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291.
Extracellular polymeric substances (EPS) are organic metabolic compounds excreted by microorganisms. They largely impact microbial aggregate structures and functions. Extracellular polysaccharides (EP) in EPS are responsible for the formation of microbial aggregates. In this work, we successfully separated and characterized EP from EPS of the bacterium Bacillus megaterium TF10. Extraction of EP from EPS was optimized using Sevag''s reagent. Chemical characteristics, functional groups, and molecular weight (MW) distribu-tion of EP were compared with the harvested EPS and soluble microbial products (SMP). We found that the polymers of lower MW and free proteins were successfully removed by Sevag''s reagent. The higher MW components of EPS were predominantly polysaccharides, while the polymers of lower MW tended to secrete to the supernatant and were described as SMP. A part of the proteins in the EP was polysaccharide-bonded. Our results can be further used in elucidating the complex flocculation mechanisms in which EP play a major role. 相似文献
292.
Runmiao Xue Ariel Donovan Haiting Zhang Yinfa M Craig Adams John Yang Bin Hu Enos Inniss Todd Eichholz Honglan Shi 《环境科学学报(英文版)》2018,30(2):82-91
When adding sufficient chlorine to achieve breakpoint chlorination to source water containing high concentration of ammonia during drinking water treatment, high concentrations of disinfection by-products(DBPs) may form. If N-nitrosamine precursors are present, highly toxic N-nitrosamines, primarily N-nitrosodimethylamine(NDMA), may also form. Removing their precursors before disinfection should be a more effective way to minimize these DBPs formation. In this study, zeolites and activated carbon were examined for ammonia and N-nitrosamine precursor removal when incorporated into drinking water treatment processes.The test results indicate that Mordenite zeolite can remove ammonia and five of seven N-nitrosamine precursors efficiently by single step adsorption test. The practical applicability was evaluated by simulation of typical drinking water treatment processes using six-gang stirring system. The Mordenite zeolite was applied at the steps of lime softening, alum coagulation, and alum coagulation with powdered activated carbon(PAC) sorption. While the lime softening process resulted in poor zeolite performance, alum coagulation did not impact ammonia and N-nitrosamine precursor removal. During alum coagulation, more than67% ammonia and 70%–100% N-nitrosamine precursors were removed by Mordenite zeolite(except 3-(dimethylaminomethyl)indole(DMAI) and 4-dimethylaminoantipyrine(DMAP)). PAC effectively removed DMAI and DMAP when added during alum coagulation. A combination of the zeolite and PAC selected efficiently removed ammonia and all tested seven N-nitrosamine precursors(dimethylamine(DMA), ethylmethylamine(EMA), diethylamine(DEA), dipropylamine(DPA), trimethylamine(TMA), DMAP, and DMAI) during the alum coagulation process. 相似文献
293.
The effect of K deactivation on V_2O_5/WO_3-TiO_2 and Ce-doped V_2O_5/WO_3-TiO_2 catalysts in the selective catalytic reduction(SCR) of NOxby NH_3 was studied.Ce-doped V_2O_5/WO_3-TiO_2 showed significantly higher resistance to K deactivation than V_2O_5/WO_3-TiO_2.Ce-doped V_2O_5/WO_3-TiO_2 with K/V = 4(molar ratio) showed 90% NOxconversion at 350°C,whereas in this case V_2O_5/WO_3-TiO_2 showed no activity.The fresh and K-poisoned V_2O_5/WO_3-TiO_2 and Ce-doped V_2O_5/WO_3-TiO_2 catalysts were investigated by means of in situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS),NH_3-temperature progress decomposition(NH_3-TPD),X-ray photoelectron spectroscopy(XPS) and H2-temperature program reduction(H_2-TPR).The effect of Ce doping on the improving resistance to K of V_2O_5/WO_3-TiO_2 were discussed. 相似文献
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随着高耗水农业的快速发展,城镇人口的急剧增加,加上持续的干旱,唐海县地下水长期处于超采状态,引起上覆咸水侵染地下淡水。分析1989—1998与2008年深层地下水氯离子浓度变化、1981—2007年咸水顶板埋深变化以及全县工农业布局,将唐海县划分为咸(海)水入侵的高度敏感区、较敏感区、一般敏感区和不敏感区,并进一步提出遏制咸(海)水入侵的措施。 相似文献
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开展幼儿环境教育实践的目的是让幼儿成为环境的主人,引导他们自主地欣赏,观察日常生活中具体的环境要素和环境问题,使他们懂得我们周围的环境与人类的一切活动息息相关,并使幼儿逐步养成与环境友善的行为习惯。 相似文献
300.
史少帅 《安全.健康和环境》2010,10(10):22-24,34
根据CFB锅炉运行的特点,重点分析了大型CFB锅炉存在的锅炉磨损、冷渣器故障、给煤系统故障、浇注料破坏脱落以及锅炉膨胀等安全问题,提出对策措施。 相似文献