活性铁锰复合氧化物滤膜吸附除砷性能研究

以化学挂膜方法制备出来的活性铁锰氧化物滤膜为研究对象,考察其表面特性及除砷性能。结果表明,应用准二级反应动力学方程(R~2=0.922)能够表征该活性铁锰复合氧化物对As(Ⅴ)的吸附过程;吸附等温线符合Langmuir方程(R~2=0.971),其饱和吸附容量为11.94 mg/g;活性铁锰氧化物滤膜的pH_(zpc)在2.5左右;天然地下水体中的碳酸根对该吸附剂的吸附除砷效果有较强的抑制作用,而其余共存阴、阳离子在中性水环境中对除砷的效果影响不大。在柱试验过程中,As(Ⅴ)浓度分别为200、280μg/L的地下水通过该滤柱处理后最终出水砷浓度均降为零,除砷效果较好。     

基于BP神经网络的地下水强化除砷建模研究

针对郑州市东周水厂铁锰复合污染条件下的含砷地下原水,经中试和生产性试验研究,在无混凝的曝气/接触氧化过滤除砷技术的基础上,建立了投药量BP神经网络模型。该模型在以出水As10μg/L为控制条件的前提下,进行不同原水水质条件下药剂投加量的模拟计算,并作为核心模拟算法模块,应用于水厂除砷自动控制加药系统中,完善了水厂当前的自控系统。     

预氧化-化学沉淀法去除水中砷的试验研究

研究了预氧化-化学沉淀法对水中砷的去除效果及其影响因素。结果表明,原水砷质量浓度为5倍标准限值时,在NaClO预氧化条件下,投加8 mg/L的聚合氯化铝可使砷去除率达到84%,且出水砷含量可以满足《生活饮用水卫生标准》(GB 5749—2006)限值要求;在KMnO4预氧化条件下,投加8 mg/L的聚合氯化铝可使砷去除率达到90%,且出水砷含量满足标准限值要求,而投加8 mg/L的聚合硫酸铁可使出水砷含量降至18.72μg/L,无法满足标准限值要求;采用聚合氯化铝作为混凝剂时的除砷效果优于聚合硫酸铁,以KMnO4作为预氧化剂时的除砷效果优于NaClO。     

针对高砷地下水的强化除砷技术优化及效能研究

利用中试研究了针对内蒙古某水厂高砷地下水的除砷技术方案,并优化了其工艺参数,初步确定了其除砷效能。结果表明,针对当地地下水水质特征,其基本除砷方案宜采用投加除砷药剂反应后进行过滤的方法。其中,除砷药剂宜采用氯化铁与高锰酸钾的复合药剂,其配比(以铁和高锰酸钾的质量计)采用4∶1;除砷药剂投加后的反应时间宜控制在2 min左右;采用锰砂与石英砂的双层过滤单元,滤层总厚度不小于1.0 m,其中锰砂厚度宜大于30 cm,且滤速控制在5~7m/h为宜。针对优化后工艺参数的长期验证试验结果表明,出水的砷、锰含量分别稳定在5μg/L和0.05 mg/L以下。     

原位生成铁锰复合氧化物在微絮凝/过滤工艺中除砷

针对传统吸附除砷(As)工艺所存在的吸附剂制备成本高、再生操作复杂以及固液分离困难等问题,开发了一种采用纤维球、锰砂作为填充滤料,使用在线加药原位生成的铁锰复合氧化物(FMBO)作为吸附剂的除砷新工艺。选用农村地区的砷污染地下水作为处理对象进行中试,在Fe³⁺、Mn⁷⁺、Mn²⁺投加量分别为1.75、0.1和0.15 mg/L,水力停留时间为15 min的最佳条件下运行了5个周期,出水砷、铁和锰浓度分别稳定在10μg/L、0.3 mg/L和0.1 mg/L以下,均达到了《生活饮用水卫生标准》(GB 5749—2022)中的限值要求,且运行成本仅约为0.91元/m³。与其他地下水除砷工艺相比,该技术更加经济高效。     

黄河水体对北郊水源地砷污染的影响研究

通过分析北郊水源地砷污染现状、黄河对地下水补给和影响以及黄河水质泥沙中砷含量与地下水关系几个方面,研究了黄河水体对地下水砷超标的影响。检测数据表明,水源地区域黄河水体中砷、铁和锰的平均含量分别为2.75μg/L、0.44 mg/L、0.14 mg/L,铁、锰含量均高于集中式生活饮用水地表水源地补充项目标准限值(0.3 mg/L和0.1 mg/L),加之水体为氧化环境,Eh为30.9~78.2 m V,致使水中微量砷会被粘土颗粒及形成的铁/锰氧化物或氢氧化物吸附沉积,并在地层中富集。由于黄河水本身含有一定浓度砷,强蒸发作用加剧了潜水-微承压含水层砷的富集,但是黄河水及沙层沉积物中砷含量释放能力有限。     

内蒙古L水厂强化除砷改造工程

L水厂是内蒙古自治区B市市区的主要供水厂,供水能力为4.4×104m3/d,目前水厂仅设置无阀滤池用于去除原水中的铁、锰,而对砷的去除效果较差。针对L水厂现有工艺状况及出水水质特征,采用投加除砷药剂后对管式静态混合器、跌水曝气、过滤等工艺进行改造。实际运行结果表明,改造后工艺出水中砷、铁、锰及浊度数值分别稳定在9μg/L、0.05 mg/L、0.02 mg/L、0.4 NTU以内,均满足现行《生活饮用水卫生标准》(GB 5749—2006)。此外,工艺改造成本约为15元/m3,运行成本增加值0.01元/m3。     

活性氧化铝吸附水中砷的动态试验研究

近年来,饮用水砷污染事件层出不穷,选择高效合适的除砷方法,已成为全球关注的问题.试验采用逆流式单床吸附柱的吸附方式,对活性氧化铝吸附砷做了动态试验研究.研究结果显示,当初始砷浓度为10mg/L时,砷的去除率均在90%以上;当初始砷浓度为50mg/L时,以5mg/L为穿透点,穿透体积为110L,动态吸附量为3.43mg/g.结果表明,在水中砷的去除方面,活性氧化铝可作为一种有效吸附剂.该研究对实际应用中的活性氧化铝改性及饮用水处理具有重要意义.     

吸附法在地下水除砷中的应用

山西某牧场地下水除砷工程采用吸附法工艺,设计规模为产水1 000 m~3/d。介绍了该工程的工艺流程、设备配置情况、工程设计参数等。运行结果表明,吸附法除砷效果显著,当进水砷为295μg/L时,砷去除率高达97.6%,出水砷降至7.10μg/L,满足《生活饮用水卫生标准》(GB5749—2006)要求。     

零价铁用于砷污染地下水修复的影响因素及效果

针对地下水无机砷污染,借助批试验和柱试验,利用铁粉(325目)开展了零价铁去除五价砷的室内研究,探讨了初始pH值、无机阴离子、重金属和腐殖酸对除砷能力的影响,考察了动态运行条件下除砷效果及水质指标的变化。批试验结果表明,当pH值=3.7时,反应120 min后对As的去除率达到78.8%,而pH值=6.9时,反应120 min后去除率达到93.9%;溶液初始pH值显著影响零价铁除砷效果,且与酸性相比中性pH值更有利于除砷;硝酸盐、磷酸盐、硫酸盐、铬和铅均显著加快且促进了零价铁除砷,而腐殖酸显著抑制了除砷能力,且其浓度越高则抑制作用越明显。柱试验结果表明,零价铁除砷效果良好且稳定,对As的去除率始终大于95.0%,出水As浓度始终低于9.5μg/L,出水pH值升至7.6~8.1,出水Eh值降至110~145 m V,出水水质满足《生活饮用水卫生标准》(GB 5749—2006)。零价铁法具有潜在的地下水原位修复工程应用潜力。     

Oxidation and removal of arsenic (III) from aerated groundwater by filtration through sand and zero-valent iron

Removing arsenic from contaminated groundwater in Bangladesh is challenging due to high concentrations of As(III), phosphate and silicate. Application of zero-valent iron as a promising removal method was investigated in detail with synthetic groundwater containing 500 microg/L As(III), 2-3mg/L P, 20mg/L Si, 8.2mM HCO3-, 2.5mM Ca2+, 1.6mM Mg2+ and pH 7.0. In a series of experiments, 1L was repeatedly passed through a mixture of 1.5 g iron filings and 3-4 g quartz sand in a vertical glass column (10mm diameter), allowing the water to re-aerate between each filtration. At a flow rate of 1L/h, up to 8 mg/L dissolved Fe(II) was released. During the subsequent oxidation of Fe(II) by dissolved oxygen, As(III) was partially oxidized and As(V) sorbed on the forming hydrous ferric oxides (HFO). HFO was retained in the next filtration step and was removed by shaking of the sand-iron mixture with water. Rapid phosphate removal provided optimal conditions for the sorption of As(V). Four filtrations lead to almost complete As(III) oxidation and removal of As(tot) to below 50 microg/L. In a prototype treatment with a succession of four filters, each containing 1.5 g iron and 60 g sand, 36 L could be treated to below 50 microg/L in one continuous filtration, without an added oxidant.     

Application of biological processes for the removal of arsenic from groundwaters

Bacteria are widespread, abundant, geochemically reactive components of aquatic environments. In particular, iron-oxidizing bacteria, are involved in the oxidation and subsequent precipitation of ferrous ions. Due to this property, they have been applied in drinking water treatment processes, in order to accelerate the removal of ferrous iron from groundwaters. Iron also exerts a strong influence on arsenic concentrations in groundwater sources, while iron oxides are efficient adsorbents in arsenic removal processes. In the present study, the removal of arsenic (III and V), during biological iron oxidation has been investigated. The results showed that both inorganic forms of arsenic could be efficiently treated, for the concentration range of interest in drinking water (50-200microg/L). In addition, the oxidation of trivalent arsenic was found to be catalyzed by bacteria, leading to enhanced overall arsenic removal, because arsenic in the form of arsenites cannot be efficiently sorbed onto iron oxides. This method comprises a cost competitive technology, which can find application in treatment of groundwaters with elevated concentrations of iron and arsenic.     

Subsurface iron and arsenic removal for shallow tube well drinking water supply in rural Bangladesh

Subsurface iron and arsenic removal has the potential to be a cost-effective technology to provide safe drinking water in rural decentralized applications, using existing shallow tube wells. A community-scale test facility in Bangladesh was constructed for injection of aerated water (∼1 m³) into an anoxic aquifer with elevated iron (0.27 mmol L⁻¹) and arsenic (0.27 μmol L⁻¹) concentrations. The injection (oxidation) and abstraction (adsorption) cycles were monitored at the test facility and simultaneously simulated in the laboratory with anoxic column experiments.Dimensionless retardation factors (R) were determined to represent the delayed arrival of iron or arsenic in the well compared to the original groundwater. At the test facility the iron removal efficacies increased after every injection-abstraction cycle, with retardation factors (R_Fe) up to 17. These high removal efficacies could not be explained by the theory of adsorptive-catalytic oxidation, and therefore other ((a)biotic or transport) processes have contributed to the system’s efficacy. This finding was confirmed in the anoxic column experiments, since the mechanism of adsorptive-catalytic oxidation dominated in the columns and iron removal efficacies did not increase with every cycle (stable at R_Fe = ∼8). R_As did not increase after multiple cycles, it remained stable around 2, illustrating that the process which is responsible for the effective iron removal did not promote the co-removal of arsenic. The columns showed that subsurface arsenic removal was an adsorptive process and only the freshly oxidized adsorbed iron was available for the co-adsorption of arsenic. This indicates that arsenic adsorption during subsurface treatment is controlled by the amount of adsorbed iron that is oxidized, and not by the amount of removed iron. For operational purposes this is an important finding, since apparently the oxygen concentration of the injection water does not control the subsurface arsenic removal, but rather the injection volume. Additionally, no relation has been observed in this study between the amount of removed arsenic at different molar Fe:As ratios (28, 63, and 103) of the groundwater. It is proposed that the removal of arsenic was limited by the presence of other anions, such as phosphate, competing for the same adsorption sites.     

Effects of water chemistry on arsenic removal from drinking water by electrocoagulation

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.     

Conventional oxidation treatments for the removal of arsenic with chlorine dioxide, hypochlorite, potassium permanganate and monochloramine

Arsenic is widespread in soils, water and air. In natural water the main forms are arsenite (As(III)) and arsenate (As(V)). The consumption of water containing high concentration of arsenic produces serious effects on human health, like skin and lung cancer. In Italy, Legislative Decree 2001/31 reduced the limit of arsenic from 50 to 10 μg/L, in agreement with the European Directive 98/83/EC. As consequence, many drinking water treatment plant companies needed to upgrade the existing plants where arsenic was previously removed or to build up new plants for arsenic removal when this contaminant was not previously a critical parameter.Arsenic removal from water may occur through the precipitation with iron or aluminum salts, adsorption on iron hydroxide or granular activated alumina (AA), reverse osmosis and ion exchange (IE). Some of the above techniques, especially precipitation, adsorption with AA and IE, can reach good arsenic removal yields only if arsenic is oxidized.The aim of the present work is to investigate the efficiency of the oxidation of As(III) by means of four conventional oxidants (chlorine dioxide, sodium hypochlorite, potassium permanganate and monochloramine) with different test conditions: different type of water (demineralised and real water), different pH values (5.7-6-7 and 8) and different doses of chemicals.The arsenic oxidation yields were excellent with potassium permanganate, very good with hypochlorite and low with monochloramine. These results were observed both on demineralised and real water for all the tested reagents with the exception of chlorine dioxide that showed a better arsenic oxidation on real groundwater than demineralised water.     

Chemical reactions between arsenic and zero-valent iron in water

Batch experiments and X-ray photoelectron spectroscopic (XPS) analyses were performed to study the reactions between arsenate [As(V)], arsenite [As(III)] and zero-valent iron [Fe(0)]. The As(III) removal rate was higher than that for As(V) when iron filings (80-120 mesh) were mixed with arsenic solutions purged with nitrogen gas in the pH range of 4-7. XPS spectra of the reacted iron coupons showed the reduction of As(III) to As(0). Soluble As(III) was formed when As(V) reacted with Fe(0) under anoxic conditions. However, no As(0) was detected on the iron coupons after 5 days of reaction in the As(V)-Fe(0) system. The removal of the arsenic species by Fe(0) was attributed to electrochemical reduction of As(III) to sparsely soluble As(0) and adsorption of As(III) and As(V) to iron hydroxides formed on the Fe(0) surface under anoxic conditions. When the solutions were open to atmospheric air, the removal rates of As(V) and As(III) were much higher than under the anoxic conditions, and As(V) removal was faster than As(III). The rapid removal of As(III) and As(V) was caused by adsorption on ferric hydroxides formed readily through oxidation of Fe(0) by dissolved oxygen.     

Removal of arsenic(III) from aqueous solutions using fresh and immobilized plant biomass

The ability of Garcinia cambogia, an indigenous plant found in many parts of India, to remove trivalent arsenic from solution was assessed. Batch experiments were carried out to characterize the As(III) removal capability of fresh and immobilized biomass of G. cambogia. It was found that the kinetic property and uptake capacity of fresh biomass were significantly enhanced by the immobilization procedure. The uptake of As(III) by fresh and immobilized biomass was not greatly affected by solution pH with optimal biosorption occurring at around pH 6--8. The presence of common ions such as Ca and Mg at concentrations up to 100mg/l had no effect on As(III) removal. However, the presence of Fe(III) at 100mg/l caused a noticeable drop in the extent of As(III) removal but the effect was minimal when Fe(III) was present at 10mg/l. The adsorption isotherms quantitatively predicted the extent of As(III) removal in groundwater samples collected from an arsenic-contaminated site in India. Immobilized biomass loaded with As(III) was amenable to efficient regeneration with NaOH solution. Column studies showed that immobilized biomass could be reused over five cycles of loading and elution. The excellent As(III) sequestering capability of fresh and immobilized G. cambogia biomass could lead to the development of a viable and cost-effective technology for arsenic removal in groundwater.     

Performance of nanofiltration for arsenic removal

Performance of rapid sand filtration inter-chlorination system was compared with nanofiltration (NF) to reduce the arsenic health risk of drinking water. It was found that rapid sand filtration with inter-chlorination is not effective in removing arsenic. If total arsenic concentration in raw water is below 50 microg/L regardless of the turbidity of raw water, arsenic can be removed below WHO guideline value of 10 microg/L by conventional coagulation (polyaluminum chloride dosage is about 1.5 mg Al/L). However, if the raw water arsenic concentration exceeds 50 microg/L, more coagulant dosage or enhanced coagulation is needed. To adopt optimum coagulant dosage for arsenic removal, it needs to monitor raw water arsenic concentration, but it is difficult because arsenic measurement is time consuming. In addition, if raw water contains As(III), it is difficult for rapid sand filtration inter-chlorination system to meet an arsenic maximum contaminant level of 2 microg/L, which would achieve reduction of cancer risk below 10(-4). On the other hand, the NF membrane (NaCl rejection 99.6%) could remove over 95% of As(V) under relatively low-applied pressure (< 1.1 MPa). Furthermore, more than 75% of As(III) could be removed using this membrane without any chemical additives, while trivalent arsenic could not be removed by rapid sand filtration system without pre-oxidation of As(III) to As(V). Because both As(V) and As(III) removals by NF membranes were not affected by source water composition, it is suggested that NF membrane can be used in any types of waters.     

Effect of synthetic iron colloids on the microbiological NH(4)(+) removal process during groundwater purification

Subsurface aeration is used to oxidise Fe in situ in groundwater that is used to make drinking water potable. In a groundwater system with pH>7 subsurface aeration results in non-mobile Fe precipitate and mobile Fe colloids. Since originally the goal of subsurface aeration is to remove iron in situ, the formation of non-mobile iron precipitate, which facilitates the metal's removal, is the desired result. In addition to this intended effect, subsurface aeration may also strongly enhance the microbiological removal of ammonium (NH(4)(+)) in the purification station. Mobile iron colloids could be the link between subsurface aeration and the positive effect on the NH(4)(+) removal process. Therefore, the objective of this study was to assess whether synthetic iron colloids could improve the NH(4)(+) removal process. The effect of synthetic iron colloids on the NH(4)(+) removal process was studied using an artificial purification set-up on a laboratory scale. Columns that purified groundwater with or without added synthetic iron colloids were set up in duplicate. The results showed that the NH(4)(+) removal was significantly ( alpha = 0.05 ) increased in columns treated with the synthetic iron colloids. Cumulative after 4 months about 10% more NH(4)(+) was nitrified in the columns that was treated with the groundwater containing synthetic iron colloids. The results support the hypothesis that mobile iron colloids could be the link between subsurface aeration and the positive effect on the NH(4)(+) removal process.