Efficient disinfection of real toilet blackwater by ultraviolet/peracetic acid process: Selective intracellular biomolecular oxidation

Abstract

Toilet blackwater (BW) disinfection is crucial for preventing microbial contamination but is hindered by its complex composition. This study explored the combined ultraviolet and peracetic acid (UV/PAA) process as a novel strategy for BW disinfection. The UV/PAA process effectively inactivated Fecal coliform (1.372 × 10⁻⁵ s⁻²) in real BW, despite presence of turbidity, suspended solids, and organic matter, which could hinder disinfection. The highly electrophilic PAA and acetoxy(peroxy) radicals were identified as crucial contributors to bacterial inactivation. Biochemical analysis and Density Functional Theory calculations revealed that the system primarily operates through selective intracellular biomolecular oxidation. Electrophilic species preferentially oxidized amino acids with highly local nucleophilicity index, particularly those containing sulfur or nitrogen moieties. This selective oxidation caused protein denaturation, inducing cells into a viable but non-culturable (VBNC) state. Meanwhile, the membrane integrity and metabolic activity was preserved, while oxidative stress and DNA disruption effectively limited bacterial regrowth, proving that this process selectively damages intracellular biomolecules, such as amino acids and DNA. Additionally, the process significantly reduced the abundance of gut microbiota and other pathogens in real BW, highlighting its broad-spectrum antimicrobial efficacy. The UV/PAA process represented a sustainable and eco-friendly advanced disinfection solution for BW treatment.