Arsenic removal from iron-containing groundwater by delayed aeration in dual-media sand filters

Md Annaduzzaman, Luuk C. Rietveld, Bilqis Amin Hoque, Md Niamul Bari, Doris van Halem

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Generally, abstracted groundwater is aerated, leading to iron (Fe2+) oxidation to Fe3+ and precipitation as Fe3+-(hydr)oxide (HFO) flocs. This practice of passive groundwater treatment, however, is not considered a barrier for arsenic (As), as removal efficiencies vary widely (15–95%), depending on Fe/As ratio. This study hypothesizes that full utilization of the adsorption capacity of groundwater native-Fe2+ based HFO flocs is hampered by rapid Fe2+ oxidation-precipitation during aeration before or after storage. Therefore, delaying Fe2+ oxidation by the introduction of an anoxic storage step before aeration-filtration was investigated for As(III) oxidation and removal in Rajshahi (Bangladesh) with natural groundwater containing 329(±0.05) µgAs/L. The results indicated that As(III) oxidation in the oxic storage was higher with complete and rapid Fe2+ oxidation (2±0.01 mg/L) than in the anoxic storage system, where Fe2+ oxidation was partial (1.03±0.32 mg/L), but the oxidized As(V)/Fe removal ratio was comparatively higher for the anoxic storage system. The low pH (6.9) and dissolved oxygen (DO) concentration (0.24 mg/L) in the anoxic storage limited the rapid oxidation of Fe2+ and facilitated more As(V) removal. The groundwater native-Fe2+ (2.33±0.03 mg/L) removed 61% of As in the oxic system (storage-aeration-filtration), whereas 92% As removal was achieved in the anoxic system.

Original languageEnglish
Article number124823
Number of pages10
JournalJournal of Hazardous Materials
Publication statusPublished - 2021


  • Anoxic storage
  • Arsenic removal
  • Drinking water treatment
  • Sand filtration

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