Disinfection-residual bacteria (DRB) after chlorine dioxide treatment: Microbial community structure, regrowth potential, and secretion characteristics

Abstract

This study investigates the effects of chlorine dioxide (ClO₂) disinfection on the community structure, regrowth potential, and metabolic product secretion of disinfection-residual bacteria (DRB) in secondary effluent (SE), denitrification filter effluent (DFE), and ultrafiltration effluent (UE). Results show that ClO₂ effectively reduces bacteria in SE and UE, achieving log removal values exceeding 3 at 1 mg/L within 30 min. A salient positive correlation (R² > 0.95) exists between changes in total fluorescence intensity and disinfection efficacy. Post-treatment, Acinetobacter abundance increased in SE, while Pseudomonas decreased in DFE and UE. At lower ClO₂ concentrations, Staphylococcus, Mycobacterium, Aeromonas, and Lactobacillus increased in DFE, but decreased at higher concentrations. After storage, bacterial counts in disinfected samples exceeded those in the control group, surpassing 10⁵ CFU/mL. Despite an initial decline, species richness and evenness partially recovered but remained lower than control levels. Culturing DRB for 72 h showed elevated extracellular polymeric substances (EPS) secretion, quantified as total organic carbon (TOC), ranging from 5 to 27 mg/L, with significantly higher EPS in the disinfection group. Parallel factor analysis with self-organizing maps (PARAFAC-SOM) effectively differentiated water sample types and EPS fluorescent substances, underscoring the potential of three-dimensional fluorescence as an indirect measure of ClO₂ disinfection efficacy.

Keywords: Chlorine dioxide; Disinfection-residual bacteria (DRB); Fluorescent substance; Reclaimed water; Regrowth characteristics.