Biofilm control in water by advanced oxidation process (AOP) pre-treatment: effect of natural organic matter (NOM)

The main goal of this study was to examine the influence of natural organic matter (NOM) on the efficiency of H₂O₂/UV advanced oxidation process (AOP) as a preventive treatment for biofilm control. Pseudomonas aeruginosa PAO1 biofilm-forming bacteria were suspended in water and exposed to various AOP conditions with different NOM concentrations, and compared to natural waters. H₂O₂/UV prevented biofilm formation: (a) up to 24 h post treatment – when residual H₂O₂ was neutralized; (b) completely (days) – when residual H₂O₂ was maintained. At high NOM concentrations (i.e. 25 mg/L NOM or 12.5 mg/L DOC) an additive biofilm control effect was observed for the combined H₂O₂/UV system compared to UV irradiation alone, after short biofilm incubation times (<24 h). This effect was H₂O₂ concentration dependent and can be explained by the high organic content of these water samples, whereby an increase in NOM could enhance ^•OH production and promote the formation of additional reactive oxygen species. In addition, maintaining an appropriate ratio of bacterial surviving conc.: residual H₂O₂conc. post-treatment could prevent bacterial regrowth and biofilm formation.