PFAS removal from water by adsorption with alginate-encapsulated plant albumin and rice straw-derived biochar

Adsorption using conventional activated carbon is considered an effective and practical method for per- and polyfluoroalkyl substances (PFAS) removal from contaminated water. However, this application can be limited by long equilibrium times, poor performance in adsorbing short-chain PFAS, and compromised adsorption in the presence of other organic compounds. In this work, rice straw-derived biochar and albumin extracted from Moringa oleifera seeds were compared after encapsulation into alginate beads which were then investigated for removing two PFAS compounds, PFOS (long-chain) and PFBS (short-chain), from aqueous solutions. The effect of albumin and biochar concentrations and the influence of different pre-treatment conditions of biochar production on PFAS removal efficiency were investigated. The batch test results showed a high removal efficiency for PFOS with 1.5 g L−1 of either albumin-alginate beads (up to 87 %) or biochar-alginate composite beads (up to 99 %) for <16 h. While PFBS removal by albumin-alginate composite beads was low (10 %), the diammonium phosphate treated biochar–alginate beads achieved nearly 40 % in <48 h, outperforming some previously reported natural material-based adsorbents that were tested under similar experimental conditions. Adsorption with biochar-alginate beads appeared not to be pH dependent, and the presence of NOM (natural organic matter) did not greatly reduce the removal of either PFOS or PFBS. Hydrophobic sorption was shown to dominate over the electrostatic interaction in the PFAS adsorption. Overall, the potential of the rice straw-derived biochar-alginate beads for the remediation of PFAS in aqueous systems was demonstrated.