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| Titel |
Biogeochemical impacts of aquifer thermal energy storage at 5, 12, 25 and 60°C investigated with anoxic column experiments |
| VerfasserIn |
M. Bonte, B. M. van Breukelen, P. W. J. J. Van Der Wielen, P. J. Stuyfzand |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250063491
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| Zusammenfassung |
| Aquifer thermal energy storage (ATES) uses groundwater to store energy for heating or
cooling purposes in the built environment. ATES systems are often located in the same
aquifers used for public drinking water supply, leading to urgent questions on its
environmental impacts. This contribution presents the results of research on the
biogeochemical impacts of ATES in anoxic column experiments at 5, 12, 25, and
60Ë C. In- and effluents are analyzed for major ions, trace elements, heavy metals,
dissolved organic carbon (DOC) and UV extinction. Terminal restriction fragment
length polymorphism (T-RFLP) of 16S rRNA genes and analysis of adenosine
triphosphate (ATP) were used to detect changes in the microbiological population and
activity.
Results from the column experiments at 5, 25, and 60Ë C compared to the reference
column at 12Ë C showed a number of changes in biogeochemical conditions: At 5Ë C, only
changes were observed in alkalinity and calcium concentrations, resulting from calcite
dissolution. The 25Ë C and 60Ë C column effluents from a sediment containing
Fe-(hydr)oxides showed an increase in arsenic concentrations, well above the drinking water
limit. This is due to either (reductive) dissolution of, or desorption from, iron(hydro)xides
containing arsenic. In addition, at these two temperatures sulfate reduction occurred while
this was undetectable at 5 and 12Ë C within the given timeframe (25 days) and analytical
accuracy. The carbon source for sulfate reduction is inferred to be sedimentary organic
carbon. Increasing DOC with residence time in the 60Ë C effluent suggests that at 60Ë C
the terminal sulfate reduction step is rate limiting, while at 25Ë C the enzymatic
hydrolization step in sulfate reducing bacteria is overall rate limiting. Specific ultraviolet
absorption (SUVA, the ratio of UV extinction and DOC) however shows a clear
decrease in reactivity of the humic acid fraction in DOC. This means that the DOC
accumulation at 60Ë C could also be interpreted as a shift from pure microbial mediated
organic carbon hydrolysis to chemical organic carbon respiration, yielding less
reactive humic acids. The results from the T-RFLP and ATP analyses showed that the
microbial population at 60Ë C was clearly different and less active than at lower
temperatures.
Overall, it is concluded that water quality can change when higher temperatures (>25 Ë
C) are invoked on anoxic sediments. Impacts from cold storage are limited. This implies that
care should be taken when positioning ATES systems at higher temperatures in aquifers that
are used for public drinking water supply. |
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