Abstract
Soil Aquifer Treatment (SAT) systems are used around the world as
tertiary treatment for waste water reclamation. In SAT systems, waste
water are infiltrated through infiltration ponds into the aquifer, in
cycles of flooding and drying. SAT systems are able to enhance water
quality using natural traits of the soil environment (such as its
microbial community, which plays an important role in organic compound
degradation), combined with site-specific hydraulic operation. While
such sites operate successfully for decades, the need to increase
infiltration with already high hydraulic fluxes (up to 100 m/year) and
low water quality create unique challenges for optimal operation. In
this work, we present a series of experiments and developments
associated with SAT operation, starting with geophysical monitoring,
treatment of entrapped air, field monitoring and column experiments
tracking the biochemical dynamics under variety of hydraulic conditions.
Our focus is on the long column experiments, designed to examine the
effect of different drying periods and influent composition on oxygen
content and redox potential in a 6-meter sand column. Our experimental
set up included four main experiments, in which three different influent
solution-types were infiltrated through the column in varying cycles of
wetting and drying. We hypothesize that the hydraulic operation of the
column during the experiments (i.e. different wetting-drying ratios and
durations) and the different influent composition will result in
different bio-geo-chemical conditions in the soil profile. Our results
confirm that the deeper parts of the column are aerated less effectively
during the drying periods compared to the upper parts, the oscillation
patterns of the oxygen concentrations throughout the wetting-drying
cycles indicate that advective fluxes are significant in almost all
parts of the column and become increasingly more dominant as depth
increases. Further, we show that oxygen supply at different depths is
dominated by different mechanisms (convection of air phase, advection
as dissolved phase, and diffusion). The longer (240 minutes) drying
periods had an advantage over the shorter (150 minutes) periods in terms
of oxygen concentrations in the upper parts of the column as well as in
the deeper parts. Chemical analysis confirmed that nitrogen species, as
well as organic carbon were found in smaller concentrations in the
experiment with longer drying times. The data we gathered show that the
duration of the drying periods is detrimental for the bio-geo-chemical
state of the soil profile. Short drying periods might be beneficial for
the aeration of the upper vadose zone but may not be substantial enough
to allow oxygen recovery in the deeper parts and thus inflow quality
will be compromised. The quick oxygen recovery after an increase in the
drying periods suggests that combining short and long drying periods in
the same infiltration campaign might be beneficial for both the amount
of influent infiltrated and reclaimed water quality. To examine this,
however, additional research is needed.
Original language | English |
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Title of host publication | EGU2019, Proceedings from the conference held 7-12 April, 2019 in Vienna, Austria |
State | Published - 1 Apr 2019 |
Event | American Geophysical Union (AGU) Fall Meeting 2019 - San Francisco , United States Duration: 9 Dec 2019 → 13 Dec 2019 https://www.agu.org/fall-meeting-2019 |
Conference
Conference | American Geophysical Union (AGU) Fall Meeting 2019 |
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Country/Territory | United States |
City | San Francisco |
Period | 9/12/19 → 13/12/19 |
Internet address |