Subsurface Iron and Arsenic Removal

Subsurface iron and arsenic removal for drinking water treatment in Bangladesh
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great potential of SIR, as the removal of iron improves
colour and taste of the water; greatly enhancing social
acceptance. From a technological perspective, the
effective removal of Fe 2+ has an additional advantage,
as the injection procedure start before arrival of Fe 2+ at
the well. Aeration is more effective in the absence of
Fe 2+ , making it easier to achieve high O 2
concentrations
without the production of iron sludge.
HWTS may never threaten the long-term
availability of a water source. For SIR/SAR this means
that a shallow tube well may not produce water of lesser
quality or quantity before, during or after use of this
technology. Clogging of the aquifer around a subsurface
iron removal well was addressed in Chapter 6, showing
that after 12 years of operation, iron had accumulated
at specific depths near the subsurface iron removal
wells. Whether it was due to preferred flow paths
or geochemical mineralogy conditions, subsurface
iron removal clearly favoured certain soil layers. The
majority of accumulated iron was characterized as
crystalline, suggesting that precipitated amorphous
iron oxides had transformed to iron oxides of higher
crystallinity. These crystalline, compact iron oxides
had not noticeably clogged the investigated well and/or
aquifer. The subsurface iron removal wells even needed
less frequent rehabilitation, as drawdown increase
was slower than in normal production wells. Other
groundwater constituents, such as manganese, arsenic
and strontium were found to co-accumulate with iron.
The accumulation of groundwater constituents
around a SIR/SAR well is a direct consequence of this
technology. And although it may seem undesirable
from a sustainability perspective, these accumulated
deposits do not harm human health or environment,
as long as they remain immobile. Both Fe and As are
abundantly available in sediments throughout the world
(Smedley and Kinniburgh, 2002), but it merely depends
on the local groundwater conditions whether these
constituents will dissolve. The remobilization of iron,
manganese, arsenic and phosphate was investigated
when a SIR well was stopped after 18 injectionabstraction
cycles (Chapter 2). At this particular
site, none of the studied constituents was found to
be released in the groundwater to concentrations
exceeding the background value for the operational
period of 2 years. The application of SIR at that site had
therefore not threatened the long-term operation of
this groundwater production well.
The future of small-scale SIR/SAR
This thesis has shown the potential of SIR as a household
drinking water treatment solution, nevertheless a
HWTS solution will only prove smart once it sustains
in the users’ environment. This elementary observation
comprises the real challenge for researchers who
design technologies for developing countries. Some
technologies might not yet be ready for implementation
in the near future, but can form a base for upcoming
trends. (Drinking water) engineers and researchers