Nic Korte

Reduction of nitrate to ammonia by zero-valent iron

Abstract The reduction of nitrate to ammonia occurs with nearly complete conversion at room temperature and pressure under aerobic conditions in the presence of iron and either HCl or a pH buffer. A 50.0 mL solution of 12.5 millimolar nitrate is rapidly reduced to ammonia when exposed to 4.00 g of 325 mesh iron at pH 5.0, 0.05 M sodium acetate/acetic acid. The pseudo-first order rate constant was 0.053 min −1 , Under conditions of pH 6.0 buffer, (i.e. 0.1 M 4-morpholineethanesulfonic acid adjusted to pH 6.0) and pH 7.0 buffer (0.1 M 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid adjusted to pH 7.0), the rate constants were 0.0408 min −1 and 0.0143 mint, respectively. In unbuffered solutions there was no loss in nitrate and no production of ammonia. A more concentrated nitrate solution (100 mL of 1.0 M sodium nitrate) was also reduced to ammonia in the presence of 2.5 M HCl with the slow addition of 50.0 g of 325 mesh iron.

A method for the rapid dechlorination of low molecular weight chlorinated hydrocarbons in water

1,1,2-Trichloroethylene (TCE), 1,1-dichloroethylene, cis and trans-1,2-dichloroethylene and tetrachloroethylene (PCE), at concentrations of 20 ppm in aqueous solutions were rapidly hydrodechlorinated to ethane (in a few minutes), on the surface of palladized iron in batch experiments that were performed in closed vials. No intermediate reaction products such as 1,1-dichloroethylene, 1,2-dichloroethylenes and vinyl chloride were detected at concentrations > 1 ppm either in the headspace or in solution. The chloromethanes, CCl4, CHCl3 and CH2Cl2 were also dechlorinated to methane on palladized iron; the CCl4 was dechlorinated in a few minutes, the CHCl3, in less than an hour and the CH2Cl2, in 4–5 h. These results indicate that an above-ground treatment method can be designed for the treatment of groundwater contaminated with low molecular weight chlorinated hydrocarbons.

Naturally occurring arsenic in groundwaters of the midwestern United States

High concentrations of naturally occurring arsenic are present in alluvial groundwater systems in the midwestern United States. These occurrences tend to be sporadic because the arsenic is mobilized only under a narrow range of redox conditions. The reducing conditions must be sufficient to reduce and dissolve iron and manganese but not to produce sulfide. Typically, the affected aquifers are relatively high in clay content and of relatively low yield. For that reason, many of these arsenic occurrences are in aquifers supplying single families. The mechanism by which the arsenic is mobilized begins with the deposition of iron oxides during streamflow while the alluvium is being deposited. The oxides have a strong affinity for dissolved arsenic and adsorb it from the streamwater. As the alluvium is buried, it eventually becomes subject to slow groundwater movement. As conditions become more reducing, ferric oxides are reduced to soluble ferrous oxides, resulting in mobilization of the adsorbed arsenic.

Field application of palladized iron for the dechlorination of trichloroethene

Abstract Palladized iron (Pd/Fe) has been tested under field conditions for the dechlorination of trichloroethene (TCE) in groundwater. Contaminated water was pumped from aquifers in Ohio (∼0.7– 1.5 mg/l TCE) and Missouri (2–9 mg/l TCE and 1,2-dichloroethene) and passed through columns of Pd/Fe. The experiments demonstrated that the dechlorination reaction occurs efficiently until the surface of the Pd/Fe becomes fouled. Regeneration of the surface with dilute (1M) hydrochloric acid is easily accomplished under laboratory conditions, but initially was unsuccessful in the field. Further experiments indicated, that reduced sulfur species, although not naturally present in the groundwater being treated, were permanently poisoning the palladium. Apparently, sulfur-reducing bacteria utilize the hydrogen produced by the Pd/Fe process and reduce the sulfate that is present. An anion exchange column was used to remove sulfate (∼20 mg/l) from groundwater at the Kansas City Plant in order to test this theory. Under these conditions, a column of Pd/Fe was repetitively regenerated for a 4-week period. A second column, not protected by sulfate removal, could not be regenerated. The results demonstrated that Pd/Fe could be used in a long-term field process if a material with more resistance to Fe and Pd losses is developed.

The effect of solvent concentration on the use of palladized-iron for the step-wise dechlorination of polychlorinated biphenyls in soil extracts.

This report describes the application of palladized iron (Pd/Fe) to the dechlorination of polychlorinted biphenyls (PCBs) at ambient temperature. Experiments supported by congener-specific analyses demonstrated that dechlorination occurs in a step-wise fashion with the meta-chlorines being more reactive than ortho-chlorines. Over the course of the laboratory experiments, complete conversion to biphenyl was observed. The process was also tested with PCBs dissolved in high (40-60%) concentrations of ethanol and isopropanol as a means of simulating solutions generated by commercial soil and solid waste extraction processes. The reaction rate was sensitive to the percentage of solvent but complete dechlorination was still indicated. Tests with soil extracts from a contaminated site demonstrated that there were no apparent interferences from asphalt and other miscellaneous debris. Short-duration tests with highly contaminated PCB solutions from a hazardous waste site demonstrated efficient dechlorination although there was a reduction in reaction rate with time.

Environmental fate of tungsten from military use.

This manuscript describes the distribution, fate and transport of tungsten used in training rounds at three small arms ranges at Camp Edwards on the Massachusetts Military Reservation (MMR), USA. Practice with tungsten/nylon rounds began in 2000 subsequent to a 1997 US Environmental Protection Agency ban on training with lead. Training with the tungsten rounds was halted in 2005 because of concerns regarding tungstens environmental mobility and potential toxicity. This study, therefore, examines how tungsten partitions in the environment when fired on a small arms training range. Soil sampling revealed surface soil concentrations, highest at the berm face, up to 2080 mg/kg. Concentrations decreased rapidly with depth--at least by an order of magnitude by 25 cm. Nonetheless, tungsten concentrations remained above background to at least 150 cm. Pore-water samples from lysimeters installed in berm areas revealed a range of concentrations (<1-400 mg/L) elevated with respect to background although there was no discernable trend with depth. Groundwater monitoring well samples collected approximately 30 m below ground surface showed tungsten (0.001-0.56 mg/L) attributable to range use.

The distribution of metals in soils and pore water at three U.S. military training facilities.

Small arms firing ranges at military training facilities can have enormous heavy metal burdens (percent level) in soils. Currently there are few published works that quantify the metal content of soils and waters at military installations or speculate on the potential for migration of these contaminants into groundwater. This article documents metals in soils and waters at nine small arms training ranges at three military installations in the U.S. Soil samples were collected from the surface and shallow subsurface. The results demonstrated that lead, antimony, copper, and zinc were the principal contaminants of interest and mapping a sites lead and copper surface distributions would adequately define the extent of impacted soil. Lower metal concentrations at three of the ranges reflected previous remediation by means of physical separation and mechanical removal of metallic fragments followed by fixation treatment with MaectiteTM. Except for the treated ranges where mixing had occurred, subsurface soil samples indicated limited vertical migration. Several of the ranges were also monitored for trace element migration in the vadose zone by means of suction-cup lysimeters. This pore-water sampling indicated ceramic suction-cup lysimeters are useful for assessing relative concentrations but require care in evaluation because of potential sorption losses. Monitoring of soil water at ranges should include antimony and zinc; the former because, in contrast to the other metals, it is typically soluble in an anionic form, and the latter because of its greater solubility and mobility.

Vapor extraction experiments with laboratory soil columns: Implications for field programs

Abstract As part of a site remediation project, laboratory soil column experiments were conducted to evaluate the effectiveness of a field vapor extraction system. Different soil types were placed in specially designed soil columns and saturated with 1,1,1-Trichloroethane and Jet-A fuel. The soil columns were connected to a vacuum pump and removal rates were monitored using mass balance, a portable photoionization detector, and a gas chromatograph. Results of the laboratory experiments indicated that the technique is useful for designing and monitoring field vapor extraction systems. Guidelines were developed for flow rate versus removal times, the effects of varying lithologies on removal rates and efficiencies, and the removal characteristics of organic mixtures consisting of varying volatile components.

Formulation of cleanup standards for trace elements with probability plots

Probability plots of trace element concentrations may be used to partition, or segregate, sample data into its constituent populations. Two populations are typically present in data from sites requiring remedial action, one representing clean, uncontaminated soil or sediment (background) and the other representing contaminated ground. The use of such plots in the analysis and evaluation of environmental data permits a statistical characterization of the background populations, from which defensible cleanup criteria may be developed. These criteria will be environmentally conservative, yet will minimize the amount of soil removed in a remedial action. An example is given from a successful cleanup of a surface impoundment.

Bioremediation of petroleum hydrocarbons in soil column lysimeters from Kwajalein Island

Soil column studies were used to evaluate petroleum hydrocarbon (PHC) remediation in soils from Kwajalein Atoll. Treatments included controls, and combinations of water, air, nutrients, and bioaugmentation with indigenous microbes (W, A, N, and M, respectively). Microbial colony forming units (CFU) decreased in the control columns and in treatments without air. Treatments including W + A + N and W + A + N + M exhibited increased CFU. One third of the PHC was removed by water and another third was removed by W + A + N and W + A + N + M treatments. Bioaugmentation with indigenous PHC degraders did not enhance bioremediation. Potential for bioremediation was demonstrated by air, water, and nutrient amendments.