Millions of people in rural South Asia are exposed to high levels of arsenic through groundwater used for drinking. Many deployed arsenic remediation technologies quickly fail because they are not maintained, repaired, accepted, or affordable. It is therefore imperative that arsenic remediation technologies be evaluated for their ability to perform within a sustainable and scalable business model that addresses these challenges. We present field trial results of a 600 L Electro-Chemical Arsenic Remediation (ECAR) reactor operating over 3.5 months in West Bengal. These results are evaluated through the lens of a community scale micro-utility business model as a potential sustainable and scalable safe water solution for rural communities in South Asia. We demonstrate ECAR's ability to consistently reduce arsenic concentrations of ~266 μg/L to <5 μg/L in real groundwater, simultaneously meeting the international standards for iron and aluminum in drinking water. ECAR operating costs (amortized capital plus consumables) are estimated as $0.83-$1.04/m(3) under realistic conditions. We discuss the implications of these results against the constraints of a sustainable and scalable business model to argue that ECAR is a promising technology to help provide a clean water solution in arsenic-affected areas of South Asia.
Millions of people are exposed to
toxic levels of dissolved arsenic
in groundwater used for drinking. Iron electrocoagulation (FeEC) has
been demonstrated as an effective technology to remove arsenic at
an affordable price. However, FeEC requires long operating times (∼hours)
to remove dissolved arsenic due to inherent kinetics limitations.
Air cathode Assisted Iron Electrocoagulation (ACAIE) overcomes this
limitation by cathodically generating H2O2 in
situ. In ACAIE operation, rapid oxidation of Fe(II) and complete oxidation
and removal of As(III) are achieved. We compare FeEC and ACAIE for
removing As(III) from an initial concentration of 1464 μg/L,
aiming for a final concentration of less than 4 μg/L. We demonstrate
that at short electrolysis times (0.5 min), i.e., high charge dosage
rates (1200 C/L/min), ACAIE consistently outperformed FeEC in bringing
arsenic levels to less than WHO-MCL of 10 μg/L. Using XRD and
XAS data, we conclusively show that poor arsenic removal in FeEC arises
from incomplete As(III) oxidation, ineffective Fe(II) oxidation and
the formation of Fe(II–III) (hydr)oxides at short electrolysis
times (<20 min). Finally, we report successful ACAIE performance
(retention time 19 s) in removing dissolved arsenic from contaminated
groundwater in rural California.
Horizontal levees are a nature-based
approach for removing nitrogen
from municipal wastewater effluent while simultaneously providing
additional benefits, such as flood control. To assess nitrogen removal
mechanisms and the efficacy of a horizontal levee, we monitored an
experimental system receiving nitrified municipal wastewater effluent
for 2 years. Based on mass balances and microbial gene abundance data,
we determined that much of the applied nitrogen was most likely removed
by heterotrophic denitrifiers that consumed labile organic carbon
from decaying plants and added wood chips. Fe(III) and sulfate reduction
driven by decay of labile organic carbon also produced Fe(II) sulfide
minerals. During winter months, when heterotrophic activity was lower,
strong correlations between sulfate release and nitrogen removal suggested
that autotrophic denitrifiers oxidized Fe(II) sulfides using nitrate
as an electron acceptor. These trends were seasonal, with Fe(II) sulfide
minerals formed during summer fueling denitrification during the subsequent
winter. Overall, around 30% of gaseous nitrogen losses in the winter
were attributable to autotrophic denitrifiers. To predict long-term
nitrogen removal, we developed an electron-transfer model that accounted
for the production and consumption of electron donors. The model indicated
that the labile organic carbon released from wood chips may be capable
of supporting nitrogen removal from wastewater effluent for several
decades with sulfide minerals, decaying vegetation, and root exudates
likely sustaining nitrogen removal over a longer timescale.
Corrosion is a major obstacle to a safe implementation of geotechnical applications. Using a novel approach that includes vertical scanning interferometry (VSI) and electrochemical impedance spectroscopy (EIS) we discuss timedependent carbon steel corrosion and film formation at geothermally relevant temperatures (80-160°C) in CO2saturated mildly acidic Na-Cl brine. Iron dissolution kinetics follows a logarithmic rate at 80 and 160°C and a linear rate at 120°C. At 80°C, high initial corrosion rates (first 24 hours) generate H2 at a minimum rate of 12 µmol h-1 cm-2 and lead to the formation of a continuous ~100 µm thick porous corrosion film. It exhibits a duplex structure with a crystalline outer FeCO3 layer and an inner layer composed of a skeletal network of Fe3C impregnated with FeCO3. Being an electrical conductor we hypothesize the Fe3C to strongly enhance corrosion rates by providing additional cathodic sites. Pseudo-passivity due to an anodic film-forming reaction (presumably Fe-oxide) was observed at 120 and 160°C, soon followed by the initiation of pitting at 120°C. Steady-state corrosion rates at 160°C are at least one order of magnitude lower than for 120°C. Our experimental approach demonstrated potential for general applicability in studying corrosion-related phenomena.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.