Electrochemical destruction and mobilization of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) in saturated soil.

Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) have attracted attention due to their widespread distribution, recalcitrance, and substantial toxicity. In this work, high concentrations of PFOA and PFOS were degraded and mobilized through electrochemical treatments in a simulated source zone of saturated soil. Under a low constant voltage and direct current of 24 V and 467-690 mA, approximately 51.7% and 33% of PFOA and PFOS were degraded, respectively. Additionally, a total defluorination mass balance of 44.7% and 23% were detected for PFOA and PFOS, respectively, which indicates that the removal of PFOA and PFOS occurs through its destruction. Substantial electromigration causes the destruction and mobilization of solid PFOA and PFOS to shift into the water phase. Although electrochemical oxidation of PFAS (per- and polyfluoroalkyl substances) were previously reported and studied, this study is one of the few that focus on simultaneous desorption, mobilization, and destruction of PFAS in saturated soil containing a low-intensity electrical field.

Oxidation of nine petroleum hydrocarbon compounds by combined hydrogen peroxide/sodium persulfate catalyzed by siderite.

A system consisting of hydrogen peroxide/persulfate (H2O2/S2O82-) catalyzed by siderite was attempted to oxidize nine representative petroleum hydrocarbon compounds [benzene, toluene, ethylbenzene, m-xylene, p-xylene, o-xylene, 1,2,4-trimethylbenzene, methyl-tert-butyl ether, and naphthalene] that tend to persist in the environment. Oxidation under different siderite dosages, H2O2:S2O82- ratios, and pH conditions were investigated. Results indicated that oxidation rates increased from 1.21-4.62 to 1.77-8.94 d-1 as siderite increased from 0.16 to 0.48 g/40 mL (H2O2:Na2S2O8 = 5:1, initial pH = 3.0), except for naphthalene (decreased from 0.58 to 0.45 d-1 with increased siderite dosage). When the H2O2:S2O82- ratio was increased from 1:1 to 5:1 (siderite = 0.16 g, initial pH = 3.0), the oxidation rates increased from 0.02-0.73 to 0.33-2.19 d-1. However, as pH increased to > 5.5 (siderite = 0.16 g, H2O2:Na2S2O8 = 2.5:1), the oxidation rates of petroleum hydrocarbons decreased to 0.003-0.09 d-1, which was approximately 90% less than that at pH = 3.0. The partial correlations and principal component analysis of the experimental data were conducted. Overall, both siderite dosage and H2O2:S2O82- ratio correlated positively with oxidation efficiency. The oxidation potential by H2O2/S2O82- mixtures towards the target petroleum hydrocarbon compounds seemed to be more sensitive to pH conditions than to siderite dosages or H2O2:S2O82- ratios.

Coal-derived compounds and their potential impact on groundwater quality during coalbed methane production.

Coalbed methane (CBM) is an important unconventional energy source and accounts for a substantial portion of the overall natural gas production in the USA. The extraction of CBM generates significant amounts of produced water, where the withdrawal of groundwater may disturb the subsurface environment and aquifers. The release of toxic recalcitrant compounds from the coal seam is of great concern for those who use groundwater for irrigation and potable water sources. Experiments were conducted that determined a small fraction of coal carbon can be extracted and solubilized in water during the CBM formation and production. These soluble components included long-chain alkanes, aromatic hydrocarbons, and humic compounds. Biometer flask assays demonstrated that these compounds are bioamenable and can be potentially degraded by microorganisms to produce methane and carbon dioxide, where these biodegradation processes may further impact groundwater quality in the coal seam.

In situ electrochemical manipulation of oxidation-reduction potential in saturated subsurface matrices.

Application of a low-intensity electric field is known to influence oxidation-reduction (redox) potential in a saturated matrix. In this study, such redox manipulation was attempted in at a site with contaminated aquifer. At the experiment field site, electrodes connected to a direct current (DC) source provided an electric field with an intensity of 1.82 V m-1. Redox potentials at locations 3.0 m and 7.9 m from the cathode decreased by 111 mV and 33 mV within a few hours, respectively, indicating that reducing conditions in the aquifer may be established within the electric field. Overall, it is possible to manipulate in situ redox potential in saturated subsurface matrices by applying low-intensity electric fields.

Low carbon renewable natural gas production from coalbeds and implications for carbon capture and storage.

Isotopic studies have shown that many of the world's coalbed natural gas plays are secondary biogenic in origin, suggesting a potential for gas regeneration through enhanced microbial activities. The generation of biogas through biostimulation and bioaugmentation is limited to the bioavailability of coal-derived compounds and is considered carbon positive. Here we show that plant-derived carbohydrates can be used as alternative substrates for gas generation by the indigenous coal seam microorganisms. The results suggest that coalbeds can act as natural geobioreactors to produce low carbon renewable natural gas, which can be considered carbon neutral, or perhaps even carbon negative depending on the amount of carbon sequestered within the coal. In addition, coal bioavailability is no longer a limiting factor. This approach has the potential of bridging the gap between fossil fuels and renewable energy by utilizing existing coalbed natural gas infrastructure to produce low carbon renewable natural gas and reducing global warming.Coalbeds produce natural gas, which has been observed to be enhanced by in situ microbes. Here, the authors add plant-derived carbohydrates (monosaccharides) to coal seams to be converted by indigenous microbes into natural gas, thus demonstrating a potential low carbon renewable natural gas resource.

Effects of bioaugmentation on sorption and desorption of benzene, 1,3,5-trimethylbenzene and naphthalene in freshly-spiked and historically-contaminated sediments.

This work investigated the frequently observed "rebounds" of contaminants of concern in groundwater systems. Specifically, influences of bioaugmented microorganisms on the sorption and desorption of representative petroleum constituents [benzene, 1,3,5-trimethylbenzene and naphthalene (BTN)] were studied in freshly-spiked and historically-contaminated sediments. Capable microorganisms were enriched and supplemented to contaminated sediments to enhance biodegradation of petroleum hydrocarbons. In freshly-spiked sediments, when petroleum-degrading microorganisms were added, concentrations of dissolved petroleum constituents appeared to increase initially, and 12.4, 14.0 and 20.0 mg/kg of benzene, 1,3,5-trimethylbenzene and naphthalene, respectively desorbed from the sediments into the water phase. In the historically-contaminated sediments, the augmentation of petroleum-degrading microorganisms led to the desorption of 0.023-0.059, 0009-0.016, and 1.731-2.763 mg/L of previously sequestrated BTN into the water phase, and also triggered the desorption of 0.051-0.223, -0.133-2.630, and 2.324-1.200 mg/kg of previously sequestrated BTN as the methanol extraction quantity. The mechanisms of the enhanced desorption at the presence of microbes remain to be determined; however, we presumed that microbially produced constituents such as biosurfactants and cell mass could have attributed to the partition of petroleum compounds from the sediments. Findings from this study may partially explain "rebounds" of certain petroleum constituents into the groundwater during in situ bioremediation practice, although such immediate rebounds sometimes are weak, and the desorbed constituents can be eventually biodegraded under proper biogeochemical conditions.

Bioelectrochemical system platform for sustainable environmental remediation and energy generation.

The increasing awareness of the energy-environment nexus is compelling the development of technologies that reduce environmental impacts during energy production as well as energy consumption during environmental remediation. Countries spend billions in pollution cleanup projects, and new technologies with low energy and chemical consumption are needed for sustainable remediation practice. This perspective review provides a comprehensive summary on the mechanisms of the new bioelectrochemical system (BES) platform technology for efficient and low cost remediation, including petroleum hydrocarbons, chlorinated solvents, perchlorate, azo dyes, and metals, and it also discusses the potential new uses of BES approach for some emerging contaminants remediation, such as CO2 in air and nutrients and micropollutants in water. The unique feature of BES for environmental remediation is the use of electrodes as non-exhaustible electron acceptors, or even donors, for contaminant degradation, which requires minimum energy or chemicals but instead produces sustainable energy for monitoring and other onsite uses. BES provides both oxidation (anode) and reduction (cathode) reactions that integrate microbial-electro-chemical removal mechanisms, so complex contaminants with different characteristics can be removed. We believe the BES platform carries great potential for sustainable remediation and hope this perspective provides background and insights for future research and development.

Enhanced bioremediation of hydrocarbon-contaminated soil using pilot-scale bioelectrochemical systems.

Two column-type bioelectrochemical system (BES) modules were installed into a 50-L pilot scale reactor packed with diesel-contaminated soils to investigate the enhancement of passive biodegradation of petroleum compounds. By using low cost electrodes such as biochar and graphite granule as non-exhaustible solid-state electron acceptors, the results show that 82.1-89.7% of the total petroleum hydrocarbon (TPH) was degraded after 120 days across 1-34 cm radius of influence (ROI) from the modules. This represents a maximum of 241% increase of biodegradation compared to a baseline control reactor. The current production in the BESs correlated with the TPH removal, reaching the maximum output of 70.4 ± 0.2 mA/m(2). The maximum ROI of the BES, deducting influence from the baseline natural attenuation, was estimated to be more than 90 cm beyond the edge of the reactor (34 cm), and exceed 300 cm should a non-degradation baseline be used. The ratio of the projected ROI to the radius of BES (ROB) module was 11-12. The results suggest that this BES can serve as an innovative and sustainable technology for enhanced in situ bioremediation of petroleum hydrocarbons in large field scale, with additional benefits of electricity production and being integrated into existing field infrastructures.

Passivation of zero-valent iron by denitrifying bacteria and the impact on trichloroethene reduction in groundwater.

Zero-valent iron (ZVI) application in groundwater remediation is limited by its vulnerability to passivation, which significantly decreases its surface reactivity. Both biological and chemical processes can potentially passivate ZVI, although the understanding of biological passivation is limited. This study was conducted in bench-scale reactors packed with fresh ZVI or ZVI pre-exposed to nitrate (NO3(-)) and in the presence or absence of a denitrifying bacterial enrichment (DNBE). The first-order rate coefficients (k) for NO3(-) reduction by ZVI in the presence and absence of DNBE were 0.20 and 0.09 s(-1), respectively, suggesting that both ZVI and microbes contribute to NO3(-) removal. Abiotic reduction of nitrate was observed in reactors with trichloroethene (TCE) if ZVI was present; however, it resulted in reduced rates of TCE reduction (k = 0.29 s(-1)) when compared to reactors with fresh ZVI and no nitrate (k = 0.55 s(-1)). The TCE reduction efficiency decreased by 49% (k = 0.15 s(-1)) in the presence of DNBE, suggesting that microbial growth on ZVI or catalyzed oxidation of ZVI surface can inhibit TCE reduction by ZVI. Contrary to the presumption that denitrification may decrease ZVI passivation by nitrate, results from this study suggest that denitrifying bacteria actually exacerbate ZVI passivation.

Electrochemical depassivation of zero-valent iron for trichloroethene reduction.

Permeable reactive barriers (PRBs) composed of zero-valent iron (ZVI) are susceptible to passivation, resulting in substantially decreased rates of chlorinated solvent removal over time. In this study, the application of low electrical direct current (DC) to restore the reductive capacity of passivated ZVI was examined. Electrical current was applied to a laboratory column reactor filled with a mixture of pre-passivated ZVI and sand. Variable voltage settings (0-12 V) were applied through two stainless steel electrodes placed at the ends of the reactor. While only partial restoration of the reductive capacity of the passivated ZVI was observed, higher rates of trichloroethene (TCE) removal were always obtained when current was applied, and the rates of TCE removal were roughly proportional to the voltage level. Although differences were observed between the rates and extent of TCE removal within the column, it is noteworthy that TCE removal was not restricted to that region of the column where the electrons entered (i.e., at the cathode). While complete "depassivation" of ZVI may be difficult to achieve in practice, the application of DC demonstrated observable restoration of reactivity of the passivated ZVI. This study provides evidence that this approach may significantly extend the life of a ZVI PRB.

Nitrate removal from groundwater in columns packed with reed and rice stalks.

Nitrate leaching contaminates groundwater. The objective of this study was to determine if reed and rice stalks could enhance denitrification and reduce nitrate leaching into groundwater. Artificial groundwater spiked with nitrate and field groundwater samples were tested in the columns in sand reactors packed with either reed or rice stalks. The maximum nitrate removal rates were determined to be 1.93 and 1.97 mg nitrate-N l(-1) h(-1), respectively, in the reed and rice stalk-packed columns. The maximum nitrate-nitrogen removal rate in reactors packed with reed stalk was 1.33 mg nitrate-N l(-1) h(-1) when experimented with natural groundwater. Chemical oxygen demand consumption was higher when rice stalk (176.1 mg l(-1)) was used as the substrate, compared to reed stalk (35.2 mg l(-1)) at the same substrate dosage. No nitrite accumulation was detected during the test. The results demonstrate that agricultural byproducts, such as reed and rice stalks, may be used as substrate amendments for enhanced denitrification in natural settings, such as lakeside lagoons, ditches or wetlands.

Feasibility of enhanced biodegradation of petroleum compounds in groundwater under denitrifying conditions.

Groundwater was collected from a petroleum hydrocarbon contaminated site and characterized for microbial and physiochemical properties to assess the feasibility of enhanced natural attenuation. Results demonstrate the depletion of nitrate and dominance of denitrifying bacteria in the groundwater. Microcosm studies of amending nitrate and nutrients were attempted to enhanced biodegradation of petroleum compounds under denitrifying condition. Results show that 75% of petroleum compounds was degraded within 152-day in microcosms amended with nitrate, compared to 25% removal in the non-amended controls. Data indicate that nitrate amendment to groundwater may offer a viable remedy for enhanced natural attenuation of petroleum compounds.

Electrically induced reduction of trichloroethene in clay.

Chlorinated compounds such as trichloroethene (TCE) are recalcitrant contaminants commonly detected in soil and groundwater. Contemporary remedies such as electron donor amendment tend to be less or ineffective in treating chlorinated compounds in matrix of lower permeability, such as clay. In this study, electrically induced reduction (EIR) was tested by inserting electrodes in saturated clay containing 122.49-125.43 mg TCE kg(-1). Weak electric potentials (E) of 6, 9, and 12 V m(-1) were applied, and up to 97% of TCE were depleted during the study period. Corresponding increases in chloride concentrations was observed during TCE depletion, indicating a reductive dechlorination pathway. No migration of TCE was observed between the two electrodes, neither were intermediate compounds such as dichloroethene (DCE) or vinyl chloride (VC). Results were also tested against a mathematical equation we previously established for field applications. Electrically induced reduction may offer a novel method for in situ degradation of chlorinated contaminants, especially in low-permeable media such as clay.

Removal of guar and humus from water by layered double hydroxides.

Natural organic matter such as guar and humus are recalcitrant to conventional pretreatment technologies and can potentially foul processes such as membranes during water treatment. An innovative method of using synthetic layered double hydroxides (LDH) was investigated for removing common natural organic matter in the form of guar gum (GG) and humic acid (HA) from water. Adsorption isotherms were evaluated with Langmuir and Freundlich models. Results show the affinity of GG and HA to LDH to be 11.31 and 9.33 mg g(-1) LDH, respectively. Kinetic isotherms indicate that the sorbing rates of LDH to GG and HA increase with initial GG and HA concentrations, fitting a pseudo-second order model. This study demonstrate that LDH may be an effective material in removing GG and HA from waters and offer an alternative to conventional pretreatment technologies for the mitigation fouling of membrane and other systems in water treatment.

Treatment of coking wastewater by using manganese and magnesium ores.

This study investigated a wastewater treatment technique based on natural minerals. A two-step process using manganese (Mn) and magnesium (Mg) containing ores were tested to remove typical contaminants from coking wastewater. Under acidic conditions, a reactor packed with Mn ore demonstrated strong oxidizing capability and destroyed volatile phenols, chemical oxygen demand (COD)(,) and sulfide from the coking wastewater. The effluent was further treated by using Mg ore to remove ammonium-nitrogen and phosphate in the form of magnesium ammonium phosphate (struvite) precipitates. When pH of the wastewater was adjusted to 1.2, the removal efficiencies for COD, volatile phenol and sulfide reached 70%, 99% and 100%, respectively. During the second step of precipitation, up to 94% of ammonium was removed from the aqueous phase, and precipitated in the form of struvite with phosphorus. The struvite crystals showed a needle-like structure. X-ray diffraction and transmission electron microscopy were used to characterize the crystallized products.

Assessment of diesel contamination in groundwater using electromagnetic induction geophysical techniques.

Determining hydrocarbon plumes in groundwater is typically accomplished through the installation of extensive monitoring wells. Issues of scale and site heterogeneities tend to introduce errors in delineating the extent of contamination and environmental impact. In this study, electromagnetic induction survey was investigated as an alternative technique for mapping petroleum contaminants in the subsurface. The surveys were conducted at a coal mining site near Gillette, Wyoming, using the EM34-XL ground conductivity meter. Data from this survey were validated with known concentrations of diesel compounds detected in groundwater from the study site. Groundwater data correlated well with the electromagnetic survey data, which was used to generate a site model to identify subsurface diesel plumes. To our knowledge, this is one of the first studies to use electromagnetic survey techniques for mapping hydrocarbon contamination in groundwater. Results from this study indicate that this geophysical technique can be an effective tool for assessing subsurface petroleum hydrocarbon sources and plumes at contaminated sites.

Biodegradation of petroleum compounds in soil by a solid-phase circulating bioreactor with poultry manure amendments.

Petroleum compounds account for the vast majority of contaminants in soils. Bioremediation is a widely accepted strategy in degrading these contaminants. This study demonstrates the effectiveness of nitrogenous nutrient (nitrogen) amendments in enhancing biodegradation of petroleum contaminants in soil by using a solid-phase circulating bioreactor (SCB). In a bench-scale SCB, total petroleum hydrocarbon (TPH) concentration (~5000 mg kg(-1)) in soil decreased 92% within 15 days. In a scaled-up SCB system containing approximately 120 kg petroleum-contaminated soil (TPH at approximately 125,000 mg kg(-1)), a degradation rate of 635 mg kg(-1)d(-1) was obtained from the poultry manure-amended treatment during a 200-day period of operation. Treatments with the same amount of nitrogen (as ammonium nitrate) attained a TPH degradation rate of 469 mg kg(-1)d(-1) during the same period. Control SCB unit, which was maintained under the same aerobic conditions but not amended with nitrogen, had a TPH degradation rate of 273 mg kg(-1)d(-1). Results from this study indicate that SCB can achieve significantly higher degradative rates than conventional landfarming (reported rates < 150 mg kg(-1)d(-1)) and poultry manure appears to be a preferred nitrogen amendment that can further enhance the biodegradation of petroleum contaminants in soils.

Bioremediation of benzene, ethylbenzene, and xylenes in groundwater under iron-amended, sulfate-reducing conditions.

Elevated concentrations of sulfide in groundwater (approximately 63 mg S(2-)/L in water and 500 mg dissolved H2S/L dissipating from the wellhead) at a field site near South Lovedale (OK, USA) were inhibiting the activity of sulfate-reducing bacteria (SRB) that are known to degrade contaminants, including benzene, toluene, ethylbenzene, and xylenes. Elevated concentrations of these contaminants, except for toluene, also were present in this groundwater. Microcosms were established in the laboratory using groundwater and sediment collected from the field site and amended with various nutrient, substrate, and inhibitor treatments. All microcosms initially were amended with FeCl2 to induce FeS precipitation and, thereby, to reduce aqueous sulfide concentrations. Complete removal of benzene, ethylbenzene, and m+p-xylenes (BEX; o-xylene not detected) was observed within 39 d in treatments with various combinations of nutrient and substrate amendments, including treatments with no amendments (other than FeCl2). This indicates that the elevated concentration of sulfide is the only limiting factor to BEX biodegradation at this site under anaerobic conditions and that treating the groundwater with FeCl2 may be a simple remedy to both facilitate and enhance BEX degradation by the indigenous SRB population.