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Laboratory and field studies have demonstrated the applicability of nanoparticles (NP) for accelerated contaminant degradation. Beside other limitations (e.g. costs, delivery, longevity, non-target specific reactions), concerns of regulators arose regarding toxicity of injected NP and particles delivered off-target (i.e. renegade particles). Renegade particles also significantly reduce the efficiency of the remediation. The delivery of particles off-target is caused, mainly, by unintended fracking, where the fractures act then as preferential flow paths changing the trajectory of the particles. Hence, the real-time monitoring of particle injection is of major importance to verify correct particle delivery and thus help to optimize the remediation strategy. However, to date NP monitoring techniques rely on the analysis of soil and water samples, which cannot provide information about clogging or the formation of fractures away of the sampling points. To overcome these limitations, in this study we investigate the applicability of complex-conductivity imaging (CCI), a geophysical electrical method, to characterize possible pore clogging and fracking during NP injections. We hypothesize that both processes are related to different electrical footprints, considering the loss of porosity during clogging and the accumulation of NP in areas away of the target after fracking. Here, we present CCI results for data collected before and during the injection of Nano-Goethite particles (NGP) applied to enhance biodegradation of a BTEX (benzene, toluene, ethylbenzene and xylene) contaminant plume. Imaging results for background data revealed consistency with the known lithology, while overall high electrical conductivity values and a negligible induced-polarization magnitude correspond with the expected response of a mature hydrocarbon plume. Monitoring images revealed a general increase (∼15 per cent) in the electrical conductivity due to the injected NGP suspension in agreement with geochemical data. Furthermore, abrupt changes in this trend, shortly before daylighting events, show the sensitivity of the method to pore clogging. Such interpretation is in line with the larger variations in CCI resolved in the unsaturated zone, clearly indicating the accumulation of renegade NGP close to the surface due to fracking. Our results demonstrate the applicability of the CCI method for the assessment of pore clogging accompanying particles injection. [ABSTRACT FROM AUTHOR]

The affinity between nanoscale zerovalent iron (nano-ZVI) and mineral surfaces hinders its mobility, and hence its delivery into contaminated aquifers. We have tested the hypothesis that the attachment of poly(acrylic acid)-coated nano-ZVI (PAA-nano-ZVI) to mineral surfaces could be limited by coating such surfaces with sodium (Na) humate prior to PAA-nano-ZVI injection. Na humate was expected to form a coating over favorable sites for PAA-nano-ZVI attachment and hence reduce the affinity of PAA-nano-ZVI for the collector surfaces through electrosteric repulsion between the two interpenetrating charged polymers. Column experiments demonstrated that a low concentration (10 mg/L) Na humate solution in synthetic water significantly improved the mobility of PAA-nano-ZVI within a standard sand medium. This effect was, however, reduced in more heterogeneous natural collector media from contaminated sites, as not an adequate amount of the collector sites favorable for PAA-nano-ZVI attachment within these media appear to have been screened by the Na humate. Na humate did not interact with the surfaces of acid-washed glass beads or standard Ottawa sand, which presented less surface heterogeneity. Important factors influencing the effectiveness of Na humate application in improving PAA-nano-ZVI mobility include the solution chemistry, the Na humate concentration, and the collector properties. [ABSTRACT FROM AUTHOR]

Abstract: The limited transport of nanoscale zero-valent iron (nZVI) in porous media is a major obstacle to its widespread application for in situ groundwater remediation. Previous studies on nZVI transport have mainly been carried out in quartz porous media. The effect of carbonate minerals, which often predominate in aquifers, has not been evaluated to date. This study assessed the influence of the carbonate minerals in porous media on the transport of polyacrylic acid modified nZVI (PAA-nZVI). Increasing the proportion of carbonate sand in the porous media resulted in less transport of PAA-nZVI. Predicted travel distances were reduced to a few centimeters in pure carbonate sand compared to approximately 1.6 m in quartz sand. Transport modeling showed that the attachment efficiency and deposition rate coefficient increased linearly with increasing proportion of carbonate sand. [Copyright &y& Elsevier]