Applications of Chemically Modified Clay Minerals and Clays to Water Purification and Slow Release Formulations of Herbicides
. MINERALS 2021
This review deals with modification of montmorillonite and other clay-minerals and clays by interacting them with organic cations, for producing slow release formulations of herbicides, and efficient removal of pollutants from water by filtration. Elaboration is on incorporating initially the organic cations in micelles and liposomes, then producing complexes denoted micelle- or liposome-clay nano-particles. The material characteristics (XRD, Freeze-fracture electron microscopy, adsorption) of the micelle- or liposome-clay complexes are different from those of a complex of the same composition (organo-clay), which is formed by interaction of monomers of the surfactant with the clay-mineral, or clay. The resulting complexes have a large surface area per weight; they include large hydrophobic parts and (in many cases) have excess of a positive charge. The organo-clays formed by preadsorbing organic cations with long alkyl chains were also addressed for adsorption and slow release of herbicides. Another examined approach includes ``adsorptive'' clays modified by small quaternary cations, in which the adsorbed organic cation may open the clay layers, and consequently yield a high exposure of the siloxane surface for adsorption of organic compounds. Small scale and field experiments demonstrated that slow release formulations of herbicides prepared by the new complexes enabled reduced contamination of ground water due to leaching, and exhibited enhanced herbicidal activity. Pollutants removed efficiently from water by the new complexes include (i) hydrophobic and anionic organic molecules, such as herbicides, dissolved organic matter; pharmaceuticals, such as antibiotics and non-steroidal drugs; (ii) inorganic anions, e.g., perchlorate and (iii) microorganisms, such as bacteria, including cyanobacteria (and their toxins). Model calculations of adsorption and kinetics of filtration, and estimation of capacities accompany the survey of results and their discussion.
Removal of geosmin and 2-methylisoborneol from aquaculture water by novel, alginate-based carriers: Performance and metagenomic analysis
. JOURNAL OF WATER PROCESS ENGINEERING 2021
Hydrophobic carriers were examined for geosmin and 2-methylisoborneol removal from water derived from an aquaculture system. A combination of adsorption and biodegradation was found to underlie the removal of the off-flavor compounds. Adsorption of these compounds by the carriers was unaffected by the presence of organic matter in the water to be treated. A model based on adsorption/desorption and first-order degradation kinetics provided an accurate prediction for experimentally determined 2-methylisoborneol removal rates. Steady removal of geosmin and 2-methylisoborneol as well as nitrate reduction were observed during long-term operation of the plug-flow reactors with water derived from an aquaculture facility. Metagenomic analysis of the microbial community on the carriers during long-term operation of the reactors revealed a predominance of denitrifying bacteria. It was found that geosmin and 2-methylisoborneol led to statistically significant changes in the abundances of 21 contigs that contained genes involved in terpene degradation. This study shows that at low ambient concentrations of geosmin and 2-methylisoborneol in nitrate and organic-rich water, such as found in aquaculture systems, their biodegradation can be accomplished by terpene-degrading denitrifiers that develop on hydrophobic carriers used for filtration of the contaminated water.