Biologically-mediated, simultaneous removal of nitrate and arsenic from drinking water sources

提案题目：生物介导，同时去除饮用水水源中的硝酸盐和砷主要研究者：Raskin， lutgard机构：密歇根大学提案号：cbet -0967707地下水受到各种氧阴离子污染物的污染一直是全球范围内提供安全饮用水的主要问题。监管压力导致了适用于处理个别污染物的技术的发展。然而，多种污染物的共存使得开发能够同时去除尽可能多的污染物的处理系统势在必行。拟议的研究将开发一种新技术，用于生物介导的同时去除地下水中经常同时出现的两种污染物，即硝酸盐和砷。饮用水的生物处理越来越受欢迎，因为多种污染物往往可以在一个反应器中转化为无害的化合物。拟议的研究将开发一个由两个固定床生物活性炭（BAC）生物反应器串联组成的系统，用于同时去除硝酸盐和砷（砷酸盐，As(V)）。当提供电子供体（如醋酸盐）时，这些污染物可作为微生物的电子受体。反硝化细菌将硝酸盐转化为二氮气体，砷酸盐可以被砷酸盐还原细菌转化为亚砷酸盐（As(III)），亚砷酸盐可以被硫化铁吸附去除。硫化铁是由硫酸盐还原菌在亚铁（Fe(II)）存在下还原硫酸盐而产生的。地下水中存在铁和硫酸盐，因此为这些反应的发生提供了所有必要的成分。如果三铁（Fe(III)）是铁的主要形式，铁还原菌可以将Fe（III）还原为Fe(II)，从而确保Fe（II）的存在与产生的硫化物相互作用。硫化铁非常有效地隔离亚砷酸盐，并防止还原动员，当其他形式的吸附砷在垃圾填埋场处理时，这是可能的。pi假设将在固定床BAC生物反应器中发展的微生物群落将能够以顺序的方式还原溶解氧、铁、硝酸盐、砷酸盐和硫酸盐。定期反冲洗反应器将去除多余的生物质，偶尔反冲洗将收集沉积在反应器中的砷固体（含砷的硫化物）。制定了三个目标和相关任务：(i)将运行一个实验规模的固定床BAC生物反应器系统，以详细研究负责污染物去除的机制。微生物群落和产生的固体将被表征，微生物群落活动和沉积固体的特征之间的关系将被研究。该系统将得到优化，以便有效和持续地去除硝酸盐和砷，使其低于检测水平。将评价废水的后处理和所生产固体的稳定性。对于试图扩大饮用水源的发达国家和发展中国家来说，开发一种占地面积小、可去除多种污染物、价格合理、操作简单、产生有限和安全的一次性废物的一步处理系统是非常可取的。与一家美国工程公司的联系确保了研究结果将在发达国家的实践中得到应用。密歇根大学社会研究所的研究人员在尼泊尔农村社区有着丰富的工作经验，他们将帮助他们探索尼泊尔受砷影响的农村人民采用拟议治疗技术的实际困难和意愿。这项工作的其他更广泛的影响包括将研究成果整合到pi教授的现有课程中，以及与现有的K-12外展计划相关的活动中，这些计划将在本项目中继续进行。

Proposal Title: Biologically-mediated, simultaneous removal of nitrate and arsenic from drinking water sourcesPrincipal Investigators: Raskin, LutgardeInstitutions: University of MichiganProposal No: CBET-0967707Contamination of groundwater with various oxy-anionic pollutants has been a major concern in the context of providing safe drinking water throughout the world. Regulatory pressures have resulted in the development of technologies suitable for the treatment of individual contaminants. However, the co-existence of multiple contaminants makes it imperative to develop treatment systems that provide simultaneous removal of as many contaminants as possible. The proposed research will develop a novel technology for the biologically-mediated, simultaneous removal of two contaminants that frequently co-occur in groundwater, i.e., nitrate and arsenic. Biological treatment of drinking water is gaining in popularity as multiple contaminants often can be converted to innocuous compounds in a single reactor. The proposed research will develop a system consisting of two fixed-bed biologically active carbon (BAC) bioreactors operated in series for the simultaneous removal of nitrate and arsenic (arsenate, As(V)). These contaminants can serve as electron acceptors for microorganisms when an electron donor (e.g., acetate) is provided. Denitrifying bacteria convert nitrate to dinitrogen gas and arsenate can be converted by arsenate reducing bacteria to arsenite (As(III)), which can be removed by sorption to iron sulfides. Iron sulfides are generated by the reduction of sulfate by sulfate reducing bacteria in the presence of ferrous iron (Fe(II)). Iron and sulfate are present in groundwater thus providing all necessary components to make these reactions take place. If ferric iron (Fe(III)) is the predominant form of iron, iron reducing bacteria can reduce Fe(III) to Fe(II), thus ensuring the Fe(II) form exists to interact with the sulfides produced. Iron sulfide sequesters arsenite very efficiently, and protects against reductive mobilization, which is possible when other forms of adsorbed arsenic are disposed in landfills. The PIs hypothesize that the microbial communities that will develop in the fixed-bed BAC bioreactors will be capable of reducing dissolved oxygen, ferric iron, nitrate, arsenate, and sulfate in a sequential manner. Regular backwashing of the reactors will remove excess biomass and occasional backwashing will allow collection of arsenic solids (sulfides laden with arsenic) deposited in the reactor. Three objectives with associated tasks were developed: (i) a bench-scale, fixed bed BAC bioreactor system will be operated to study the mechanisms responsible for contaminant removal in detail. The microbial community and the produced solids will be characterized and the relationship between microbial community activity and the characteristics of the deposited solids will be studied. (ii) The system will be optimized for efficient and sustained removal of nitrate and arsenic to below detection. (iii) Post-treatment of the effluent and stability of produced solids will be evaluated. The development of a one-step treatment system with a small footprint that can remove multiple contaminants, is affordable and simple to operate, and produces limited and safely disposable waste is highly desirable for developed and developing countries trying to expand drinking water sources. The link with a U.S. engineering firm ensures that the results will be applied in practice in developed countries. Researchers of the Institute for Social Research at the University of Michigan, who have extensive experience working with rural communities in Nepal, will help them explore the practical difficulties and willingness of arsenic-affected rural people of Nepal to adopt the proposed treatment technology. Additional broader impacts from this work include the integration of research results into existing courses taught by the PIs and into activities associated with existing K-12 outreach programs that will be continued with this project.