Fate and Transport of Cyanotoxins and Natural Organic Matter through Virgin and Reactivated Granular Activated Carbons

Cyanotoxins, including microcystins (MCs) and cylindrospermopsin (CYN), are potent hepatotoxins produced during cyanobacterial algal blooms. Understanding how readily these compounds are removed by granular activated carbon (GAC) is important for protecting aquatic ecosystem and public health. Since GAC is often reused after reactivation, the potential exists for reactivated carbon to exhibit performance deterioration after numerous reactivations. This study compared the removal of cyanotoxins with virgin and reactivated GAC using rapid small-scale column tests (RSSCTs) using three model cyanotoxins (i.e., MC-LR, MC-RR, and CYN) at two different concentrations (i.e., 10 and 40 μg/L) spiked into conventionally treated Ohio River water from a local treatment facility. Among the three tested toxin variants, MC-LR and MC-RR did not show breakthrough during 16 RSSCT run days (or 28,800 bed volume), even with reactivated GAC columns at spiked concentrations of 40 μg/L. CYN shows the weakest adsorption, as suggested by its earlier breakthrough in reactivated GAC at approximately 16 RSSCT days. These results imply that water treatment utilities should consider a finite number of reactivation cycles of GAC because GAC pores could be widened during thermal reactivation, ultimately reducing the removal efficiency of more hydrophilic cyanotoxin variants in the presence of natural organic matter.