Efficacy of Alternate Disinfection Processes for Wastewater Treatment: Ozone and Performic acid

Abstract: Water companies in the United Kingdom are facing increasing pressure to deliver environmentally sustainable practices that comply with inland and coastal bathing water standards. Traditional ultraviolet (UV) systems present challenges related to energy use, carbon footprint and aging infrastructure. This study evaluated alternative wastewater disinfection technologies using performic acid (PFA) and ozone. A systematic review and meta-analysis identified suitable viral and bacterial surrogates, and bench-scale experiments quantified inactivation kinetics across wastewater matrices. The findings will guide development of dose-response guidance and support future regulatory engagement. Background: Wastewater disinfection is essential for public health, preventing transmission of pathogens responsible for diseases such as cholera and giardiasis. Historically, UK water companies have relied on UV disinfection to meet compliance while avoiding chlorinated byproducts; but it's high cost, energy demand, aging infrastructure and sensitivity to water quality pose challenges amid stricter environmental targets. Emerging disinfectants such as ozone and peroxyacids offer lower-carbon footprint and flexible approaches. Peracetic acid is widely adopted globally and PFA is gaining interest for its strong antimicrobial activity. Ozone, though costly, adds benefits such as micropollutant transformation. However, comprehensive performance data under real wastewater conditions remain limited, particularly for viruses. Objectives: The primary objective was to develop an environmentally sustainable wastewater disinfection approach aligned with customer and regulatory expectations by 2050. Specific goals included: 1. Comparative Efficacy: Evaluate PFA and ozone relative to UV for inactivating bacteria (E. coli) and pathogenic viruses (Norovirus). 2. Dose/Response Relationships: Establish clear dose/response relationships for PFA and ozone disinfection processes. 3. Regulatory Compliance: Ensure alternative methods meet environmental standards and support Water Industry National Environment Programme (WINEP) obligations for both inland and coastal waters. Methodology: This study integrated a systematic literature review, meta-analysis, and mechanism-focused inquiry to assess PFA and ozone performance relative to UV. Due to challenges in working with human norovirus, appropriate bacterial and viral surrogates were identified and evaluated across wastewater matrices and laboratory buffers, considering the influence of water quality on inactivation kinetics. Chick-Watson modelling guided interpretation, and rate constants were extracted for E. coli, Enterococci, cultivated phage, norovirus and norovirus surrogates. Beyond efficacy, mechanisms of inactivation, oxidative pathways and potential byproduct formation were examined. Ozone's versatility– including its ability to degrade pharmaceuticals and endocrine disruptors was considered alongside upstream pretreatment requirement and risks of bromate and NDMA formation. PFA was assessed for its potential for microbial inactivation without generating disinfection byproducts, with comparisons to peracetic acid highlighting advantage for inactivating E. coli and Enterococci. Bench-scale tests at the University of Brighton (UK) used buffered water and real secondary effluent to evaluate PFA (jar tests), ozone (batch tests), and UV (collimated beam). Experiments targeted E. coli and Enterococci and MS2, measuring disinfectant demand, decay and microbial inactivation via culture and molecular methods. A second laboratory validation phase at the University of Michigan (USA) included MS2 and murine norovirus (MNV) in buffered water. Findings and Results: The systematic literature review (Figure 1) identified 39 high-quality studies suitable for rate constant extraction. Norovirus surrogates with closest genetic and capsid similarity provide the strongest predictive alignment. Inactivation behaviors differed between laboratory buffers and wastewater, matrices underscoring the need for condition-specific testing. Unexpectedly, enterococci showed faster inactivation than E. coli exposures (Figure 2) contrary to literature reports. Typically, enterococci which has thicker peptidoglycan layers compared to E. coli has thinner cell wall is expected to be more resistant to UV damage. Both Ozone and PFA achieved strong bacterial inactivation; ozone demonstrated broad-spectrum performance and <2-log viral inactivation (MS2 and MNV). PFA showed rapid bacterial inactivation but limited effect on MS2 at typical doses. High PFA demand was observed with non-purified MS2 (Figure 3), likely due to activation by metals generating reactive species and enhancing inactivation while results for PFA appear to suggest that MS2 may be resistant to typical PFA doses tested in wastewater. Significance and Impact: This study lays the groundwork for sustainable disinfection, supporting dose guidance development, regulatory engagement, and positioning emerging oxidants as viable solutions for UK's long-term environmental and public health goals. Findings from literature and bench-scale work, and historical data from full-scale demonstrations at UK Water companies will be presented.