on the effect of alginate coated Ca-Fe bimetallic composite biochar microspheres on the removal of short-chain PFAS.

The remediation of short-chain per- and poly-fluoroalkyl substances (PFAS) contamination is challenging, and the low adsorption capacity and slow adsorption kinetics of conventional adsorbents for short-chain PFAS inhibit their application. In this study, alginate coated Ca-Fe bimetallic biochar balls (CA/Ca-Fe/BC) were prepared using pomelo peel and corn stover as biochar materials. The removal of short-chain PFAS involves two key processes: adsorption and degradation, and the removal efficiency is better than that of existing adsorption materials. The results of adsorbent characterisation and intermittent adsorption experiments showed that the adsorption of short-chain PFAS by CA/Ca-Fe/BC was dominated by electrostatic interactions and ion-exchange, and the degradation was mainly dominated by the reduction of iron groups and advanced oxidation. The microbeads reached adsorption equilibrium within 40 min. The highest adsorption capacity of CA/Ca-Fe/BC for PFHxA, PFBS and PFBA was 68.91 mg/g, 48.95 mg/g and 42.64 mg/g and the adsorption capacity was correlated with C-F chain length. The highest removal efficiency was PFHxA (62.65 %) > PFBS (45.56 %) > PFBA (37.89 %). The mechanism and regenerative properties of microbeads for the removal of short-chain PFAS were investigated. It was shown that CA/Ca-Fe/BC can be used as an eco-friendly, cost-effective and efficient adsorbent material for the removal of short-chain PFAS from water, with good application prospects.