Solid-phase characterisation of an effective household sand filter for As, Fe and Mn removal from groundwater in Vietnam
Solid-phase characterisation of an effective household sand filter for As, Fe and Mn removal from groundwater in Vietnam
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DOI：
10.1071/en14011
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发表时间：
2014-01-01
影响因子：
4.3
通讯作者：
Steininger, Ralph
中科院分区：
文献类型：
--
作者：
Voegelin, Andreas;Kaegi, Ralf;Steininger, Ralph
家用砂滤器在越南被广泛用于去除作为饮用水资源的缺氧地下水中的As，Fe和Mn。为了扩大过滤器功能的机械知识，我们调查了大量和微米级分布的铁，砷，磷和锰和形态的铁，锰和砷在砂过滤器8年的操作后，使用大量和微聚焦X射线荧光光谱法（XRF）和X射线吸收光谱法（XAS）和扫描电子显微镜加上能量色散X射线检测（SEM-EDX）。缺氧地下水的有效充氧使得滤砂中的Fe、As和Mn被氧化去除。我们的研究结果表明，铁被保留在过滤器中作为2线的铁铁矿样的Fe-III沉淀物，涂层砂粒，并作为积累占主导地位的五价砷酸盐。非常密切的空间相关性，积累的As和P与整个过滤砂的铁，并下降到微米级和有效的Fe，P和As的保留在估计的平均水停留时间只有30分钟表明，它们的吸收是由快速吸附反应，表面催化的Fe-II氧化和介导的As-III共氧化的组合。与此相反，锰保留在单独的Mn-IV/III-（羟基）氧化物涂层和结核，可能是由于耦合的表面催化和微生物Mn-II氧化。硅酸盐吸附到铁铁矿样的Fe-III-涂层抑制其结晶和相关的再活化的P和As。过滤器的定期排水和通风有利于任何残留的Fe-II和As-III的氧化以及致密的Fe沉淀物的形成，从而可能有助于过滤器在几年内的有效运行。
Household sand filters are widely used in Vietnam to remove As, Fe and Mn from anoxic groundwater used as a drinking water resource. To expand the mechanistic knowledge of the filter functioning, we investigated the bulk and micrometre-scale distribution of Fe, As, P and Mn and the speciation of Fe, Mn and As in a sand filter after 8 years of operation using bulk and micro-focussed X-ray fluorescence spectrometry (XRF) and X-ray absorption spectroscopy (XAS) and scanning electron microscopy coupled with energy dispersive X-ray detection (SEM-EDX). Effective oxygenation of the anoxic groundwater enables the oxidative removal of Fe, As and Mn in the filter sand. Our results show that Fe is retained in the filter as a 2-line ferrihydrite-like Fe-III-precipitate that coats sand grains, and that As accumulates dominantly as pentavalent arsenate. The very close spatial correlation of accumulated As and P with Fe throughout the filter sand and down to the micrometre-scale and the effective Fe, P and As retention at an estimated average water residence time of only 30min suggest that their uptake is governed by a combination of fast sorption reactions, surface-catalysed Fe-II oxidation and mediated As-III co-oxidation. In contrast, Mn is retained in separate Mn-IV/III-(oxyhydr)oxide coatings and concretions, probably as a result of coupled surface-catalysed and microbial Mn-II oxidation. Silicate sorbed to the ferrihydrite-like Fe-III-coatings inhibits their crystallisation and associated remobilisation of P and As. The periodic drainage and aeration of the filter favours the oxidation of any residual Fe-II and As-III and the formation of dense Fe precipitates and may thereby contribute to effective filter operation over several years.