Automated Ozone Disinfection Control in Reclaimed Water: The Surrogate Parameters- and Spectral Characteristics-Based Real-Time Feedback System for Microbial Inactivation Monitoring

It is critical to balance the effective inactivation of microorganisms with the formation of disinfection byproducts and associated processing costs during ozone disinfection in water reuse. Through systematic ozone disinfection experiments, the specific ozone dose, ultraviolet (UV) absorbance at 254 nm, total fluorescence, and characteristic fluorescence peak A were identified as surrogate parameters for predicting the inactivation efficacy of indigenous fecal coliforms, heterotrophic plate count, and Pseudomonas aeruginosa by ozone in four different reclaimed waters. Corresponding empirical logistic regression models were established to correlate surrogate abatement with microbial inactivation (R2 = 0.743–0.970) within a high ozone dosage range (0–8 mg/L). A spectral surrogate-based monitoring system for real-time surveillance and online control of ozone disinfection was designed and further validated through laboratory experiments, demonstrating that fluorescence peak intensities at the characteristic excitation wavelengths of 240, 280, or 335 nm could predict microbial inactivation properly by logistic regression models (R2 = 0.793–0.991) using portable UV light sources and miniaturized fluorescence signal detection instruments. Taken together, this study provides a viable approach for reliable economical and quick-response ozone disinfection in reclaimed water.