Enhancing Virus Reduction in Water Reclamation: Investigation of Long-Term Trends and Treatment Optimization Strategies

Abstract

Persistent enteric and respiratory viruses, shed into wastewater by symptomatic and asymptomatic individuals, pose significant public health risks if not adequately treated. Existing research often lacks resolution on treatment-level virus removal mechanisms and relies on idealized conditions, limiting its practical applicability. Building on long-term monitoring of SARS-CoV-2 genetic markers in wastewater across the Truckee Meadows region in Nevada, this study aimed to address the critical gaps in demonstrating the predictive power of wastewater concentrations towards public health, investigating the role fate mechanisms have in virus removal and demonstrating the removal efficiency of viral genetic markers in water reclamation. The specific objectives of this work are 1.) identify long-term trends in genetic marker shedding and assess wastewater's potential for predicting disease outbreaks; 2.) quantify the role of factors like adsorption, microbial predation, and endogenous decay in the removal of viral genetic markers in water reclamation processes; and 3.) demonstrate the efficacy of ozonation combined with soil aquifer treatment (SAT) in improving the removal of viral markers before groundwater recharge, especially in water resource-limited communities. The first phase of the work focused on monitoring SARS-CoV-2 genetic markers in untreated wastewater, correlating concentrations with reported clinical case data to identify trends and lead times in disease incidence, with notable peaks aligning with seasonal respiratory virus circulation. Consistent trends were observed, with peaks in disease incidents aligning with seasonal respiratory virus circulation and a 7-day lead-time identified through wastewater surveillance during the early pandemic. However, this was not observed during the circulation of the Delta and post-Omicron variants, possibly due to pandemic management, including vaccinations. Further research quantified viral genetic marker loss through conventional water reclamation processes, revealing negligible removal during primary treatment (p-value: 0.267) and highlighting adsorption during secondary treatment as a critical mechanism, with waste-activated sludge showing a peak concentration of 9.75 log10 GC/day for SARS-CoV-2 genetic markers. Finally, ozonation-SAT enhanced the removal of persistent viral genetic markers and recalcitrant chemical contaminants, including pharmaceuticals. For example, ozonation resulted in a >4-log reduction in norovirus genetic markers and a 2.35 ± 0.4 log reduction for PMMoV, with no significant difference observed between ozonated and non-ozonated SAT processes in PMMoV removal (p-value > 0.999). The ozonation-SAT system also significantly improved the removal of pharmaceuticals such as Sulfamethoxazole (95 ± 0.1%), Meprobamate (73 ± 0.1%), and Primidone (83 ± 0.1%), outperforming conventional SAT processes. These findings highlight the potential for integrating ozonation into existing treatment infrastructure to improve virus and contaminant removal for water reuse applications through SAT and groundwater recharge, particularly in communities with limited resources