Positive impact of microorganisms on the performance of laboratory-scale permeable reactive iron barriers

Degradation efficiencies of zerovalent iron (Fe0) containing different bacterial inocula, i.e., an iron(III)-reducing Geobacter sulfurreducens strain and/or a bacterial consortium, were compared to degradation efficiencies of noninoculated Fe0 in a laboratory-scale column experiment. Contaminant removal efficiencies and hydrogen production rates indicated an increasing reactivity in time for all inoculated iron columns, while reactivity of the noninoculated columns remained the same. The main mineral precipitates, including carbonate green rust, ferrous hydroxy carbonate, aragonite, and to a lesser extent goethite, were observed under all imposed conditions. The higher reactivity of the inoculated column material is explicable by the reduction of ferric iron species by iron(III)-reducing bacteria, resulting in the observed higher amounts of highly reactive carbonate green rust. However, contributions of other bacteria could not be excluded. Although different groups of hydrogen-consuming bacteria were detected in the columns, no indication was found that hydrogen consumption was sufficiently high to affect reactivity or permeability of the iron matrix, as the abiotic generation of H2 was substantially exceeding its potential consumption.     

Influence of Anionic Cosolutes and pH on Nanoscale Zerovalent Iron Longevity: Time Scales and Mechanisms of Reactivity Loss toward 1,1,1,2-Tetrachloroethane and Cr(VI)

Nanoscale zerovalent iron (NZVI) was aged over 30 days in suspension (2 g/L) with different anions (chloride, perchlorate, sulfate, carbonate, nitrate), anion concentrations (5, 25, 100 mN), and pH (7, 8). During aging, suspension samples were reacted periodically with 1,1,1,2-tetrachloroethane (1,1,1,2-TeCA) and Cr(VI) to determine the time scales and primary mode of NZVI reactivity loss. Rate constants for 1,1,1,2-TeCA reduction in Cl(-), SO(4)(2-), and ClO(4)(-) suspensions decreased by 95% over 1 month but were generally equivalent to one another, invariant of concentration and independent of pH. In contrast, longevity toward 1,1,1,2-TeCA depended upon NO(3)(-) and HCO(3)(-) concentration, with complete reactivity loss over 1 and 14 days, respectively, in 25 mN suspensions. X-ray diffraction suggests that reactivity loss toward 1,1,1,2-TeCA in most systems results from Fe(0) conversion into magnetite, whereas iron carbonate hydroxide formation limits reactivity in HCO(3)(-) suspensions. Markedly different trends in Cr(VI) removal capacity (mg Cr/g NZVI) were observed during aging, typically exhibiting greater longevity and a pronounced pH-dependence. Notably, a strong linear correlation exists between Cr(VI) removal capacities and rates of Fe(II) production measured in the absence of Cr(VI). While Fe(0) availability dictates longevity toward 1,1,1,2-TeCA, this correlation suggests surface-associated Fe(II) species are primarily responsible for Cr(VI) reduction.     

碱剂对丝绸活性染料冷堆印花固着率的影响

丝绸活性染料冷堆印花工艺中,可采用色浆直接加碱法和面料轧碱法进行固色试验.比较这两种施碱方法中碱剂类型和用量对印花固着率影响的试验结果表明,色浆直接加碱工艺宜采用2%碳酸氢钠(除活性橙F2R需要用6%外),面料轧碱法的碱剂为氢氧化钠/碳酸钠组合,最佳用量为2.5%/5.0%;面料轧碱法的固着率比色浆直接加碱法略高,但耗能多,且面料表面存在颜色不匀、泛黄等问题;色浆直接加碱法则简单易行,冷堆印花质量较好.     

Effects of carbonate precipitates on long-term performance of granular iron for reductive dechlorination of TCE

Long-term column experiments were conducted to evaluate the effects of secondary carbonate minerals on permeability and reactivity of commercial granular iron treating trichloroethene (TCE). The results showed that carbonate precipitates caused a decrease in reactivity of the iron, and spatially and temporally varying reactivity loss resulted in migration of mineral precipitation fronts, as well as profiles of TCE, pH, alkalinity, calcium, and dissolved iron. In the columns receiving solutions of dissolved calcium carbonate, porosity gradually decreased in proportion to the source concentrations, as carbonate minerals accumulated. However, the rate of porosity loss slowed over time because of the declining reactivity of the iron. Thus, secondary minerals are not likely to accumulate to the extent that there is a substantial reduction in hydraulic conductivity. The reactivity of the iron was found to decrease as an exponential function of the carbonate mineral volume fraction. This changing reactivity of iron should be incorporated into predictive models for improved designs of iron permeable reactive barriers (PRBs).     

Chloride effect on TNT degradation by zerovalent iron or zinc during water treatment

Addition of corrosion promoters, such as sodium and potassium chloride, accelerated TNT degradation during water treatment using zerovalent zinc and iron. It was theorized that corrosion promoters could be used to accelerate electron generation from metallic species, create new reactive sites on the surface of metals during contaminated water treatment, and minimize passivating effects. The surface area normalized pseudo-first-order rate constant for the reaction of zerovalent zinc with TNT in the absence of KCl was 1.364 L x m(-2) x h(-1). In the presence of 0.3 mM and 3 mM KCI, the rate constant increased to 10.5 L x m(-2) x h(-1) and 51.0 L x m(-2) x h(-1), respectively. For the reaction with zerovalent iron and TNT, the rate constant increased from 6.5 (L/m2 x h) in the absence of KCl to 37 L x m(-2) x h(-1) using 3 mM KCl. The results demonstrate that chloride based corrosion promoters enhance the rate of TNT degradation. The in-situ breakage of the oxide layer using corrosion promoters was applied as a treatment to maintain the long-term activity of the metallic species. Zinc maintained a high reactivity toward TNT, and the reactivity of iron increased after 5 treatment cycles using 3 mM KCI. Zinc and iron scanning electron micrographs indicate that TNT degradation rate enhancement is caused by the pitting corrosion mechanism.     

Major anion effects on the kinetics and reactivity of granular iron in glass-encased magnet batch reactor experiments

The relative effects of sulfate (SO4(2-)), chloride (Cl-), nitrate (NO3-), and bicarbonate (HCO3-) (8 mM ionic strength solutions, adjusted to pH 10) on the reactivity of Master Builders iron was investigated using a low-abrasion batch reactor with a glass-encased magnet (GEM). Reactivity of the granular iron surface was assessed by measuring the reduction rate of 4-chloronitrobenzene (4ClNB) as a function of initial 4CINB concentration and anion type. Relative to a similarly prepared perchlorate (ClO4-) solution, in which perchlorate was assumed not to interact with the iron surface, nitrate and bicarbonate inhibited the reduction of the probe compound (4ClNB). Chloride and sulfate enhanced reactivity. Thus, the anions were ranked SO4(2-) > Cl- > or = ClO4- > NO3- > HCO3 (from most enhanced to most inhibited) in their influence on granular iron reactivity toward 4ClNB. Kinetic studies of 4CINB were conducted under conditions that caused the iron surface to saturate with the reacting compound (saturation kinetic studies). These experiments, conducted in the various anion solutions indicated above, showed that the gains in reactivity that occurred in the presence of Cl- and SO4(2-) were due to either increased surface reactivity or sorption capacity. The losses in reactivity that occurred in the presence of NO3- were due to decreases in one or both of these same two factors. However, reactivity declines in the presence of CO3(2-) appear to have been due, in large part, to a reduced affinity of 4ClNB for the iron surface.     

Reactive transport modeling of trichloroethene treatment with declining reactivity of iron

Evolving reactivity of iron, resulting from precipitation of secondary minerals within iron permeable reactive barriers (PRBs), was included in a reactive transport model for trichloroethene (TCE) treatment. The accumulation of secondary minerals and reactivity loss were coupled using an empirically derived relationship that was incorporated into an existing multicomponent reactive transport code (MIN3P) by modifying the kinetic expressions. The simulation results were compared to the observations from long-term column experiments, which were designed to assess the effects of carbonate mineral formation on the performance of iron for TCE treatment. The model successfully reproduced the evolution of iron reactivity and the dynamic changes in geochemical conditions and contaminant treatment. Predictions under various hydrogeochemical conditions showed that TCE would be treated effectively for an extended period of time without a significant loss of permeability. Although there are improvements yet to be made, this study provides a significant advance in our ability to predict long-term performance of iron PRBs.     

Nitrate reduction by zerovalent iron: effects of formate, oxalate, citrate, chloride, sulfate, borate, and phosphate

Recent studies have shown that zerovalent iron (Fe0) may potentially be used as a chemical medium in permeable reactive barriers (PRBs) for groundwater nitrate remediation; however, the effects of commonly found organic and inorganic ligands in soil and sediments on nitrate reduction by Fe0 have not been well understood. A 25.0 mL nitrate solution of 20.0 mg of N L(-1) (1.43 mM nitrate) was reacted with 1.00 g of Peerless Fe0 at 200 rpm on a rotational shaker at 23 degrees C for up to 120 h in the presence of each of the organic acids (3.0 mM formic, 1.5 mM oxalic, and 1.0 mM citric acids) and inorganic acids (3.0 mM HCl, 1.5 mM H2SO4, 3.0 mM H3BO3, and 1.5 mM H3PO4). These acids provided an initial dissociable H+ concentration of 3.0 mM available for nitrate reduction reactions under conditions of final pH < 9.3. Nitrate reduction rates (pseudo-first-order) increased in the order: H3PO4 < citric acid < H3BO3 < oxalic acid < H2SO4 < formic acid < HCl, ranging from 0.00278 to 0.0913 h(-1), corresponding to surface area normalized rates ranging from 0.126 to 4.15 h(-1) m(-2) mL. Correlation analysis showed a negative linear relationship between the nitrate reduction rates for the ligands and the conditional stability constants for the soluble complexes of the ligands with Fe2+ (R2 = 0.701) or Fe3+ (R2 = 0.918) ions. This sequence of reactivity corresponds also to surface adsorption and complexation of the three organic ligands to iron oxides, which increase in the order formate < oxalate < citrate. The results are also consistent with the sequence of strength of surface complexation of the inorganic ligands to iron oxides, which increases in the order: chloride < sulfate < borate < phosphate. The blockage of reactive sites on the surface of Fe0 and its corrosion products by specific adsorption of the inner-sphere complex forming ligands (oxalate, citrate, sulfate, borate, and phosphate) may be responsible for the decreased nitrate reduction by Fe0 relative to the chloride system.     

Understanding nitrate reactions with zerovalent iron using tafel analysis and electrochemical impedance spectroscopy

This study investigated the reaction mechanisms of nitrate (NO3-) with zerovalent iron (ZVI) media under conditions relevantto groundwatertreatment using permeable reactive barriers (PRB). Reaction rates of NO3- with freely corroding and with cathodically or anodically polarized iron wires were measured in batch reactors. Tafel analysis and electrochemical impedance spectroscopy (EIS) were used to investigate the reactions occurring on the iron surfaces. Reduction of NO3- by corroding iron resulted in near stoichiometric production of NO2-, which did not measurably react in the absence of added Fe(II). Increasing NO3- concentrations resulted in increasing corrosion currents. However, EIS and Tafel analyses indicated that there was little direct reduction of NO3- at the ZVI surface, despite the presence of water reduction. This behavior can be attributed to formation of a microporous oxide on the iron surfaces that blocked reduction of NO3- and NO2- but did not block water reduction. This finding is consistent with previous observations that NO3- impedes reduction of organic compounds by ZVI. Nitrite concentrations greater than 4 mM resulted in anodic passivation of the iron, but passivation was not observed with NO3- concentrations as high as 96 mM. This indicates that the passivating oxide preventing NO3- reduction was permeable toward cation migration. Since reaction with Fe(0) can be excluded asthe mechanism for NO3- and NO2- reduction, reaction with Fe(II)-containing oxides coating the iron surface is the most likely reaction mechanism. This suggests that short-term batch tests requiring little turnover of reactive sites on the iron surface may overestimate long-term rates of NO3- removal because the effects of passivation are not apparent in batch tests conducted with high initial Fe(II) to NO3- ratios.     

Precipitates on granular iron in solutions containing calcium carbonate with trichloroethene and hexavalent chromium

Mineralogical examination, using scanning electron microscopy (SEM), X-ray diffractometry (XRD), and optical microscopy, was conducted on the Fe0-bearing reactive materials derived from long-term column experiments undertaken to assess the treatment capacity of Fe0 under different geochemical conditions. The columns received either deionized water or solutions of differing dissolved calcium carbonate concentrations, together either with trichloroethene (TCE) or hexavalent chromium (Cr(VI)). The major reaction product in the columns receiving deionized water was magnetite-maghemite, and for the columns receiving dissolved calcium carbonate, the main products were iron hydroxy carbonate and aragonite. Replacement of Fe0 by reaction products occurred mainly at the edges of the Fe0 particles, and penetrative replacement was focused along cracks and along and around graphitic inclusions. Fibrous or flake-shaped iron hydroxy carbonate mostly replaced the edges of the Fe0 particles. Aragonite had needle-shaped morphology, and some occurred as clusters of crystals. Aragonite was deposited on iron hydroxy carbonate, thus providing at least a partial armoring effect. The mineral was also observed to cement groups of Fe0 particles into compact aggregates. The Cr was present mostly as Cr(III) in Cr(III)-Fe(III) (oxy)hydroxides and in trace amounts in iron hydroxy carbonate.     

Use of caustic magnesia to remove cadmium, nickel, and cobalt from water in passive treatment systems: column experiments

In the present study caustic magnesia obtained from calcination of magnesium carbonate was tested in column experiments as an alternative material for passive remediation systems to remove divalent metals. Caustic magnesia reacts with water to form magnesium hydroxide, which dissolves increasing the pH to values higher than 8.5. At these pH values, cadmium is precipitated as otavite and to a minor amount as a hydroxide. Cobalt and nickel are precipitated as hydroxides which form isostructural solids with brucite. Thus, metal concentrations as high as 75 mg/L in the inflowing water are depleted to values below 10 microg/L. Magnesia dissolution is sufficiently fast to treat flows as high as 0.5 m3/m2 x day. For reactive grain size of 2-4 mm, the column efficiency ends due to coating of the grains by precipitates, especially when iron and aluminum are present in the solution.     

活性冷轧堆染色的染料和工艺优选

纯棉机织物冷轧堆染色早有应用,但仍缺少染料与工艺选择较明确的理论指导。通过研究活性染料类型、碱剂种类和堆置时间对纯棉机织物冷轧堆染色的影响,重点分析不同碱剂和堆置时间对活性黄3RS、汽巴克隆红C-2BL、青RGB和海军蓝BES等4种不同类型活性染料染色色深和固色率的影响,给出的最佳染色工艺为:活性黄3RS和汽巴克隆红C-2BL以纯碱40 g/L为碱剂,堆置时间分别为15 h和10 h;RGB青和BES海军蓝则采用烧碱4 g/L和纯碱40 g/L混合碱剂,堆置15 h。     

Neutralization of acid in the rumen by magnesium oxide and magnesium carbonate

Two reagent and two feed grade magnesium oxides and reagent grade magnesium carbonate, sodium bicarbonate, and calcium carbonate were evaluated to ascertain their ability to neutralize acid in the rumen. Rumen fluid pH was increased in vitro, compared to the control, by antacid compounds, and their increased ranked: calcium carbonate less than feed grade magnesium oxide A less than light magnesium oxide and feed grade magnesium oxide B less than heavy magnesium oxide less than magnesium carbonate less than sodium bicarbonate. Titrations at constant pH's ranging from 3.0 to 7.5 indicated that these magnesium compounds were reactive at pH's normally in the rumen although reactivity decreased with increasing pH. Intraruminal doses of feed grade magnesium oxide A and calcium carbonate did not change rumen fluid pH for other compounds ranked: feed grade magnesium oxide B less than magnesium carbonate less than heavy magnesium oxide. Feeding of heavy magnesium oxide or magnesium carbonate increased rumen fluid pH as compared to the control diet. Feeding feed grade magnesium oxide B in three quantities to cattle resulted in proportional increased in fecal pH and fluidity of feces. Two feed grade magnesium oxides differed in their ability to neutralize acid in the rumen.     

Impact of microbial activities on the mineralogy and performance of column-scale permeable reactive iron barriers operated under two different redox conditions

The present study focuses on the impact of microbial activities on the performance of various long-term operated laboratory-scale permeable reactive barriers. The barriers contained both aquifer and Fe0 compartments and had received either sulfate or iron(III)-EDTA to promote sulfate-reducing and iron(III)-reducing bacteria, respectively. After dismantlement of the compartments after almost 3 years of operation, DNA-based PCR-DGGE analysis revealed the presence of methanogenic, sulfate-reducing, metal-reducing, and denitrifying bacteria within as well as up- and downgradient of the Fe0 matrix. Under all imposed conditions, the main secondary phases were vivianite, siderite, ferrous hydroxy carbonate, and carbonate green rust as found by scanning electron microscopy (SEM) combined with energy dispersive X-ray analysis (EDX), and X-ray diffraction (XRD). Under sulfate-reduction promoting conditions, iron sulfides were formed in addition, resulting in 7 and 10 times higher degradation rates for PCE and TCE, respectively, compared to unreacted iron. These results indicate that the presence of sulfate-reducing bacteria in or around iron barriers and the subsequent formation of iron sulfides might increase the barrier reactivity.     

Longevity of granular iron in groundwater treatment processes: solution composition effects on reduction of organohalides and nitroaromatic compounds

Although granular iron permeable reactive barriers (PRBs) are increasingly employed to contain subsurface contaminants, information pertaining to system longevity is sparse. The present investigation redresses this situation by examining the long-term effects of carbonate, silica, chloride, and natural organic matter (NOM) on reactivity of Master Builders iron toward organohalides and nitroaromatic contaminants. Six columns were operated for 1100 days (approximately 4500 pore volumes) and five others for 407 days (approximately 1800 pore volumes). Nine were continuously exposed to mixtures of contaminant species, while the other two were only intermittently exposed in order to differentiate deactivation induced by water (and inorganic cosolutes) from that resulting from contaminant reduction. Contaminants investigated were trichloroethylene, 1,2,3-trichloropropane, 1,1-dichloroethane, 2-nitrotoluene, 4-nitroacetophenone, and 4-nitroanisole. Column reactivity declined substantially over the first 300 days and was dependent on the feed solution chemistry. High carbonate concentrations enhanced reactivity slightly within the first 90 days but produced poorer performance over the long term. Both silica and NOM adversely affected reactivity, while chloride evinced a somewhat mixed effect. Observed contrasts in relative reactivities suggest that trichloroethylene, 1,2,3-trichloropropane, and nitroaromatic compounds all react at different types of reactive sites. Our results indicate that differences in groundwater chemistry should be considered in the PRB design process.     

鸡爪清洗工艺研究

以解冻鸡爪为原料,用氨水、碳酸钠、碳酸氢钠、氢氧化钠作为清洗加工助剂,以L值及感官评价为指标,得到鸡爪清洗工艺的适宜条件为:清洗助剂为碳酸氢钠、浓度1%、温度50℃、时间40 min,其L值可达到90.4;通过对其漂洗工艺进行研究,以感官评分为主要考查指标,0.2%的醋酸液漂洗40 min即可达到最佳的漂洗效果。     

Use of pretreatment zones and zero-valent iron for the remediation of chloroalkenes in an oxic aquifer

Pretreatment zones (PTZs) composed of sand, 10% zero-valent iron [Fe(0)]/sand, and 10% pyrite (FeS2)/sand were examined for their ability to prolong Fe(0) reactivity in above ground column reactors and a subsurface permeable reactive barrier (PRB). The test site had an acidic, oxic aquifer contaminated with tetrachloroethylene (PCE) and trichloroethylene (TCE). The 10% FeS2 and 10% Fe(0) PTZs removed dissolved oxygen and affected the pH and E(h) in the PTZ. None of the PTZs had any effect on pH or E(h) in the 100% Fe(0) zone. Nitrate and sulfate were removed more quickly in the Fe(0) zones preceded by either the 10% Fe(0) PTZ or 10% FeS2. PCE first-order degradation rate constants (k(obs)) decreased significantly (> 80%) with increasing column pore volumes regardless of the PTZ material used. k(obs) finally leveled off after approximately 1 yr of operation. The column results predict that the PRB will experience a breakthrough of PCE in 3-5 yr and illustrate the importance of incorporating temporal variations in degradation rate constants when designing PRBs.     

Effects of potassium buffers on feed intake in lactating dairy cows and on rumen fermentation in vivo and in vitro

Twenty-four Holstein cows were used to compare acceptance of concentrates and complete rations containing 1) no buffer, 2) 1.8% potassium bicarbonate, 3) 1.2% potassium carbonate, or 4) 1.5% sodium bicarbonate in the concentrate. When concentrate and a forage blend were offered separately (comparison period 1), concentrate intake did not differ among treatments, but forage blend consumption and complete ration intake was greater with the potassium carbonate ration (comparison period 2). Rumen pH did not differ, but urine pH was higher in cows fed complete rations containing buffers. Cows fed potassium carbonate had higher milk fat percentages than cows fed sodium bicarbonate during the first comparison period and higher than controls during the second comparison period and produced more 3.5% fat-corrected milk and solids-corrected milk than cows fed sodium bicarbonate in both comparison periods. Milk protein percentage was lower in cows fed potassium carbonate diets as compared with those fed sodium bicarbonate diets, but total protein production was similar. In three continuous culture in vitro trials, potassium carbonate maintained fermenter pH comparably to sodium bicarbonate, and total volatile fatty acid and acetate production were similar.     

Effect of precipitation on low frequency electrical properties of zerovalent iron columns

We conducted column studies to investigate the application of a noninvasive electrical method to monitor precipitation in Fe0 columns using (a) Na2SO4 (0.01 M, dissolved oxygen (DO) = 8.8 ppm), and (b) Na2CO3 (0.01 M, DO = 2.3 ppm) solutions. An increase in complex conductivity terms (maximum 40% in sulfate column and 23% in carbonate column) occurred over 25 days. Scanning electron microscopy (SEM) identified mineral surface alteration, with greater changes in the high DO sulfate column relative to the low DO carbonate column. X-ray diffractometry (XRD) identified reduced amounts of hematite/maghemite in both columns, precipitation of goethite/akaganeite in the sulfate column, and precipitation of siderite in the carbonate column. Nitrogen adsorption measurements showed increases in specific surface area of iron minerals (27.5% for sulfate column and 8.2% for carbonate column). As variations in electrolytic conductivity and porosity were minimal, electrical changes are attributed to (1) higher complex interfacial conductivity due to increased surface area and mineralogical alteration and (2) increased electronic conduction due to enhanced electron transfer across the iron-fluid interface. Our results show that electrical measurements are a proxy indicator of Fe0 surface alteration.     

Using yeast RNA as a probe for generation of hydroxyl radicals by earth materials

Inhalation of certain types of particulate matter can lead to lung disease. The reactivity of these particles and, in part, the pathologic responses that result are dictated by their physicochemical properties. The ability of particles to induce the generation of reactive oxygen species (ROS), especially hydroxyl radicals in vivo, is one property that has been correlated to the development of lung disease. Several minerals, such as quartz and asbestos, are known to generate hydroxyl radicals and cause lung disease, but many other minerals have never been tested. Here, we describe a technique employing yeast RNA as a probe to screen for mineral-generated hydroxyl radicals. The stability of RNA in the presence of hydrogen peroxide, ferrous iron, hydroxyl radicals, and several common minerals (quartz, albite, forsterite, fayalite, hematite, magnetite, coal, and pyrite) was examined. 3'-(p-Aminophenyl) fluorescein (APF) was used to verify mineral generation of ROS. RNA is stable in the presence of hydrogen peroxide, quartz, and albite; while it degrades in the presence of ferrous iron, hydroxyl radicals, and the other minerals. Coal and pyrite are the most reactive both in RNA degradation and hydroxyl radical generation. This noncellular technique provides a straightforward way to compare many different particles simultaneously. Those particles showing reactivity toward RNA using this method are high-priority candidates for further in vitro and possibly in vivo tests.