Leon Morales, Carlos Felipe:

Influence of biofilms on the transport of colloids and contaminants through porous media

Duisburg, Essen (2007), XVI, 147 Bl.
Dissertation / Fach: Chemie
Fakultät für Chemie » Biofilm Center
Flemming, Hans-Curt (Doktorvater, Betreuerin)
Förstner, Ulrich; Beech, Iwona (GutachterIn)
The main objective of this thesis was to investigate the influence of
biofilms on colloid transport in model sediment columns, at changing
fluid ionic conditions. Sandpacked columns and sandpacked microscopy
flow cells were used to determine colloid transport. The artificial
clay colloid laponite RD (LRD), and the biofilm forming bacterium,
Pseudomonas aeruginosa SG81 were used as model colloid and biofilm
forming microorganism, respectively. Changing ionic conditions were
simulated by using Ca2+ and Na+ based solutions as influents and then
switching to very low ionic strength solutions. Colloid transport
parameters as well as microbiological parameters were obtained using a
combination of online optical detection methods and offline
microbiological and biochemical analytical methods. In absence of
biofilms, a sodium chloride concentration of 7 x 10−2 M caused
complete retention of LRD within the sand columns. Although at 2000 mg
L−1 LRD, massive aggregation was observed and clogging occurred,
aggregation alone was not responsible for LRD retention at lower
concentrations (i.e., 200 or 20 mg L−1). P. aeruginosa SG81 showed
relatively low mobility at all ionic strengths tested and some (albeit
reduced) mobility when introduced to the columns in 1 M NaCl, the
highest concentration tested. In sterile columns, the presence of Na+
and Ca2+ ions in the influent followed by a low ionic strength
solution did not cause LRD retention. The colloid was mobile with
collision efficiencies from 0.05 to 0.08 (SE ≤ 20 %; n = 9). In the
presence of biofilms and after Na+ exposure, no colloid retention
occurred but in some cases altered or enhanced colloid transport was
observed. Colloid collision efficiency after 3 weeks of biofilm growth
was 0.03 (SE ≤ 10 %; n = 3). In contrast, after Ca2+ ions exposure,
colloid retention increased with biofilm age. After 3 weeks, almost
complete retention was observed with a collision efficiency of 0.9 (SE
≤ 20 %; n = 3). Similar observations were made in columns packed with
material from slow sand filtration units. EPS analysis from Ca2+
treated columns, showed that colloid retention also increased with an
increase in EPS content. Protein content was found to increase with
time in relation to other EPS components and to be significantly
correlated to colloid retention (0.999) at the established confidence
level. These data reveal the complex interactions between biofilms,
ions and colloid transport. Changes in the electrolyte composition of
water percolating the subsurface can frequently occur as well as
changes in the relative abundance of microbial biofilms. This has to
be considered when modeling colloid transport through the subsurface.