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1.
Selective demineralization of water by nanofiltration application to the defluorination of brackish water 总被引:4,自引:0,他引:4
Nanofiltration is generally used to separate monovalent ions from divalent ions, but it is also possible to separate ions of the same valency by careful application of the transfer mechanisms involved. Analysis of the retention of halide salts reveals that small ions like fluoride are the best retained, and that this is even more marked under reduced pressure when selectivity is greatest. The selectivity desalination of fluorinated brackish water is hence feasible and drinking water can be produced directly at much lower cost than using reverse osmosis by optimizing the pressure for the type of water treated. 相似文献
2.
Globally distributed and highly stable, perfluorooctanoic acid (PFOA) has prompted much concern regarding its accumulation in the natural environment and its threats to ecosystems. Therefore, it is desirable to develop an effective treatment against PFOA pollution. In this study, a photo-reduction method is developed and evaluated for the decomposition of perfluorooctanoic acid (PFOA) in aqueous phase with potassium iodide (KI) as a mediator. The experiment was conducted under 254 nm irradiation at room temperature and pH 9 under anaerobic conditions. Ultraviolet photolysis of iodide solutions led to the generation of hydrated electrons (eaq−, Eaq/e°= −2.9 V), which contributed to the defluorination of PFOA. Defluorination was confirmed by fluoride release of 98%, indicating almost complete defluorination of PFOA. Kinetic analysis indicated that the PFOA decomposition fit the first-order model with a rate constant of 7.3 × 10−3 min−1. Besides fluoride ions, additional intermediates identified and quantified include formic acid, acetic acid, and six short-chain perfluorocarboxylic acids (C1-C6). Furthermore, small amounts of CF3H and C2F6 were also detected as reaction products by using GC/MS. With observation of the degradation products and verification via an isotopic labeling method, two major defluorination pathways of PFOA are proposed: direct cleavage of C-F bonds attacked by hydrated electrons as the nucleophile; and stepwise removal of CF2 by UV irradiation and hydrolysis. This method was applied to the decomposition of PFOA in wastewater issued from a fluorochemical plant and proved to be effective. 相似文献
3.
Effects of water chemistry on arsenic removal from drinking water by electrocoagulation 总被引:1,自引:0,他引:1
Wei WanTroy J. Pepping Tuhin BanerjiSanjeev Chaudhari Daniel E. Giammar 《Water research》2011,45(1):384-392
Exposure to arsenic through drinking water poses a threat to human health. Electrocoagulation is a water treatment technology that involves electrolytic oxidation of anode materials and in-situ generation of coagulant. The electrochemical generation of coagulant is an alternative to using chemical coagulants, and the process can also oxidize As(III) to As(V). Batch electrocoagulation experiments were performed in the laboratory using iron electrodes. The experiments quantified the effects of pH, initial arsenic concentration and oxidation state, and concentrations of dissolved phosphate, silica and sulfate on the rate and extent of arsenic removal. The iron generated during electrocoagulation precipitated as lepidocrocite (γ-FeOOH), except when dissolved silica was present, and arsenic was removed by adsorption to the lepidocrocite. Arsenic removal was slower at higher pH. When solutions initially contained As(III), a portion of the As(III) was oxidized to As(V) during electrocoagulation. As(V) removal was faster than As(III) removal. The presence of 1 and 4 mg/L phosphate inhibited arsenic removal, while the presence of 5 and 20 mg/L silica or 10 and 50 mg/L sulfate had no significant effect on arsenic removal. For most conditions examined in this study, over 99.9% arsenic removal efficiency was achieved. Electrocoagulation was also highly effective at removing arsenic from drinking water in field trials conducted in a village in Eastern India. By using operation times long enough to produce sufficient iron oxide for removal of both phosphate and arsenate, the performance of the systems in field trials was not inhibited by high phosphate concentrations. 相似文献
4.
M. N. Saprykina 《Journal of Water Chemistry and Technology》2012,34(5):240-245
A new design of the electrocoagulation apparatus consisting of an inert anode and cathode made of stainless steel was developed. The formation of a coagulant takes place due to the corrosion of ferrous plates located in the anode plane. The following optimum parameters for the operation of the apparatus were defined: current density??21 mA/cm2, current strength??60 mA, area of ferrous plates??3 cm2. The application of this apparatus makes possible to convert efficiently Fe2+ to Fe3+ allowing the user to reduce the consumption of coagulant and remove to the maximum extent contaminants including micromycetes from water. 相似文献
5.
Serge Tchamango Charles P. Nanseu-Njiki Dimiter Hadjiev 《The Science of the total environment》2010,408(4):947-251
This work sets out to examine the efficiency of an electrolytic treatment: electrocoagulation, applied to dairy effluents. The experiments were carried out using a soluble aluminium anode on artificial wastewater derived from solutions of milk powder. The flocks generated during this treatment were separated by filtration. The analysis of the filtrates showed that the chemical oxygen demand (COD) was reduced by up to 61% while the removal of phosphorus, nitrogen contents, and turbidity were 89, 81 and 100%, respectively. An analogous treatment applied to phosphate and lactose solutions revealed that lactose was not eliminated, a fact that could account for the rather poor lowering of the COD. Compared to the chemical coagulation treatment with aluminium sulphate, the efficiency of the electrocoagulation technique was almost identical. However the wastewaters treated by electrocoagulation differed by the fact that they exhibited a lower conductivity and a neutral pH value (by contrast to the acid nature of the solution treated by the chemical coagulation). This result (low conductivity, neutral pH) tends to show that it may be possible to recycle the treated water for some industrial uses. Moreover, the electrocoagulation process uses fewer reagents: the mass of the aluminium anode dissolved during the treatment is lower compared to the quantity of the aluminium salt used in chemical coagulation. These two observations clearly show that the electrocoagulation technique is more performing. 相似文献
6.
Comparative study of arsenic removal by iron using electrocoagulation and chemical coagulation 总被引:1,自引:0,他引:1
This research studied As(III) and As(V) removal during electrocoagulation (EC) in comparison with FeCl3 chemical coagulation (CC). The study also attempted to verify chlorine production and the reported oxidation of As(III) during EC. Results showed that As(V) removal during batch EC was erratic at pH 6.5 and the removal was higher-than-expected based on the generation of ferrous iron (Fe2+) during EC. As(V) removal by batch EC was equal to or better than CC at pH 7.5 and 8.5, however soluble Fe2+ was observed in the 0.2-μm membrane filtrate at pH 7.5 (10-45%), and is a cause for concern. Continuous steady-state operation of the EC unit confirmed the deleterious presence of soluble Fe2+ in the treated water. The higher-than-expected As(V) removals during batch mode were presumed due to As(V) adsorption onto the iron rod oxyhydroxides surfaces prior to the attainment of steady-state operation. As(V) removal increased with decreasing pH during both CC and EC, however EC at pH 6.5 was anomalous because of erratic Fe2+ oxidation. The best adsorption capacity was observed with CC at pH 6.5, while lower but similar adsorption capacities were observed at pH 7.5 and 8.5 with CC and EC. A comparison of As(III) adsorption showed better removals during EC compared with CC possibly due to a temporary pH increase during EC. In contrast to literature reports, As(III) oxidation was not observed during EC, and As(III) adsorption onto iron hydroxides during EC was only 5-30% that of As(V) adsorption. Also in contrast to literature, significant Cl2 was not generated during EC, in fact, the rods actually produced a significant chlorine demand due to reduced iron oxides on the rod. Although Cl2 generation and As(III) oxidation are possible using a graphite anode, a combination of graphite and iron rods in the same EC unit did not produce As(III) oxidation. However, a two-stage process (graphite anode followed by iron anode in separate chambers) was effective in As(III) oxidation and removal. The competing ions, silica and phosphate interfered with As(V) adsorption during both CC and EC. However, the degree of interference depends on the concentration and presence of other competing ions. In particular, the presence of silica lowered the effect of phosphate with increasing pH due to silica’s own significant effect at high pHs. 相似文献
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随着我国对粘土实心砖限时禁用政策的实施,各地利用煤矸石、页岩等工业废渣替代粘土生产烧结空心砖的建设项目越来越多.然而这些废渣在焙烧过程中释放出的SO2、HF等有害气体,严重影响人体健康、动植物的生长,破坏生态环境,给国民经济造成了巨大的损失.据有关资料介绍,砖瓦行业应对因排放SO2而引起的酸雨污染负有40%的责任.我国对这些有害气体的排放有明确的控制指标,国家标准GB9078-1996<工业窑炉大气污染物排放标准>中,对二类区内砖瓦行业窑炉排放烟气中要求SO2浓度<850mg/m3,氟化物浓度<6mg/m3,随着国家对环保的重视,排放标准在未来几年将更为严格. 相似文献
9.
A. H. Mahvi M. Malakootian M. R. Heidari 《Journal of Water Chemistry and Technology》2011,33(6):377-385
Removal of natural organic matter (NOM) is one of the most important objectives of water treatment plants but reducing these
pollutants either present in water as dissolved or suspended form is not as efficient as is required in conventional treatment
plants. The purpose of this study was comparison performance of composite polyaluminum silicate chloride (PASiC) and electrocoagulation
(EC) process by aluminum electrodes in NOM removal from raw surface water. In this study, the effects of turbidity, total
organic compounds (carbons) (TOC), adsorption at a wavelength of 254 nm (UV254), chemical oxygen demand (COD), alkalinity,
residual aluminum in finished water by application of EC process and PASiC were investigated. The results demonstrate that
PASiC coagulant at optimum concentration of 1–5 ml/L was capable of removing TOC, COD, U.V., and turbidity from raw water
by 93.77, 93.5, 63 and 95 %, respectively. In contrast, EC process, removed TOC, COD, UV and turbidity from raw water by 89,
99.75, 37 and 50%, respectively. The pilot-scale results demonstrated the significant advantage of PASiC compared to EC process
in removal of NOM and turbidity form raw water. Residual aluminum in finished water was below the recommended WHO guidelines
0.2 mg/L for both processes. Finally it can be concluded that PASiC and EC process are reliable, efficient and cost-effective
methods for removal of NOM from surface water. 相似文献
10.
S. K. Smolin L. V. Nevinnaya A. V. Sinel’nikova N. Z. Titarenko N. A. Klimenko 《Journal of Water Chemistry and Technology》2009,31(4):256-263
The paper has studied features of biosorption filtration of phenol, o-nitrophenol, and o-aminobenzoic acid through activated carbon. The study has shown antibate relationship between the value of the variation
of free energy of Gibbs adsorption and the removal rate from the water of aromatic compounds by a layer of activated carbon
in the mode of biostabilization. 相似文献
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E. S. Melnik 《Journal of Water Chemistry and Technology》2016,38(1):45-50
An alternative design of electrocoagulator for the chromium-containing wastewater treatment has been proposed. The processes of electrocoagulation treatment of such water were investigated. Effective design and operating parameters have been determined that allow the specified wastewater to be purified in accordance with normative requirements. 相似文献
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E. G. Filatova 《Journal of Water Chemistry and Technology》2016,38(3):167-172
The article proposes results on optimization of electrocoagulation technology of purifying of ions of heavy metals. A phase composition of electrogenerated aluminum hydroxide in a neutral medium was established. Found conditions for floatation of the mass of coagulated pollutants and their successful removal off water surface. Optimized are parameters of coagulation with aluminum anodes presented in an upgraded edition of SNiPa 2.04.03-85, namely: current anodic density, specific aluminum consumption, etc. 相似文献
15.
落石运动模式与运动特征现场试验研究 总被引:1,自引:0,他引:1
落石试验是寻找落石运动敏感因素、探求运动规律和获取运动参数的较好方法.为厘清落石形状、块度大小和运动模式对其运动特征的影响规律,进行了112块落石现场试验;以落石形状、质量和运动弹跳次数为变量,统计分析了水平运动距离、运动速度的变动规律.试验结果表明:不管何种形状落石,运动模式均为滚动和弹跳,无明显滑动段;切坡平台和公... 相似文献
16.
在简要介绍研究区水文地质条件的基础上,初步选定了三种开采方案,并用数学模型的有限元法评价了地下水资源的允许开采量,同时提出和论证了最佳开采方案,这对于研究区地下水的合理开发具有重要的指导意义。 相似文献
17.
Comparison of electrocoagulation and chemical coagulation pretreatment for enhanced virus removal using microfiltration membranes 总被引:1,自引:0,他引:1
This research studied virus removal by iron electrocoagulation (EC) followed by microfiltration (MF) in water treatment using the MS2 bacteriophage as a tracer virus. In the absence of EC, MF alone achieved less than a 0.5-log removal of MS2 virus, but, as the iron-coagulant dosage increased, the log virus removal increased dramatically. More than 4-log virus removal, as required by the Surface Water Treatment Rule, was achieved with 6-9 mg/L Fe3+. The experimental data indicated that at lower iron dosages and pH (<∼8 mg Fe/L and pH 6.3 and 7.3) negatively charged MS2 viruses first adsorbed onto the positively charged iron hydroxide floc particles before being removed by MF. At higher iron dosages and pH (>∼9 mg Fe/L and pH 8.3), virus removal was attributed predominantly to enmeshment and subsequent removal by MF. Additionally, the experimental data showed no obvious influence of ionic strength in the natural water range of 10−7-10−2 M on MS2 virus removal by EC-MF. Finally, EC pretreatment significantly outperformed chemical coagulation pretreatment for virus removal. The proposed mechanism for this improved performance by EC is that locally higher iron and virus concentrations and locally lower pH near the anode improved MS2 enmeshment by iron flocs as well as adsorption of MS2 viruses onto the iron floc particles. 相似文献
18.
《Planning》2016,(6)
目的:总结和分析寄生虫感染患者外周血嗜酸性粒细胞的临床变化特点。
方法:收集北京协和医院2010年1月至2014年12月期间收治并明确诊断为寄生虫感染的患者临床资料,回顾性分析患者外周血嗜酸性粒细胞与感染寄生虫种类及临床受累系统的相关情况。
结果:符合纳入标准的寄生虫感染患者共87例,33.3%的患者(29/87)外周血嗜酸性粒细胞绝对计数升高,14.9%(13/87)的患者绝对计数高于1.5×109/L。卫氏并殖吸虫(100%)、血吸虫(83.3%)及华支睾吸虫(57.1%)是引起外周血嗜酸性粒细胞增高的最常见三种寄生虫。呼吸系统和消化系统受累患者出现外周血嗜酸性粒细胞升高的最高,分别有71.4%及50%,出现嗜酸性粒细胞明显升高的分别有28.6%及33.3%。
结论: 出现外周血嗜酸性粒细胞增高的患者比例随感染寄生虫种类或主要受累脏器部位不同而有所不同。当遇到高嗜酸细胞血症患者时,应注意寄生虫感染的鉴别诊断。 相似文献
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《建设科技(建设部)》2009,(23):34-34
以创建全国节水型城市为契机,沈阳市城市节水管理力度也在不断加强,目前,沈阳市工业用水单位已基本纳入计划用水管理范围,对日供水量5立方米以上的大生活用水单位也逐步实行了计划管理。在工业用水方面,积极采用循环用水、一水多用、串联使用和污水处理回用等节水技术措施,使全市工业用水重复利用率达到80%,间接冷却水循环利用率达到95.5%,城市污水处理率达到81%.工业废水排放达标率达到100%。 相似文献