Defining quality assurance guidance for effective selection of technical grade zero-valent iron production batch for groundwater remediation using permeable reactive barrier.

ABSTRACT

Zero-valent iron (ZVI) applied to the remediation of contaminated groundwater (GW) in situ, especially using engineered permeable reactive barriers (PRBs), has been proven to be an effective reactive material. However, many of ZVI brands do not represent tailored reagents specifically regarding destroying pollutants in GW. Thus, their reactivity towards certain contaminants in GW may vary significantly in a wide range even with different production batches of the same ZVI brand. This issue has rarely been known and consequently not addressed to a higher extend so far. Therefore, this study implemented extensive, long-term column experiments followed by short-term batch experiments for chlorinated volatile organic compounds (cVOCs) degradation for developing a semi-empirical test methodology to thoroughly resolve this pivotal issue by achieving an improved quality assurance guidance regarding proper field-scale emplacement of different ZVI brands and their production batches. The results showed that during column experiments perchloroethylene (PCE) led to a significant degradation up to a certain period but sulfate-reducing microorganisms enhanced the dehalogenation and led approximately to 100 % PCE removal. However, the efficacy varied for different ZVI brands, i.e., Gotthart Maier (GM) and Sponge Iron (Responge®). Furthermore, it could be shown that it might even vary among different production batches of the same ZVI brand. It was also observed that evolution of sulfate-reducing microorganisms may improve the efficacy of PCE degradation vastly that occur at different intensities with different ZVI brands and their respective production batches over time. Further, comparing comprehensive long-term column (kobs = 0.0488 1/h) and short-term batch experiments (kobs = 0.07794 1/h) as well as refined kinetic analyses (kobs = 0.0424 1/h) clearly prove that an appropriate guidance protocol for successful full-scale in situ remediation is required for properly select the right ZVI brand and production batch before it is loaded to a PRB in the field.