Preliminary assessment of the performance of oyster shells and chitin materials as adsorbents in the removal of saxitoxin in aqueous solutions.

Silvia P Melegari,William G Matias

doi:10.1186/1752-153x-6-86

Abstract

BackgroundThis study evaluated the adsorption capacity of the natural materials chitin and oyster shell powder (OSP) in the removal of saxitoxin (STX) from water. Simplified reactors of adsorption were prepared containing 200 mg of adsorbents and known concentrations of STX in solutions with pH 5.0 or 7.0, and these solutions were incubated at 25°C with an orbital shaker at 200 RPM. The adsorption isotherms were evaluated within 48 hours, with the results indicating a decrease in STX concentrations in different solutions (2–16 μg/L). The kinetics of adsorption was evaluated at different contact times (0–4320 min) with a decrease in STX concentrations (initial concentration of 10 μg/L). The sampling fractions were filtered through a membrane (0.20 μm) and analyzed with high performance liquid chromatography to quantify the STX concentration remaining in solution.ResultsChitin and OSP were found to be efficient adsorbents with a high capacity to remove STX from aqueous solutions within the concentration limits evaluated (> 50% over 18 h). The rate of STX removal for both adsorbents decreased with contact time, which was likely due to the saturation of the adsorbing sites and suggested that the adsorption occurred through ion exchange mechanisms. Our results also indicated that the adsorption equilibrium was influenced by pH and was not favored under acidic conditions.ConclusionsThe results of this study demonstrate the possibility of using these two materials in the treatment of drinking water contaminated with STX. The characteristics of chitin and OSP were consistent with the classical adsorption models of linear and Freundlich isotherms. Kinetic and thermodynamic evaluations revealed that the adsorption process was spontaneous (ΔGads < 0) and favorable and followed pseudo-second-order kinetics.

Highlights

This study evaluated the adsorption capacity of the natural materials chitin and oyster shell powder (OSP) in the removal of saxitoxin (STX) from water
Another technology employed in recent years to remove cyanotoxins from aqueous solutions is carbon nanotubes, which have a high adsorption capacity compared to activated charcoal and other conventional adsorbents, such as mineral clays [13], but this technology has not been comprehensively tested for its toxicology effects
Effects of STX concentration and contact time STX was removed from aqueous solution when it came into contact with the adsorbents being tested (Figure 1), and the kinetics of its adsorption, with respect to contact time at each pH used for chitin and OSP, indicated significant removal of STX by both materials (≥ 50% removal) when tested for 18 h of contact time

Summary

Introduction

This study evaluated the adsorption capacity of the natural materials chitin and oyster shell powder (OSP) in the removal of saxitoxin (STX) from water. Different alternatives for removing cyanotoxins by adsorption and with others techniques have been tested [9,10,11,12], but the evidence regarding the usefulness of filters made from natural materials to remove cyanotoxins, in particular saxitoxin (STX), is still unreliable. Another technology employed in recent years to remove cyanotoxins from aqueous solutions is carbon nanotubes, which have a high adsorption capacity compared to activated charcoal and other conventional adsorbents, such as mineral clays [13], but this technology has not been comprehensively tested for its toxicology effects. Water treatment systems can eliminate cyanobacteria and their toxins from raw water, but conventional water treatment has proven ineffective at removing dissolved cyanotoxins from water [12,20]

Methods

Results

Conclusion