25th International Meeting on Organic Geochemistry IMOG 2011

P-397
Impact of different operating modes on the indigenous microbial
ecosystems in energy storage systems in the North German
Basin: Compositional changes and membrane phospholipid
adaptation
Alexandra Vetter 1 , Kai Mangelsdorf 1 , Stephanie Lerm 1 , Mashal Alawi 1 , Andrea Seibt 2 ,
Markus Wolfgramm 3 , Hilke Würdemann 1 , Andrea Vieth-Hillebrand 1
1 GFZ German Research Centre for Geosciences, Potsdam, Germany, 2 BWG Geochemische Beratung GbR,
Neubrandenburg, Germany, 3 Geothermie Neubrandenburg GmbH (GTN), Neubrandenburg, Germany
(corresponding author:vetter@gfz-potsdam.de)
The composition of microbial communities was
examined in three geothermal energy storages in the
North German Basin. These aquifer thermal energy
storages (ATES) differ in depth (20 to 1250 m), in fluid
chemistry (freshwater, brine), and functionality
(heat/cold storage). To investigate the microbial
ecosystems the bacterial membrane phospholipid
fatty acid (PLFA) composition and the fluid chemistry,
especially, of potential nutrient for the indigenous
microorganisms such as sulfate, nitrate, low
molecular weight organic acids and DOC as well as
its carbon isotopic composition was evaluated.
A solar assisted heat storage located in a quaternary
freshwater aquifer in 15 to 30 m depth was monitored
concerning its microbial composition with respect to
the seasonal changes of charge and discharge of
heat. The plant stores the surplus heat with
temperatures of 50°C from the solar energy
production during summertime (charge mode).
Therefore, water is pumped from the cold side with
temperatures of 8 to 20°C, loaded with heat in a heat
exchanger and re-injected into the warm well.
Discharge of heat is carried out in wintertime, when
heat demand increases for space heating and
domestic hot water preparation in multi-family houses.
In wintertime, the PLFA composition of the indigenous
microbial community, mainly 16:1, 16:0, 18:1, 18:0,
and branched fatty acids (FA) with 15 and 17 carbon
atoms, showed an adaptation of the cell membrane
during the discharge mode, when temperature
decreases from 50 to 13.7°C during time of heat
extraction. This is reflected by a shift of 13.4 %
towards more unsaturated fatty acids (FA) and of 10.8
% towards more FAs with shorter chain length.
Moreover, the anteiso/iso ratio was higher at cooler
temperatures indicating a membrane temperature
adaptation of these microorganisms.
World‘s deepest heat storage in the North German
Basin (1250 m depth) stores surplus heat from a gas
and steam cogeneration plant in summertime, which
is used in wintertime for district heating. The fluid is
NaCl dominated with high sulfate concentration (ca. 1
g/L) and the DOC can account for 18 mg C/L.
Temperature ranges on the warm side from 90 to
65°C and on the cold side from 50 to 45°C. PLFA
profiles are dominated by iso- and anteiso-15:0 on the
cold side, while on the warm side 16:0 is the major
compound. Moreover, the PLFA patterns indicate
different compositions of the microbial communities
on the warm and cold side.
In contrast to shallow and deep heat storages,
another system, located in 30 to 60 m depth, in the
North German Basin is used as a cold storage for air
conditioning of buildings in summertime (discharge
mode). In wintertime (charge mode) the freshwater
from the warm side is pumped up, cooled down by an
air cooler and subsequently re-injected into the cold
side. Temperature ranges on the warm side from 14
to 30°C and on the cold side from 6 to 10°C. Within a
four years monitoring, two clogging events occur
during the discharge phase and the injection rates on
the warm side was reduced. PLFA pattern clearly
reveals changes in the microbial community
composition during the clogging events. During these
events the 16:1�7 fatty acid and 18:1�7 significantly
increase compared to the normal operating mode.
These fatty acids are known to be main constituents
of the iron oxidizing bacterium Gallionella [1] and the
sulphur oxidizing bacterium Thiothrix [2]. Both
bacteria are known to be involved in clogging events.
Microbiological analysis confirmed the occurrence of
these species during the disturbance time in the
storage system and inorganic investigations reveal
iron scales in the plant.
The study shows clearly that microorganisms are
capable to adapt to specific conditions within short
times and can influence the working reliability of
geothermal energy storages.
[1] Sahl et al. (2008) Appl. Environ. Microbiol., 74(1),
143-152.
[2] Zhang et al. (2005) Appl. Environ. Microbiol.,
71(4), 2106-2112.
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