Sequential Fe&lt;sup&gt;2+&lt;/sup&gt; oxidation to mitigate the inhibiting effect of phosphate and silicate on arsenic removal

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

doi:10.1016/j.gsd.2022.100749

Sequential Fe²⁺ oxidation to mitigate the inhibiting effect of phosphate and silicate on arsenic removal

Title

Sequential Fe²⁺ oxidation to mitigate the inhibiting effect of phosphate and silicate on arsenic removal

Author

Annaduzzaman, M. (TU Delft Sanitary Engineering)
Rietveld, L.C. (TU Delft Water Management)
Hoque, Bilqis Amin (Environment and Population Research Centre)
van Halem, D. (TU Delft Sanitary Engineering)

Department

Water Management

Date

2022

Abstract

Sequential iron (as Fe²⁺) oxidation has been found to yield improved arsenic (as As(III)) uptake than the single-step oxidation. The objective of this study was to gain a better understanding of interactions with phosphate (PO₄³⁻) and silicate (SiO₄²⁻) during sequential Fe²⁺ and As(III) oxidation and removal, as these are typically found in groundwater and known to interfere with As removal. The laboratory experiments were performed using single and multi-step jar tests with an initial As(III/V), Fe²⁺, PO₄³⁻, SiO₄²⁻ concentrations, and pH of 200 μg/L, 2.5 mg/L, 2 mg/L, 16 mg/L and 7.0, respectively representing the targeted natural groundwater in Rajshahi district, Bangladesh. The sequential Fe²⁺ and As(III) oxidation in the multi-step jar tests indicated that the PO₄³⁻ hindrance on As removal in the first Fe²⁺ oxidation step was compensated for in the second. Moreover, smaller Fe flocs (<0.45 μm) were observed in the presence of SiO₄²⁻, potentially providing more surface area during the second Fe²⁺ oxidation step leading to better overall As removal. Altogether it may be concluded that controlling the As(III) and Fe²⁺ oxidation sequence is beneficial for As removal compared to single-step Fe²⁺ oxidation, both in the presence and absence of PO₄³⁻ and/or SiO₄²⁻.