Adsorption kinetics and diffusion of Saxitoxins on granular-activated carbon: influence of pore size distribution

Abstract

Saxitoxin (STX) is the most toxic non-protein substance known. STX-producing cyanobacteria have been identified in most continents and are being detected more widely because of global warming, threatening human drinking water supplies worldwide. Removal of these components can be accomplished by adsorption on granular-activated carbon (GAC) but little is yet known about the kinetics of the process. This research investigated adsorption kinetics and diffusion behaviour of a decarbomoyl saxitoxin (dc-STX) and a carbamate toxin (STX) on four coconut shell-based GAC samples with different pore size distribution. It was observed that equilibrium concentration was reached within 24 h and that a pseudo-second-order model best represented experimental data. Of the four GAC samples tested, the example with the largest volume of mesopores adsorbed more STX and with a faster upload rate, while dc-STX was adsorbed equally in all four GAC samples.

Recent Advancements in the Removal of Cyanotoxins from Water Using Conventional and Modified Adsorbents—A Contemporary Review

“…Like PAC, the performance of GAC in the treatment of cyanotoxins depends on the GAC properties which facilitate the electrostatic attraction. The application of GAC in the removal of decarbamoylsaxitoxin (dc-STX) exhibited a repulsive force between positively charged GAC and cationic saxitoxins [50]. Silva Buarque et al [50] further studied the effect of pore size on the adsorption of saxitoxin, and it was found that mesopores played an essential role in promoting adsorption capacity and adsorption kinetics of coconut GAC.…”

Physico-chemical treatment for the degradation of cyanotoxins with emphasis on drinking water treatment—How far have we come?

“…For example, in a recent study by Silva et al, (2015) [76], in a GAC filter treatment, saxitoxin and decarbomoyl saxitoxin (dc-STX) exhibited cationic nature (between mono-cationic and dicationic) in their molecular structure due to the presence of the amine group at neutral pH, which further helped these molecules to get removed due to the electrostatic repulsion [91]. However, these electrostatic repulsions might vary among different cyanotoxins based on the size and charges.…”

“…For example,Tak et al, (2018) [91] it was found that ozone alone (2 mg/L) degraded 68% of anatoxin while ozone with H 2 O 2 and Fe (II) degraded 100% and 85% respectively[108]. The overall mechanism works in a way that hydrogen peroxide in aqueous solution dissociates into HO 2 -which reacts with the ozone molecule providing a chain of reactions to produce more hydroxyl ions.…”

Pre-purification by membrane filtration of paralytic shellfish toxins from Alexandrium minutum dinoflagellate

“…Methanol and water can also be used as solvent as well as supercritical fluids (Haque et al 2017, Pyo et al 2004. Neurotoxins such as saxitoxins can also be adsorbed on powder activated carbon (Ho et al 2009, Westrick et al 2010, Buarque et al 2015. Nevertheless, the desorption can be difficult without molecule damage.…”