Removal of Hexavalent Chromium-Contaminated Water and Wastewater: A Review

Cr(VI) is a well-known highly toxic metal, considered a priority pollutant. Industrial sources of Cr(VI) include leather tanning, cooling tower blowdown, plating, electroplating, anodizing baths, rinse waters, etc. This article includes a survey of removal techniques for Cr(VI)-contaminated aqueous solutions. A particular focus is given to adsorption, membrane filtration, ion exchange, and electrochemical treatment methods. The primary objective of this article is to provide recent information about the most widely used techniques for Cr(VI) removal.     

Hexavalent Chromium Removal by a Trichoderma inhamatum Fungal Strain Isolated from Tannery Effluent

A fungal strain possibly capable of removing hexavalent chromium was to be isolated from industrial effluent from a leather factory located in the city of Guadalajara, state of Jalisco, Mexico. The strain was identified as Trichoderma inhamatum by the D1/D2 domain sequence of the 28S rDNA gene. Batch cultures of T. inhamatum in media containing initial Cr(VI) concentrations from 0.83 to 2.43 mM Cr(VI) were prepared. Experimental results suggest that the fungus is capable of transforming hexavalent chromium to trivalent chromium; a transformation of a highly toxic contaminant to a low toxic form. The specific and volumetric rates of Cr(VI) reduction by T. inhamatum cultures decreased as the initial Cr(VI) concentration increased. The fungus exhibited a remarkable capacity to tolerate and completely reduce Cr(VI) concentrations up to 2.43 mM. These results indicate that the T. inhamatum fungal strain may have potential applications in bioremediation of Cr(VI)-contaminated wastewaters.     

动态条件下壳聚糖稳定纳米铁去除水体中Cr（Ⅵ）的研究

以重金属Cr（Ⅵ）为目标污染物,在两种实验条件下（实验柱Ⅰ为模拟污染水样,实验柱Ⅱ为实际污染水样）考察了壳聚糖稳定纳米铁对Cr（Ⅵ）的去除能力。实验柱Ⅰ和实验柱Ⅱ分别在第160PV和127PV时发生了击穿效应。与实验柱Ⅰ相比,实验柱Ⅱ中壳聚糖稳定纳米铁对Cr（VI）的去除能力降低了25％。SEM表征显示,实验柱Ⅱ中壳聚糖稳定纳米铁的表面形成了许多葡萄状晶体,它们的存在导致实验柱Ⅱ中纳米铁的去除能力明显低于实验柱Ⅰ。XPS表征显示,由于Ca和Mg的氢氧化物替代了部分铁氢氧化物,导致实验柱Ⅱ中壳聚糖稳定纳米铁表面Fe原子的相对含量低于实验柱Ⅰ。Cr元素高分辨率XPS能谱分析显示,在实验柱Ⅰ的条件下CKVI）被还原得更充分,而且在两种实验条件下都有部分Cr（VI）被吸附在纳米铁表面最终没有被零价铁所还原。     

Simultaneous Removal of Greases and Hexavalent Chromium from Electroplating and Chromate Conversion Coating Waste Solution by Electrocoagulation

Simultaneous removal of oil droplets and hexavalent chromium from synthetic wastewater of chromium plating and chromate conversion coating plants by electrocoagulation in a new cell design was studied under different conditions of pH, initial Cr⁶⁺ concentration, NaCl concentration, and current density. Under optimum conditions, more than 90% of oil content and Cr⁶⁺ were removed. Percent removal was found to increase with decreasing Cr⁶⁺; high Cr⁶⁺ concentrations tend to passivate the aluminum anode and decrease the percent removal of Cr⁶⁺ and oil. The effect of NaCl concentration shows a maximum percent removal at 1.5%. The pH range 4–5 was found to give the highest percent removal. Increase of current density was found to improve the percent removal of Cr⁶⁺ and oil droplets. The favorable effect the combined oil and Cr⁶⁺ removal on the capital and operating costs of wastewater remediation was pointed out. Potential merits of the present cell design compared to the traditional parallel plate cell were highlighted.     

Hexavalent Chromium Removal by Candida sp. in a Concentric Draft-Tube Airlift Bioreactor

The main purpose of this work was to conduct a kinetic study on cell growth and hexavalent chromium [Cr(VI)] removal by Candida sp. FGSFEP in a concentric draft-tube airlift bioreactor. The yeast was batch-cultivated in a 5.2-l airlift bioreactor containing culture medium with an initial Cr(VI) concentration of 1.5 mM. The maximum specific growth rate of Candida sp. FGSFEP in the airlift bioreactor was 0.0244 h^?1, which was 71.83% higher than that obtained in flasks. The yeast strain was capable of reducing 1.5 mM Cr(VI) completely and exhibited a high volumetric rate [1.64 mg Cr(VI) l^?1 h^?1], specific rate [0.95 mg Cr(VI) g^?1 biomass h^?1] and capacity [44.38 mg Cr(VI) g^?1 biomass] of Cr(VI) reduction in the airlift bioreactor, with values higher than those obtained in flasks. Therefore, culture of Candida sp. FGSFEP in a concentric draft-tube airlift bioreactor could be a promising technological alternative for the aerobic treatment of Cr(VI)-contaminated industrial effluents.     

Chromium Removal from Modjo Tannery Wastewater Using Moringa stenopetala Seed Powder as an Adsorbent

An electrokinetic technique was used to remediate As-, Cu-, and Pb-contaminated paddy soil in a real field on a pilot scale. A hexagonal electrode placement with one anode at the center and six cathodes at the vertices of the hexagon was installed in the field. After operation for 4 weeks, the average removal of Pb was 64.9 % in the top layer (0–0.4 m), 81.2 % in the middle layer (0.4–0.8 m), and 66.9 % in the bottom layer (0.8–1.2 m). The removal of As was 28.2 % in the top layer, 43.2 % in the middle layer, and 24.5 % in the bottom layer. The removal of Cu was 17.7 % in the middle layer and was not observed in the other layers. The relatively high removal of Pb might come from the more labile fraction of Pb in soil compared to As and Cu. However, the circulation of anolyte using an alkaline solution to enhance removal of As failed because the electrolyte leaked between the anode and surrounding soil. Effective circulation might enhance the performance of the electrokinetic process.     

Hexavalent Chromium Dynamics and Uptake in Manure-Added Soil

The soil dynamics of hexavalent Cr, a particularly mobile and toxic metal, is of a great environmental concern, and its availability to plants depends on various soil properties including soil organic matter. Thus, in a pot experiment, we added 50?mg Cr(VI) kg^?1 soil and studied Cr(VI) soil extractability and availability to spinach, where we applied both natural (zeolite), synthetic adsorptive materials (goethite and zeolite/goethite) and organic matter with farmyard manure. We found that, compared to the unamended control plants, dry matter weight in the Cr(VI)-added soil was greatly decreased to 17?% of the control, and height was decreased to 34?% of the control, an indication of Cr toxicity. Also, exchangeable Cr(VI) levels in soil decreased back to the unamended control even in the first soil sampling time. This was much faster than the exchangeable Cr(VI) levels in the mineral-added soil, where Cr(VI) levels were decreased to the levels of the unamended control in the third sampling time. The positive effect of organic matter was also indicated in the Cr quantity soil-to-plant transfer coefficient (in grams of Cr in plant per kilogram of Cr added in soil), a phyto-extraction index, which was significantly higher in the manure-amended (1.111?g?kg^?1) than in the mineral-added treatments (0.568?g?kg^?1). Our findings show that organic matter eliminates the toxicity of added Cr(VI) faster than the mineral phases do and enhances the ability of spinach to extract from soil greater quantities of Cr(VI) compared to mineral-added soils.     

Chromium-Resistant Bacterial Populations from a Site Heavily Contaminated with Hexavalent Chromium

Chromium-containing industrial effluents are primarily responsible for environmental contamination by toxic and highly mobile, hexavalent chromium. The dilution plate-count method, using media amended with Cr(VI) at concentrations ranging from 0 to 1000 mg L^-1, was used to compare the sizes of Cr(VI)-resistant bacterial populations from a soil contaminated with 25 100 mg kg^-1 total Cr [12 400 mg kg^-1 Cr(VI)] to those isolated from a slightly contaminated soil (99.6 mg kg^-1 total Cr) and two other soils without any history of Cr contamination. Bacterial populations resistant to 500 mg L^-1 Cr(VI) were isolated from all soils except the heavily contaminated soil. To determine whether Cr-resistant bacterial populations were indigenous to both the contaminated and the uncontaminated soils, enrichment cultures containing Cr(VI) at concentrations ranging from 0 to 1000 mg L^-1 were employed. Bacterial populations, as high as 10⁵ (colony forming units) CFU g^-1 soil, tolerant of 500 mg L^-1 Cr(VI) were isolated from all soils within 48 h of enrichment suggesting that the presence of aerobic Cr(VI)-resistant bacterial populations is unrelated to contamination levels or contamination history. However, identification of these resistant bacteria using fatty acid profiles was unsuccessful suggesting that these populations may have unique characteristics. Fungal colonies resistant to 1000 mg L^-1 Cr(VI) were routinely isolated from both uncontaminated and contaminated soils. The results suggest that Cr-resistant microorganisms may be present in soils, even those with no history of Cr contamination.     

Characterization of Reactive Red-120 Decolorizing Bacterial Strain Acinetobacter junii FA10 Capable of Simultaneous Removal of Azo Dyes and Hexavalent Chromium

Continual discharge of textile wastewaters loaded with a variety of synthetic dyes and metals is considered as a huge threat to surrounding ecosystems. In order to treat these undesirable pollutants, microbial bioremediation is considered as an efficient and economical technique. This study was conducted to evaluate the use of bacterial strains for simultaneous removal of azo dyes and hexavalent chromium [Cr(VI)]. Fifty-eight bacterial strains were isolated from Paharang drain wastewater and tested for their potential to decolorize reactive red-120 (RR-120) in the presence of 25 mg L^?1 of Cr(VI). Among the tested isolates, FA10 decolorized the RR-120 most efficiently and was identified as Acinetobacter junii strain FA10. Based on quadratic polynomial equation and response surfaces given by the response surface methodology (RSM), Cr concentration and pH were found to be the main factors governing the RR-120 decolorization by FA10. The strain FA10 also exhibited a substantial salt resistance since it showed a considerable decolorization of RR-120 even in the presence of 150 g L^?1 of NaCl. Moreover, the strain FA10 also showed the potential to simultaneously remove the Cr(VI) and the selected azo dyes in the same medium. More than 80 % of the initially added Cr(VI) was removed over 72 h of incubation along with the appreciable decolorization efficiency. The strain FA10 also exhibited good tolerance to considerable levels of different heavy metals. The findings of this study suggest that the strain FA10 might serve as an efficient bioresource to develop the biotechnological approaches for simultaneous removal of different azo dyes and heavy metals including Cr(VI).     

Biostimulation of Soil Microbial Activity Through Organic Fertilizer and Almond tree Association

Many studies have confirmed the validity of plant cover and organic farming in ameliorating soil quality. The goal of this study was to investigate the efficiency of rehabilitation practices in a degraded soil ecosystem consisting of: (i) organic or inorganic fertilization; and (ii) presence or absence of almond trees. The experiments were carried out for 2 years in the South of Italy in three fields characterized by different slope (0%, 2%, and 6%). Each field was split up into two parts, one assigned to organic fertilization and the other assigned to mineral fertilization, and planted with almond trees using GF677 or Franco rootstocks. The results showed that the organic fertilization, particularly in the presence of the Franco rootstock, resulted more effective in increasing soil organic matter content and microbial activity especially in the 0% and 2% slopes. However, in the 6% slope, where a lower soil metabolism was observed, an improvement of chemical and biochemical soil properties was generally evident for both fertilization systems. The Franco rootstock improved soil quality and maintaining a good production, whereas the GF677 has exploited more soil resources, resulting in a higher growth and yield; therefore, the use of almond tree with Franco rootstock associated with organic matter application is a useful practice in order to preserve soil quality and to rehabilitate degraded soils. Copyright © 2013 John Wiley & Sons, Ltd.     

六价铬对黄颡鱼仔鱼和稚鱼的急性毒性效应研究

利用静水式鱼类急性毒性测试法,分别以黄颡鱼（Pelteobagrus fulvidraco）仔鱼和稚鱼为受试对象,通过六价铬的急性毒性试验,获得24、48、72、96 h相应的半数致死浓度LC50值,比较了六价铬对黄颡鱼仔鱼和稚鱼的致毒敏感性,计算了六价铬对黄颡鱼的安全质量浓度并对六价铬对于黄颡鱼急性毒性等级进行了评价。旨在通过开展我国本土水生生物的急性毒性效应的研究,获得相应的毒理学数据,为推导符合我国生态分区特点的水质基准提供基础信息。结果表明,在水温为（23±2）℃条件下,六价铬对黄颡鱼仔鱼24、48、72、96 h的半数致死浓度LC50分别为28.32、21.99、17.70、15.79 mg.L-1,而对黄颡鱼稚鱼24、48、72、96 h的LC50分别为138.5、88.36、68.55、57.98 mg.L^-1,说明黄颡鱼仔鱼对于六价铬毒性的敏感性明显高于稚鱼。六价铬对黄颡鱼仔鱼和稚鱼的安全浓度分别为1.579、5.798 mg.L^-1,依据急性毒性结果和鱼类急性毒性分级标准,六价铬对于黄颡鱼毒性等级属于中等毒性。     

高氯酸盐与铬复合污染对水稻幼苗生长的影响

通过营养液沙培盆栽试验,研究了水稻幼苗的根长、株高和鲜重对高氯酸盐（ClO4^-）、六价铬（Cr^6＋）及其复合污染（ClO4^-＋Cr^6＋）胁迫的响应。结果表明,随着污染物处理浓度的提高,ClO4^-、Cr^6＋和ClO4^-＋Cr^6＋对水稻幼苗主要生长指标根长、株高和鲜重的抑制作用越明显,呈现出明显的浓度-效应关系;在同一浓度下,ClO4^-、Cr^6＋和ClO4^-＋Cr^6＋对水稻幼苗根长、株高和鲜重的抑制率呈明显的时间-效应关系,处理时间越长,抑制率越高;复合污染对水稻生长的抑制效应大于其中任一污染物在同浓度条件下的单一污染的影响,且随着浓度和时间的增加,抑制作用也越明显;复合污染对水稻幼苗生长的交互作用类型因处理时间和浓度组合的不同而更趋复杂。     

几种植物去除污染水体中养分效果研究

对城市尾水和人工模拟富营养化水体进行了静态培养试验.通过比较不同植物对城市尾水中氮、磷去除效果,以及它们在不同磷浓度条件下对不同形态氮素去除效果研究,目的在于筛选出适合治理富养分污染水体的植物品种.研究结果表明,空心菜(Ipomiea aquatica)、酸模(Rumex acetosa)、莎草(Cyperus glomeratus)3种植物都能很好地吸收尾水中的营养物质,且生长状况良好.经3种植物处理的城市尾水,其氮、磷浓度随水培时间的增加而降低.莎草、酸模对污水中TN的去除率达90%以上,其中莎草最高,达93.4%;空心菜对全磷的去除率最高达76.9%.NH_4~+-N在处理前期变化显著,且莎草的净化效果最好达94.4%;污水中NO_3~--N含量随着水培时间的增加而逐渐下降,但在试验后期NO_3~--N又有所增加.酸模去除NO_3~--N效果最好,达65.4%.另外3种植物对NH4+-N和NO_3~--N都具有一定的吸收作用,并且优先吸收NH_4~+-N.且从对于NH_4~+-N和NO_3~--N净化效果看,莎草>酸模>空心菜.     

Preparation of Fe@GAC and Fe@GAR and Their Application for Removal of Crystal Violet from Wastewater

Two types of granular adsorbents-supported zero-valent iron (ZVI) were prepared and applied to remove crystal violet (CV). One type of ZVI was synthesized by the chemical reduction method and deposited on the surface of granular porous adsorbent (Fe@GAC). The other type of ZVI was synthesized by direct reduction of iron ore tailing powder with the coke in high temperature reducing atmosphere and was embedded in granular porous adsorbent (Fe@GAR). Fe@GAC and Fe@GAR were characterized by SEM, EDX, XRD, FTIR, and BET. The effect of parameters like contact time, initial CV concentration, pH values, and temperature on the removal of CV was investigated. According to the results, the Langmuir model was in good agreement with the experimental data, where the maximum removal capacity of Fe@GAC and Fe@GAR was found to be 95.24 mg/g and 123.45 mg/g at 293 K, respectively. The kinetic studies indicated that the pseudo-second-order kinetic model agreed well with the experimental data. Thermodynamic parameters were calculated and analyzed, which suggested that the removal processes were spontaneous and endothermic. The mechanism of CV removal by Fe@GAC and Fe@GAR included adsorption and simultaneous chemical reduction. Compared with Fe@GAC, Fe@GAR owned more amount of ZVI, larger specific surface area and higher removal capacity, which made it a more promising adsorbent in wastewater treatment.     

DTC类重金属捕集剂对猪场废水中Cu、Zn的去除试验研究

通过黄原酸化反应将二硫代氨基甲酸(DTC)基团引入至壳聚糖,制备DTC类重金属捕集剂,用以去除猪场废水Cu、Zn。结果表明,DTC类重金属捕集剂对Cu、Zn的捕集性能受废水初始p H值和捕集剂投加量的影响,p H值有一个适宜范围,即p H 3.0~5.0;随着捕集剂投加量的增加,去除效果逐渐增加,但增加速率逐渐减缓。捕集剂性能受进水Cu、Zn浓度以及废水温度的干扰不很明显。在废水p H值5.0,捕集剂投加量2.0 g·L-1(废水),初始Cu、Zn浓度25~200 mg·L-1时,捕集剂对Cu、Zn的去除率可达到99%以上,且处理后Cu、Zn浓度低于污水综合排放标准(GB 8978—1996)一级标准限值规定。DTC类重金属捕集剂对Cu、Zn的等温吸附特征可用Langmuir方程进行拟合,其吸附平衡时间约为20 min左右。     

Chemical Reduction of Hexavalent Chromium and Its Immobilisation Under Batch Conditions Using a Slurry Reactor

Water, Air, & Soil Pollution - Risks posed by antifouling agents (irgarol 1051, diuron and dichlofluanid) to the aquatic environment of the Gulf of Napoli have been estimated. Seawater samples...     

Experimental Study on Adsorption of Hexavalent Chromium with Microwave-Assisted Alkali Modified Fly Ash

Coal fly ash, a kind of solid waste generated from coal-fired power stations, can be used as an absorbent for Cr(VI) from aqueous solution. The adsorption characteristics of microwave-assisted alkali modified fly ash to hexavalent chromium had been investigated. Many experimental conditions including pH, contact time, temperature, and fly ash dosage have significant impacts on adsorption performance of modified fly ash. The optimum conditions for the preparation of modified fly ash were as follows: microwave power 600 W, microwave temperature 60 °C, and microwave time 10 min. Batch experiments on adsorption isothermal characteristics of the fly ash modified under the optimal conditions were carried out. The results show that the adsorption of hexavalent chromium ions by modified fly ash is in accordance with the Freundlich and Langmuir isotherm adsorption models, which indicates that the adsorption process is monomolecular adsorption. Environmental-benign utilization of fly ash as low-cost adsorbents in wastewater treatment would bring long-term economic and environmental benefits.     

Colour Removal from Synthetic Dye Wastewater Using a Bioadsorbent

Removal of dyes (Crystal Violet, Methylene Blue, Malachite Greenand Rhodamine B) from aqueous solutions at differentconcentrations, pH and temperatures by Neem sawdust has beencarried out successfully. The percentage of the dye adsorbed byNeem sawdust decreased from 91.56 to 78.94 and 84.93 to 71.25 for Crystal Violet and Malachite Green, respectively, when the concentration of the dye was increased from 6 to 12 mg L^-1 at atemperature 30 ± 1 °C and pH 7.2. Adsorption ofother dyes (Methylene Blue and Rhodamine B) also decreased withincreasing concentration of the dye in solutions. The values ofthe rate constant of adsorption (k _ad) of Crystal Violet at25, 35 and 45 °C were found to be 10.80, 10.52 and 10.25 × 10^-2 min^-1, respectively. The values of the Langmuir constant for adsorption capacity (Q ^o) of Crystal Violet on the adsorbent varied from 4.44 to3.99 mg g^-1, respectively, with the increase of temperaturebetween 25 to 45 °C. The equilibrium data followed theLangmuir model of adsorption. The variation in the extent ofremoval with pH has been explained on the basis of surfaceionisation and complexation. Thermodynamic parameters(ΔG, ΔH and ΔS) have also been determinedto explain the results.     

农药污染土壤生物刺激修复技术研究进展

生物刺激作为一种环境友好且高效的生物修复技术,在污染土壤治理中具有独特优势,已成为国内外学者研究热点.针对当前农药污染土壤现状,本文综述了农药污染土壤及生物刺激修复技术的概念和范畴,重点从营养底物、表面活性剂、有机改良剂等角度阐述了生物刺激的方法和种类,探讨了影响生物刺激法修复农药污染土壤的主要因素,提出了生物刺激法目...