PFOA remediation from aqueous media using CTAB impregnated activated carbon: A closed-loop sustainable study with comprehensive selectivity analysis

Abstract

PFASs have been attracting worldwide attention in recent years. In this study, a novel surface-impregnated activated carbon (AC) has been optimally synthesized utilizing waste Karanja shells. Surface functional group modification has been performed using Cetyltrimethylammonium bromide (CTAB). PFOA-selectivity analysis of the adsorbent against different background species present at typical river water concentration was performed. To make the process sustainable, the development of regenerant specifications as well as recovery of the regenerant and PFOA from the spent regenerant solution were investigated. A biomass/acid ratio of 1:2.5, temperature 450 °C, and 1 % CTAB solution was found to be optimum synthesis parameters for the CTAB-modified AC (CTAB_K-AC) for PFOA removal. By CTAB-impregnation, the PFOA uptake capacity of the adsorbent increased up to threefold. The maximum PFOA adsorption capacities exhibited by Karanja AC (K_AC) and CTAB_K-AC were 157.1 mg/g & 455.8 mg/g, respectively. The adsorbent exhibited high PFOA selectivity against all background co-contaminants i.e., NOM (humic acid), clay (bentonite), anions, and cations, and removed ~90 % PFOA. The regenerant (50 % ethanol with 1 % NH4OH aqueous solution) showed 80–90 % PFOA recovery. The distillation process at ~80 °C temperature recovered ~90 % PFOA and 80–90 % of the regenerant reagents from the spent regenerant solution. The packed-bed column run of the adsorbent showed high PFOA removal capacity from the river water matrix and the breakthrough data was well fitted with Thomas and Yoon Nelson Model with R2 values of 0.97 for both the models. The results showed that novel CTAB_K-AC can be an effective adsorbent for PFOA adsorptive remediation from aqueous media with high treatment selectivity towards the PFOA in a materially closed-loop sustainable process.