title: 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.
authors.forename: Yun
authors.initials: Y
authors.lastname: Shen
authors.forename: Conghui
authors.initials: C
authors.lastname: Huang
authors.forename: Guillermo L
authors.initials: GL
authors.lastname: Monroy
authors.forename: Dao
authors.initials: D
authors.lastname: Janjaroen
authors.affiliation: Eawag: Swiss Federal Institute of Aquatic Science and Technology , 8600 Dübendorf, Switzerland.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Derlon
authors.forename: Jie
authors.initials: J
authors.lastname: Lin
authors.forename: Rosa
authors.initials: R
authors.lastname: Espinosa-Marzal
authors.affiliation: Eawag: Swiss Federal Institute of Aquatic Science and Technology , 8600 Dübendorf, Switzerland.|Institute of Environmental Engineering, ETH Zürich , 8093 Zürich, Switzerland.
authors.forename: Eberhard
authors.initials: E
authors.lastname: Morgenroth
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Boppart
authors.affiliation: School of Public Health, University of Alberta , Edmonton, AB T6G 2G7 Canada.
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Ashbolt
authors.forename: Wen-Tso
authors.initials: WT
authors.lastname: Liu
authors.forename: Thanh H
authors.initials: TH
authors.lastname: Nguyen
mesh_terms: D018441:Biofilms / Q000187:drug effects*; D018533:Biomass; D002700:Chloramines / Q000494:pharmacology; D002713:Chlorine / Q000494:pharmacology; D004202:Disinfectants / Q000494:pharmacology*; D004203:Disinfection / Q000379:methods; D060766:Drinking Water / Q000382:microbiology*; D055119:Elastic Modulus; D018625:Microscopy, Atomic Force; D013997:Time Factors; D041623:Tomography, Optical Coherence; D018508:Water Purification / Q000379:methods*
chemical_list: D002700:Chloramines; D004202:Disinfectants; D060766:Drinking Water; D002713:Chlorine; C030816:chloramine