Abstract
Commercially available particulate amendments demonstrate high reactivity for effective treatment of water soluble organic and inorganic contaminants in laboratory studies; however, transport of these particles is constrained in the subsurface. In many field applications, particulate amendments are mixed with organic polymers to enhance mobility for direct push applications or stabilize suspensions for high mass loadings. As such, the interactions between particulate amendments, organic polymers and contaminant species need to be systematically investigated to properly understand mechanistic processes that facilitate predictive performance metrics for specific applications in situ. In this study, batch experiments were conducted to quantify the effects of organic polymers (xanthan gum, guar gum, and sodium alginate), polymer concentration (800 and 4,000 mg/L), and aging (up to 28 days) on chromate treatment rate and capacity by two classes of amendments: reductants [granular zero-valent iron (gZVI), micron-ZVI (mZVI), sulfur modified iron (SMI)], and an adsorbent (bismuth sub-nitrate). When particulate amendments were suspended in polymer solutions, reductants retained between 84–100% of the amendment treatment capacity. Conversely, the adsorbent maintained 63–97% relative treatment capacity of the no-polymer control. Polymer solutions had a more pronounced impact on the rate of chromate removal; first order rates of chemical reduction decreased by as much as 70% and adsorption by up to 81% relative to the no-polymer controls. Polymer–amendment aging experiments also showed decreased Cr(VI) treatment capacity; reductants decreased by as much as 24% and adsorption decreased by as much as 44% after 28 days of incubation. While polymer suspensions are needed to aid the injection of particulate amendments into the subsurface, the results from this study indicate potential losses of treatment capacity and a decrease in the rate of remedial performance due to the physical and chemical interactions between polymer suspensions and reactive particulate amendments. Simple batch systems provide baseline characterization of tripartite interactions for the removal of Cr(VI). Additional work is needed to quantify the full impact of polymers on remedial outcomes under site relevant conditions at field scale.
Highlights
In situ remediation of sediment and groundwater often necessitates the introduction of reagents or reactive amendments to promote the degradation, mobilization, or stabilization of organic and inorganic contaminants within an acceptable timeframe (Muller et al, 2020)
Velimirovic et al (2016) found milled zero valent iron (ZVI) suspension stability was slightly improved with increased agar concentration, indicating the stability difference invoked by different types of polymers
Slight decreases in the treatment capacity of granular zero-valent iron (gZVI) were measured in suspensions of 800 mg/L xanthan gum, guar gum, and sodium alginate; corresponding to 7.0 ± 0.1, 0.8 ± 0.1, and 12 ± 0.0%, respectively, less capacity than the gZVI no-polymer control (Figure 1A; Table 2)
Summary
In situ remediation of sediment and groundwater often necessitates the introduction of reagents or reactive amendments to promote the degradation, mobilization, or stabilization of organic and inorganic contaminants within an acceptable timeframe (Muller et al, 2020). To overcome mobility challenges facing particulate amendment delivery in field implementation, particle size can be reduced, surface properties modified, or chemical additives used to enhance suspension stability, and extend particle penetration in heterogenous media (e.g., Fan et al, 2017; Lowry and Phenrat, 2019; Pavelková et al, 2020; Tiraferri et al, 2008; Tosco et al, 2014a; Truex et al, 2011; Velimirovic et al, 2012; Velimirovic et al, 2016) Such modifications introduce tradeoffs in remedial efficiency, treatment or reaction time, and potential cost. To help better understand these tradeoffs in advance, the complex and varied interactions between chemical additives, remedial amendments, contaminant species, and representative site conditions can be systematically investigated to gain a more predictive understanding of the mechanistic interactions that control subsurface reactions and influence remedial outcomes
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
