Explosion properties of highly concentrated ozone gas

The explosive self-decomposition characteristics of gaseous ozone with a concentration of up to almost 100 vol% were quantitatively investigated using a closed system with an electric spark device. The lower self-decomposition (explosion) limit for ozone diluted with oxygen at room temperature and atmospheric pressure was 10–11 vol%, and so ozone at more than 10–11 vol% will lead to an explosive chain decomposition reaction leading to its complete conversion to oxygen in a vessel. The lower explosion limit shifts to a higher concentration with a decrease in pressure. The limit was about 80 vol% under a reduced pressure of 10 Torr. We also confirmed that explosion trigger energy (minimum ignition energy) is strongly dependent on ozone concentration and pressure. For example, the minimum trigger energy for 15 vol% ozone at a pressure of 76 Torr (about 220 mJ) was more than 20-fold that at atmospheric pressure (about 10 mJ), and that for 13 vol% ozone (about 580 mJ) was approximately 30 times higher than that for 20 vol% (about 20 mJ) at the same pressure of 76 Torr. Moreover, the physical characteristics of the trigger energy sources (e.g. spark gap and electrode tip angle) leading to the decomposition (explosion) of ozone were investigated under various conditions.     

In situ reduction of chromium(VI) in heavily contaminated soils through organic carbon amendment

Chromium has become an important soil contaminant at many sites, and facilitating in situ reduction of toxic Cr(VI) to nontoxic Cr(III) is becoming an attractive remediation strategy. Acceleration of Cr(VI) reduction in soils by addition of organic carbon was tested in columns pretreated with solutions containing 1000 and 10 000 mg L(-1) Cr(VI) to evaluate potential in situ remediation of highly contaminated soils. Solutions containing 0,800, or 4000 mg L(-1) organic carbon in the form of tryptic soy broth or lactate were diffused into the Cr(VI)-contaminated soils. Changes in Cr oxidation state were monitored through periodic micro-XANES analyses of soil columns. Effective first-order reduction rate constants ranged from 1.4 x 10(-8) to 1.5 x 10(-7) s(-1), with higher values obtained for lower levels of initial Cr(VI) and higher levels of organic carbon. Comparisons with sterile soils showed that microbially dependent processes were largely responsible for Cr(VI) reduction, except in the soils initially exposed to 10 000 mg L(-1) Cr(VI) solutions that receive little (800 mg L(-1)) or no organic carbon. However, the microbial populations (< or = 2.1 x 10(5) g(-1)) in the viable soils are probably too low for direct enzymatic Cr(VI) reduction to be important. Thus, synergistic effects sustained in whole soil systems may have accounted for most of the observed reduction. These results show that acceleration of in situ Cr(VI) reduction with addition of organic carbon is possible in even heavily contaminated soils and suggest that microbially dependent reduction pathways can be dominant.     

Distribution of chromium contamination and microbial activity in soil aggregates

Biogeochemical transformations of redox-sensitive chemicals in soils can be strongly transport-controlled and localized. This was tested through experiments on chromium diffusion and reduction in soil aggregates that were exposed to chromate solutions. Reduction of soluble Cr(VI) to insoluble Cr(II) occurred only within the surface layer of aggregates with higher available organic carbon and higher microbial respiration. Sharply terminated Cr diffusion fronts develop when the reduction rate increases rapidly with depth. The final state of such aggregates consists of a Cr-contaminated exterior, and an uncontaminated core, each having different microbial community compositions and activity. Microbial activity was significantly higher in the more reducing soils, while total microbial biomass was similar in all of the soils. The small fraction of Cr(VI) remaining unreduced resides along external surfaces of aggregates, leaving it potentially available to future transport down the soil profile. Using the Thiele modulus, Cr(VI) reduction in soil aggregates is shown to be diffusion rate- and reaction rate-limited in anaerobic and aerobic aggregates, respectively. Thus, spatially resolved chemical and microbiological measurements are necessary within anaerobic soil aggregates to characterize and predict the fate of Cr contamination. Typical methods of soil sampling and analyses that average over redox gradients within aggregates can erase important biogeochemical spatial relations necessary for understanding these environments.     

Iron-induced decomposition of perfluorohexanesulfonate in sub- and supercritical water

Decomposition of perfluorohexanesulfonate (PFHS), a bioaccumulative analogue of perfluorooctanesulfonate (PFOS), in sub- and supercritical water was investigated. Although PFHS was only slightly reactive in pure subcritical water at 350 degrees C, it decomposed to F(-) and SO(4)(2-) ions when the temperature was increased to 380 degrees C, at which temperature the water became supercritical state. Addition of zerovalent iron to the reaction system dramatically accelerated PFHS decomposition to F(-) ions in both sub- and supercritical water: for example, when the initial PFHS concentration was 741microM, the F(-) yields at 350 degrees C were 4.13-16.0 times as high as those in the absence of iron, depending on the amount and the particle size of the iron powder. After the reactions, small amounts of CO(2) and CF(3)H were also detected in the gas phase; these increased with temperature, and the amount of CF(3)H increased markedly when the reaction was carried out in supercritical water. Increasing the specific surface area of the iron powder markedly increased PFHS consumption and F(-) formation in the aqueous phase, which indicates that the reactions occurred on the iron surface and that the increased specific surface area was a key factor in accelerating the decomposition of PFHS to F(-) ions.     

Transport and deposition of functionalized CdTe nanoparticles in saturated porous media

Comprehensive understanding of the transport and deposition of engineered nanoparticles (NPs) in subsurface is required to assess their potential negative impact on the environment. We studied the deposition behavior of functionalized quantum dot (QD) NPs (CdTe) in different types of sands (Accusand, ultrapure quartz, and iron-coated sand) at various solution ionic strengths (IS). The observed transport behavior in ultrapure quartz and iron-coated sand was consistent with conventional colloid deposition theories. However, our results from the Accusand column showed that deposition was minimal at the lowest IS (1mM) and increased significantly as the IS increased. The effluent breakthrough occurred with a delay, followed by a rapid rise to the maximum normalized concentration of unity. Negligible deposition in the column packed with ultrapure quartz sand (100mM) and Accusand (1mM) rules out the effect of straining and suggests the importance of surface charge heterogeneity in QD deposition in Accusand at higher IS. Data analyses further show that only a small fraction of sand surface area contributed in QD deposition even at the highest IS (100mM) tested. The observed delay in breakthrough curves of QDs was attributed to the fast diffusive mass transfer rate of QDs from bulk solution to the sand surface and QD mass transfer on the solid phase. Scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis were used to examine the morphology and elemental composition of sand grains. It was observed that there were regions on the sand covered with layers of clay particles. EDX spectra collected from these regions revealed that Si and Al were the major elements suggesting that the clay particles were kaolinite. Additional batch experiments using gold NPs and SEM analysis were performed and it was observed that the gold NPs were only deposited on clay particles originally on the Accusand surface. After removing the clays from the sand surface, we observed negligible QD deposition even at 100mM IS. We proposed that nanoscale charge heterogeneities on clay particles on Accusand surface played a key role in QD deposition. It was shown that the value of solution IS determined the extent to which the local heterogeneities participated in particle deposition.     

Acid washing and stabilization of an artificial arsenic-contaminated soil.

An acid-washing process was studied on a laboratory scale to extract the bulk of arsenic(V) from a highly contaminated Kuroboku soil (Andosol) so as to minimize the risk of arsenic to human health and the environment. The sorption and desorption behavior of arsenic in the soil suggested the possibility of arsenic leaching under acidic conditions. Artificially contaminated Kuroboku soil (2830 mg As/kg soil) was washed with different concentrations of hydrogen fluoride, phosphoric acid, sulfuric acid, hydrogen chloride, nitric acid, perchloric acid, hydrogen bromide, acetic acid, hydrogen peroxide, 3:1 hydrogen chloride-nitric acid, or 2:1 nitric acid-perchloric acid. Phosphoric acid proved to be most promising as an extractant, attaining 99.9% arsenic extraction at 9.4% acid concentration in 6 h. Sulfuric acid also attained high percentage extraction. The arsenic extraction by these acids reached equilibrium within 2 h. Elovich-type equation best described most of the kinetic data for dissolution of soil components as well as for extraction of arsenic. Dissolution of the soil components could be minimized by ceasing acid washing in 2 h. The acid-washed soil was further stabilized by the addition of lanthanum, cerium, and iron(III) salts or their oxides or hydroxides which form insoluble complex with arsenic. Both salts and oxides of lanthanum and cerium were effective in immobilizing arsenic in the soil attaining less than 0.01 mg/l As in the leaching test.     

Evaluation of remediation process with plant-derived biosurfactant for recovery of heavy metals from contaminated soils

A washing process was studied to evaluate the efficiency of saponin on remediating heavy metal contaminated soils. Three different types of soils (Andosol: soil A, Cambisol: soil B, Regosol: soil C) were washed with saponin in batch experiments. Utilization of saponin was effective for removal of heavy metals from soils, attaining 90-100% of Cd and 85-98% of Zn extractions. The fractionations of heavy metals removed by saponin were identified using the sequential extraction. Saponin was effective in removing the exchangeable and carbonated fractions of heavy metals from soils. In recovery procedures, the pH of soil leachates was increased to about 10.7, leading to separate heavy metals as hydroxide precipitates and saponin solute. In addition recycle of used saponin is considered to be effective for the subsequent utilization. The limits of Japanese leaching test were met for all of the soil residues after saponin treatment. As a whole, this study shows that saponin can be used as a cleaning agent for remediation of heavy metal contaminated soils.     

Blood levels of PCDDs,PCDFs, and coplanar PCBs in Yusho mothers and their descendants: Association with fetal Yusho disease

Maternal exposure to polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs) may result in adverse health effects in their children. In Japan in 1968, an accidental human exposure to rice oil contaminated with PCDDs, PCDFs, and PCBs, led to the development of Yusho disease. Yusho mothers delivered descendants with low birth weights and hyperpigmented skin and mucosa, which are characteristic of fetal Yusho disease (FYD). The Yusho cohort was used to evaluate the effect of maternal exposure to PCDDs, PCDFs, and PCBs on the development of FYD. Blood samples, obtained from 64 Yusho mothers (117 descendants: 10 with FYD and 107 without FYD), were analyzed for congeners of seven PCDDs, 10 PCDFs, and four coplanar PCBs. We investigated the association between the maternal estimated blood levels of dioxins at delivery and the risk of fetal Yusho disease. We also studied the differences in dioxin blood levels in 24 mother–descendant pairs (5 with FYD and 19 without FYD). The estimated levels of total PCDD TEQ, total PCDF TEQ, total coplanar PCB TEQ, and total TEQ in the maternal blood at delivery were associated with significantly increased risk of FYD. The odds ratios, which present the risk of FYD for a 10-fold increase in blood dioxin, were largest for 1,2,3,6,7,8-HexaCDD (odds ratio = 28.6, 95% confidence interval = 1.67–489.9, p = 0.02). The levels of 1,2,3,6,7,8-HexaCDD in both the Yusho mothers and their descendants with FYD were higher than the levels in those without FYD. These findings suggest that 1,2,3,6,7,8-HexaCDD is the most important causative congener for the development of FYD.     

Extraction of heavy metals from MSW incinerator fly ash using saponins

An extraction process with saponins was evaluated for removing heavy metals from MSW (municipal solid waste) incinerator fly ashes. Two different fly ashes, A and B, were treated on a laboratory scale with three triterpene-glycoside type of saponins, M, Q, and T, in the pH range 4-9. The results were compared with those of the HCI and EDTA treatment. The treatment with saponins extracted 20-45% of Cr from the fly ashes. Saponins were also effective in extracting Cu from fly ash A attaining 50-60% extraction. Saponin T extracted 100% of Pb from fly ash A at pH around 4. The extraction of Zn with the saponin treatment was similar to that of the HCl treatment. Further, Cr, Cu, Pb, and Zn were fractionated by sequential extraction to investigate the effect of saponins on each fraction. Extraction behavior of other elements during the saponin treatment was also studied. The leaching test on the residues received after the saponin treatment showed that the fly ashes were successfully detoxified to meet the landfilling guideline.