Seok-Young Oh

Oxidation of polyvinyl alcohol by persulfate activated with heat, Fe2+, and zero-valent iron

The oxidation of polyvinyl alcohol (PVA) by persulfate (S(2)O(8)(2-)) activated with heat, Fe(2+), and zero-valent iron (Fe(0)) was investigated via batch experiments. It was hypothesized that elevated temperature and the addition of Fe(2+) or Fe(0) into a persulfate-water system could enhance the oxidation of PVA by activated persulfate. Increasing the temperature from 20 to 60 degrees C or 80 degrees C accelerated the oxidation rate of PVA, which achieved complete oxidation in 30 and 10 min, respectively. At 20 degrees C, the addition of Fe(2+) or Fe(0) to the persulfate-water system significantly enhanced the oxidation of PVA. The optimal persulfate-to-Fe(2+) or Fe(0) molar ratio was found to be 1:1. Complete oxidation of PVA was obtained by Fe(0)-activated persulfate in 2h. Synergistic activation of persulfate by heat and Fe(2+) or Fe(0) was also shown to enhance the oxidation of PVA in the persulfate-water system. By using GC-MS analysis, an oxidation product of PVA was identified as vinyl acetic acid (C(4)H(6)O(2)), which is readily biodegradable. Our results suggest that the oxidative treatment of PVA by activated persulfate is a viable option for the pretreatment of PVA-laden wastewater to enhance its biodegradability.

Degradation of 2,4-dinitrotoluene by persulfate activated with zero-valent iron

The oxidation of 2,4-dinitrotoluene (DNT) by persulfate (S(2)O(8)(2-)) activated with zero-valent iron (Fe(o)) was studied through a series of batch experiments. The mechanism for Fe(o) activation was investigated by comparing with Fe(2+), and the effects of persulfate-to-iron ratio and pre-reduction on DNT oxidation were examined. DNT was stable in the presence of persulfate and transformed only when Fe(o) was added. Most DNT was degraded oxidatively by Fe(o)-activated persulfate, whereas direct reduction of DNT by Fe(o) was unimportant. The rate of DNT degradation increased with higher Fe(o) dose, presumably due to increasing activation of persulfate by Fe(o) and Fe(2+). In contrast to the Fe(o)-persulfate system, where complete oxidation DNT was achieved, only </=20% of DNT was degraded and the reaction was terminated rapidly when Fe(o) was replaced with equimolar Fe(2+). This indicates that Fe(o) is more effective than Fe(2+) as activating agent and potentially more suitable for environmental applications. The reduction products of DNT were more rapidly oxidized by persulfate than DNT, suggesting that converting the nitro groups of NACs to amino groups prior to oxidation can greatly enhance their oxidation. This suggests that a sequential Fe(o) reduction-persulfate oxidation process may be an effective strategy to promote NAC degradation.

Sorption of triclosan onto activated carbon, kaolinite and montmorillonite: effects of pH, ionic strength, and humic acid.

Sorption of triclosan on three sorbents, viz., activated carbon, kaolinite and montmorillonite was studied as a function of pH, ionic strength and humic acid (HA) concentration through controlled batch experiments. Triclosan sorption was found to be higher in the acidic pH range, as varying pH showed significant influence on the surface charge of the sorbents and degree of ionization of the sorbate. Sorption capacity of the sorbents increased with an increase in the ionic strength of solution. At low pH (pH 3), the overall increase in triclosan sorption was 1.2, approximately 4 and 3.5 times, respectively for activated carbon, kaolinite and montmorillonite when ionic strength was increased from 1x10(-3) to 5x10(-1) M. Triclosan sorption onto activated carbon decreased from 31.4 to 10.6 mg g(-1) by increasing the HA concentration to 200 mg C L(-1). However, during sorption onto kaolinite and montmorillonite, the effect of HA was very complex probably due to (i) hydrophobicity (log K(ow)=4.76) of triclosan; and (ii) complexation of HA with triclosan. Though triclosan sorption onto activated carbon is higher, the potential of kaolinite and montmorillonite in controlling the transport of triclosan in subsurface environment can still be appreciable.

Enhanced reduction of nitrate by zero-valent iron at elevated temperatures

Kinetics of nitrate reduction by zero-valent iron at elevated temperatures was studied through batch and column experiments. It was hypothesized that under increased solution temperatures, the zero-valent iron may accelerate the reduction of nitrate by overcoming the activation energy barrier to nitrate reduction. The results of the batch experiment showed the synergistic effects of elevated temperature (75 degrees C) and a buffered condition (pH 7.4 with 0.1 M HEPES) to enhance the rate of nitrate reduction by zero-valent iron from 0.072+/-0.006 h(-1) ((0.35+/-0.03) x 10(-4) L m(-2) h(-1)) at room temperature to 1.39+/-0.23 h(-1) ((1.03+/-0.07) x 10(-3) L m(-2) h(-1)). Complete nitrate removal was obtained in a Fe(0) column after 30 min under both buffered and unbuffered conditions at 75 degrees C. These results indicate that a temperature increase could overcome the energy barrier. We suggest that an iron reduction process at moderately elevated temperature (50-75 degrees C) may be a suitable method for removing nitrate from industrial discharges.

Biochar-mediated reductive transformation of nitro herbicides and explosives.

Biochar, a subset of black carbon produced via pyrolysis of biomass, has received much attention in recent years due to its potential to address many important issues, from energy and climate to agriculture and environmental quality. Biochar is known to influence the fate and transport of organic contaminants, although its role has been generally assumed to be as an adsorbent. In this study, the authors investigated the ability of biochar to catalyze the reductive reactions of nitro herbicides and explosives. Two biochars, derived from poultry litter and wastewater biosolids, were found to promote the reductive removal of the dinitro herbicides pendimethalin and trifluralin and the explosives 2,4-dinitrotoluene and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) by dithiothreitol. Parallel experiments using another black carbon material, graphite powder or granular activated carbon, in place of a biochar resulted in comparable rate enhancement to show reduction products, such as 2,4-diaminotoluene and formaldehyde. A cyclization product of trifluralin and reduction products of dinitrotoluene and RDX were detected only when biochar and dithiothreitol were both present, supporting the ability of biochar to promote redox reactions. Three possible catalysts, including graphene moieties, surface functional groups, and redox-active metals, in biochar may be responsible for the biochar-mediated reactions. The environmental significance, implications, and applications of this previously unrecognized role of biochar are discussed.

Reductive transformation of 2,4,6-trinitrotoluene, hexahydro-1,3,5-trinitro-1,3,5-triazine, and nitroglycerin by pyrite and magnetite

Reductive transformation of 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and nitroglycerin (NG) by pyrite (FeS(2)) and magnetite (Fe(3)O(4)) was investigated to determine the role of Fe(II)-bearing minerals on the fate of toxic explosives in Fe/S-rich natural environment. Results from batch experiments showed that 65% of TNT and 45% of RDX were transformed from solution in the presence of pyrite under pH 7.4 buffered conditions within 32 days. Without a buffered solution, transformation of TNT and RDX decreased. NG was continuously and rapidly transformed by pyrite under both conditions. Complete removal of NG was achieved in 32 days under buffered conditions. NH(4)(+) was identified as a reduction product for RDX and NG in the pyrite-water system. Reductive transformation of RDX and NG by magnetite was slower than that by pyrite. The results suggest that abiotic transformation of the explosives by pyrite and magnetite may be considered when determining the fate of explosives in Fe/S-rich subsurface environments.

Treatment of Diesel-Contaminated Soil by Fenton and Persulfate Oxidation with Zero-Valent Iron

The objective of this research is to investigate Fenton and persulfate oxidation with zero-valent iron [Fe(0)] as a batch type ex-situ remediation technology for the treatment of diesel-contaminated soil. Results from batch experiments indicate that Fe(0) is a better catalyst for H2O2 and persulfate than Fe2+ for the enhancement of Fenton and persulfate oxidation in a batch system. Maximum removal was obtained after 12 h when 1 and 2 g of Fe(0) were added to hydrogen peroxide (250 mg/L) and persulfate (250 mg/L), respectively, in a soil-water system. As the amounts of Fe(0) and persulfate were increased three times at the optimal ratio, the removal of total petroleum hydrocarbon (TPH) was enhanced accordingly. More than 90% of the TPH was removed in 3 h, and the treated soil met the Korean regulation level (500 mg/kg) for TPH. Increased amounts of Fe(0) and hydrogen peroxide (up to 10 g and 1250 mg/L, respectively) also significantly enhanced degradation under the optimal conditions. The results of our study suggest that Fe(0)-assisted Fenton and persulfate oxidation in a batch reactor may be an alternative option to treat diesel-contaminated soil.

Sorption of halogenated phenols and pharmaceuticals to biochar: affecting factors and mechanisms

The feasibility of using biochar as a sorbent to remove nine halogenated phenols (2,4-dichlorophenol, 2,4-dibromophenol, 2,4-difluorophenol, 2-chlorophenol, 4-chlorophenol, 2-bromophenol, 4-bromophenol, 2-fluorophenol, and 4-fluorophenol) and two pharmaceuticals (triclosan and ibuprofen) from water was examined through a series of batch experiments. Types of biochar, synthesized using various biomasses including fallen leaves, rice straw, corn stalk, used coffee grounds, and biosolids, were evaluated. Compared to granular activated carbon (GAC), most of the biochar samples did not effectively remove halogenated phenols or pharmaceuticals from water. The increase in pH and deprotonation of phenols in biochar systems may be responsible for its ineffectiveness at this task. When pH was maintained at 4 or 7, the sorption capacity of biochar was markedly increased. Considering maximum sorption capacity and properties of sorbents and sorbates, it appears that the sorption capacity of biochar for halogenated phenols is related to the surface area and carbon content of the biochar and the hydrophobicity of halogenated phenols. In the cases of triclosan and ibuprofen, the sorptive capacities of GAC, graphite, and biochars were also significantly affected by pH, according to the point of zero charge (PZC) of sorbents and deprotonation of the pharmaceuticals. Pyrolysis temperature did not affect the sorption capacity of halogenated phenols or pharmaceuticals. Based on the experimental observations, some biochars are good candidates for removal of halogenated phenols, triclosan, and ibuprofen from water and soil.

Detoxification of PAX-21 ammunitions wastewater by zero-valent iron for microbial reduction of perchlorate

US Army and the Department of Defense (DoD) facilities generate perchlorate (ClO(4)(-)) from munitions manufacturing and demilitarization processes. Ammonium perchlorate is one of the main constituents in Armys new main charge melt-pour energetic, PAX-21. In addition to ammonium perchlorate, hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and 2,4-dinitroanisole (DNAN) are the major constituents of PAX-21. In order to evaluate microbial perchlorate reduction as a practical option for the treatment of perchlorate in PAX-21 wastewater, we conducted biodegradation experiments using glucose as the primary sources of electrons and carbon. Batch experiments showed that negligible perchlorate was removed in microbial reactors containing PAX-21 wastewater while control bottles containing seed bacteria and glucose rapidly and completely removed perchlorate. These results suggested that the constituents in PAX-21 wastewater may be toxic to perchlorate reducing bacteria. A series of batch toxicity test was conducted to identify the toxic constituents in PAX-21 and DNAN was identified as the primary toxicant responsible for inhibiting the activity of perchlorate reducing bacteria. It was hypothesized that pretreatment of PAX-21 by zero-valent iron granules will transform toxic constituents in PAX-21 wastewater to non-toxic products. We observed complete reduction of DNAN to 2,4-diaminoanisole (DAAN) and RDX to formaldehyde in abiotic iron reduction study. After a 3-day acclimation period, perchlorate in iron-treated PAX-21 wastewater was rapidly decreased to an undetectable level in 2 days. This result demonstrated that iron treatment not only removed energetic compounds but also eliminated the toxic constituents that inhibited the subsequent microbial process.

Chemical extraction of arsenic from contaminated soil under subcritical conditions

In this research, we investigated a chemical extraction process, under subcritical conditions, for arsenic (As)-contaminated soil in the vicinity of an abandoned smelting plant in South Korea. The total concentration of As in soil was 75.5 mg/kg, 68% of which was As(+III). X-ray photoelectron spectroscopy analysis showed that the possible As(+III)-bearing compounds in the soil were As(2)O(3) and R-AsOOH. At 20°C, 100 mM of NaOH could extract 26% of the As from the soil samples. In contrast, 100 mM of ethylenediaminetetraacetic acid (EDTA) and citric acid showed less than 10% extraction efficiency. However, as the temperature increased to 250 and 300°C, extraction efficiencies increased to 75-91% and 94-103%, respectively, regardless of the extraction reagent used. Control experiments with subcritical water at 300°C showed complete extraction of As from the soil. Arsenic species in the solution extracted at 300°C indicated that subcritical water oxidation may be involved in the dissolution of As(+III)-bearing minerals under given conditions. Our results suggest that subcritical water extraction/oxidation is a promising option for effective disposal of As-contaminated soil.