Microbial processes and iron-mineral formation in household sand filters used to remove arsenic from drinking water in Vietnam
Final Report Abstract
Human consumption of arsenic-containing groundwater is putting the health of millions of people at risk, all over the world. Arsenic (As) acts as a toxin, and prolonged exposure to this metalloid causes lifethreatening diseases. For this reason, the world health organization (WHO) introduced a maximum level of 10 µg L^-1 for As in drinking water. Household sand filters are efficient at bringing As levels in water to or below the WHO limit, if the groundwater also contains iron (Fe) and manganese (Mn). These sand filters are widely used in areas of rural Vietnam and are practical for domestic use. Until now it was mostly unclear how exactly the As is retained in sand filters and if the As removal form groundwater is purely governed by abiotic processes, or if microorganisms are involved in the water treatment processes. Moreover, it was unknown whether microorganisms inhabiting the sand filter cause As re-mobilization and information regarding the effect of varying the frequency and duration of sand filter use, as well as sand replacement on residual As concentrations, was lacking. Therefore, the goals of this research project were to identify important abiotic and biotic processes contributing to or inhibiting As removal from groundwater, and to investigate the water treatment capacity of one sand filter in Vietnam. Comprehensive geochemical, mineralogical, microbial, and molecular biological approaches were used to address these gaps in knowledge. Our investigations showed that As and Fe redox transformations in the filter are driven to a large extent by abiotic processes, while Mn oxidation is mainly biotic. Fe(II), Mn(II), and As(III) oxidation, in particular the link of microbial Mn(II) oxidation and abiotic As(III) and Fe(II) oxidation by the microbially formed Mn(IV) oxides, contribute to the efficiency of the sand filter, with no evidence for Fe(III) or As(V) re-reduction. One further important outcome of our studies was that we showed that periods of intense daily filter use followed by periods of non-use, and even sand replacement did not significantly effect As removal efficiency. This interdisciplinary study provides a basis for the optimization and control of toxic metalloids in other sand filters and water treatment systems, which are applied to treat water contaminated by undesirable components. Thus, improvement of water treatment technologies for domestic use can greatly increase the quality of life in low-income and third-world countries.
Publications
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(2014). Solid-phase characterisation of an effective household sand filter for As, Fe and Mn removal from groundwater in Vietnam. Environmental Chemistry, 11(5): 566-578
Voegelin, A.; Kaegi, R.; Berg, M.; Nitzsche, K. S.; Kappler, A.; Lan, V. M.; Trang, P. T. K.; Göttlicher, J.; Steininger, R.
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(2015). Arsenic removal from drinking water by a household sand filter in Vietnam – effect of filter usage practices on arsenic removal efficiency and microbiological water quality. Science of the Total Environment, 502: 526-536
Nitzsche, K. S.; Lan, V. M.; Trang, P. T. K.; Viet, P. H.; Berg, M.; Voegelin, A.; Planer-Friedrich, B.; Zahoransky, J.; Müller, S.-K.; Byrne, J. M.; Schröder, C.; Behrens, S.; Kappler, A.
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(2015). Microbial community composition indicates nitrification as an important process in a household sand filter used to remove arsenic from drinking water in Vietnam; Chemosphere, 138: 47-59
Nitzsche, K. S.; Weigold, P.; Lösekann-Behrens, T.; Kappler, A.; Behrens, S.
