Radisav D. Vidic

Spatial and Temporal Correlation of Water Quality Parameters of Produced Waters from Devonian-Age Shale following Hydraulic Fracturing

The exponential increase in fossil energy production from Devonian-age shale in the Northeastern United States has highlighted the management challenges for produced waters from hydraulically fractured wells. Confounding these challenges is a scant availability of critical water quality parameters for this wastewater. Chemical analyses of 160 flowback and produced water samples collected from hydraulically fractured Marcellus Shale gas wells in Pennsylvania were correlated with spatial and temporal information to reveal underlying trends. Chloride was used as a reference for the comparison as its concentration varies with time of contact with the shale. Most major cations (i.e., Ca, Mg, Sr) were well-correlated with chloride concentration while barium exhibited strong influence of geographic location (i.e., higher levels in the northeast than in southwest). Comparisons against brines from adjacent formations provide insight into the origin of salinity in produced waters from Marcellus Shale. Major cations exhibited variations that cannot be explained by simple dilution of existing formation brine with the fracturing fluid, especially during the early flowback water production when the composition of the fracturing fluid and solid-liquid interactions influence the quality of the produced water. Water quality analysis in this study may help guide water management strategies for development of unconventional gas resources.

Vapor-phase elemental mercury adsorption by activated carbon impregnated with chloride and chelating agents

The dynamic adsorption capacity for vapor-phase elemental mercury (Hg0) of commercially available granular activated carbon (BPL) impregnated with copper chloride (BPL-C), β-aminoanthraquinone (BPL-A), 2-(aminomethyl)pyridine (BPL-P), and 2-aminoethanethiol (BPL-T) was studied in an attempt to produce economical and effective sorbents for the control of elemental mercury emissions from combustion processes. The dynamic adsorption capacity of BPL-C was found to increase as empty bed contact time (EBCT) and chloride content increased and to decrease with an increase in operating temperature when dry nitrogen was used as a carrier gas. BPL carbon impregnated with 5 wt.% chloride exhibited a higher dynamic adsorption capacity than sulfur impregnated carbon tested previously. However, the observation of oxidized forms of mercury in the effluent from a fixed-bed adsorber under all experimental conditions used in this study indicates that the bond between adsorbed mercury and BPL-C is unstable or that the BPL-C itself lacks the thermal stability required for full-scale applications. BPL-A and BPL-T exhibited high dynamic adsorption capacities at 25°C but had much lower dynamic adsorption capacities at 140°C, while BPL-P showed very poor performance at both temperatures. Due to the high production costs, these chelating agent-impregnated carbons would likely be considerably less cost-effective for the full-scale removal of mercury from combustion flue gases than the chloride- or sulfur-impregnated carbons. Impregnation with thiol was the only promising approach that could provide effective mercury sorbents at room temperature.

Individual and combined effects of copper and silver ions on inactivation of Legionella pneumophila

Abstract Copper/silver ionization is a new disinfection method that is being used to eradicate Legionella pneumophila from hospital hot water recirculating systems. The objective of this study was to determine the susceptibility of L. pneumophila serogroup 1 to copper and silver ions alone and in combination. L. pneumophila serogroup 1 ( L. p. sg-1) was completely inactivated (6-log reduction) at copper concentration of 0.1 mg/l within 2.5 h, whereas more than 24 h was required to achieve a similar reduction at the highest silver ion concentration tested (0.08 mg/l). Checkerboard method and Gard additive model prediction demonstrated that copper and silver ions in combination could result in additive or synergistic effect depending on the concentration of copper and silver ions. Under the experimental conditions used in this study, synergism of copper/silver ions in eradicating L. p. sg-1 was observed at higher concentration combinations of copper/silver ions (e.g. 0.04/0.04 mg/l) while only an additive effect was observed at lower concentration combinations (e.g. 0.02/0.02 mg/l). This study suggested that both copper and silver ions are effective in inactivating L. pneumophila and the combined effect is greater than that seen with either ion alone.

Impact of surface properties of activated carbons on oxidative coupling of phenolic compounds

Abstract Previous studies showed that activated carbons exhibit significantly different behavior for the removal of phenolic compounds in the presence and absence of molecular oxygen. Increase in capacity under oxic conditions (presence of oxygen) as high as 2.5 fold was observed for 2-methylphenol adsorption on a bituminous coal-based activated carbon. The present study was initiated to evaluate some of the possible mechanisms of oxidative coupling of phenols that are promoted by the activated carbon surface and result in such a significant increase in capacity. In particular, acidic and basic surface functional groups and metals and metal oxide complexes that are commonly present on activated carbon surface were investigated for their role in catalyzing oxidative coupling of phenolic compounds under oxic conditions. Bituminous coal-based carbon and a carbonaceous resin were used as model adsorbents, while 2-methylphenol and 2-chlorophenol were used as model adsorbates in this study. Metal content was altered either by prolonged acid washing of activated carbon or by addition of metal oxides to the carbonaceous resin using the incipient wetness method. Oxygen containing acidic and basic surface functional groups were modified by outgassing at different temperatures or by exposure of outgassed carbons to oxygenated water. Freundlich isotherm parameters and solvent extraction efficiencies for virgin and modified varieties of these adsorbents have shown that none of the parameters investigated in this study have a significant impact on the exhibited adsorptive and catalytic properties of activated carbon under oxic and anoxic conditions. It appears that oxygen-containing basic surface functional groups are primarily responsible for the catalytic properties of activated carbon towards oxidative coupling of phenolic compounds.

Negative Effect of High pH on Biocidal Efficacy of Copper and Silver Ions in Controlling Legionella pneumophila

ABSTRACT Copper-silver (Cu-Ag) ionization has effectively controlled Legionella spp. in the hot water systems of numerous hospitals. However, it was ineffective at controlling Legionella in one Ohio hospital despite the confirmation of adequate total concentrations of copper and silver ions. The pH of the water at this hospital was found to be 8.5 to 9.0. The purpose of this study was to investigate the impact of pH and other water quality parameters, including alkalinity (HCO3−), hardness (Ca2+ and Mg2+), and amount of dissolved organic carbon (DOC), on the control of Legionella by Cu-Ag ionization. Initial concentrations of Legionella and copper and silver ions used in batch experiments were 3 × 106 CFU/ml and 0.4 and 0.08 mg/liter, respectively. Changes in bicarbonate ion concentration (50, 100, and 150 mg/liter), water hardness (Ca2+ at 50 and 100 mg/liter; Mg2+ at 40 and 80 mg/liter), and level of DOC (0.5 and 2 mg/liter) had no significant impact on the efficacy of copper and silver ions in killing Legionella at a neutral pH. When the pH was elevated to 9 in these experiments, copper ions achieved only a 10-fold reduction in the number of Legionella organisms in 24 h, compared to a millionfold decrease at pH 7.0. Silver ions were able to achieve a millionfold reduction in 24 h at all ranges of water quality parameters tested. Precipitation of insoluble copper complexes was observed at a pH above 6.0. These results suggest that pH may be an important factor in the efficacy of copper-silver ionization in controlling Legionella in water systems.

Microbial Community Changes in Hydraulic Fracturing Fluids and Produced Water from Shale Gas Extraction

Microbial communities associated with produced water from hydraulic fracturing are not well understood, and their deleterious activity can lead to significant increases in production costs and adverse environmental impacts. In this study, we compared the microbial ecology in prefracturing fluids (fracturing source water and fracturing fluid) and produced water at multiple time points from a natural gas well in southwestern Pennsylvania using 16S rRNA gene-based clone libraries, pyrosequencing, and quantitative PCR. The majority of the bacterial community in prefracturing fluids constituted aerobic species affiliated with the class Alphaproteobacteria. However, their relative abundance decreased in produced water with an increase in halotolerant, anaerobic/facultative anaerobic species affiliated with the classes Clostridia, Bacilli, Gammaproteobacteria, Epsilonproteobacteria, Bacteroidia, and Fusobacteria. Produced water collected at the last time point (day 187) consisted almost entirely of sequences similar to Clostridia and showed a decrease in bacterial abundance by 3 orders of magnitude compared to the prefracturing fluids and produced water samplesfrom earlier time points. Geochemical analysis showed that produced water contained higher concentrations of salts and total radioactivity compared to prefracturing fluids. This study provides evidence of long-term subsurface selection of the microbial community introduced through hydraulic fracturing, which may include significant implications for disinfection as well as reuse of produced water in future fracturing operations.

Adsorption isotherms: illusive capacity and role of oxygen

This paper examines the influence of molecular oxygen on the adsorptive capacity of GAC. A new experimental procedure for determining adsorption isotherms is introduced. This procedure, denoted as “anaerobic”, differs from the currently used techniques, denoted as “aerobic”, in that oxygen is repeatedly purged from the test environment. The results show that the capacity of GAC for the retention of o-cresol can increase up to 3-fold in the presence of oxygen when compared to the anaerobic capacity. The same trend is observed for the adsorption of phenol and 3-ethylphenol. It is shown that this increase in capacity cannot be attributed to biological degradation of these adsorbates in the presence of oxygen. It is speculated that this phenomenon is due to some chemical reactions between the adsorbates and molecular oxygen that are catalyzed by the activated carbon surface and occur at a different time scale than physical adsorption. Initial portions of breakthrough curves for o-cresol are very accurately predicted using capacities depicted by the anaerobic isotherm, while the total GAC adsorptive capacity for o-cresol, as determined from breakthrough experiments, appears to agree closely with the capacity predicted from the aerobic isotherm.

Microbial communities in flowback water impoundments from hydraulic fracturing for recovery of shale gas

Hydraulic fracturing for natural gas extraction from shale produces waste brine known as flowback that is impounded at the surface prior to reuse and/or disposal. During impoundment, microbial activity can alter the fate of metals including radionuclides, give rise to odorous compounds, and result in biocorrosion that complicates water and waste management and increases production costs. Here, we describe the microbial ecology at multiple depths of three flowback impoundments from the Marcellus shale that were managed differently. 16S rRNA gene clone libraries revealed that bacterial communities in the untreated and biocide-amended impoundments were depth dependent, diverse, and most similar to species within the taxa γ-proteobacteria, α-proteobacteria, δ-proteobacteria, Clostridia, Synergistetes, Thermotogae, Spirochetes, and Bacteroidetes. The bacterial community in the pretreated and aerated impoundment was uniform with depth, less diverse, and most similar to known iodide-oxidizing bacteria in the α-proteobacteria. Archaea were identified only in the untreated and biocide-amended impoundments and were affiliated to the Methanomicrobia class. This is the first study of microbial communities in flowback water impoundments from hydraulic fracturing. The findings expand our knowledge of microbial diversity of an emergent and unexplored environment and may guide the management of flowback impoundments.

Uptake of Elemental Mercury Vapors by Activated Carbons

The adsorptive capacities of virgin and sulfur-impregnated activated carbons (GAC) for gas-phase mercury were evaluated as a function of temperature and influent mercury concentration. The virgin activated carbon showed little adsorptive capacity, especially at temperatures above 90 °C. The isothermal representation of the adsorptive capacity for virgin GAC exhibited a semi-logarithmic relationship at 50 °C, 90 °C, and 140 °C. The pronounced effect of temperature on the adsorptive capacity evidences a physical adsorption mechanism between the mercury and virgin GAC. Sulfur-impregnated activated carbons exhibited enhanced mercury removal efficiency over the non-impregnated varieties, due to formation of mercuric sulfide on the carbon surface. This chemisorption process is enhanced by increased temperatures between 25 °C and 90 °C, yielding increased removal efficiency of elemental mercury. However, at 140 °C a decrease in adsorptive capacity occurs, indicating reduced formation of mercuric sulfide. The method used for impregnating GAC with sulfur had a pronounced effect on mercury removal capacity. The chemical bonding of sulfur at 600 °C provides a more uniform distribution of sulfur throughout the GAC pore structure than is achieved by conventional condensation techniques, yielding improved performance.

Process Based Life-Cycle Assessment of Natural Gas from the Marcellus Shale

The Marcellus Shale (MS) represents a large potential source of energy in the form of tightly trapped natural gas (NG). Producing this NG requires the use of energy and water, and has varying environmental impacts, including greenhouse gases. One well-established tool for quantifying these impacts is life-cycle assessment (LCA). This study collected information from current operating companies to perform a process LCA of production for MS NG in three areas--greenhouse gas (GHG) emissions, energy consumption, and water consumption--under both present (2011-2012) and past (2007-2010) operating practices. Energy return on investment (EROI) was also calculated. Information was collected from current well development operators and public databases, and combined with process LCA data to calculate per-well and per-MJ delivered impacts, and with literature data on combustion for calculation of impacts on a per-kWh basis during electricity generation. Results show that GHG emissions through combustion are similar to conventional natural gas, with an EROI of 12:1 (90% confidence interval of 4:1-13:1), lower than conventional fossil fuels but higher than unconventional oil sources.