Kolloider Stofftransport bei der Regenwasserversickerung (KORESI)
- Einfluß von Biofilmen auf die Mobilität von Kolloiden (KORESI)
- Verbundprojekt, gefördert durch die Deutsche Forschungsgemeinschaft (DFG) (Juni 2001 bis November 2003; fortgesetzt: April 2003 bis April 2005)
- Beteiligt sind neben der Universität Duisburg-Essen die Universität Karlsruhe, die TU Hamburg-Harburg und die TU München.
Leon-Morales, F., Leis, A.P., Strathmann, M., Flemming, H.-C. (2004): Interactions between laponite and microbial biofilms in porous media: implications for colloid transport and biofilm stability. Wat. Res. 38, 3614-3626
It is now widely accepted that the transport of colloids including biocolloids in the subsurface has important implications for the fate of diverse contaminants. Several studies have focused on studying the transport of particles under a wide variety of electrochemical and physicochemical conditions. The necessity to closely characterise a system in situ has limited somehow the acquirement of more realistic data by studying the transport of colloids in isolated conditions. This is evidenced by the not unusual disagreement between data coming from the field and that coming from the laboratory. By combining two experimental approaches, quartz sand packed columns and quartz sand packed flow cells, we report here interactions among two types of colloids as they undergo transport processes in saturated porous media. The artificial clay laponite RD was used as model inorganic colloid and a known biofilm forming bacterium, Pseudomonas aeruginosa SG81, was used as a biocolloid representative. Both types of colloids obeyed similar physicochemical laws concerning initial attachment and aggregation processes. P. aeruginosa SG81 additionally was found to colonise the media and form patchy localised biofilms on top of sand grains with the nutrient load provided. The transport of laponite through colonised sand was altered in a complex way by a combination of indirect effects like changes in porous medium chemical and hydrodynamic conditions due to biofilm growth, and direct interactions with attached bacteria and/or biofilm components like extracellular polymeric substances, EPS. A clear increment on cell detachment rate is observed which also implies alterations on biofilm physiology and activity. These observations are relevant for natural environments in which the potential interaction among different colloids and biofilms could result in altered transport patterns of contaminants which cannot be explained usually by the existent theoretical models.
Leon-Morales, F., Strathmann, M., Flemming, H.-C. (submitted): Influence of biofilms on the movement of colloids in porous media. Implications for colloid facilitated transport in subsurface environments. Wat. Res.
Colloid transport through porous media can be influenced by the presence of biofilms. Sterile and non-sterile sand columns were investigated using Laponite RD as model colloid and a highly mucoid strain of Pseudomonas aeruginosa as model biofilm former. Laponite RD was marked specifically by fluorescent complexes with rhodamine 6G. Breakthrough curves (BTC´s) were used as parameters for determination of colloid transport characteristics. In the sterile columns, the colloid was mobile (collision efficiencies from 0.05 to 0.08) both after the presence of Na+ and Ca2+ ions followed by deionised water influent. In the biofilm-grown column, the same treatment did not result in colloid retention in the case of Na+ exposure, but in altered or enhanced colloid transport due probably to co-elution effects or electrostatic repulsion. In the case of Ca2+ ions exposure, colloid retention increased with biofilm age. After 3 weeks, almost complete retention was observed. Similar observations were made in columns packed with material from slow sand filtration units. These data reveal the complex interactions between biofilms, cations and colloid transport. Changes in the electrolyte composition of water percolating the subsurface can frequently occur and will result in different colloid transport characteristics with regard to the dominating species of ions and the relative abundance of microbial biofilms. This has to be considered when modelling colloid transport through the subsurface.