REFLECT partners from the Netherlands Organisation for Applied Scientific Research (TNO), the University of Neuchatel (UNINE) and the Helmholtz Centre Potsdam – German Research Centre for Geosciences (GFZ) have jointly investigated the effect of organic compounds and microorganisms in the formation and precipitation of colloids using artificial brines. The University of Neuchatel provided the biological material (active and inactive bacteria/fungi) from its culture collection, which includes strains isolated from geothermal brines. A selection of organic compounds was made based on the analysis of the dissolved organic compounds from sampled fluids performed by GFZ. For the experiments on colloid formation, a method developed by TNO using dynamic light scattering (DLS) was used. This approach has proven to be a new way to study important aspects of homogeneous nucleation like induction time and relative amounts of precipitate formed.
Figure: Scanning Electron Microscope (SEM) pictures of the CaCO3 precipitates/scaling formed at 50 °C after 1 hour reaction time in the flow-loop set-up: (Left) on one biofilm (EPS and networks of hyphae (filamentous structures) of Penicillium citrinum) covered areas of the stainless steel substrate and (Right) on areas of the stainless steel substrate with no biofilm (residues) coverage.
First, an investigation of the effect of several common carboxylic acids on the formation of homogeneous calcium carbonate scale was conducted. All carboxylic acids tested had an inhibitory effect on the precipitation of calcium carbonate.
The second part of the work was dedicated to investigate the effect of a biofilm on the formation of calcium carbonate scale. The developed method using a small-scale dynamic set-up as well as a flow-loop set-up showed that the biofilm consisting of colonies of the bacterium Thermaerobacter sp., the fungus Penicillium citrinum, and formed (bacterial) extracellular polymeric substances (EPS) dissolve in flow configuration, especially at higher (≥ 50 °C) temperatures, making detailed kinetic investigations impossible.
However, the biofilm components seem to develop intense interaction with the ions, nuclei and/or crystals formed during the executed experiments, which could be shown by detailed microscopic studies.
The results from these investigations have been recently published in the REFLECT Deliverable 2.6 – Role of microorganisms and organic compounds.
