Abstract
Although earlier circumstantial observations have suggested the presence of iron oxidizing bacteria (IOB) in groundwater-fed rapid sand filters (RSF), ferrous iron (Fe(II)) oxidation in this environment is often considered a chemical process due to the highly oxic and circumneutral pH conditions. The low water temperature (5–10°C), typical of groundwaters, on the other hand, may reduce the rates of chemical Fe(II) oxidation, which may allow IOB to grow and compete with chemical Fe(II) oxidation. Hence, we hypothesized that IOB are active and abundant in groundwater-fed RSFs. Here, we applied a combination of cultivation and molecular approaches to isolate, quantify, and confirm the growth of IOB from groundwater-fed RSFs, operated at different influent Fe(II) concentrations. Isolates related to Undibacterium and Curvibacter were identified as novel IOB lineages. Gallionella spp. were dominant in all waterworks, whereas Ferriphaselus and Undibacterium were dominant at pre-filters of waterworks receiving groundwaters with high (>2 mg/l) Fe(II) concentrations. The high density and diversity of IOB in groundwater-fed RSFs suggest that neutrophilic IOB may not be limited to oxic/anoxic interfaces.
Highlights
Rapid sand filters (RSFs) receive continuous inputs from groundwater sources and this input may vary depending on the temporal and spatial dynamics of the aquifer (Gülay et al, 2016)
In Islevbro drinking water treatment plants (DWTPs) the groundwater is subjected to RSF with the following treatment chain: aeration, prefiltration in a rock filter bed, and after-filtration in 12 sand bed filters with coarse grained sand (Supplementary Figure S2b; particle diameter 2–5 mm) overlaying a supporting gravel medium layer (Supplementary Figure S2a)
Gallionella and Leptothrix lineages were assumed to constitute the diversity of iron oxidizing bacteria (IOB) in RSFs and quantifications of IOB in RSFs have been made using specific 16S rRNA gene primers
Summary
Rapid sand filters (RSFs) receive continuous inputs from groundwater sources and this input may vary depending on the temporal and spatial dynamics of the aquifer (Gülay et al, 2016). Ferrous iron [Fe(II)] is a commonly occurring constituent in anaerobic groundwaters. Fe(II) concentrations vary significantly between the aquifers depending on the specific geological conditions (Søgaard and Madsen, 2013). Presence of Fe(II) in source waters requires a strict treatment to produce drinking water, as iron can cause bad taste, discoloration, turbidity and can support microbial growth in distribution systems (Sharma et al, 2005). Are Novel IOB oxidation by intensive aeration, and subsequent removal of iron oxyhydroxide precipitates by RSF (Twort et al, 2000)
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