Effect of dissolved metal ions on PCE decomposition by gamma-rays

This study investigates the effect of initial tetrachloroethylene (PCE) concentration, irradiation dose and dissolved metal ions such as Cr3+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+ and Zn2+ on removal of PCE by gamma irradiation. The amount of removed PCE decreased with increase in initial PCE concentration and increased with increase in irradiation dose. PCE removal reached a maximum in the presence of Fe3+, while Cu2+ strongly hindered PCE decomposition. Except for Cu2+, the amount of removed PCE in the presence of metal ions was linearly dependent on the standard reduction potential of the metal ions. The extraordinary inhibition of Cu2+ in PCE removal was caused by the action of Cu2+ as a strong *OH scavenger, that was directly confirmed by electron paramagnetic resonance spectroscopy.     

乙酸强化下通电方式对电动修复受重金属污染高岭土的影响

电动修复作为一种绿色的土壤污染修复技术,因具有成本低、操作简单、不易造成二次污染等特点而有巨大的应用前景。以高岭土作为实验材料,研究了不同电场施加方式条件下铜、锌重金属的去除规律。为了进一步提高效率,实验配制pH为3.5的乙酸溶液并加入高岭土中,加入后可以加快土壤酸化并降低重金属沉淀区域的影响。相比于电解液为蒸馏水的情况,pH突变点向阴极靠近,从S3、S4片层移动到了S4、S5片层。加入乙酸后,实验最大电流和反应384 h后的电流相比未加乙酸升高较为明显。在相同条件下,电场强度为0.5 V·cm-1时反应最高电流为60~139 mA,电场强度为1.0 V·cm-1时为108~170 mA,电场强度为1.5 V·cm-1时为152~290 mA。在相同条件下反应384 h后的实验最低电流,电场强度为0.5 V·cm-1时为33~70 mA,电场强度为1.0 V·cm-1时为41~83 mA,电场强度为1.5 V·cm-1时为71~123 mA。高电场强度有利于去除土壤中的低浓度重金属污染物。相比电极室未添加乙酸的实验组,污染物去除率提高15%以上。     

Effect of complexation with humic substances on diffusion of metal ions in water

Most studies on diffusion of metal ions in various water-rock systems have dealt with free ions (hydrated ions). However, it is often the case that metal ions are dissolved as complexed species such as with humic substances (HS) in natural waters. Hence, we need to study the diffusion behavior of these complexes in order to understand fully the diffusion phenomenon in natural. In this study, the diffusion coefficients of free metal ions (M(z+)) and their complexes with HS (M-HS) were compared to understand the effect of complexation with HS on the diffusion of metal ions such as Co(2+), Cd(2+), and rare earth elements (REE(3+)). Although the diffusion coefficients of free metal ions depend on ionic potential, such dependence was not observed in the presence of HS. Comparing the diffusion coefficients of metal complexes with ethylenediaminetetraacetate (EDTA), fulvic acid, and humic acid showed that the molecular weight (MW), or the size of the ligand, is of primary importance for the diffusion of M-HS. As a consequence, the diffusion coefficients of all REE(3+) were similar in the presence of HS, while they were different in the absence of HS due to the different size of each REE(3+). The similarity among the diffusion coefficients of REE-HS was caused by the much larger size of HS compared with each ion. However, the distribution coefficients of M-HS were not similar among REE(3+), Cd(2+), and Co(2+). REE(3+) and Cd(2+) which have higher affinities for larger MW fraction in HS diffused slower than Co(2+) which favors smaller MW fraction. The results show that the affinity for different MW fractions among HS controls the diffusion of M-HS, which must be important to predict precisely the diffusion behavior of metal ions bound to HS in natural systems.     

Effects of humic substances on the decomposition of 2,4-dichlorophenol by ozone after extraction from water into acetic acid through activated carbon

The objectives of this study are to clarify the behavior of humic substances throughout the processes of 2,4-dichlorophenol (2,4-DCP) adsorption on granular activated carbon (GAC) from water and extraction into acetic acid, and the influence of the extracted humic substances on the decomposition of 2,4-DCP by ozone in the acetic acid. The adsorption capacity of GAC for 2,4-DCP was not influenced by the humic substances preloaded to have equilibrium concentration of 24.9mg Cl(-1) (14.5mg Cg(-1)). The adsorption capacity of GAC for 2,4-DCP decreased to one tenth of new GAC after the first adsorption-extraction step because of only 16% desorption in the first step. However, 2,4-DCP adsorbed on GAC was completely extracted after the second step suggesting that GAC can be used as adsorbent to transfer 2,4-DCP from water to acetic acid. The concentration ratio of 2,4-DCP from water into acetic acid was around 2x10(5), whereas the concentration ratio of humic substances was about 3.5, indicating that 2,4-DCP was selectively adsorbed and extracted by this system. The first order degradation rate constant for 2,4-DCP by ozone in acetic acid increased with the addition of humic substances. The rate constant with 16mg Cl(-1) of humic substances was 2.6 times as high as that without humic substances. Humic substances behaved as a promoter for the degradation of 2,4-DCP by ozone.     

Competitive complexation of metal ions with humic substances

The surface complexation model was applied to simulate the competitive complexation of Ni, Ca and Al with humic substances. The presence of two types of binding sites in humic acid, carboxylic and phenolic functional groups, were assumed at both low and high pH conditions. Potentiometric titrations were used to characterize the intrinsic acidity constants of the two binding sites and their concentrations. It was found that the diffuse-layer model (DLM) could fit the experimental data well under different experimental conditions. Ni and Ca ions strongly compete with each other for reactions with the humic acid but Al showed little influence on the complexation of either Ni or Ca due to its hydrolysis and precipitation at pH approximately 5. The surface complexation constants determined from the mono-element systems were compared with those obtained from the multiple-element system (a mixture of the three metal ions). Results indicate little changes in the intrinsic surface complexation constants. Modeling results also indicate that high concentrations of Ca in the contaminated groundwater could strongly inhibit the complexation of Ni ions whereas an increase in pH and the humic concentration could attenuate such competitive interactions. The present study suggests that the surface complexation model could be useful in predicting interactions of the metal ions with humic substances and potentially aid in the design of remediation strategies for metal-contaminated soil and groundwater.     

Photocatalytic ozonation of terephthalic acid: a by-product-oriented decomposition study

Terephthalic acid (TA) is considered as a refractory model compound. For this reason, the TA degradation usually requires a prolonged reaction time to achieve mineralization. In this study, vanadium oxide (V_xO_y) supported on titanium oxide (TiO₂) served as a photocatalyst in the ozonation of the TA with light-emitting diodes (LEDs), having a bandwidth centered at 452 nm. The modified catalyst (V_xO_y/TiO₂) in combination with ozone and LEDs improved the TA degradation and its by-products. The results obtained by this system were compared with photolysis, single ozonation, catalytic ozonation, and photocatalytic ozonation of V_xO_y/TiO₂ with UV lamp. The LED-based photocatalytic ozonation showed almost the same decomposition efficiency of the TA, but it was better in comparison with the use of UV lamp. The oxalic acid accumulation, as the final product of the TA decomposition, was directly influenced by either the presence of V_xO_y or/and the LED irradiation. Several by-products formed during the TA degradation, such as muconic, fumaric, and oxalic acids, were identified. Besides, two unidentified by-products were completely removed during the observed time (60 min). It was proposed that the TA elimination in the presence of V_xO_y/TiO₂ as catalyst was carried out by the combination of different mechanisms: molecular ozone reaction, indirect mechanism conducted by ·OH, and the surface complex formation.     

Effect of metal ions and humic acid on the dechlorination of tetrachloroethylene by zerovalent iron

The dechlorination of tetrachloroethylene (PCE) by zerovalent iron (Fe(0)) in the presence of metal ions and humic acid was investigated. In the absence of metal ion and humic acid, 64% of the initial PCE was dechlorinated after 125 h with the production of ethane and ethene as the major end products. The dechlorination followed pseudo-first-order kinetics and the normalized surface rate constant (k(SA)) for PCE dechlorination was (3.43+/-0.61)x10(-3)lm(-2)h(-1). Addition of metal ions enhanced the dechlorination efficiency and rate of PCE, and the enhancement effect followed the order Ni(II)>Cu(II)>Co(II). The k(SA) for PCE dechlorination in the presence of metal ions were 2-84 times higher than that in the absence of metal ions. X-ray photoelectron spectroscopy (XPS) showed that Cu(II) and Ni(II) were reduced by Fe(0) to zerovalent metals, and resulted in the formation of bimetallic system to accelerate the dechlorination reaction. On the contrary, humic acid out-competed the reactive sites on iron surface with PCE, and subsequently decreased the dechlorination efficiency and rate of PCE by Fe(0). However, the reactivity of Fe(0) for PCE dechlorination in the presence of metal ions and humic acid increased by a factor of 3-161 when compared to the iron system containing humic acid alone. Since humic acid and metal ions are the most often found co-existing compounds in the contaminated aquifers with chlorinated hydrocarbons, results obtained in this study is useful to better understand the feasibility of using Fe(0) for long-term application to the remediation of contaminated sites.     

Degradation of acetic acid with sulfate radical generated by persulfate ions photolysis

The photolysis of was studied for the removal of acetic acid in aqueous solution and compared with the H₂O₂/UV system. The radicals generated from the UV irradiation of ions yield a greater mineralization of acetic acid than the OH radicals. Acetic acid is oxidized by radicals without significant formation of intermediate by-products. Increasing system pH results in the formation of OH radicals from radicals. Maximum acetic acid degradation occurred at pH 5. The results suggest that above this pH, competitive reactions with the carbon mineralized inhibit the reaction of the solute with and also OH radicals. Scavenging effects of two naturally occurring ions were tested; in contrast to ions, the presence of Cl⁻ ions enhances the efficiency of the /UV process towards the acetate removal. It is attributed to the formation of the Cl radical and its great reactivity towards acetate.     

臭氧对饮用水管网中溶解性有机物的影响

利用生物膜环状反应器模拟配水管网系统,将水厂砂滤池出水经过臭氧氧化后投加氯然后进入该模拟管网,另外把水厂砂滤池出水加氯后通入另一模拟管网作为对照实验。通过对两管网出水余氯、总铁、浊度、溶解性有机物(DOC)、以及消毒副产物三卤甲烷(THMs)、卤乙酸(HAAs)生成情况的测定,研究了饮用水臭氧处理对管网出水水质的影响。单因素方差分析结果表明,两管网出水的余氯、总铁、浊度以及THMs、HAAs含量相差不大,但DOC在臭氧氯管网中消耗较多。同时通过高效凝胶色谱(HPSEC), 红外光谱(FTIR)和三维荧光光谱(EEM)表征了不同管网进出水DOC变化,结果表明,臭氧氧化后的管网出水中溶解性有机物荧光光谱中三区富里酸和五区腐植酸荧光峰值(ФⅢ+Ⅴ,n)减小较多,管网出水消毒副产物稍有增加。     

The formation and fate of chlorinated organic substances in temperate and boreal forest soils

Background, aim and scope  Chlorine is an abundant element, commonly occurring in nature either as chloride ions or as chlorinated organic compounds (OCls). Chlorinated organic substances were long considered purely anthropogenic products; however, they are, in addition, a commonly occurring and important part of natural ecosystems. Formation of OCls may affect the degradation of soil organic matter (SOM) and thus the carbon cycle with implications for the ability of forest soils to sequester carbon, whilst the occurrence of potentially toxic OCls in groundwater aquifers is of concern with regard to water quality. It is thus important to understand the biogeochemical cycle of chlorine, both inorganic and organic, to get information about the relevant processes in the forest ecosystem and the effects on these from human activities, including forestry practices. A survey is given of processes in the soil of temperate and boreal forests, predominantly in Europe, including the participation of chlorine, and gaps in knowledge and the need for further work are discussed. Results  Chlorine is present as chloride ion and/or OCls in all compartments of temperate and boreal forest ecosystems. It contributes to the degradation of SOM, thus also affecting carbon sequestration in the forest soil. The most important source of chloride to coastal forest ecosystems is sea salt deposition, and volcanoes and coal burning can also be important sources. Locally, de-icing salt can be an important chloride input near major roads. In addition, anthropogenic sources of OCls are manifold. However, results also indicate the formation of chlorinated organics by microorganisms as an important source, together with natural abiotic formation. In fact, the soil pool of OCls seems to be a result of the balance between chlorination and degradation processes. Ecologically, organochlorines may function as antibiotics, signal substances and energy equivalents, in descending order of significance. Forest management practices can affect the chlorine cycle, although little is at present known about how. Discussion  The present data on the apparently considerable size of the pool of OCls indicate its importance for the functioning of the forest soil system and its stability, but factors controlling their formation, degradation and transport are not clearly understood. It would be useful to estimate the significance and rates of key processes to be able to judge the importance of OCls in SOM and litter degradation. Effects of forest management processes affecting SOM and chloride deposition are likely to affect OCls as well. Further standardisation and harmonisation of sampling and analytical procedures is necessary. Conclusions and perspectives  More work is necessary in order to understand and, if necessary, develop strategies for mitigating the environmental impact of OCls in temperate and boreal forest soils. This includes both intensified research, especially to understand the key processes of formation and degradation of chlorinated compounds, and monitoring of the substances in question in forest ecosystems. It is also important to understand the effect of various forest management techniques on OCls, as management can be used to produce desired effects.     

臭氧氧化对二级出水有机物(EfOM)特性机制的影响

开展了臭氧氧化对二级出水有机物(effluent organic matter,EfOM)的去除效能研究,并进一步采用超滤分离、三维荧光光谱等方法,系统研究了不同臭氧投加量下,EfOM的分子量分布、亲疏水特性以及荧光特性的变化规律。结果表明,臭氧化去除EfOM的效果有限,但能够有效分解二级出水中具有强烈紫外吸收的有机物。此外,臭氧能优先氧化分解二级出水中大分子有机物,有效提高二级出水的可生化性。臭氧氧化过程中,分子质量(molecular weight,MW)>100 kDa的有机物组分被完全氧化分解,10 kDa< MW< 100 kDa和1 kDa< MW< 10 kD的有机物组分含量总体呈下降趋势,而MW<1 kDa的有机物组分随臭氧投加时间的延长含量不断上升。臭氧化后,EfOM中疏水组分减少,亲水组分升高;酸性组分减少。随着臭氧投量的增加,蛋白质与腐殖酸类物质的荧光吸收强度迅速下降。     

白洋淀沉水植物腐解溶解性有机物与重金属的相互作用

针对白洋淀秋冬季节水生植物腐解释放大量溶解性有机物(DOM)的问题,利用紫外可见光谱(UV-Vis)和激发发射光谱(EEMs)结合平行因子分析法(PARAFAC)对DOM样品进行表征和分离。实验结果表明,PARAFAC共分离出4种组分(C1、C2、C3和C4),类腐殖酸组分C1和C2、类蛋白组分C3、含有类蛋白组分和类富里酸组分共同组成的C4。此外,对样品进行荧光淬灭滴定实验来研究DOM与重金属(Cu (Ⅱ)和Cd (Ⅱ))的相互作用,发现Cu (Ⅱ)对所有组分都存在明显的淬灭效果,并可以较好地拟合出络合常数(lgK),而Cd (Ⅱ)只与C4有较好的络合效果,这是由于C4中的类富里酸成分所造成的。研究进一步发现,样品U2中类蛋白组分C3和C4对重金属的淬灭效果比样品U0的类蛋白组分明显。这是由于样品U2中所添加的植物量较多,而植物腐解所释放的主要成分为类蛋白物质,有助于增强类蛋白组分的络合能力。研究结果可为科学评价水生植物腐解释放DOM对水体中重金属的迁移转化提供依据。     

2,4-二氯苯氧乙酸臭氧氧化动力学研究

研究了臭氧氧化条件下2,4-二氯苯氧乙酸在鼓泡反应器内的去除动力学,考察了pH、温度、气体流量、初始浓度等因素对反应的影响,得到反应动力学速率常数与温度和pH的关系。     

铜铈二元材料催化臭氧降解草酸的研究

采用水热/焙烧法合成了铜铈二元复合催化剂(CuO-CeO2),并通过X射线衍射、扫描电子显微镜和透射电子显微镜对其进行了表征.以草酸为模型化合物,应用CuO-CeO2为催化剂进行连续流催化臭氧降解动态试验.结果表明:25 min时草酸去除率达到97.66％,远高于臭氧(2.66％)、CuO/臭氧(7.38％)和CeO2...     

含铁化合物对有机氯化物的脱氯处理技术研究

综述了钯 /铁、二硫化铁、硫化铁、三氧化二铁、绿锈等含铁化合物在降解六氯乙烷、四氯化碳、五氯乙烷、四氯乙烷、三氯乙烷、三氯乙烯、四氯乙烯等有机氯化物中的应用以及降解机理     

Removal of metal ions and humic acid from water by iron-coated filter media

Iron oxide is an excellent, regenerable adsorbent, and often controls free metals through adsorption reaction. The utilization of heating process for coating iron oxide on sand surface allowed the media to be used in a packed column. Iron-coated sand was investigated for adsorbing metal ions and natural organic matter from water by batch and column experiments. Chemical analysis (energy dispersive analysis of X-ray, EDAX) was used for characterizing the copper and lead adsorption sites on iron-coated sand. From the batch experiment results, the copper and lead ions could be removed simultaneously by the iron-coated sand in the competition adsorption system. The interaction between copper, lead ions and iron oxide on sand surface was primarily the chemical bonds. The maximum adsorption capacities of iron-coated sand for copper and lead were 0.259 mg Cu/g-sand and 1.211 mg Pb/g-sand, respectively. The presence of humic acid led to increase the adsorption of copper and lead. Results from column experiments indicated that the copper ions, lead ions and humic acid could be removed completely before the breakpoint. Consequently, the iron-coated sand may be applied for the adsorption/filtration of metal ions and natural organic matters from water.     

Decomposition of trichloroethylene and 2,4-dichlorophenol by ozonation in several organic solvents

The effects of chemical characteristics of organic solvents on the decomposition rate constants of undissociative trichloroethylene (TCE) and dissociative 2,4-dichlorophenol (2,4-DCP) by ozonation were studied. The TCE and 2,4-DCP decomposition by ozonation in organic solvents followed to the first-order reaction kinetics with respect to TCE or 2,4-DCP concentration. The orders of the rate constants among organic solvents for undissociative TCE and dissociative 2,4-DCP were different indicating that the ozonation rates for undissociative and dissociative compounds were dependent on the chemical property of organic solvent. The decomposition of undissociative TCE by ozonation was a simple electrophilic reaction, which was dependent on acceptor number (AN) of the solvent. On the other hand, the decomposition of dissociative 2,4-DCP was dependent on by the dissociation of the compounds and would be dependent on donor number (DN) of the solvent. Finally, TCE in acetic acid was transformed to chlorinated intermediates and chloride ion and then these intermediates were continuously oxidized to chlorine gas.     

Fate of biodegradable dissolved organic carbon produced by ozonation on biological activated carbon

The adsorption and desorption characteristics of BDOC produced by ozonation and the replacement of BDOC by non-BDOC on BAC was studied. The fate of BDOC produced by ozonation in the BAC column was also evaluated by comparative experiment between the BAC supplied with the mixture of BDOC and non-BDOC and the BAC supplied only with non-BDOC. Fulvic acids extracted from two river sediments and one forest soil were used. BDOC produced by ozonation showed the same or lower adsorption capacity than non-BDOC after biodegradation. The adsorption rate of BDOC on GAC was lower than that of non-BDOC. BDOC produced by ozonation had low desorbability and majority of BDOC produced were not replaced by non-BDOC. BDOC in the ozonated fulvic acid did not affect the breakthrough of the ozonated fulvic acid on GAC in the early stage of adsorption, suggesting that most of BDOC were biodegraded on the surface of GAC before adsorption. Therefore, the production of BDOC by ozonation before the GAC treatment is very effective for the extension of GAC service life and the reduction of DOC loading to GAC.     

金属铁还原脱氯处理有机氯化物的研究进展

本文对金属铁在还原降解六氯乙烷、四氯化碳、氯仿、三氯乙烯、四氯乙烯、二氯乙烯、氯乙烯、五氯酚、多氯联苯等有机氯化物中的应用作了评述 ,讨论了金属铁降解有机氯化物的反应机理及动力学。     

Investigation of metal ions binding of humic substances using fluorescence emission and synchronous-scan spectroscopy

The binding site interactions of IHSS humic substances, Suwannee River Humic Acid, Suwannee River Fulvic Acid, Nordic Fulvic Acid, and Aldrich Humic Acid with various metals ions and a herbicide, methyl viologen were investigated using fluorescence emission and synchronous-scan spectroscopy. The metal ions used were, Fe(III), Cr(III), Cr(VI), Pb(II), Cu(II) and Ni(II). Stern-Volmer constants, Ksv for these quenchers were determined at pH 4 and 8 using an ionic strength of 0.1 M. For all four humic substances, and at both pH studied, Fe(III) was found to be the most efficient quencher. Quenching efficiency was found to be 3-10 times higher at pH 8. The bimolecular quenching rate constants were found to exceed the maximum considered for diffusion controlled interactions, and indicate that the fluorophore and quencher are in close physical association. Synchronous-scan spectra were found to change with pH and provided useful information on binding site interactions between humic substances and these quenchers.