Reactivity recovery of guar gum coupled mZVI by means of enzymatic breakdown and rinsing

Pressure-controlled injection of guar gum stabilized microscale zerovalent iron for groundwater remediation

“…The appearance of intermediateand end-products of chlorinated hydrocarbons dehalogenation (namely chloroethane CA, vinyl chloride VC, ethene and ethane) proved that the observed decrease in CAHs concentration was not only due to dilution by the injected fluid. Indeed increased concentrations of CA, ethene and ethane after injection were measured and are explicable by reduction processes initiated by injected mZVI, while the presence of VC as an intermediate product can be explained by a partial hydrogenolysis pathway, which can be attributed to the impact of guar gum on iron reactivity (Velimirovic et al, 2012). The accumulation of cDCE observed 57 days after injection suggests that also biological processes may have been induced by mZVI injection, as a consequence of hydrogen gas production, pH increase, reducing conditions (Truex et al, 2011;Wei et al, 2010) and guar gum degradation.…”

“…Nevertheless, HQ particles, if dispersed in pure water, are very unstable and prone to partial aggregation and fast sedimentation, due to their micrometric size, high density (close to bulk iron density of 7.8 g/cm 3 ), and weak attractive forces among particles. The colloidal stability was therefore improved by means of a food-grade guar gum (HV700, RANTEC, United States) characterized by high molecular weight and fast degradation rate in the presence of enzymes (Di Molfetta and Sethi, 2006;Gastone et al, 2014a;Tiraferri and Sethi, 2009;Velimirovic et al, 2012). HV700 is provided as dry powder with a medium to fine granulation (nominal maximum grain size equal to 75 μm), which can be easily dissolved in water increasing fluid viscosity and forming a shear thinning solution (Comba and Sethi, 2009;Gastone et al, 2014a;Gastone et al, 2014b;Wang et al, 2008).…”

“…Since the adsorption of biopolymer chains can hinder the reactivity, it is important to use easily biodegradable biopolymers (e.g. guar gum) which can be removed by enzymatic breakdown (Di Molfetta and Sethi, 2006;Gastone et al, 2014a;Kirschling et al, 2011;Reddy et al, 2011;Velimirovic et al, 2012) or by soil microbial population (Velimirovic et al, 2014b). If the polymer is dosed in significantly higher concentrations (in the order of grams per liter), part of the polymer chains adsorb onto the ZVI surface, until saturation, and part stay in suspension, increasing the viscosity of the dispersing fluid (kinetic stabilization) and consequently significantly reducing aggregation and sedimentation rate (Dalla Vecchia et al, 2009b;Tiraferri et al, 2008;Velimirovic et al, 2012;Xue and Sethi, 2012).…”

“…guar gum) which can be removed by enzymatic breakdown (Di Molfetta and Sethi, 2006;Gastone et al, 2014a;Kirschling et al, 2011;Reddy et al, 2011;Velimirovic et al, 2012) or by soil microbial population (Velimirovic et al, 2014b). If the polymer is dosed in significantly higher concentrations (in the order of grams per liter), part of the polymer chains adsorb onto the ZVI surface, until saturation, and part stay in suspension, increasing the viscosity of the dispersing fluid (kinetic stabilization) and consequently significantly reducing aggregation and sedimentation rate (Dalla Vecchia et al, 2009b;Tiraferri et al, 2008;Velimirovic et al, 2012;Xue and Sethi, 2012). Stabilization approaches based on the use of polymeric solutions, characterized by a non-Newtonian shear thinning behavior, showed promising results also in improving particles mobility in porous media (Cantrell et al, 1997;Comba and Sethi, 2009;Dalla Vecchia et al, 2009b;Gastone et al, 2014b;Kocur et al, 2013;Tiraferri and Sethi, 2009;Tiraferri et al, 2008;Tosco et al, 2014a;Xue and Sethi, 2012).…”

Nano‐Composites for Water Remediation: A Review

“…Surfactants or polymers can be added to the NP surfaces to encourage steric hindrance and alter the surface charge to prevent electrostatic attraction. The NPs can also be incorporated into other mobile structures such as carbon forms, silica and colloidal clays .…”