Complex waters and microbial control challenges

BACKGROUND: While disinfectants are paramount to controlling pathogens and problematic microbes of various types of water systems, treatment effectiveness can be hampered by inherent constituents of a water environment. Biofilm as a common component of water microcosms can obstruct treatment by limiting the interaction of disinfectant molecules with microbes embedded within the biofilm matrix. In this study, turbid water was examined to understand the dynamics of diffusion through and disinfectant reactivity with suspended biofilm. METHODS: Estuarine recreational beach water of the Magothy River (Chesapeake Bay watershed) was examined microscopically (brightfield and polarized light) to characterize suspended biofilm architecture. Turbid water samples (untreated and dispersed by chemical and physical treatments) were compared to understand the significance of intact biofilm as a barrier to diffusivity and disinfectant reactivity. Diffusion rates of intact and dispersed biofilm were derived from uptake of a cationic compound (methylene blue). Disinfectant reactivity of intact and dispersed biofilm was based on chlorine (HOCl/OCl-) consumption rates. Biofilm disaggregation was evaluated by quantifying release of UV-absorbing materials. RESULTS: Water turbidity consisted primarily of floccular biofilm masses harboring the vast majority of microbial populations. Significant disaggregation of biofilm by chemical and physical treatments was demonstrated by microscopic examination and release of UV-absorbing material. Barrier properties of intact biofilm were illustrated by lower diffusivity and disinfectant reactivity as compared with dispersed samples. CONCLUSION: Biofilms can degrade microbial control effectiveness by limiting disinfectant reaching and reacting with microorganisms. Microbial control strategies that include biofilm disruption could render microbes more susceptible to disinfectant and improve treatment.