Removal of chlorinated organic solvents from hydraulic fracturing wastewater by bare and entrapped nanoscale zero-valent iron

Abstract

With the increasing application of hydraulic fracturing, it is urgent to develop an effective and economically feasible method to treat the large volumes of fracturing wastewater. In this study, bare and entrapped nanoscale zero-valent iron (nZVI) were introduced for the removal of carbon tetrachloride (CT) and 1,1,2-trichloroethane (TCA) in model high-salinity fracturing wastewater. With increasing ionic strength (I) from Day-1 (I = 0.35 M) to Day-90 (I = 4.10 M) wastewaters, bare nZVI presented significantly lower removal efficiency of CT (from 53.5% to 38.7%) and 1,1,2-TCA (from 71.1% to 21.7%) and underwent more serious Fe dissolution from 1.31 ± 1.19% in Day-1 to 5.79 ± 0.32% in Day-90 wastewater. Particle aggregation induced by high ionic strength was primarily responsible for the lowered performance of nZVI due to less available reactive sites on nZVI surface. The immobilization of nZVI in alginate with/without polyvinyl alcohol provided resistance to particle aggregation and contributed to the superior performance of entrapped nZVI in Day-90 wastewater for 1,1,2-TCA removal (62.6-72.3%), which also mitigated Fe dissolution (4.00-4.69%). Both adsorption (by polymer matrix) and reduction (by immobilized nZVI) were involved in the 1,1,2-TCA removal by entrapped nZVI. However, after 1-month immersion in synthetic fracturing wastewater, a marked drop in the reactivity of entrapped nZVI for 1,1,2-TCA removal from Day-90 wastewater was observed with significant release of Na and total organic carbon. In summary, bare nZVI was sensitive to the nature of the fracturing wastewater, while the use of environmentally benign entrapped nZVI was more promising for wastewater treatment.

Nanomaterials for sustainable remediation of chemical contaminants in water and soil

“…Entrapped nZVI in the alginate polymer matrix showed enhanced removal capacity of 1,1,2trichloroethane (TCA) during the treatment of hydraulic fracturing wastewater (Lei et al, 2018).…”

Nanoparticled Titanium Dioxide to Remediate Crude Oil Exposure. An In Vivo Approach in Dicentrarchus labrax

“…Before employing nanomaterials in nanoremediation activities, it is important to assess their harmlessness with respect to the environment so that they do not act as pollutants themselves, posing an additional threat to the biota. For example, zero valent iron (nZVI) showed a great potential in the remediation of contaminated water, but it also exerted toxic effects during environmental applications [ 8 ].…”

Separation and Analysis of Nanoscale Zero-Valent Iron from Soil

“…Nanoscale zero-valent iron (nZVI) has been widely applied to remove various contaminants from soil and groundwater, for example, chlorinated organics, − nitrates, , heavy metals, , and emerging contaminants . Field studies demonstrated that gram per liter or gram per kilogram level of nZVI was needed for efficient remediation. , The extensive application of nZVI particles for water and soil remediation increases their environmental concentration and risk .…”