Enhanced Bioremediation of Fuel-Oil Contaminated Soils: Laboratory Feasibility Study

In this study, microcosm experiments were conducted to evaluate the effectiveness of (1) nutrients, hydrogen peroxide (H2O2), and cane molasses addition; (2) soil washing by biodegradable surfactant [Simple Green (SG)]; and (3) soil pretreatment by Fenton-like oxidation on the bioremediation of fuel-oil contaminated soils. The dominant native microorganisms in the fuel-oil contaminated soils after each treatment process were determined via polymerase chain reaction, denaturing gradient gel electrophoresis, and nucleotide sequence analysis. Results show that approximately 32 and 56% of total petroleum hydrocarbon (TPH) removal (initial concentration of 5,000?mg?kg?1) were observed in microcosms with the addition of nutrient and cane molasses (1,000?mg?L?1), respectively, compared to only 9% of TPH removal in live control microcosms under intrinsic conditions (without amendment) after 120 days of incubation. Addition of cane molasses would cause the increase in microbial population and thus enhance the TPH degradation rate. Results also show that approximately 61% of TPH removal was observed in microcosms with the addition of H2O2(100?mg?L?1) and nutrient after 120 days of incubation. This indicates that the addition of low concentration of H2O2(100?mg?L?1) would cause the desorption of TPH from soil particles and increase the dissolved oxygen and subsequent bioremediation efficiency in microcosms. Approximately 95 and 69% of TPH removal were observed in microcosms with SG (100?mg?L?1) and higher dose of H2O2(900?mg?L?1) addition, respectively. Moreover, significant increases in microbial populations were observed and two TPH biodegraders (Pseudomonas sp. and Shewanella sp.) might exist in microcosms with SG or H2O2 addition. This indicates that the commonly used soil remedial techniques, biodegradable surfactant flushing, and Fenton-like oxidation would improve the TPH removal efficiency and would not cause adverse effects on the following bioremediation process.     

Reduction of 2,4,6-Trinitrotoluene and Hexahydro-1,3,5-trinitro-1,3,5-triazine by Hydroxyl-Complexed Fe(II)

The reduction kinetics of two explosives, 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), by Fe(II) was investigated in aqueous systems. A dilute ferrous iron solution effectively reduces these nitroaromatic (NAC) and nitramine (NAM) compounds between pH 6.75 and 9.2. Observed reaction rates are first order in monohydroxl and dihydroxyl ferrous iron [FeOH+ or Fe(OH)20], and NAC/NAM concentrations. The reaction does not require the presence of a mediating surface. Intrinsic rate constants for TNT and RDX reduction by monohydroxyl ferrous iron are 2.00(±0.17)E+09 and 2.04(±0.24)E+06?M?2?s?1, respectively. The reduction half-lives at neutral pH were on the order of minutes for TNT and hours for RDX, yielding rates faster than any known natural process or current bioremediation technique. The use of a mobile reductant, such as hydroxyl-complexed Fe(II) or other aqueous Fe(II) complexes, for NAC/NAMs could be an effective remediation technique at contaminated sites.     

Advanced Oxidation for Treatment of Aqueous Extracts from EDTA Extraction of Pb and Zn Contaminated Soil

The feasibility of using advanced oxidation processes (AOPs): ozone, ozone/sonification, and ozone/ultraviolet (UV) irradiation in treatment to remove heavy metals and ethylenediamine tetraacetate (EDTA) from aqueous extracts, obtained after soil extraction with EDTA, was examined. Extraction of soil contaminated with 1,243?mg?kg?1 Pb and 1,190?mg?kg?1 Zn with 40?mmol?kg?1 EDTA removed 41.8±0.9 and 7.2±.0.2% of Pb and Zn. Of the AOPs tested, only the use of ozone/UV enabled the decomposition of EDTA–heavy metals complexes in aqueous soil extracts, and recovery of released Pb and Zn by sorption on a commercial sorbent Slovakite. After treatment, the concentration of Pb, Zn, and EDTA in the extracts was fairly low (2.87±1.15?mg?L?1, 7.58±2.12?mg?L?1, and 0.012±0.002?mmol?L?1, respectively), and could presumably be reduced even further with a continuation of treatment. The treated extract was used for subsequent soil rinsing, which removed an additional 12.7±1.6 and 2.7±0.1% of soil Pb and Zn. The results of our study indicate that the use of ozone/UV is a feasible option for treatment of aqueous soil extracts from EDTA extraction. Treated extracts could be safely discharged or reused to lower requirements for process water.     

Evaluation of Chemical Treatments for a Mixed Contaminant Soil

Treatability tests were conducted on soil from the reservoir No. 2 burning ground at the former Plum Brook Ordnance Works in Sandusky, Ohio. This soil is contaminated with explosives 2,4,6-trinitrotolune (TNT) and 2,4/2,6-dinitrotoluene (DNT), polychlorinated biphenyls (PCB, Aroclor 1260), as well as lead. Lime treatment (alkaline hydrolysis) and persulfate oxidation were tested individually and in combination to treat explosives and PCBs. Lime treatment removed 98% of TNT, 75% of DNT, and 80% of PCBs. Similar removal levels were found for persulfate treatment as well as lime followed by persulfate. The percentage of contaminant removal was found to be independent of initial contaminant concentrations. Treatments of the most contaminated soil did not meet the preliminary remediation goals for explosives or PCBs but would allow for disposal in a nonhazardous waste landfill. Treatment of soil with lower initial concentrations easily met the residential (most stringent) preliminary remediation goals of 16, 61, and 0.22?mg?kg?1 for TNT, 2,6-DNT, and PCB (Aroclor 1260), respectively. Neither alkaline hydrolysis nor persulfate oxidation transferred more than 0.02% of the lead from the soil into the reaction waters. Lead was successfully stabilized via phosphate addition.     

Preliminary Evaluation of Microbially Mediated Precipitation of Cadmium, Chromium, and Nickel by Rhizosphere Consortium

Elevated heavy metal soils and water contamination have been shown to impose toxic effects on plants, animals, and human health. The extent of toxicity depends on the nature of the metals, soil and aquatic system characteristics, and the complex interactions between metals and the environment. Recent studies have shown that metal–microbe interactions may be effective for the remediation of contaminated media. This study investigated the effectiveness of an isolated rhizosphere bacterial consortium for treating an aqueous solution containing 600 mg/L of Cd, Cr, and Ni. The consortium was resistant to the metal toxicity as evidenced by an increase of population density of more than 6×1011?cfu/mL. The microbial activity facilitated a reduction in aqueous metal concentration with a metal precipitation selectivity of Cr?Cd>Ni.     

Initial-phase optimization for bioremediation of munition compound-contaminated soils

We examined the bioremediation of soils contaminated with the munition compounds 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine, and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetraazocine by a procedure that produced anaerobic conditions in the soils and promoted the biodegradation of nitroaromatic contaminants. This procedure consisted of flooding the soils with 50 mM phosphate buffer, adding starch as a supplemental carbon substrate, and incubating under static conditions. Aerobic heterotrophs, present naturally in the soil or added as an inoculum, quickly removed the oxygen from the static cultures, creating anaerobic conditions. Removal of parent TNT molecules from the soil cultures by the strictly anaerobic microflora occurred within 4 days. The reduced intermediates formed from TNT and hexahydro-1,3,5-trinitro-1,3,5-triazine were removed from the cultures within 24 days, completing the first stage of remediation. The procedure was effective over a range of incubation temperatures, 20 to 37 degrees C, and was improved when 25 mM ammonium was added to cultures buffered with 50 mM potassium phosphate. Ammonium phosphate buffer (50 mM), however, completely inhibited TNT reduction. The optimal pH for the first stage of remediation was between 6.5 and 7.0. When soils were incubated under aerobic conditions or under anaerobic conditions at alkaline pHs, the TNT biodegradation intermediates polymerized. Polymerization was not observed at neutral to slightly acidic pHs under anaerobic conditions. Completion of the first stage of remediation of munition compound-contaminated soils resulted in aqueous supernatants that contained no munition residues or aminoaromatic compounds.     

Clean up of Petroleum-Hydrocarbon Contaminated Soils Using Enhanced Bioremediation System: Laboratory Feasibility Study

The objective of this study was to assess the potential of applying enhanced bioremediation on the treatment of petroleum-hydrocarbon contaminated soils. Microcosm experiments were conducted to determine the optimal biodegradation conditions. The control factors included oxygen content, nutrient addition, addition of commercially available mixed microbial inocula, addition of wood chip and rice husk mixtures (volume ratio = 1:1) as bulking agents, and addition of organic amendments (chicken manures). Results indicate that the supplement of microbial inocula or chicken manures could significantly increase the microbial populations in soils, and thus enhance the efficiency of total petroleum hydrocarbon (TPH) removal (initial TPH = 5,500?mg/kg). The highest first-order TPH decay rate and removal ratio were approximately 0.015?day?1 and 85%, respectively, observed in microcosms containing microbial inocula (mass ratio of soil to inocula = 50:1), nutrient, and bulking agent (volume ratio of soil to bulking agent = 10 to 1) during 155 days of incubation. Results indicate that the first-order TPH decay rates of 0.015 and 0.0142?day?1 can be obtained with the addition of microbial inocula and chicken manures, respectively, compared with the decay rate of 0.0069?day?1 under intrinsic conditions. Thus, chicken manures have the potential to be used as substitutes of commercial microbial inocula. The decay rate and removal ratio can be further enhanced to 0.0196?day?1 and 87%, respectively, with frequent soil shaking and air replacement. Results will be useful in designing an ex situ soil bioremediation systems (e.g., biopile and land farming) for practical application.     

Effect of Oil on Polychlorinated Biphenyl Phase Partitioning during Land Biotreatment of Impacted Sediment

This study evaluated the partitioning of polychlorinated biphenyls (PCBs) during long-term, passive, land biotreatment of PCB-impacted industrial lagoon sediments. Over six years under field conditions, two land treatment units (LTUs) experienced 40% total PCB reductions from initial concentrations of 8–10?mg/kg. A third LTU with 113?mg/kg initial total PCBs showed little reduction over five years. In each unit throughout the study, oil concentrations declined at a rate greater than that for PCBs. Measured aqueous equilibrium concentrations for the PCB-impacted sediments were typically an order of magnitude or more smaller than values estimated using correlations based on total organic matter partitioning. Measured aqueous PCB concentrations agreed with predictions based on equilibration with a PCB-containing oil phase, best modeled by Raoult’s law. It was postulated that, as a consequence of PCB oil-phase partitioning, biotreatment would lead to higher PCB concentrations in the oily matter and thus increased PCB partitioning to the aqueous phase if the degradation of oily matter proceeded faster compared to PCBs. Such was the case in this study, wherein low-level aqueous phase PCB concentrations of tetrachloro PCBs increased several fold over the years as oily matter was degraded. The contribution of oil to PCB partitioning needs to be incorporated in the assessment of risk and treatability goals for land biotreatment of contaminated sediments from industrial sites.     

Evaluating Ozone as a Remedial Treatment for Removing RDX from Unsaturated Soils

Years of wastewater discharge at the Department of Energy’s Pantex Plant have contaminated the vadose zone and underlying perched aquifer with hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). Because the vadose zone is acting as a continual source of groundwater contamination, removing RDX from the unsaturated zone is paramount to prevent further contamination. We determined the efficacy of ozone to degrade and mineralize RDX. Solution experiments showed that ozone (27?mg?L?1; 150?mL?min?1) was effective in mineralizing 80% of the RDX (30?mg?RDX?L?1) provided that some Pantex soil was present to buffer the solution pH. Soil columns treated with ozone produced 50% RDX mineralization within 1 day and >80% within 7 day. Experiments designed to evaluate aerobic biodegradation following partial ozonation of a RDX solution showed that ozone-generated RDX products were much more biodegradable than untreated controls in aerobic microcosms (35 versus <0.3% cumulative mineralization). These results support the use of ozone as a remedial treatment for the contaminated vadose zone at the Pantex facility.     

Sorption Behavior and Mechanism of Pb(II) on Chinese Loess

Lead pollution is common in Western China and has caused serious public health problems recently. The treatment of wastewater containing Pb(II) is stringent for the sustainable development of local economics. The Chinese loess proved effective to remove Pb(II) from aqueous solution and applicable in the treatment of wastewater from lead–zinc ore mining sites. The adsorption capacity of Chinese loess about Pb(II) is determined as high as 270.26?mg?g?1 in this study. Factors affecting the adsorption of Pb(II) include slurry concentration, solution pH, temperature, and equilibrating duration. The optimum conditions for Pb(II) adsorption include sorbent dosage ≥ 0.05?g/50?mL, pHi ≥ pHzpc, temperature = 55°C, and equilibration duration ≥ 30?min. The isotherms and kinetic data are well fitted with Langmuir model and pseudo-first order kinetics, respectively. The thermodynamic behavior reveals the exothermic and spontaneous nature of the adsorption. The adsorption of Pb(II) on loess involves chemical reaction with calcite and surface complexation with clay minerals and hydrolysis of quartz; the former is considered as the dominant mechanism. X-ray diffraction and Fourier transform infrared patterns confirmed these speculations.     

Biodegradation of Naphthalene-Contaminated Soils in Slurry Bioreactors

The effects of naphthalene concentrations and soil constituents (sand, clay, organic matter) on biodegrading naphthalene-contaminated soils using an acclimated Flavobacterium sp. were examined in continuously stirred slurry bioreactors. Soils with and without organic matter (1%) and kaolinite clay (20%) were used. Studies showed that sorption of naphthalene can be represented by the Freundlich isotherm. Among the soils investigated, clayey soil retarded the biodegradation process the most due to its desorption characteristics. Increasing the naphthalene contamination level from 500 mg∕kg to 25,000 mg∕kg doubled the biodegradation time in the slurry reactor with a soil loading of 10 g∕L. A pseudo first-order kinetic was observed for naphthalene biodegradation, and the biodegradation constant was determined to be 0.20 mg∕L∕h. A kinetic model was developed to simulate the biodegradation of naphthalene in a continuously stirred batch slurry reactor and to understand the role of solubilization (solid phase naphthalene), desorption, and biodegradation in the removal of naphthalene. Predictions using the numerical model agreed with the experimental data.     

Evaluation of Granular Surfactant-Modified/Zeolite Zero Valent Iron Pellets As a Reactive Material for Perchloroethylene Reduction

The use of permeable reactive barriers (PRBs) for groundwater remediation is based on two distinct mechanisms: sorption and transformation. With sorption as the main mechanism, contaminants sorb on the PRB materials and are retarded. With transformation as the main mechanism, the contaminants react with the PRB materials and then converted to less toxic or innocuous substances. In this study, we tested surfactant-modified zeolite/zero valent iron (SMZ/ZVI) pellets as a PRB material to retard and degrade perchloroethylene (PCE), utilizing both sorption and transformation processes. Batch PCE kinetic studies showed instantaneous PCE removal from the aqueous phase due to sorption and subsequent removal with time due to reduction. The separation of sorption from reduction can be used to obtain both the PCE distribution coefficient (Kd) and the pseudofirst-order reduction rate constant (μobs) from a single batch experiment. The calculated Kd and μobs values are 3.0 and 0.5?L/kg and 0.14 and 0.05?h?1 for SMZ/ZVI and Z/ZVI pellets, respectively. Column experiments were performed at linear flow velocities of 0.07, 0.14, and 0.20?cm/min. The results were modeled using the one-dimensional advection–dispersion equation with linear sorption and first-order transformation. The Kd values were 2.3±0.4 and 0.5±0.1?L/kg for SMZ/ZVI and Z/ZVI pellets, respectively, in agreement with those of the batch study. The PCE transformation constants varied between 0.077 and 0.199?h?1 for the SMZ/ZVI pellets and between 0.037 and 0.144?h?1 for the Z/ZVI pellets, indicating that an enhanced transformation of PCE occurred with the sorbing SMZ/ZVI pellets. The PCE reduction rates were faster at slower flow rates, indicating that the reduction was not a mass-transfer-limited process.     

Microwave-Enhanced Thermal Desorption of Polyhalogenated Biphenyls from Contaminated Soil

The effect of microwave (MW) field on the rate of thermal desorption of polychlorinated biphenyls (PCBs) from long-term contaminated soil was examined in the laboratory environment. For these purposes a modified MW oven was used, with a uniformly extended MW field and a power consumption of 200–600 W. The weight of the soil samples was 100 g, the sum of concentrations of seven indicative congeners of PCB Nos. 28, 52, 101, 118, 153, 138, and 180 was, on average, 264 mg/kg of dry matter. It was experimentally proven that the efficiencies of PCB desorptions were high, over 99.9%. The maximal desorption temperature of 600°C was reached within 15–17 min. It came to light that the presence of alkaline additives in the soil (such as carbonates and alkaline metal hydroxides) did not have an apparent effect on the desorption of PCBs under those conditions. The results concerning the efficiency of PCB separations are in agreement with our previous findings regarding the efficiency of thermal desorption without using MWs in the pilot (input 35 kg) and industrial (input 15 t) desorption chambers with a stationary layer of the same type of contaminated soil. The main disadvantage of experiments with thermal desorption without the action of MWs was the low rate of heating up the soil. This study was focused to solve the problem of contamination in a complex way; we also studied the effect of MWs on the rate of the deterioration of the separated PCBs in aqueous condensates, the deterioration of PCBs in contaminated waste water containing alkaline agents (soda and lye), and on the catalytic reductive dechlorination of PCBs in the system Pd supported on active coal with sodium formate as the hydrogen donor. Experiments with the MW-enhanced catalytic reductive oxidation show over 98.5% reduction in the concentration of PCBs. An important and new finding is the more than 98% reduction in the concentration of PCBs when the MW field was applied on the contaminated water into which only 2.5% of Na2CO3 was added. Further studies on possible influences of MWs on the reaction kinetic are needed. Meanwhile we attribute the positive MW effects to their thermal properties rather than to their influence on the reaction mechanism.     

Field and Laboratory Evaluation of the Impact of Tall Fescue on Polyaromatic Hydrocarbon Degradation in an Aged Creosote-Contaminated Surface Soil

A field study was initiated in 1997 to assess the ability of tall fescue grass to remediate an aged creosote-contaminated surface soil. Field monitoring was combined with aerobic microcosm experiments, microbial enumerations, and plant tissue analysis to determine the impact of tall fescue on the degradation of six polycyclic aromatic hydrocarbons (PAHs), acenaphthene, fluorene, phenanthrene, fluoranthene, pyrene, and chrysene, and to elucidate the mechanisms of remediation. Fescue grass had a beneficial impact on the degradation of all PAHs except phenanthrene. Mean concentrations of the three-ring PAHs, acenaphthene and fluorene, were lower in fescue cells compared to unvegetated cells after 36 months. In microcosms with soil from fescue cells, acenaphthene had a significantly higher degradation rate and lower final concentration after 180 days than in microcosms prepared with soil from unvegetated cells. Mean concentrations of the four-ring PAHs, fluoranthene, pyrene, and chrysene, were statistically similar in the field study; however, the 10th and 20th percentile concentrations were lower in fescue cells during all sampling periods. Microcosm studies showed increased degradation of fluoranthene and pyrene in soil samples taken from tall fescue rhizosphere compared to unvegetated soil and abiotic controls. Degradation of four-ring PAHs was enhanced in the shallow zones (10–15 cm below ground surface) of vegetated cells. The root mass was approximately 35% greater in shallow zones than in medium depth zones (15–21 cm below ground surface). Microbial populations on solid mineral media plates with pyrene and chrysene as the sole carbon source were two times higher in soils from tall fescue plots than from unvegetated soils, suggesting that the increased PAH degradation was a result of increased microbial activity in the rhizosphere. Gas chromatography/mass spectrometry analysis of fescue shoots indicated that no uptake or translocation of PAHs or PAH degradation intermediates into the shoots was occurring.     

Biodegradation of Aqueous Organic Matter over Seasonal Changes: Bioreactor Experiments with Indigenous Lake Water Bacteria

Artificial groundwater recharge for drinking water production involves infiltration of surface water through sandy soil and its capture into a groundwater aquifer. The transformation of aqueous organic matter is one of the central issues in this process. The purpose of this work was to assess the potential of indigenous microorganisms in the source water to contribute in the aqueous organic matter biodegradation. For this purpose, microorganisms were enriched from the source water in a fluidized-bed reactor (FBR) and used for kinetic studies on biodegradation of organic matter at ambient temperature range. Lake water (total organic carbon 5.8?mg?L?1) was continuously fed to the FBR containing porous carrier material to support biomass retention. In the inlet and outlet water there were on average 21±6 and 13±5×105?cells?mL?1, respectively. Biofilm accumulation (as volatile solids) reached 13.1?mg?g?1 dw carrier. In the continuous-flow mode and the batch tests, the highest oxygen consumption rate appeared in the summer, followed by the fall, spring, and winter. At low temperatures, the biodegradation of aqueous organic matter was relatively rapid initially for labile fractions followed by a slower phase for refractory fractions. The average temperature coefficient (Q10) in the system was 2.3 illustrating a strong temperature dependency of oxygen consumption. The isotopic analysis of dissolved inorganic carbon δ13CDIC analysis revealed 27 and 69% mineralizations of dissolved organic carbon at 23 and 6°C over 65 and 630 min, respectively. These results can be used to construct additional input parameters in modeling applications of artificial groundwater recharge process. The biological component especially, i.e., the biodegradation, is difficult to predict for on-site applications without experimental proof and thus the interpretation in this study will help formulate design predictions for the process.     

Aerobic Biodegradation of Methyl Tert-Butyl Ether in Gasoline-Contaminated Aquifer Sediments

Intrinsic biodegradation of methyl tert-butyl ether (MTBE) in aquifer sediments under oxic conditions was investigated using laboratory microcosms. Aquifer samples were collected from three different areas (source area, upgradient, and downgradient) of a shallow gasoline-contaminated aquifer within the Atlantic Coastal Plain Province located in Virginia. Biodegradation of MTBE was observed in the source-area microcosms in which MTBE declined from a starting concentration of 2.7 to 0.28 mg/L over a 58-day period, following an initial lag period of 20 days. The same set of microcosms was respiked with MTBE to an initial concentration of 4.8 mg/L and MTBE concentrations declined to 0.20 mg/L over a 52-day period with no lag in biodegradation. First-order MTBE biodegradation rates for the first and second periods were 0.037±0.003 and 0.063±0.003 day?1, respectively. When another set of source-area microcosms was spiked with MTBE (5 mg/L), toluene and ethylbenzene (1 mg/L each), the initial lag period increased to 33 days but there was no significant change in the MTBE biodegradation rate (0.065±0.026 day?1) and MTBE was not detected after 134 days. Biodegradation of MTBE was also observed in the microcosms constructed using aquifer sediment with only limited exposure to MTBE but the degradation rate was lower and statistically different (0.022±0.005 day?1) than the source area microcosms. Biodegradation of MTBE ceased when oxygen was depleted. Methyl tert-butyl ether did not biodegrade in the uncontaminated, upgradient microcosms; however, rapid biodegradation of toluene was observed. Methyl tert-butyl ether biodegradation appears to be limited in the absence of dissolved oxygen and in aquifer sediments where petroleum hydrocarbons including MTBE were not previously observed.     

Cyclodextrin-Enhanced Electrokinetic Remediation of Soils Contaminated with 2,4-Dinitrotoluene

The removal of 2,4-dinitrotoluene (2,4-DNT), a munitions waste constituent and an industrial intermediate, from contaminated soils was evaluated using enhanced electrokinetic (EK) remediation. Two model soils were spiked with 480?mg of 2,4-DNT/kg of dry soil for the EK experiments. The spiked soils were kaolin, a low-buffering clayey soil, and glacial till, a high-buffering silty soil. The glacial till was obtained from a field site and contained 2.8% organic matter. Deionized (DI) water and cyclodextrin solutions were used as the EK purging solutions. Cyclodextrin was selected as a nonhazardous solubility enhancer for enhancing the desorption and removal of 2,4-DNT from soils in EK remediation. Two aqueous solutions of hydroxypropyl β-cyclodextrin (HPCD) at concentrations of 1 and 2% were selected for kaolin and glacial till, respectively, based on results for batch extraction of 2,4-DNT from the same soils. During the EK experiments, greater current and electro-osmotic flow were observed for HPCD solutions than for DI water. After the completion of the EK experiments, the soils in the EK cell were extruded and the residual 2,4-DNT in the soils was determined. Less 2,4-DNT remained in the kaolin soil (up to 94% transformed) than in the glacial till soil (20% transformed) due to strong retention of 2,4-DNT by the soil organic matter in glacial till. For kaolin, less 2,4-DNT remained in the soil using HPCD solutions than using DI water. For glacial till, comparable levels of 2,4-DNT remained in the soil for both EK solutions. Since no 2,4-DNT was detected in the effluents from the EK cells, the decrease in 2,4-DNT concentration in the kaolin and glacial till soils was attributed to electrochemical transformation of 2,4-DNT to other species.     

Kinetics of Liquid-Phase Hydrogenation of Toluene Catalyzed by Hydrogen Storage Alloy MlNi_5

Asacleanandhigh efficiencyenergyresource ,hydrogenisthoughttobethemostpromisingsubstituteoffossilfuels .Storingandutilizingtheenergybyus ingthehydrogenasenergycarrieristhemostfavor ablemethodtosolvetheenergycrisis ,whichattractsthefocusoftheworld .Therehavebeenconsiderableprogressesinthetechnologyofhydrogen energyinre centyears .Reillyetal .[1] firstproposedtheconceptofthemetalhydrideslurryin 1 980s ,inwhichthede formationorruptureofthevesselsduetotheparticlepulverizationandthepoorheattransfer…     

Kinetics and mechanism of an NADPH-dependent succinic semialdehyde reductase from bovine brain

An NADPH-dependent succinic semialdehyde reductase has been purified from bovine brain by several chromatographic procedures. The preparation appeared homogeneous on SDS/PAGE. The enzyme is a monomeric protein with a molecular mass of 28 kDa. A number of properties of the bovine brain enzyme, such as substrate specificity, specific activity, molecular mass, optimum pH, amino acid composition, and kinetic parameters, have been determined and compared with those reported for preparations from other sources. The results indicate that the enzyme isolated from bovine brain in the present study is different from those reported for preparations from other sources. The inhibition kinetic patterns obtained when the products of the reaction or substrate analogs are used as inhibitor of the reaction catalyzed by the enzyme are consistent with an ordered sequential mechanism involving the formation of an intermediate ternary complex and in which NADPH is the first substrate to bind the enzyme.