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

Annaduzzaman, M.; Rietveld, L.C.; Amin Hoque, Bilqis; Bari, Md Niamul; van Halem, D.

doi:10.1016/j.jhazmat.2020.124823

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

Title

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

Author

Annaduzzaman, M. (TU Delft Sanitary Engineering)
Rietveld, L.C. (TU Delft Sanitary Engineering)
Amin Hoque, Bilqis (Environment and Population Research Center)
Bari, Md Niamul (Rajshahi University of Engineering & Technology)
van Halem, D. (TU Delft Sanitary Engineering)

Date

2021

Abstract

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.