Rheological characterisation of alginate-like exopolymer gels crosslinked with calcium

Rheological characterisation of alginate-like exopolymer gels crosslinked with calcium

Pfaff, N.M. (TU Delft BT/Environmental Biotechnology; TU Delft BT/Biotechnologie; Wetsus, European Centre of Excellence for Sustainable Water Technology)
Dijksman, J. A. (Wageningen University & Research)
Kemperman, A. J.B. (University of Twente; Wetsus, European Centre of Excellence for Sustainable Water Technology)
van Loosdrecht, Mark C.M. (TU Delft BT/Environmental Biotechnology; TU Delft BT/Biotechnologie)
Kleijn, J. M. (Wageningen University & Research)

BT/Biotechnologie

2021

Bacterial alginate-like exopolymers (ALE) gels have been used in this work as a model for the extracellular polymeric matrix of biofilms. Aim was to relate the mechanical properties and strength of this matrix that make biofilms as persistent to cleaning as they are, to the complex cohesive molecular interactions involved. Mechanical properties of the gels as a function of CaCO₃ concentration were investigated using dynamic and static rheology. Gels with relatively low CaCO₃ concentrations, between 100 μmol and 300 μmol per g ALE, were found to exhibit similar viscoelastic behaviour as real biofilms, with elastic moduli between 50 Pa and 100 Pa and dissipation factors between 0.2 and 0.3. Increasing CaCO₃ concentrations resulted in an increase of the elastic modulus up to 250 Pa, accompanied by an increase in brittleness. At a CaCO₃ concentration of 1250 μmol per g ALE this trend stopped, probably due to disturbance of the continuous ALE network by precipitation of salts. Therefore, overdosing of Ca salts can be an adequate approach for the removal of biofouling. All gels exhibited permanent strain hardening under medium strain, and their mechanical properties showed dependency on their strain history. Even after application of an oscillatory strain with 200% amplitude that caused the gel structure to collapse, the gels recovered 65 to 90% of their original shear modulus, for the major part within the first 20 s. Recovery was slightly less for gels with high CaCO₃ concentration. In creep tests fitted with a Burgers model with multiple Kelvin elements at least three different interactions in the ALE gels could be distinguished with characteristic retardation times in the range of 10, 100 and 1000 s. Further identification of the mechanisms underlying the gel mechanics will allow the development of targeted strategies to undermine the mechanical strength of biofouling and aid the cleaning process.

http://resolver.tudelft.nl/uuid:a0bac9ef-3534-4d5f-9b00-847ac59fcb31

https://doi.org/10.1016/j.watres.2021.117835

0043-1354

Water Research, 207

Institutional Repository

journal article

© 2021 N.M. Pfaff, J. A. Dijksman, A. J.B. Kemperman, Mark C.M. van Loosdrecht, J. M. Kleijn