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971.
Min H Ye YF Chen ZY Wu WX Yufeng D 《Journal of environmental science and health. Part. B》2001,36(5):581-595
This paper reports the influences of the herbicide butachlor (n-butoxymethlchloro -2', 6'-diethylacetnilide) on microbial populations, respiration, nitrogen fixation and nitrification, and on the activities of dehydrogenase and hydrogen peroxidase in paddy soil. The results showed that the number of actinomycetes declined significantly after the application of butachlor at different concentrations ranging from 5.5 microg g(-1) to 22.0 microg g(-1) dried soil, while that of bacteria and fungi increased. Fungi were easily affected by butachlor compared to the bacteria. The growth of fungi was retarded by butachlor at higher concentrations. Butachlor however, stimulated the growth of anaerobic hydrolytic fermentative bacteria, sulfate-reducing bacteria (SRB) and denitrifying bacteria. The increased concentration of butachlor applied resulted in the higher number of SRB. Butachlor inhibited the growth of hydrogen-producing acetogenic bacteria. The effect of butachlor varied on methane-producing bacteria (MPB) at different concentrations. Butachlor at the concentration of 1.0 microg g(-1) dried soil or less than this concentration accelerated the growth of MPB, while at 22.0 microg g(-1) dried soil showed an inhibition. Butachlor enhanced the activity of dehydrogenase at increasing concentrations. The soil dehydrogenase showed the highest activity on the 16th day after application of 22.0 microg g(-1) dried soil of butachlor. The hydrogen peroxidase could be stimulated by butachlor. The soil respiration was depressed during the period from several days to more than 20 days, depending on concentrations of butachlor applied. Both the nitrogen fixation and nitrification were stimulated in the beginning but reduced greatly afterwards in paddy soil. 相似文献
972.
973.
This study examined the photocatalytic degradation of three azo dyes, acid orange 7 (AO7), procion red MX-5B (MX-5B) and reactive black 5 (RB5) using a new type of nitrogen-doped TiO2 nanocrystals. These newly developed doped titania nanocatalysts demonstrated high reactivity under visible light (lambda>390 nm), allowing more efficient usage of solar light. The doped titania were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Experiments were conducted to compare the photocatalytic activities of nitrogen-doped TiO2 nanocatalysts and commercially available Degussa P25 powder using both UV illumination and solar light. It is shown that nitrogen-doped TiO2 after calcination had the highest photocatalytic activity among all three catalysts tested, with 95% of AO7 decolorized in 1 h under UV illumination. The doped TiO2 also exhibited substantial photocatalytic activity under direct sunlight irradiation, with 70% of the dye color removed in 1h and complete decolorization within 3 h. Degussa P25 did not cause detectable dye decolorization under identical experimental conditions using solar light. The decrease of total organic carbon (TOC) and evolution of inorganic sulfate (SO4(2-)) ions in dye solutions were measured to monitor the dye mineralization process. 相似文献
974.
975.
Copper adsorption kinetic properties in batch and fixed-bed reactors were studied in this paper. The isothermal adsorption experiments showed that the copper adsorption capacity of a granular activated carbon (Filtrasorb 200) increased when ionic strength was higher. The presence of EDTA diminished the adsorption. An intraparticle diffusion model and a fixed-bed model were successfully used to describe the batch kinetic and fixed-bed operation behaviors. The kinetics became faster when the solution pH was not controlled, implying that the surface precipitation caused some metal uptake. The external mass transfer coefficient, the diffusivity and the dispersion coefficient were obtained from the modeling. It was found that both external mass transfer and dispersion coefficients increased when the flow rate was higher. Finally effects of kinetic parameters on simulation of fixed-bed operation were conducted. 相似文献
976.
Samir Kumar Khanal Wen-Hsing Chen Ling Li Shihwu Sung 《Water environment research》2006,78(2):110-117
The goal of the proposed project was to develop an anaerobic fermentation process that converts negative-value organic wastes into hydrogen-rich gas in a continuous-flow reactor under different operating conditions, such as hydraulic retention time (HRT), heat treatment, pH, and substrates. A series of batch tests were also conducted in parallel to the continuous study to evaluate the hydrogen conversion efficiency of two different organic substrates, namely sucrose and starch. A heat shock (at 90 degrees C for 15 minutes) was applied to the sludge in an external heating chamber known as a sludge activation chamber, as a method to impose a selection pressure to eliminate non-spore-forming, hydrogen-consuming bacteria and to activate spore germination. The experimental results showed that the heat activation of biomass enhanced hydrogen production by selecting for hydrogen-producing, spore-forming bacteria. The batch feeding at a shorter HRT of 20 hours (or higher organic loading rate) favored hydrogen production, whereas, at a longer HRT of 30 hours, methane was detected in the gas phase. The major organic acids of hydrogen fermentation were acetate, butyrate, and propionate. Up to 23.1% of influent chemical oxygen demand was consumed in biomass synthesis. Batch tests showed that the hydrogen-production potential of starch was lower than sucrose, and better conversion efficiency from starch was obtained at a lower pH of 4.5. However, addition of sucrose to starch improved the overall hydrogen-production potential and hydrogen-production rate. This study showed that sustainable biohydrogen production from carbohydrate-rich substrates is possible through heat activation of settled sludge. 相似文献
977.
有机粘土矿物对水中低浓度菲的吸附性能和机理 总被引:2,自引:0,他引:2
分别选用十六烷三甲基溴化铵(HDTMA-Br)、四甲基溴化铵(TMA-Br)、聚乙二醇(PEG)表面活性剂改性天然粘土矿物,研究其对水中低浓度多环芳烃类难降解有机物菲的吸附性能和机理,并讨论了有机粘土的用量对吸附菲的性能的影响,验证了有机粘土矿物吸附菲后的稳定性.3种有机粘土矿物对菲的吸附等温线均呈中凹型,表现为分配系数(Kp)逐渐增大,表明吸附是分配作用和溶剂化效应共同作用的结果.根据Kp及土样有机碳含量(foc)所得的经有机碳归一化的分配系数(Koc)基本为常数,远远高于天然土壤/沉积物的Koc.在相同实验条件下,3种有机粘土矿物中HDTMA改性粘土矿物对菲的吸附性能最强,PEG改性粘土矿物次之,TMA改性粘土矿物最差. 相似文献
978.
To understand the dechlorination ability of chlorobenzenes (CBs) and polychlorinated biphenyls (PCBs) by untamed microorganisms under anaerobic condition and to correlate gas chromatographic properties with the occurrence of reductive dechlorination, introduction of CBs and PCBs in the culture medium inoculated with microorganisms from sludge and sediment, respectively, were performed. Three kinds of culture media preparing from sludge, river water and a synthetic medium were used in the experiments. HCB was degraded to 1,3,5-trichlorobenzene (1,3,5-TCB) and 1,3-dichlorobenzene (1,3-DCB) in both sludge medium and synthetic medium with inoculated microorganisms. Three PCB congeners including 2,3,4-, 3,4,5- and 2,3,4,5-CBp (chlorinated biphenyl) were not found to be dechlorinated in the river water medium with inoculation culture but to be dechlorinated in the synthetic medium. MNDO methodology was used to compute theoretical dechlorination reaction heats and GC-ECD techniques were used to estimate chromatographic data of CB and PCB congeners. Both CB and PCB congeners showed that dechlorination by untamed microorganisms under anaerobic mixed cultures were more likely to occur when larger amounts of energy were released and greater deltaln RRT value between the parent congener and the daughter product was observed. Deltaln RRT provided a more precise information on the singularity of PCBs ortho-dechlorination in an aspect of thermodynamic favorable rule. 相似文献
979.
980.
Tsai CH Huang YJ Chen JC Liao WT Fang GC 《Journal of the Air & Waste Management Association (1995)》2003,53(10):1225-1232
The traditional technologies for odor removal of thiol usually create either secondary pollution for scrubbing, adsorption, and absorption processes, or sulfur (S) poisoning for catalytic incineration. This study applied a laboratory-scale radio-frequency plasma reactor to destructive percentage-grade concentrations of odorous dimethyl sulfide (CH3SCH3, or DMS). Odor was diminished effectively via reforming DMS into mainly carbon disulfide (CS2) or sulfur dioxide (SO2). The removal efficiencies of DMS elevated significantly with a lower feeding concentration of DMS or a higher applied rf power. A greater inlet oxygen (O2)/DMS molar ratio slightly improved the removal efficiency. In an O2-free environment, DMS was converted primarily to CS2, methane (CH4), acetylene (C2H2), ethylene (C2H4), and hydrogen (H2), with traces of hydrogen sulfide (H2S), methyl mercaptan (CH3SH), and dimethyl disulfide. In an O2-containing environment, the species detected were SO2, CS2, carbonyl sulfide, carbon dioxide (CO2), CH4, C2H4, C2H2, H2, formaldehyde, and methanol. Differences in yield of products were functions of the amounts of added O2 and the applied power. This study provided useful information for gaining insight into the reaction pathways for the DMS dissociation and the formation of products in the plasmolysis and conversion processes. 相似文献