Aligning monitoring of virus barriers in potable reuse with unit process treatment mechanisms and time scales: A critical review and research needs

Interest is growing in potable reuse in response to water scarcity and the desire for sustainable supplies. While potable reuse systems must control a variety of physical, chemical, and microbiological contaminants, human enteric viruses are particularly concerning and drive process performance objectives due to their often-high occurrence in source waters, small size, potential resistance to treatment, and laborious methods to determine infectivity. This paper reviews the alignment of online monitoring practices with the mechanisms and time scales of the various barriers for enteric viruses. While there are numerous studies and reviews of individual barriers, no other review has been identified that covers operational monitoring of the entire potable reuse system. This paper also provides a critical assessment of the efficacy of current practices for operational and verification monitoring of the integrity of barriers to enteric viruses in potable reuse systems. The prevalence of human enteric viruses in wastewater and associated challenges of quantifying them through treatment are discussed within the risk management frameworks currently in use or under development for potable reuse systems. Monitoring approaches are then reviewed throughout the potable reuse water cycle. Current monitoring practices are compared with treatment process mechanisms and time scales, for the treatment barriers of biological wastewater treatment, membrane bioreactors, microfiltration/ultrafiltration, reverse osmosis, ultraviolet irradiation/advanced oxidation, ozonation, granular media/biologically active filtration, and chlorination. Monitoring and pathogen removal mechanisms are also reviewed for both environmental and engineered buffers. Implications are then discussed for future areas of research in potable reuse.