Biocides are critical components of hydraulic fracturing ("fracking") fluids used for unconventional shale gas development. Bacteria may cause bioclogging and inhibit gas extraction, produce toxic hydrogen sulfide, and induce corrosion leading to downhole equipment failure. The use of biocides such as glutaraldehyde and quaternary ammonium compounds has spurred a public concern and debate among regulators regarding the impact of inadvertent releases into the environment on ecosystem and human health. This work provides a critical review of the potential fate and toxicity of biocides used in hydraulic fracturing operations. We identified the following physicochemical and toxicological aspects as well as knowledge gaps that should be considered when selecting biocides: (1) uncharged species will dominate in the aqueous phase and be subject to degradation and transport whereas charged species will sorb to soils and be less bioavailable; (2) many biocides are short-lived or degradable through abiotic and biotic processes, but some may transform into more toxic or persistent compounds; (3) understanding of biocides' fate under downhole conditions (high pressure, temperature, and salt and organic matter concentrations) is limited; (4) several biocidal alternatives exist, but high cost, high energy demands, and/or formation of disinfection byproducts limits their use. This review may serve as a guide for environmental risk assessment and identification of microbial control strategies to help develop a sustainable path for managing hydraulic fracturing fluids.
We present data for batch-to-batch variation of silver nanoparticles (AgNPs) synthesized with orange peel extract. These samples were prepared in the CEM microwave for 15 min. The relative standard deviation (as a measure of precision) is provided and is, in most cases, less than 20%.
Hydraulic fracturing fluid (HFF) additives are used to enhance oil and gas extraction from unconventional shale formations. Several kilometers downhole, these organic chemicals are exposed to temperatures up to 200 °C, pressures above 10 MPa, high salinities, and a pH range from 5-8. Despite this, very little is known about the fate of HFF additives under these extreme conditions. Here, stainless steel reactors are used to simulate the downhole chemistry of the commonly used HFF biocide glutaraldehyde (GA). The results show that GA rapidly (t < 1 h) autopolymerizes, forming water-soluble dimers and trimers, and eventually precipitates out at high temperatures (∼140 °C) and/or alkaline pH. Interestingly, salinity was found to significantly inhibit GA transformation. Pressure and shale did not affect GA transformation and/or removal from the bulk fluid. On the basis of experimental pseudo-second-order rate constants, a kinetic model for GA downhole half-life predictions for any combination of these conditions within the limits tested was developed. These findings illustrate that the biocidal GA monomer has limited time to control microbial activity in hot and/or alkaline shales, and may return along with its aqueous transformation products to the surface via flowback and produced water in cooler, more acidic, and saline shales.
The
objective of this study was to assess the antibacterial activity
and inhibition of biofilm formation of silver nanoparticles (AgNPs)
against Escherichia coli (MG1655), Bacillus subtilis, Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus
aureus, and Janthinobacterium lividum. The AgNPs utilized in this study were prepared through one-pot
microwave-assisted syntheses guided by principles of green chemistry.
The AgNPs were synthesized in three different schemes by reducing
Ag+ ions (from AgNO3) with reducing agents dextrose,
arabinose, and soluble starch. Formation of AgNPs occurred in less
than 15 min, and nanoparticles had diameters of 30 nm or less. Successful
synthesis of AgNPs was confirmed using multiple orthogonal approaches,
including UV–visible spectroscopy, fluorescence emission spectroscopy,
powder X-ray diffraction, and transmission electron microscopy, while
size analysis was gathered from transmission electron microscopy images
and dynamic light scattering. All AgNPs prepared in this study exhibited
antibacterial effects on a variety of organisms as determined by a
well diffusion assay with no antibacterial effects observed in the
control wells.
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