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441.
Sorption of iron-cyanide complexes on goethite in the presence of sulfate and desorption with phosphate and chloride 总被引:1,自引:0,他引:1
Soils are contaminated with potentially toxic iron-cyanide complexes by some industrial activities. The influence of sulfate on the sorption of the iron-cyanide complexes ferricyanide, [Fe(CN)6]3-, and ferrocyanide, [Fe(CN)6]4-, on goethite was investigated in batch experiments. The experiments were conducted as influenced by pH and varying sulfate/iron-cyanide complex concentration ratios. Furthermore, the desorption of iron-cyanide complexes sorbed on goethite was studied using phosphate and chloride solutions as influenced by pH and anion concentration. Over the whole pH range (pH 3.5 to 8), ferricyanide and sulfate showed similar affinities for the goethite surface. The extent of ferricyanide sorption strongly depended on sulfate concentrations and vice versa. In contrast, ferrocyanide sorption was only decreased (approximately 12%) by sulfate additions at pH 3.5. Ferricyanide was completely desorbed by 1 M chloride, ferrocyanide not at all. Unbuffered phosphate solutions (pH 8.3) desorbed both iron-cyanide complexes completely. Even in 70-fold excess, pH-adjusted phosphate solutions could not desorb ferrocyanide completely at pH 3.5. For ferricyanide we propose a sorption mechanism that is similar to the sulfate sorption mechanism, including outer-sphere and weak inner-sphere surface complexes on goethite. Ferrocyanide appears to form inner-sphere surface complexes. Additionally, we assume that ferrocyanide precipitates probably as a Berlin Blue-like phase at pH 3.5. Hence, ferrocyanide should be less mobile in the soil environment than ferricyanide or sulfate. 相似文献
442.
A technical and economic comparison of biofiltration and wet chemical oxidation (scrubbing) for odor control at wastewater treatment plants 总被引:2,自引:0,他引:2
Li Gao Tim C. Keener Lian Zhuang Kaniz F. Siddiqui 《Environmental Engineering and Policy》2001,2(4):203-212
An economic and technical comparison of two odor control systems, a biofilter and a chemical wet scrubber, was conducted over a 1-year time period at a large municipal wastewater treatment plant. The biofilter system was designed to remove hydrogen sulfide gas and other oxidizable sewage odors from four covered gravity sludge thickeners, a gravity sludge thickener effluent channel and an influent splitter box for the gravity sludge thickeners. The sodium hypochlorite/sodium hydroxide wet scrubber was designed to control hydrogen sulfide gas and other oxidizable sewage odors from the covered primary settling tanks, influent distribution channels and effluent channel, and the mixing tank effluent channel. The technical comparison comprised their overall removal rates and efficiencies based on inlet H2S concentrations and other operating variables. The economic comparison was designed to provide the cost per cubic meter of H2S removed for each system. Influent and effluent gas samples were collected on a weekly basis. H2S concentration levels were determined through the use of gas chromatography with a flame photometric detector. The results showed that the H2S inlet gas concentration has a seasonal change with a maximum value occurring in August and September. The effluent H2S concentration was lower than 2 ppmv for both systems for most of the samples. The efficiency for both the biofilter and wet scrubber was above 95%, and was related to the operating and ambient conditions. The economic comparison revealed that the actual unit cost for the biofilter was higher than for the wet scrubber (U.S.160 /m < SUP > 3 < /SUP > H < SUB > 2 < /SUB > S removed versus U.S.160 /m3 H2S removed versus U.S.131 /m3 H2S removed). For both the biofilter and the wet scrubber, the investment costs are affected by the size/scale of the system, the design flow and other factors. For these systems, the mulch change costs, chemical usage costs, maintenance costs and power usage costs were mainly dependent on the actual odor gas loadings which showed substantial seasonal fluctuations as a function of the seasonal temperature. The worst case conditions reported here indicate that the H2S concentrations generated during the summer months should be used to determine the design load. 相似文献
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John Box Andrew Douse Tim Kohler 《Journal of Environmental Planning and Management》1994,37(3):361-367
Many counties in England have systems of non‐statutory sites of importance for nature conservation in addition to the statutory National Nature Reserves, Sites of Special Scientific Interest and Local Nature Reserves. The paper describes the evolution of such a system over the past 20 years in the metropolitan county of the West Midlands. The system has been recognized by the local planning authorities who have included appropriate policies for the conservation of these sites in statutory development plans. The authority of such a system derives from the use of published criteria for the selection of sites, consensus over the application of these criteria, and consultation with the owners and occupiers of the sites. 相似文献
446.
By committing to green procurement, the UK government has taken a key initial step towards sustainable development. But can this be put into practice? This policy analysis explores the background to green procurement in English local government through desk research and data collection, including interviews with five local authorities. It finds that green procurement has been encouraged through legislation, providing information and dismantling barriers, but momentum was lost following the Gershon review. Implementation of the new action plan would ensure green procurement becomes embedded within government procurement. New information to link up green procurement with organisational goals would also expand the horizons of green procurement. 相似文献
447.
颗粒载体生物滴滤床处理低浓度污水对比试验研究 总被引:1,自引:0,他引:1
选用生物陶粒和Hat Creek煤两种颗粒载体,应用于滴滤床颗粒填料生物反应器模型中,进行去除有机污染物的性能对比试验研究。研究表明,生物陶粒可作为滴滤床填料去除低浓度污水中的有机污染物,但在贫营养条件时,处理效果不如Hat Creek煤;而在进水浓度或水量增加,营养不成为限定因素的运行条件下,其极限负荷与处理效果明显要优于Hat Creek煤。 相似文献
448.
Polluting firms with advanced abatement technology at their disposal have incentives or disincentives to share this technology with other polluting firms. The ‘direction’ and extent of those incentives depends on the liability rule applicable and the way technical change impacts marginal abatement costs. We establish that incentives for diffusion are socially optimal under strict liability and socially suboptimal under negligence if technical change lowers marginal abatement costs for all levels of abatement. Negligence may, however, induce better diffusion incentives than strict liability if technical change decreases (increases) marginal abatement costs for low (high) levels of abatement. 相似文献
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Alteration of DNA methylation is a major epigenetic mechanism associated with the effects of nongenotoxic carcinogens. We evaluated the effects of two environmental pollutants, hexabromocyclododecane (HBCD), 17-beta oestradiol (E(2)) as well as 5-aza 2' deoxycytidine (5AdC) on global DNA methylation levels (5-methyl 2' deoxycytidine) in the liver and gonads of the three-spine stickleback (Gasterosteus aculeatus). HBCD at 30 and 300 ng/L of water did not produce statistically significant differences in global genomic methylation in liver of female stickleback. On the other hand, the methylation inhibitor, 5-aza-2'-deoxycytidine, significantly lowered hepatic global methylation levels in these fish by 14% (P<0.05). The naturally occurring oestrogen, 17-beta oestradiol (E(2)) at 100 ng/L also decreased global DNA methylation levels in female liver but this effect was not statistically significant. In contrast, both E(2) and 5AdC caused statistically significant (P<0.001 and P<0.01 respectively) global genomic hypermethylation in the gonads of male sticklebacks although the increase seen in the female gonads was not statistically significant. The male gonad effect though unexplained may potentially be an indirect response to hypomethylation in other tissues (such as the liver) and may have important implications regarding oestrogenic effects in fish. The contrasting effects of HBCD and E(2) on global DNA methylation in stickleback should contribute to the integrated risk assessment of these environmental chemicals. 相似文献