利用氧化铝-改性硅胶联柱分离测定水中多氯联苯

本文介绍一种多氯联苯(PCBs)与农药的分离和气相色谱分析PCBs新方法.富集浓缩后的样品首先经浓硫酸酸洗.排除大多数干扰PCBs测定的有机化合物,然后利用氧化铝-硅胶(Ag~+)联柱实现了PCBs和干扰其测定的农药的完全分离,应用毛细管气相色谱分析测试了水样中多氯联苯多种同系物、同分异构体的含量.其方法的回收率在79—88%之间.     

Metabolism of palmitic,linoleic, and linolenic acids in adult oysters,Crassostrea virginica

This study investigated incorporation and metabolism of saturated [(1-¹⁴C) 16:0] and unsaturated [(1-¹⁴C) 18:26 and (1-¹⁴C) 18:33] fatty acids in adult eastern oysters,Crassostrea virginica Gmelin (spawned from parents obtained in 1986 from Mobjack Bay, Virginia, USA), and the influence of temperature on these processes. InC. virginica, incorporation of injected palmitic (16:0) and linolenic (18:33) acids was increased when oysters which had been grown in warm water (22 to 23°C) were transfered to cold water (5 to 7°C) for 8 to 18 d. Incorporation of linoleic acid (18:26) was unchanged under these conditions. The changes in concentration may have been linked to depression of metabolism in these oysters, in particular that of 16:0, which was reduced by 90%. Oxidation of incorporated fatty acids was much higher in warm than in cold water. Cold-temperature conditioning ofC. virginica altered the distribution of fatty acids among the neutral and polar lipid fractions. Long-term exposure to cold water increased the proportion of fatty acids in the polar fraction, which may be related to maintenance of membrane fluidity. Short-term exposure to cold water had the opposite effect, which may be due to increased energy requirements as the oyster adapts to new conditions. Reutilization of¹⁴C-acyl groups demonstrated de novo synthesis of 16:0 and 18:0 fatty acids. Only limited elongation and no desaturation of the administered fatty acids was observed.     

The system design of UV-assisted catalytic oxidation process--degradation of 2,4-D

Unlike the conventional first- or second-order model, a novel approach to design for the removal of 2,4-dichlorophenoxy (2,4-D) by the UV-catalytic oxidation process (UVCOP) was investigated. Two distinctive parameters, initial decay rate and maximum oxidative capacity, were characterized. By using these parameters, the performance of the degradation of 2,4-D by UVCOP regarding to the reagent dosages could be successfully predicted. Low concentrations of ferrous ion was found to be a rate-limiting factor for the process while the dosage of hydrogen peroxide was concluded as a dominant species in determining the maximum oxidation capacities. This information can be used to optimize the treatment process and achieve the expected performance target; an "optimal-dose model" was developed accordingly. The model is an intelligent and useful tool to evaluate the optimal doses of hydrogen peroxide with the minimum dose of ferrous ion, which leads to a better design of the treatment process.     

低温厌氧处理低浓度废水研究进展

对低温下厌氧处理低浓度废水的最新进展进行了较全面综述。高效厌氧反应器为这一发展提供了可能。首选反应器是膨胀颗粒污泥床 (EGSB)反应器。若废水中颗粒有机物含量较高 ,采用两级系统 (两个EGSB ,水解上流式污泥床(HUSB)反应器 +EGSB ,上流式厌氧污泥床 (UASB)反应器 +EGSB等 )处理效果较好。新兴的厌氧膜生物反应器也是该领域的一个发展方向。低温 ( 3— 12℃ )、低浓度 (COD <10 0 0mg L)废水中培养的嗜温种泥保持令人满意的产甲烷活性。其最佳代谢温度仍在中温范围 ( 30— 40℃ ) ,表明主要菌群仍是嗜温菌。     

Analysis and structure prediction of chlorinated polycyclic aromatic hydrocarbons released from combustion of polyvinylchloride

Chlorinated polycyclic aromatic hydrocarbons (Cl-PAHs) released from combustion of polyvinylchloride (PVC) at different furnace temperatures were investigated. A laboratory-scale tube-type furnace with electric heating was utilized to control combustion conditions. Glass fabric filters and adsorbents were used to collect the combustion emissions. Following Soxhlet extraction, concentration and column chromatography purification, isomers separation, selective detection and identification of Cl-PAHs were performed on GC/MS system on the basis of retention data and mass spectra. Their quantification was accomplished by using external standard calibration technique. About 18 Cl-PAHs were determined, most of which were monochlorinated derivatives of naphthalene, biphenyl, fluorene, phenanthrene, anthracene, fluoranthene and pyrene. Only two dichlorophenanthrenes or anthracenes were identified. The possible positions of chlorine atoms attached to the aromatic rings are predicted by quantitative structure-property relationship. The levels of these compounds were in the range of 0.30-29.08 microg/g PVC. The relationship between the formation of Cl-PAHs and PAHs was discussed.     

Chlorination of dibenzofuran and dibenzo-p-dioxin vapor by copper (II) chloride

Dibenzofuran (DF) is formed from phenol and benzene in combustion gas exhaust streams prior to particle collection equipment. Subsequent chlorination at lower temperatures on particle surfaces is a potential source of chlorinated dibenzofuran (CDF). Gas streams containing 8% O₂ and approximately 0.1% DF vapor were passed through particle beds containing copper (II) chloride (0.5% Cu, mass) at temperatures ranging from 200 to 400 °C to investigate the potential for CDF formation during particle collection. Experiment duration was sufficient to provide an excess amount of DF (DF/Cu=3). The efficiency of DF chlorination by CuCl₂ and the distribution of CDF products were measured, with effects of temperature, gas velocity, and experiment duration assessed. Results of a more limited investigation of dibenzo-p-dioxin (DD) chlorination by CuCl₂ to form chlorinated DD (CDD) products are also presented.The efficiency of DF/DD chlorination by CuCl₂ was high, both in terms of CuCl₂ utilization and DF/DD conversion. Total yields of Cl on CDF/CDD products of up to 0.5 mole Cl per mole CuCl₂ were observed between 200 and 300 °C; this suggests that nearly 100% CuCl₂ was utilized, assuming a conversion of two moles of CuCl₂ to CuCl per mole Cl added to DD/DF. In a short duration experiment (DF/Cu=0.3), nearly 100% DF adsorption and conversion to CDF was achieved. The degree of CDF chlorination was strongly dependent on gas velocity. At high gas velocity, corresponding to a gas–particle contact time of 0.3 s, mono-CDF (MCDF) yield was largest, with yields decreasing with increasing CDF chlorination. At low gas velocity, corresponding to a gas–particle contact time of 5 s, octa-CDF yield was largest. DF/DD chlorination was strongly favored at lateral sites, with the predominant CDF/CDD isomers within each homologue group those containing Cl substituents at only the 2,3,7,8 positions. At the higher temperatures and lower gas velocities studied, however, broader isomer distributions, particularly of the less CDD/CDF products, were observed, likely due to preferential destruction of the 2,3,7,8 congeners.     

Magnetic resonance imaging of nonaqueous phase liquid during soil vapor extraction in heterogeneous porous media

Soil vapor extraction (SVE) is commonly used to remediate nonaqueous phase liquids (NAPLs) from the vadose zone. This paper aims to determine the effect of grain size heterogeneity on the removal of NAPL in porous media during SVE. Magnetic resonance imaging (MRI) was used to observe and quantify the amount and location of NAPL in flow-through columns filled with silica gel grains. MRI is unique because it is nondestructive, allowing three-dimensional images to be taken of the phases as a function of space and time. Columns were packed with silica gel in three ways: coarse grains (250-550 microm) only, fine grains (32-63 microm) only, and a core of fine grains surrounded by a shell of coarse grains. Columns saturated with water were drained under a constant suction head, contaminated with decane, and then drained to different decane saturations. Each column was then continuously purged with water-saturated nitrogen gas and images were taken intermittently. Results showed that at residual saturation, a sharp volatilization front moved through the columns filled with either coarse-grain or fine-grain silica gel. In the heterogeneous columns, the volatilization front in the core lagged just behind the shell because gas flow was greater through the shell and decane in the core diffused outward to the shell. When decane saturation in the core was above residual saturation, decane volatilization occurred near the inlet, the relative decane saturation throughout the core dropped uniformly, and decane in the core flowed in the liquid phase to the shell to replenish volatilized decane. These results indicate that NAPL trapped in low-permeability zones can flow to replenish areas where NAPL is lost due to SVE. However, when residual NAPL saturation is reached, NAPL flow no longer occurs and diffusion limits removal from low-permeability zones.     

Effects of oxalic acid on the regrowth of heterotrophic bacteria in the distributed drinking water

Three laboratory-scale water pipe systems were set up to study the effects of adding oxalic acid on the bacterial regrowth and biofilm formation in the distributed drinking water. The results of water pipe experiment displayed that around 38% carbon in the oxalic acid could be converted to bacterial biomass. The maximum HPCs in biofilm were equal to 3.5x10(4), 3.38x10(5) and 2.8x10(6) CFUcm(-2) while the maximum HPCs of free bacteria were equal to 1.2x10(3), 2.54x10(3) and 3.78x10(4) CFUml(-1) for the blank and with addition of 10 and 50 micrograms OA eq-Cl(-1), respectively. These results imply that the addition of oxalic acid to distributed water has positive effect on the assimilable organic carbon content of drinking water and bacterial regrowth in water pipe. This effect is enhanced with addition of high-level oxalic acid. Batch tests were also conducted using water samples collected from a Taiwanese drinking water distribution system. The bacterial regrowth potentials (BRPs) of the blank were equal to 4.25x10(3), 1.46x10(4), 4.9x10(4) and 7.54x10(4) CFUml(-1) for water samples collected from treatment plant effluent, commercial area, mixed area, and residential area, respectively. These results show that the biological stability of distributed drinking water is the highest in treatment plant effluent, the moderate in the commercial area and mixed area, and the lowest in the residential area.     

Separating method and dynamic processes of Nano-Al13

In order to investigate the characteristics of pure Nano-Al₁₃, Nano-Al₁₃ was separated and purified from a series of poly-aluminum chloride (PAC) solutions which had the same Al₁₃ percentage but different total Al concentrations, by using column chromatography, ethanol-acetone resolving and SO^2? ₄/Ba²⁺ displacement. The Al₁₃ species yield was characterized by Al-ferron timed complexation spectrophotometry and ²⁷Al-NMR (nuclear magnetic resonance). The coagulation efficiency of Nano-Al₁₃, PAC and AlCl₃ in synthetic water was also investigated by Jar tests. The dynamic process and aggregation state of kaolin suspensions coagulating with Nano-Al₁₃, PAC and AlCl₃ were similarly investigated using a photometric dispersion analyzer 2000 (PDA2000). The experimental results indicated that the ethanol-acetone resolving method was simple and could separate the PAC solution at different concentrations, while column chromatography could separate PAC solutions at low concentrations. The SO₄ ^2?/Ba²⁺ displacement method could separate PAC solutions at high concentrations. However, extra inorganic cation and anion could be added in the solution during separation. The coagulation efficiency and dynamic experimental results showed that Nano-Al₁₃ with high positive-charged species was effective in removing turbidity and color. The dynamic process results showed that Nano-Al₁₃ also had the best recovery capability after shearing compared with PAC and AlCl₃ because the Nano-Al₁₃ conformation is more effective in charge neutralization.