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| Titel |
Transformations of Nitrogen from Secondary Treated Wastewater when Infiltrated in Managed Aquifer Recharge Schemes |
| VerfasserIn |
Matthew Silver, Annette Wefer-Roehl, Christine Kübeck, Christoph Schüth |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250125300
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| Publikation (Nr.) |
 EGU/EGU2016-4862.pdf |
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| Zusammenfassung |
| The EU FP7 project MARSOL seeks to address water scarcity challenges in arid regions,
where managed aquifer recharge (MAR) is an upcoming technology to recharge depleted
aquifers using alternative water sources. Within this framework, we conduct column
experiments to investigate transformations of nitrogen species when secondary treated
wastewater (STWW) is infiltrated through two natural soils being considered for managed
aquifer recharge. The soils vary considerably in organic matter content, with total organic
matter determined by loss on ignition of 6.8 and 2.9 percent by mass for Soil 1 and Soil 2,
respectively. Ammonium (NH4+) concentrations as high as 8.6 mg/L have been measured in
pore water samples from Soil #1, indicating that ammonium could be a contaminant of
concern in MAR applications using STWW, with consideration of the EU limit of 0.5 mg/L
for NH4+.
The two forms of nitrogen with the highest concentrations in the secondary treated
wastewater are nitrate (NO3−) and dissolved organic nitrogen (DON). In water samples taken
from the soil columns, a mass balance of measured ions shows a deficit of nitrogen
in ionic form in the upper to middle depths of the soil, suggesting the presence
of unmeasured species. These are likely nitrous oxide or dinitrogen gas, which
would signify that denitrification is occurring. Measurements of N2O from water
samples will verify its presence and spatial variation. The ammonium concentrations
increase slowly in the upper parts of the soil but then increase more sharply at greater
depth, after NO3− is depleted, suggesting that DON is the source of the produced
NH4+.
The production of NH4+ is presumed to be facilitated microbiologically. It is
hypothesized that at higher organic carbon to total nitrogen (C:N) ratios, more NH4+ will be
formed. To test this, in the experiments with Soil #2, three different inflow waters are used,
listed in order of decreasing C:N ratio: STWW, STWW with NO3− added to a concentration
of 80 mg/L, and STWW diluted with tapwater and with NO3− added to 80 mg/L. Soil pore
water samples show that at 30 cm depth, NH4+ concentrations are highest with the original
STWW, and progressively lower with the NO3− enriched STWW and the tapwater-diluted
STWW. This shows that the C:N ratio of the inflow water is positively correlated
with NH4+ concentration in soil water and suggests lower inflow C:N ratios may
diminish NH4+ production. In addition, outflow rates from the column with unaltered
STWW are approximately 15% higher than outflow rates from the column with
added NO3−, an effect that could be caused by gas (N2 or N2O) clogging of the
soil.
As MAR is an upcoming technology already being practiced, these results will be used to
develop guidance on how to mitigate the impact of pollutants to groundwater (NH4+) and the
atmosphere (N2O). Key factors diminishing the production of NH4+ appear to be lower
organic matter content of the soil and elevated NO3− concentrations in the inflow water,
although the latter could have adverse effects with respect to emission of N2O. |
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