Microbial processes and iron-mineral formation in household sand filters used to remove arsenic from drinking water in Vietnam

受砷污染的地下水和饮用水是一个全球性的环境问题，全球约有1%-2%的人口受到影响。饮用水砷含量上限(10μg/L)经常超标，特别是在越南等亚洲国家。家用滤砂器已经被用作去除水中砷的一种非常简单和经济高效的处理方法。地下水中溶解的铁(Fe(II))被氧化后，在砂滤池中形成稀溶的铁(氢)氧化物颗粒(Fe(III)OOH)，结合带负电荷的砷物种，降低水中砷的浓度。亚砷酸盐(As(III)；H3AsO_3)与金属氧化物的结合强度一般低于砷酸盐(As(V)；H_2AsO_4-/HAsO_4~(2-))，因此As(V)的去除比As(III)有效得多。这就是为什么As(III)氧化成As(V)对于去除饮用水中的砷特别有意义。目前尚不清楚铁和亚砷酸盐氧化菌的活动是否以及如何有助于家用砂滤池的有效除砷。因此，本研究的目标之一是从过滤器中分离、鉴定和量化Fe(II)和As(III)氧化微生物，并研究它们的铁和砷的氧化还原活性。以培养为基础的工作将得到独立于培养的分子技术的补充，以确定和量化在过滤操作期间的不同时间点(无论是在现场还是在人工实验室过滤系统中)从不同过滤位置采集的样本中的微生物群落。将对分离的氧化铁和亚砷酸盐细菌进行研究，以了解它们沉淀铁矿物(在有或没有砷的情况下)和氧化亚砷酸盐的能力。将对实验室分离菌株、越南沙子过滤材料和人工实验室过滤系统中分离的菌株形成的生物和非生物铁矿物进行鉴定和表征，并对砷的吸附进行表征。我们将确定生物和非生物过程如何有助于从含砷铁矿物相中动员砷，并随着时间的推移影响过滤器的性能。这项研究的长期目标是更好地了解在天然和工程系统(如家用砂过滤器)中驱动砷/铁矿物相互作用的微生物氧化还原转化过程，并为改进过滤器的使用和过滤材料处理提出建议。

Arsenic-contaminated ground- and drinking water is a global environmental problem with about 1-2% of the world’s population being affected. The upper drinking water limit for arsenic (10 μg/L) is often exceeded, especially in Asian countries, such as Vietnam. Household sand filters are already used as one very simple and cost-efficient treatment to remove arsenic from water. Oxidation of dissolved iron (Fe(II)) present in the groundwater leads to the formation of sparsely soluble iron(hydr)oxide particles (Fe(III)OOH) in the sand filter, which bind negatively charged arsenic species and reduce arsenic concentrations in the water. Arsenite (As(III); H3AsO3) binds generally less strong to metal oxides than arsenate (As(V); H2AsO4 -/HAsO4 2-), therefore As(V) is removed much more effectively than As(III). This is why As(III) oxidation to As(V) is of special interest for arsenic removal from drinking water. Whether and how the activity of iron- and arsenite-oxidizing bacteria contributes to effective arsenic removal in household sand filters is currently not known. One of the goals of this study therefore is to isolate, identify, and quantify Fe(II)- and As(III)-oxidizing microorganisms from filters and to study their iron and arsenic redox activities. Cultivation-based work will be complemented by molecular, cultivation-independent techniques to characterize and quantify the microbial communities in samples from different filter locations taken at various time points during filter operation (both at field sites and in artificial laboratory filter systems). The isolated iron- and arsenite-oxidizing bacteria will be studied with respect to their abilities to precipitate iron minerals (in the presence or absence of arsenic) and oxidize arsenite. Biogenic and abiogenic iron minerals formed by the isolated strains in the lab, on the sand filter material in Vietnam and in artificial laboratory filter systems will be identified and characterized, also with respect to arsenic sorption. And we will determine how biotic and abiotic processes that contribute to arsenic mobilization from arsenic-loaded iron mineral phases affect filter performance over time. The long-term goal of this research is to better understand the microbial redox transformation processes that drive arsenic/iron mineral interactions in natural and engineered systems, such as household sand filters and to give recommendations for improved filter use and filter material disposal.