Sonochemical Degradation of Perfluorooctane Sulfonate (PFOS) and Perfluorooctanoate (PFOA) in Landfill Groundwater: Environmental Matrix Effects

Perfluorinated chemicals such as perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are environmentally persistent and recalcitrant to most conventional chemical and microbial treatment technologies. In this paper, we show that sonolysis is able to decompose PFOS and PFOA present in groundwater beneath a landfill. However, the pseudo first-order rate constant for the sonochemical degradation in the landfill groundwater is reduced by 61 and 56% relative to MilliQ water for PFOS and PFOA, respectively, primarily due to the presence of other organic constituents. In this study, we evaluate the effect of various organic compounds on the sonochemical decomposition rates of PFOS and PFOA. Organic components in environmental matrices may reduce the sonochemical degradation rates of PFOS and PFOA by competitive adsorption onto the bubble−water interface or by lowering the average interfacial temperatures during transient bubble collapse events. The effect of individual organic compounds depends on the Langmuir adsorption constant, the Henry’s law constant, the specific heat capacity, and the overall endothermic heat of dissociation. Volatile organic compounds (VOCs) are identified as the primary cause of the sonochemical rate reduction for PFOS and PFOA in landfill groundwater, whereas the effect of dissolved natural organic matter (DOM) is not significant. Finally, a combined process of ozonation and sonolysis is shown to substantially recover the rate loss for PFOS and PFOA in landfill groundwater

Reductive defluorination of aqueous perfluorinated alkyl surfactants : effects of ionic headgroup and chain length

Perfluorinated chemicals (PFCs) are distributed throughout the environment. In the case of perfluorinated alkyl carboxylates and sulfonates, they can be classified as persistent organic pollutants since they are resistant to environmentally relevant reduction, oxidation, and hydrolytic processes. With this in mind, we report on the reductive defluorination of perfluorobutanoate, PFBA (C_3F_7CO_2−), perfluorohexanoate, PFHA (C_5F_(11)CO_2−), perfluorooctanoate, PFOA (C_7F_(15)CO_2−), perfluorobutane sulfonate, PFBS (C_4F_9SO_3−), perfluorohexane sulfonate, PFHS (C_6F_(13)SO_3−), and perfluorooctane sulfonate, PFOS (C_8F_(17)SO_3−) by aquated electrons, eaq−, that are generated from the UV photolysis (λ = 254 nm) of iodide. The ionic headgroup (-SO_3− vs -CO_2−) has a significant effect on the reduction kinetics and extent of defluorination (F index = −[F−]_(produced)/[PFC]_(degraded)). Perfluoroalkylsulfonate reduction kinetics and the F index increase linearly with increasing chain length. In contrast, perfluoroalkylcarboxylate chain length appears to have a negligible effect on the observed kinetics and the F index. H/F ratios in the gaseous fluoro-organic products are consistent with measured F indexes. Incomplete defluorination of the gaseous products suggests a reductive cleavage of the ionic headgroup occurs before complete defluorination. Detailed mechanisms involving initiation by aquated electrons are proposed

TWO- AND THREE-DIMENSIONAL SIMULATIONS OF ASTEROID OCEAN IMPACTS

We have performed a series of two-dimensional and three-dimensional simulations of asteroid impacts into an ocean using the SAGE code from Los Alamos National Laboratory and Science Applications International Corporation. The SAGE code is a compressible Eulerian hydrodynamics code using continuous adaptive mesh refinement for following discontinuities with a fine grid while treating the bulk of the simulation more coarsely. We have used realistic equations of state for the atmosphere, sea water, the oceanic crust, and the mantle. In two dimensions, we simulated asteroid impactors moving at 20 km/s vertically through an exponential atmosphere into a 5 km deep ocean. The impactors were composed of mantle material (3.32 g/cc) or iron (7.8 g/cc) with diameters from 250m to 10 km. In our three-dimensional runs we simulated asteroids of 1 km diameter composed of iron moving at 20 km/s at angles of 45 and 60 degrees from the vertical. All impacts, including the oblique ones, produce a large underwater cavities with nearly vertical walls followed by a collapse starting from the bottom and subsequent vertical jetting. Substantial amounts of water are vaporized and lofted high into the atmosphere. In the larger impacts, significant amounts of crustal and even mantle material are lofted as well. Tsunamis up to a kilometer in initial height are generated by the collapse of the vertical jet. These waves are initially complex in form, and interact strongly with shocks propagating through the water and the crust. The tsunami waves are followed out to 100 km from the point of impact. Their periods and wavelengths show them to be intermediate type waves, and not (in general) shallow-water waves. At great distances, the waves decay as the inverse of the distance from the impact point, ignoring sea-floor topography. For all impactors smaller than about 2 km diameter, the impacting body is highly fragmented and its remains lofted into the stratosphere with the water vapor and crustal material, hence very little trace of the impacting body should be found for most oceanic impacts. In the oblique impacts, the initial asymmetry of the transient crater and crown does not persist beyond a tsunami propagation length of 50 km

Simulation von Token Ring Netzwerken

Diese Arbeit beschäftigt sich mit der Entwicklung eines empirischen Modells zur Simulation von TokenRing-Netzwerken auf Basis eines MonteCarlo-Ansatzes. Desweiteren werden die Ergebnisse aus verschiedenen Beispielsimulationsläufen dargelegt und diskutiert. Hierbei werden vor allem die Auswirkungen der einzelnen Protokolle und Protokollebenen auf die Systemleistung und -auslastung betrachtet

Impact of Wind Power Plants on the Environment and Possibilities of Increasing of Their Installed Output in the Czech Republic

Předložená bakalářská práce pojednává o větrných elektrárnách, jejich technickém řešení a jejich vlivu na životní prostředí. Dále popisuje význam větru jako obnovitelného zdroje energie a historii větrné energetiky. Obsahuje také statistický přehled o větrné energetice na území Evropy a České republiky za rok 2018. V závěru popisuje předpokládaný vývoj větrné energeticky na území České republiky v následujících letech.The submitted bachelor thesis deals with wind power plants, their technical solution and their impact on the environment. Then there is a description of value of wind such as renewable resource of energy and the history of wind energy. Bachelor thesis contains the statistical overview about wind energy in Europe and the Czech Republic for 2018. In the final section of bachelor thesis there is a presumed development of wind energy in the Czech Republic in the following years.546 - Katedra environmentálního inženýrstvívýborn

Sonochemical Degradation of Perfluorooctane Sulfonate (PFOS) and Perfluorooctanoate (PFOA) in Groundwater: Kinetic Effects of Matrix Inorganics

Ultrasonic irradiation has been shown to effectively degrade perfluorinated chemicals (PFCs) such as perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) in aqueous solution. Reduced PFC sonochemical degradation rates in organic-rich groundwater taken from beneath a landfill, however, testify to the negative kinetic effects of the organic groundwater constituents. In this study, the PFOX (X = S or A) sonochemical degradation rates in a groundwater sample with organic concentrations about 10 times lower than those in the groundwater taken from beneath a landfill are found to be 29.7% and 20.5% lower, respectively, than the rates in Milli-Q water, suggesting that inorganic groundwater constituents also negatively affect PFC sonochemical kinetics. To determine the source of the groundwater matrix effects, we evaluate the effects of various inorganic species on PFOX sonochemical kinetics. Anions over the range of 1−10 mM show Hofmeister effects on the sonochemical degradation rates of PFOX, k_(ClO_4)^(−PFOX) > k_(NO_3)^(−PFOX) ~ k_(Cl^−)^(−PFOX) ≥ k_(MQ)^(−PFOX) > k_(HCO_3)^(−PFOX) ~ k_(SO_(4)^(2−)^(−PFOX). In contrast, common cations at 5 mM have negligible effects. Initial solution pH enhances the degradation rates of PFOX at 3, but has negligible effects over the range of 4 to 11. The observed inorganic effects on sonochemical kinetics are hypothesized to be due to ions’ partitioning to and interaction with the bubble−water interface. Finally, it is shown that the rate reduction in the groundwater in this study is primarily due to the presence of bicarbonate and thus can be fully rectified by pH adjustment prior to sonolysis

Sonochemical Degradation of Perfluorooctanesulfonate in Aqueous Film-Forming Foams

Aqueous film-forming foams (AFFFs) are fire extinguishing agents developed by the Navy to quickly and effectively combat fires occurring close to explosive materials and are utilized today at car races, airports, oil refineries, and military locations. Fluorochemical (FC) surfactants represent 1−5% of the AFFF composition, which impart properties such as high spreadability, negligible fuel diffusion, and thermal stability to the foam. FC’s are oxidatively recalcitrant, persistent in the environment, and have been detected in groundwater at AFFF training sites. Ultrasonic irradiation of aqueous FCs has been reported to degrade and subsequently mineralize the FC surfactants perfluorooctanoate (PFOA) and perfluorooctanesulfonate (PFOS). Here we present results of the sonochemical degradation of aqueous dilutions of FC-600, a mixture of hydrocarbon (HC) and fluorochemical components including cosolvents, anionic hydrocarbon surfactants, fluorinated amphiphilic surfactants, anionic fluorinated surfactants, and thickeners such as starch. The primary FC surfactant in FC-600, PFOS, was sonolytically degraded over a range of FC-600 aqueous dilutions, 65 ppb < [PFOS]_i < 13100 ppb. Sonochemical PFOS−AFFF decomposition rates, R_(AFFF)^(−PFOS), are similar to PFOS−Milli-Q rates, R_(MQ)^(−PFOS), indicating that the AFFF matrix only had a minor effect on the sonochemical degradation rate, 0.5 < R_(AFFF)^(−PFOS)/R_(MQ)^(−PFOS) < 2.0, even though the total organic concentration was 50 times the PFOS concentration, [Org]_(tot)/[PFOS] ~50, consistent with the superior FC surfactant properties. Sonochemical sulfate production is quantitative, Δ[SO_4^(2−)]/Δ[PFOS] ≥ 1, indicating that bubble-water interfacial pyrolytic cleavage of the C−S bond in PFOS is the initial degradation step, in agreement with previous studies done in Milli-Q water. Sonochemical fluoride production is significantly below quantitative expectations, Δ[F^−]/Δ[PFOS] ~4 vs 17, suggesting that in the AFFF matrix, PFOS’ fluorochemical tail is not completely degraded, whereas Milli-Q studies yielded quantitative F− production. Measurements of time-dependent methylene blue active substances and total organic carbon indicate that the other FC-600 components were also sonolytically decomposed

Reductive degradation of perfluoroalkyl compounds with aquated electrons generated from iodide photolysis at 254 nm

The perfluoroalkyl compounds (PFCs), perfluoroalkyl sulfonates (PFXS) and perfluoroalkyl carboxylates (PFXA) are environmentally persistent and recalcitrant towards most conventional water treatment technologies. Here, we complete an in depth examination of the UV-254 nm production of aquated electrons during iodide photolysis for the reductive defluorination of six aquated perfluoroalkyl compounds (PFCs) of various headgroup and perfluorocarbon tail length. Cyclic voltammograms (CV) show that a potential of +2.0 V (vs. NHE) is required to induce PFC oxidation and −1.0 V is required to induce PFC reduction indicating that PFC reduction is the thermodynamically preferred process. However, PFCs are observed to degrade faster during UV(254 nm)/persulfate (S2O82−) photolysis yielding sulfate radicals (E° = +2.4 V) as compared to UV(254 nm)/iodide (I−) photolysis yielding aquated electrons (E° = −2.9 V). Aquated electron scavenging by photoproduced triiodide (I3−), which achieved a steady-state concentration proportional to [PFOS]0, reduces the efficacy of the UV/iodide system towards PFC degradation. PFC photoreduction kinetics are observed to be dependent on PFC headgroup, perfluorocarbon chain length, initial PFC concentration, and iodide concentration. From 2 to 12, pH had no observable effect on PFC photoreduction kinetics, suggesting that the aquated electron was the predominant reductant with negligible contribution from the H-atom. A large number of gaseous fluorocarbon intermediates were semi-quantitatively identified and determined to account for [similar]25% of the initial PFOS carbon and fluorine. Reaction mechanisms that are consistent with kinetic observations are discussed