Groundwater arsenic in the Red River delta, Vietnam ... - Fiva

Noteworthy is, that the ratio of Fe/As ratio and concentration of phosphate in the
bank infiltrated water may be less favourable for successful treatment for As,
than that of non-river sourced groundwater. This was the case in our pumping
experiment. For example, the percentage of As removed by sand filtration
estimated according to Berg et al. (2006) from the concentration of dissolved Fe
dropped from 78% in the original groundwater to 64% in the bank filtrate. Even
at the lowered As concentration of the bank infiltrated water (from 250 to 150
μg/L) a higher final As concentration in the treated bank infiltrated water of 54
μg/L, relative to 50 μg/L in treated groundwater, is estimated. Hug et al. (2008)
provided a simple relationship for assessing the As removal which infers a
preferential removal of phosphate over As by sand filtration: RAs/Fe/P = (mFe–
1.8*mP)/mAs where m denotes a concentration in moles of Fe, As and P,
respectively. According to Hug et al. (2008) values of RAs/Fe/P above 54 are
needed for efficient As removal. However, in our pumping experiment, RAs/Fe/P
decreased from 61 in the unperturbed groundwater to just 30 in the infiltrated
channel water. If these conclusions apply more generally, then bank infiltration
appears to be preferable only if the groundwater resource becomes subject to
excessive utilization, as is the case in Hanoi (Berg et al., 2008), but currently not
in the rural areas of the Red River delta.
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