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Updated: Jun 16, 2026
Atomic Force Microscopy Cantilever-Based Nanoindentation: Mechanical Property Measurements at the Nanoscale in Air and Fluid
Published on: December 2, 2022
Change in surface properties of Microthrix parvicella upon addition of polyaluminium chloride as characterized by
Jildiz Hamit-Eminovski1, Krister Eskilsson, Thomas Arnebrant
1Faculty of Health and Society, Biomedical Laboratory Science and Technology, Malmo University, Malmo, Sweden. jildiz.hamit@mah.se
Abstract:
The filamentous bacterium Microthrix parvicella causes severe separation and foaming problems at wastewater treatment plants (WWTPs). An effective control of the bacterium in activated sludge WWTPs can be accomplished by dosage with polyaluminium chloride (PAX-14). The purpose of this study was to investigate whether addition of PAX-14 affects surface properties such as the hydrophobicity of the bacterium and to study the exopolymers of M. parvicella that host surface-associated enzymes. To this end, force measurements by atomic force microscopy were carried out to measure the interactions between hydrophilic and hydrophobized tips and the bacterium surface. Addition of PAX-14 caused no changes in the hydrophobicity of the bacterium surface but the data indicate that it collapsed the polymeric layer likely due to electrostatic screening. It is concluded that the collapse of the polymeric layer may affect the transport of substrates (eg free fatty acids) to the bacterium and hence the competitiveness of M. parvicella compared to the other bacteria present in activated sludge.
Insights
Polyaluminium chloride (PAX-14) effectively controls Microthrix parvicella in wastewater treatment. While it doesn't alter bacterial hydrophobicity, PAX-14 collapses the exopolymer layer, potentially impacting substrate transport and M. parvicella's competitiveness.
Area of Science:
- Environmental microbiology
- Wastewater treatment technologies
Background:
- Microthrix parvicella is a filamentous bacterium causing operational issues like foaming in wastewater treatment plants (WWTPs).
- Polyaluminium chloride (PAX-14) is utilized for controlling M. parvicella in activated sludge systems.
Purpose of the Study:
- To investigate the effect of PAX-14 on the surface properties, specifically hydrophobicity, of M. parvicella.
- To examine the exopolymers of M. parvicella and their role in hosting surface-associated enzymes.
Main Methods:
- Atomic force microscopy (AFM) was employed to conduct force measurements.
- Interactions between the M. parvicella surface and both hydrophilic and hydrophobized AFM tips were analyzed.
Main Results:
- PAX-14 addition did not induce changes in the hydrophobicity of the M. parvicella surface.
- Data suggest that PAX-14 induced a collapse of the bacterium's polymeric layer, likely through electrostatic screening.
Conclusions:
- The collapse of the exopolymer layer by PAX-14 may hinder substrate transport to M. parvicella.
- This altered transport could affect the competitive advantage of M. parvicella over other bacteria in activated sludge.
