Response of Simulated Drinking Water Biofilm Mechanical and Structural Properties to Long-Term Disinfectant Exposure

Abstract

Mechanical and structural properties of biofilms influence the accumulation and release of pathogens in drinking water distribution systems (DWDS). Thus, understanding how long-term residual disinfectants exposure affects biofilm mechanical and structural properties is a necessary aspect for pathogen risk assessment and control. In this study, elastic modulus and structure of groundwater biofilms was monitored by atomic force microscopy (AFM) and optical coherence tomography (OCT) during three months of exposure to monochloramine or free chlorine. After the first month of disinfectant exposure, the mean stiffness of monochloramine- or free-chlorine-treated biofilms was 4 to 9 times higher than those before treatment. Meanwhile, the biofilm thickness decreased from 120 ± 8 µm to 93 ± 6–107 ± 11 µm. The increased surface stiffness and decreased biofilm thickness within the first month of disinfectant exposure was presumably due to the consumption of biomass. However, by the second to third month during disinfectant exposure, the biofilm mean stiffness showed a 2- to 4-fold decrease, and the biofilm thickness increased to 110 ± 7–129 ± 8 µm suggesting that the biofilms adapted to disinfectant exposure. After three months of the disinfectant exposure process, the disinfected biofilms showed 2–5 times higher mean stiffness (as determined by AFM) and 6–13-fold higher ratios of protein over polysaccharide, as determined by differential staining and confocal laser scanning microscopy (CLSM), than the nondisinfected groundwater biofilms. However, the disinfected biofilms and nondisinfected biofilms showed statistically similar thicknesses (t test, p > 0.05), suggesting that long-term disinfection may not significantly remove net biomass. This study showed how biofilm mechanical and structural properties vary in response to a complex DWDS environment, which will contribute to further research on the risk assessment and control of biofilm-associated-pathogens in DWDS.

Optical coherence tomography in biofilm research: A comprehensive review

“…Such high values have previously only be reported from MRI/MRM experiments by Manz et al (). Thin biofilms of 30–40 μm were analyzed on membranes (Shen et al, ). OCT was also used to reveal how grazers in an oligotrophic environment control the mean biofilm thickness in a range of 50–250 μm.…”

“…From Equation (3) it can be derived that the higher the refractive index, the better the axial resolution. As OCT devices and software tools (e.g., ImageJ/Fiji, Schindelin et al, 2012) to date do only allow to set a single refractive index for the complete dataset, the refractive index of a biofilm is assumed to be n ¼ 1.333 (20 C) equal to that of water (Blauert et al, 2015;Dreszer et al, 2014;Fortunato et al, 2017b;Shen et al, 2016;Wagner et al, 2010b). This might be an acceptable assumption for an unaltered, sponge-like biofilm structure containing a high fraction of water.…”

Biosand Filter (BSF): Types and Mechanisms behind Its Efficiency

“…While DLVO theory is based on the assumption of a smooth and spherical particle, real colloidal systems in the environment may not fall into this homogeneous morphology and chemistry. In fact, discrepancies between DLVO predictions and experimental results have been noticed by many works [40][41][42][43][44][45][46][47]. These discrepancies lead to more in-depth investigations of the effects of surface topography and shape of the collector on particle interaction [40,43,[45][46].…”

“…Besides colloidal particles, pathogen adhesion on surfaces in an aqueous system has been of interest to many researchers in the past years [21,42,[48][49]. For example, bacteria attaching to the surface can lead to bio-layer formation.…”

Disinfection Processes

“…, Huang, Monroy, Janjaroen, Derlon, Lin, Espinosa-Marzal, Morgenroth, Boppart, Ashbolt,Liu and Nguyen (2016) monitored elastic modulus and structure of groundwater biofilms by atomic force microscopy and optical coherence tomographyduring three months of exposure to monochloramine or free chlorine. The study showed how biofilm mechanical and structural properties varied in response to a complex DWDS environment.Stanish et al (2016) assessed chemical and microbiological constituents of 17 municipal distribution systems to understand regional variations in drinking water microbiology in the upper Ohio River watershed.…”