纳米零价铁耦合氢自养反硝化去除水中硝酸盐

首先采用液相还原法制备纳米零价铁粒子,然后将制得的纳米零价铁与氢自养反硝化菌进行耦合,组成纳米零价铁-氢自养反硝化耦合体系,考察了不同温度、pH值、Fe/N值、初始硝酸盐浓度和H_2对耦合体系去除硝酸盐的影响,并对硝酸盐去除机理进行了讨论。结果表明,纳米零价铁-氢自养反硝化耦合体系对硝酸盐有很好的去除作用,反应速率高于单一的化学还原或生物反硝化过程。Fe/N值对硝酸盐还原速率的影响不大,却对反应产物影响显著,试验条件下,纳米零价铁的最佳投量为10 mL。不同pH值条件下耦合体系对硝酸盐的去除趋势非常接近。温度对耦合体系降解硝酸盐的速率有一定影响,温度越高,硝酸盐的去除速率越快,但整体差别不大。初始硝酸盐浓度为25、65、105和150 mg/L时,对硝酸盐的平均去除速率分别为13. 64、11. 63、16. 55和13. 73 mg/(L·h)。给予耦合体系充足氢气的情况下,硝酸盐的降解速率较快,高于不额外供给氢气的耦合体系。     

硫酸铝强化纳米铁还原硝酸盐氮的研究

在水体溶解氧较高的条件下,采用投加硫酸铝的方式强化纳米铁对硝酸盐氮的去除效果。结果表明,投加硫酸铝可明显提高纳米铁对硝酸盐氮的去除效果,当硝酸盐氮初始浓度为10mg/L、纳米铁投量为5g/L、硫酸铝投量为100mg/L时,反应6h后对硝酸盐氮的去除率可达到83%,而不投加硫酸铝的情况下仅为51%。纳米铁对硝酸盐氮的还原过程符合拟一级反应动力学规律,其反应速率常数k随纳米铁投量和硫酸铝投量的增加而增大;纳米铁对硝酸盐氮的去除率随pH的降低而升高,随初始硝酸盐氮浓度的增加而下降;纳米铁还原硝酸盐氮的表观活化能较低,还原反应在常温下即很容易进行;硝酸盐氮的最终还原产物为氨氮。     

负载型纳米铁化学反硝化法去除硝酸盐氮的研究

采用液相还原法制备了以石墨为载体的负载型纳米铁，并以其为还原剂进行化学反硝化，考察了此种材料还原硝酸盐氮的特性。结果表明，负载型纳米铁在中性条件下能够快速将硝酸盐氮还原而去除；铁量相同而不同铁碳比的负载型纳米铁还原硝酸盐氮的速率有所不同；体系初始pH值越低则负载型纳米铁还原硝酸盐氮的速率越快，pH值为2时可在15min内将浓度为80mg／L的硝酸盐氮全部去除；体系中的溶解氧会与NO3^-争夺电子，在pH值较低时NO3^-的还原受溶解氧的影响较大；负载型纳米铁可构成微小原电池，在化学反硝化反应中Fe起主要作用，Fe^2＋对反应有促进作用。     

化学/生物联合PRB技术去除地下水中的硝酸盐

设计了三层结构可渗透反应格栅(PRB),进行了地下水硝酸盐污染处理的可行性研究。反应柱按水流方向依次填充零价铁、锯末和沸石,利用化学、生物作用去除硝酸盐,再通过沸石吸附去除化学还原产生的氨氮。试验结果表明:反应柱启动迅速,第3天对硝酸盐氮的去除率已达到99.68%;稳定运行期间,出水中的"三氮"浓度均保持在较低水平,pH值最高为8.64,未超过pH值=10的微生物生存环境极限,由此认为采用多层结构化学/生物联合PRB技术去除地下水中的硝酸盐是可行的。     

硫磺/零价铁联合强化潜流人工湿地脱氮除磷性能

污水处理厂尾水中的氮、磷含量显著高于地表水环境质量标准，在其排放前有必要进行进一步深度净化。构建了四组潜流湿地系统，在系统HRT=2 d时，对比研究了硫磺、零价铁、硫磺+零价铁的添加对潜流湿地脱氮除磷效能的影响。为期10个月自然状态下的连续运行结果表明，硫磺能够显著提高湿地系统的反硝化脱氮性能，总氮平均去除率达到80%以上，但是出水中硫酸根含量会超过250 mg/L；零价铁能够将出水中总磷含量降至0.1 mg/L以下，但是脱氮强化作用不显著；硫磺与零价铁联合能够显著提高湿地系统脱氮除磷能力，出水中硫酸根和总铁含量也处于较低水平，且湿地系统的氧化亚氮排放量也处于较低水平，表明硫磺/零价铁联合适用于潜流湿地深度净化污水处理厂尾水。     

不同pH下铁腐蚀产物对铁粉还原硝酸盐的影响

对不同初始pH下铁粉还原硝酸盐时所形成的腐蚀产物进行了试验研究.结果表明:腐蚀产物的主要成分是Fe3O4和FeO(OH),随反应体系初始pH值的降低,Fe3O4的比例逐渐增大;腐蚀产物表面呈多孔疏松结构,对Fe2+具有一定的吸附作用,可在一定程度上促进铁粉对硝酸盐的还原;铁腐蚀产物的形成总体上降低了铁对硝酸盐的还原效果,较低pH值条件下形成的铁腐蚀产物对硝酸盐去除效果的影响较小.     

平板型3D-BER去除地下水中硝酸盐氮的优化研究

采用平板型三维生物膜电极反应器(3D-BER)对地下水中的硝酸盐氮进行处理,研究了电流强度、进水硝酸盐氮浓度、进水pH和水力停留时间(HRT)等因素对处理效果的影响,结果表明:电流强度为40mA时,硝酸盐氮被还原的速率最快,且去除率可达到最大值90.15%;进水硝酸盐氮浓度为30mg/L时,脱氮效果最好,最佳进水pH范围及HRT分别为7～8和12h.通过正交实验确定反应器的最佳运行工况为电流强度40mA,进水硝酸盐氮浓度为30mg/L,进水pH为7,水力停留时间为14h.     

多孔介质中纳米零价铁运移行为的试验研究

纳米零价铁是一种前景广阔的环境修复材料,目前针对应用纳米零价铁进行地下水污染修复已经开展了广泛的研究。然而,现有研究多关注于注入纳米零价铁的运移能力,对于负载污染物后纳米零价铁的迁移行为缺少研究。本文研究了磷负载前后纳米零价铁的团聚趋势以及运移能力,分析了流速、离子浓度、多孔介质粒径级配等因素对磷负载纳米零价铁运移能力的影响。结果表明,磷负载纳米零价铁的团聚趋势相对于反应前纳米零价铁较低,其运移能力则强于吸附磷之前的纳米零价铁,这是由于吸附磷增加了纳米零价铁的表面负电荷进而阻碍了颗粒团聚。离子浓度对于磷负载纳米零价铁的运移能力有显著的影响,低离子浓度、高流速有利于磷负载纳米零价铁的运移。磷负载纳米零价铁在中玻璃珠中的运移能力强于细玻璃珠和粗玻璃珠,在天然砂中的运移能力则小于在中玻璃珠中的运移能力。利用DLVO理论以及胶体的粒桥、颗粒阻塞和表面沉积等多种滞留机理对试验中观察到的现象进行了解释。在含有高岭土的天然砂中,磷负载纳米零价铁的运移能力很弱,且沉降试验表明高岭土可以促进磷负载纳米零价铁的团聚沉降,这表明磷负载纳米零价铁有可能富集在含有高岭土的土层中。在应用纳米零价铁吸附地下水中的污染物时,应考虑污染物对于纳米零价铁运移能力的影响,并结合环境条件对该影响进行评估和控制。     

金属铁还原去除饮用水中硝酸盐的研究进展

在综述铁还原水中硝酸盐氮研究进展的基础上,重点对反应机理、反应条件因素进行了详细阐述,探讨了铁还原法今后的研究发展方向,对提高硝酸盐的去除效率具有重要意义。     

氢气还原针铁矿制备的纳米铁去除硝酸盐的研究

采用氢气还原天然针铁矿法制备出粒径为14 nm的单质铁纳米材料,考察了该纳米铁对水中硝酸盐的去除特性及影响因素,并与普通铁粉进行了对比.结果表明,与普通铁粉相比,纳米铁粉对硝酸盐的去除效果受pH值的影响较小;在纳米铁粉与硝酸盐的质量比为40:1、反应时间为5 h、硝酸盐初始浓度为60 mg/L的条件下,纳米铁对硝酸盐具有较高的还原活性,对硝酸盐的去除率可达90%以上,且还原产物中基本无亚硝酸盐;溶解氧和天然针铁矿粒径对纳米铁去除硝酸盐的影响不大.采用氢气还原天然针铁矿制备纳米铁的方法简单且成本较低,在去除地下水中的硝酸盐方面具有很好的应用前景.     

Chemical reduction of nitrate by nanosized iron: kinetics and pathways

This study was conducted to investigate chemical reduction of nitrate by nanoscale zero-valent iron (ZVI) in aqueous solution and related kinetics and pathways. In the last decade, employment of micro-scale ZVI has gained its popularity in nitrate reduction. To further study chemical reduction of nitrate, nanosized iron was synthesized and tested in this work. It has a size in the range of 50-80 nm and a BET surface area of 37.83 m(2)g(-1). Chemical reduction of nitrate by nanosized iron under various pHs was carried out in batch experiments. Experimental results suggest that nitrate reduction by nanosized ZVI primarily is an acid-driven surface-mediated process. A stronger acidic condition is more favorable for nitrate reduction. Results of the kinetics study have indicated that a higher initial concentration of nitrate would yield a greater reaction rate constant. Additional test results also showed that the reduction rate of nitrate increased as the dose of nanosized ZVI increased. In all tests, reaction rate equations developed do not obey the first- or pseudo-first-order reaction kinetics with respect to the nitrate concentration. Based on the research findings obtained, two possible reaction pathways for nitrate reduction by nanoscale iron particles have been proposed in this work.     

海绵铁还原水中硝酸盐的初步研究

研究了海绵铁还原水中硝酸盐的各项性能.通过单因素的影响试验,讨论了pH、进水硝酸盐浓度、粒径及添加锰砂对硝酸盐还原效果的影响.结果表明,当pH值为5时1 g海绵铁反应60 min还原硝酸盐的量为0.30 mg;小粒径有利于海绵铁还原硝酸盐;进水硝酸盐浓度在11～220 mg/L范围内,海绵铁还原硝酸盐的量呈先上升后趋于平缓之状;锰砂的添加使海绵铁还原硝酸盐的量增加了约1倍.还通过电镜扫描观察了不同pH值下海绵铁在反应前后的表观变化,这为进一步的研究提供了理论依据.     

Effects of low pH on nitrate reduction by iron powder

The effect of low pH (2-4.5) on nitrate reduction in an iron/nitrate/water system was investigated through batch experiments conducted in a pH-stat. The results showed that nitrate could be rapidly reduced to ammonium at pH 2-4.5. A black coating, consisted of both Fe(II) and Fe(III), was formed on the surface of iron grains as an iron corrosion product. X-ray diffractometry indicated that the black coating was poorly crystalline, and its spectrum could not be matched with commonly known iron oxides/hydroxides/oxide hydroxides or green rust I/II. The black coating does not inhibit the reactivity of Fe0 (at least at pH < 3). The black coating was unstable and evolved with time into other oxides under certain conditions. A kinetic model incorporating the effects of pH on nitrate reduction and Langmuir adsorption of nitrate was proposed, and the parameters were estimated by nonlinear curve fitting. Based on this model, the two major effects of pH on the kinetics of nitrate reduction are that: (a) H+ ions directly participate in the redox reaction of nitrate reduction following first-order kinetics; and (b) H+ ions affect the nitrate adsorption onto reactive sites.     

An electrokinetic/Fe0 permeable reactive barrier system for the treatment of nitrate-contaminated subsurface soils

Effective nitrate removal by Fe⁰ permeable reactive barriers (Fe⁰ PRB) has been recognized as a challenging task because the iron corrosion product foamed on Fe⁰ hinders effective electron transfer from Fe⁰ to surface-bound nitrate. The objectives of this study were (i) to demonstrate the effectiveness of an electrokinetic/Fe⁰ PRB system for remediating nitrate-contaminated low permeability soils using a bench-scale system and (ii) to deepen the understanding of the behavior and fate of nitrate in the system. Bench-scale laboratory experiments were designed to investigate the influence of the Fe⁰ content in the permeable reactive barrier, the pH in the anode well, and the applied voltage on remediation efficiency. The experimental results showed that the major reaction product of nitrate reduction by Fe⁰ was ammonium and that nitrate reduction efficiency was significantly influenced by the variables investigated in this study. Nitrate reduction efficiency was enhanced by either increasing the Fe⁰ content in the Fe⁰ reactive barrier or decreasing the initial anode pH. However, nitrate reduction efficiency was reduced by increasing the applied voltage from 10 V to 40 V due to the insufficient reaction time during nitrate migration through the Fe⁰ PRB. For all experimental conditions, nearly all nitrate nitrogen was recovered in either anode or cathode wells as nitrate or ammonium within 100 h, demonstrating the effectiveness of the system for remediating nitrate-contaminated subsurface soils.     

Arsenic removal from geothermal waters with zero-valent iron--effect of temperature, phosphate and nitrate

Field column studies and laboratory batch experiments were conducted in order to assess the performance of zero-valent iron in removing arsenic from geothermal waters in agricultural regions where phosphates and nitrates were present. A field pilot study demonstrated that iron filings could remove arsenic, phosphate and nitrate from water. In addition, batch studies were performed to evaluate the effect of temperature, phosphate and nitrate on As(III) and As(V) removal rates. All batch experiments were conducted at three temperatures (20, 30 and 40 degrees C). Pseudo-first-order reaction rate constants were calculated for As(III), As(V), phosphate, nitrate and ammonia for all temperatures. As(V) exhibited greater removal rates than As(III). The presence of phosphate and nitrate decreased the rates of arsenic removal. The temperature of the water played a dominant role on the kinetics of arsenic, phosphate and nitrate removal. Nitrate reduction resulted in the formation of nitrite and ammonia. In addition, the activation energy, Eact, and the constant temperature coefficient, theta were determined for each removal process.     

Prognose zur Entwicklung der Nitrat- und Sulfatkonzentration in einem tiefen Grundwasserleiter durch hydrogeochemische Untersuchungen

The areas within the ‘Niederrheinische Tiefebene’ are intensively used for agricultural production. The underlying hydrogeologic structure of the area is composed of multiple layers of productive unconsolidated aquifers. The high input of nitrate in the near-surface aquifers restricts the pumping of groundwater only from the deep aquifers which increases the vertical hydraulic gradient. This leads to enhanced flow from the upper aquifers into the deeper systems. Simultaneously, the concentrations of several hydrochemical indicator parameters (chloride, sulphate, iron, calcium, total carbon dioxide) have increased. Nitrate is removed by the reaction with sulphide minerals within the deeper aquifers. In this paper, the relevant processes in the anaerobic system are described, with special emphasis on lithotrophic dentrification at the Rasseln water works. The aim is to predict the prospective trend of the water quality in the deep aquifer with a focus on nitrate. Therefore, the behaviour of a conservative component (chloride) was also analysed relative to the behaviour of more reactive components (sulphate, iron, nitrate). As a result of this analysis, a long-term reduction of nitrate in the deep aquifer (Neurather Sand, Horizont 6D) at the Rasseln water works, which leads to a low concentration of nitrate in the raw water, was predicted. Furthermore, the results have shown that the sulphate concentration will likely not reach the legal limit for drinking water (240?mg/l, TVO 2001).     

Identifikation und Regionalisierung von Nitratabbauprozessen in einem Grundwasserleiter – Möglichkeiten und Nutzen für die Wassergewinnung

Denitrification with pyrite or organic carbon compounds in aquifers can lead to the release of ferrous iron, sulfate and bicarbonate into the groundwater. For the water catchment, Ortheide (Emsdetten, Germany), nitrate reduction with pyrite also causes an increased well clogging with iron hydroxides in some of the wells. With the help of hydrogeochemical modelling (PhreeqC), the main processes in the aquifer of the catchment area were identified and quantified. The presence or absence of pyrite in the aquifer sediments was determined based on groundwater compositions. This allowed the regionalization of autolithotrophic denitrification in the aquifer and the distinction of so called “origin zones” of nitrate, ferrous iron and bicarbonate. Based on these zones, the comparative sensitivity of agricultural areas towards nitrate concentrations in the raw water and the clogging tendency of the wells could be estimated.