Removal of Cyanotoxins–Microcystins from Water by Filtration through Granulated Composites of Bentonite with Micelles of the Cation Octadecyltrimethyl Ammonium (ODTMA)

Abstract

Cyanobacteria and their toxins present potential hazards to consumers of water from lakes, reservoirs and rivers; thus, their removal via water treatment is essential. Previously, we demonstrated that nanocomposites of octadecyltrimethyl ammonium (ODTMA) complexed with clay could efficiently remove cyanobacteria and their toxins from laboratory cultures and lake water. In this study, we determined the capacity of ODTMA nanocomposites to remove cyanotoxins, namely microcystins (MCs), from water to below 1 µg/L via filtration. This capacity was 1500 mg MC-LR per Kg of nanocomposite. Similar capacities were estimated for the removal of other MC congeners (MC-WR, MC-3aspWR and MC-YR), whereas substantially lower capacities were recorded for more positively charged MC congeners, such as MC-RR and MC-3aspRR. Filtration results were simulated with a filtration model, which considers convection and adsorption/desorption of one to several toxins. Model calculations for the removal of MC-LR, under a variety of situations, fitted well with all the experimentally measured values and also estimated the co-removal of several MC congeners. In agreement with model predictions, results demonstrated that in the presence of MC-WR, the emerging concentrations of MC-RR congeners eventually exceed their solution values. In conclusion, granulated nanocomposites of ODTMA–bentonite can be applied for the removal of microcystins from drinking water.

Cyanobacterial Harmful Algal Blooms in Aquatic Ecosystems: A Comprehensive Outlook on Current and Emerging Mitigation and Control Approaches

“…Filtration results were simulated with a filtration model that considers the convection and adsorption/desorption of one to several toxins. This further supports the possibility that granulated nano-composites of ODTMA-bentonite can be applied for the removal of microcystins from drinking water [ 199 ].…”

“…Other chemical properties of cyanotoxins such as hydrophobicity and functional groups affect the adsorption efficiency by GAC. For example, the order of removal efficiency for MCs is MC-RR > MC-YR > MC-LR > MC-LA [ 198 , 199 ]. In addition, the efficiency of a particular type of activated carbon for a certain toxin depends not only on matrix properties (number and size of the adsorption sites or pores) but also on other DOC components in the treated water that compete for adsorption and may reduce the removal of cyanotoxins [ 178 ].…”

Removal of Emerging Contaminants by Degradation during Filtration: A Review of Experimental Procedures and Modeling

“…The results in [42] indicated a more efficient removal of the main toxins MC-LR and MC-YR by filtration using a granulated ODTMA-clay complex compared to GAC, whereas the more positively charged congener MC-RR was removed more efficiently by GAC.…”

“…One conclusion of this study was that a filter with the granulated complex can be applied in the removal of microcystins from drinking water. The calculations in [42] showed a capacity of 4.3 m 3 /kg of the complex for the removal of MC-LR from a 5.5 µg/L solution (for an emerging toxin concentration below 1 µg/L), whereas for a 10 µg/L solution, the capacity corresponded to 3 m 3 /kg of the complex. These capacities are not economical.…”

“…Sukenik et al [7] demonstrated adsorption of the toxins microcystins (MCs) and cylindrospermopsin (CYN) from a suspension by 1 g/L of a micelle (ODTMA)-clay complex. This was followed by [42], who determined experimentally and modeled the removal of several microcystins by filters, including a granulated micelle (ODTMA)-clay (bentonite) complex. The MC congeners MC-LR, MC-YR, MC-WR, and MC-3aspWR were removed more efficiently than the more positively charged ones (MC-RR and MC-3aspRR).…”