Rethinking water treatment targets: Bacteria regrowth under unprovable conditions

Area of Science:

• Environmental microbiology
• Water treatment technologies
• Wastewater microbiology

Background:

• Ozonation effectively removes contaminants from urban wastewater (UWW).
• Bacterial regrowth in stored ozonated UWW has been observed.
• This regrowth was previously attributed to assimilable organic carbon.

Purpose of the Study:

• To investigate if ozonation by-products drive bacterial regrowth in stored ozonated UWW.
• To analyze the bacterial resistome before and after ozonation.
• To understand the role of surviving bacteria in nutrient-poor environments.

Main Methods:

• Ozonation of secondary treated UWW.
• Resuspension of ozonation-surviving bacteria in sterile mineral water (MW).
• Metagenomic analysis of the bacterial resistome (dMAGs).

Main Results:

• Bacterial regrowth occurred in both ozonated UWW and pristine MW, indicating survival and adaptation.
• Dominant bacteria (e.g., Acinetobacter, Pseudomonas) demonstrated resilience in oligotrophic conditions.
• Antibiotic resistance genes (ARGs) were prevalent in surviving bacteria, some linked to mobile genetic elements.

Conclusions:

• Bacterial regrowth is driven by the inherent ability of surviving bacteria to adapt to nutrient-poor conditions, not solely by ozonation by-products.
• Ozonation does not eliminate antibiotic resistance genes; some taxa harbor significant resistance.
• Future wastewater treatment strategies must address bacterial community imbalance and antibiotic resistance propagation during storage.