Contributions of homogeneous, heterogeneous and biological iron(II) oxidation in aeration and rapid sand filtration (RSF) in field sites

“In groundwater treatment, after aeration, iron(II) is precipitated in rapid sand filtration (RSF) by
homogeneous, heterogeneous and biological oxidation. The contribution of homogeneous iron(II)
oxidation may be calculated from equations and constants available in literature. Heterogeneous iron
(II) oxidation produces hydrous ferric oxides coated filter sand, resulting in a growing filter bed height,
from which the contribution of heterogeneous iron(II) oxidation may be estimated. The complement
is contributed by biological iron(II) oxidation. At present this contribution may also be estimated by
Gallionella spp. counts by quantitative real-time polymerase chain reaction. Based on field data of
drinking water treatment plants from the Netherlands and Belgium, it appears that at pH ≈ 7.5
biological iron(II) oxidation is the main iron(II) removal process. At higher pH homogeneous iron(II)
oxidation becomes dominant, while at lower pH heterogeneous iron(II) oxidation delivers a relevant
contribution. The distribution of these oxidation processes is influenced by RSF operation such as
presence of supernatant water, wet or dry (trickle) filtration, oxygen concentration, filter velocity, etc.
Experience shows that the distribution between these three iron(II) oxidation processes may change
over time. These results are important for RSF operation, iron sludge production, and fields like
chemical well clogging.”

© IWA Publishing 2015

(Citaat: van Beek, C.G.E.M., Dusseldorp, J. et al. Contributions of homogeneous, heterogeneous and biological iron(II) oxidation in aeration and rapid sand filtration (RSF) in field sites – Journal of Water Supply Research and Tech. Aqua 65(2016)3, p.195-207)