Subsurface Iron and Arsenic Removal

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2 Subsurface iron removal in the Netherlands Fe 2+ adsorption. In the dual well design, two wells are intermittently used for injection or abstraction. The single-well design can be found most in Dutch drinking water production practices, as a normal production well can be relatively easily transitioned into a subsurface iron removal well. Apart from iron removal, the SIR technology has also been applied for the removal of manganese and arsenic, with varying results (van Beek, 1985; Rott et al., 2002; van Halem et al., 2010). In the Netherlands it is even operated at some locations to enhance the nitrification process in subsequent biosand filters (de Vet et al., 2009), illustrating the beneficial side effects of SIR. Although subsurface iron removal has been applied for several decades in Europe it has not found widespread attention elsewhere. The objective of this study was to present an overview of the experience at two water treatment plants (WTPs) in the Netherlands that have operated subsurface iron removal for several decades: WTP Corle and WTP Lekkerkerk. The overview includes information on the site-specific conditions and Fe removal efficacies, resulting in an analysis of the current knowledge on the influence of groundwater matrix and operational mode on the longterm and sustainable application of SIR. Subsurface iron removal sites Vitens Water Supply Company The majority of the subsurface iron removal treatment plants are located in the eastern provinces of the Netherlands (Figure 2.4). Vitens Water Supply Company is currently responsible for the operation of 10 SIR plants. SIR wells have been operated since 1977 at WTP Vorden and WTP ‘t Klooster, whereas WTP Corle, WTP Eerbeek and WTP de Pol started subsurface treatment in 1980. A decade later, WTP Aalten was constructed in 1990 and has been applying SIR ever since. The number of SIR wells varies per location with 4 wells at WTP Aalten up to 14 wells at WTP De Pol; in total 77 SIR wells are currently in operation by Vitens. In general, Vitens operates their SIR wells based on the volumetric V/Vi ratio, where iron concentration may never exceed 1.8 µmol.L -1 . The V/Vi ratio is determined for every well individually and then operated for several years before this ratio is retested, unless of course, iron concentrations exceed the limit of 1.8 µmol.L -1 . At a number of the water treatment plants Vitens has started to enrich the injection water with pure oxygen to increase the oxygen content from 0.28 mmol.L -1 to 0.55 mmol.L -1 in order to operate at higher V/Vi ratios. Currently, the treatment plants of Vitens operate their SIR wells with injection volumes of 2,000 or 3,000 m 3 and V/Vi ratios varying between 6 and 20. 2 27
Subsurface iron and arsenic removal for drinking water treatment in Bangladesh 2 Oasen Drinking Water Company The three locations in the west of the Netherlands, WTP Lekkerkerk (since 1998), WTP De Put (1981- 1988, and 1996-current) and WTP ‘t Kromme Gat (1983-2010), are operated by Oasen Drinking Water Company. Oasen operates subsurface aeration, a less intensive form of subsurface iron removal, since 1980. The operation of the injection-abstraction wells are not optimized to target iron removal, but the purpose of 1. Aalten 2. Corle 3. De Pol 4. Dinxperlo 5. Gorssel 6. Noordijk 7. ‘Klooster 8. Vorden 9. Zutphen 10. Eerbeek 11. Lekkerkerk 12. ’t Kromme Gat 13. De Put subsurface aeration is the enhancement of nitrification in the dry biofilters (de Vet, 2011). After subsurface aeration the water is mixed with other sources before treatment. The total amount of injection water is only 1% of the total abstracted raw water. The retention of iron, arsenic and phosphate is, in this case, a side effect observed during subsurface treatment for enhanced nitrification. As iron and other constituents are allowed to arrive at elevated concentrations in the well, the measurements at these locations provide information on the constituent behaviour during an injectionabstraction cycle. Influence of pH The pH of the groundwater influences the efficiency of subsurface iron removal both during injection (oxidation) and abstraction (adsorption). During injection the heterogeneous oxidation reaction is catalyzed at higher pH ranges (Tamura et al., 1980; Sung and Morgan, 1980): d [ Fe ] dt Equation 2.3 [ S − OH ][ Fe ][ O ] [ H ] 0 2+ 2+ 2 hetero = − k 2 + Figure 2.4 Geographical locations of subsurface iron removal WTPs in the Netherlands (Gorssel has been shut down) The value of k 2 depends on the type of mineral structure, being lowest for the more crystalline iron (oxy)hydroxides (goethite, lepidocrocite). When 28
Page 1 and 2: Doris van Halem Subsurface Iron and
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5 Cation exchange during subsurface
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5 Cation exchange during subsurface
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6 Characterization of accumulated d
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7 Catalysis by accumulated deposits
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8 Influence of groundwater composit
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Concluding remarks9
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9 Concluding remarks outlook is giv
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9 Concluding remarks with SIR in th
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9 Concluding remarks have the tende
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9 Concluding remarks Sharma S.K. (2
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Summary Subsurface iron and arsenic
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Summary Apart from adsorptive-catal
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Samenvatting Ondergrondse ijzer-en
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Samenvatting Fe 3+ oxiden. Niettemi
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Samenvatting drinkwaterkwaliteit, m
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List of publications List of public
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List of publications Disaster Relie
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Subsurface Iron and Arsenic Removal

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