Effectiveness of monochloramine for inactivation of coronavirus in reclaimed water

Fecal shedding of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) by infected persons into wastewater was documented early during the COVID-19 pandemic, thereby stimulating inquiries into the effectiveness of municipal wastewater treatment processes for the reduction of infectious viruses. In wastewater treatment plants, free chlorine has traditionally been the disinfectant utilized due to its low cost and high efficacy. However, regulations limiting disinfection by-products have prompted a shift to chloramination in many areas of the United States. While studies regarding the effectiveness of free chlorine against many viral agents are abundant, the efficacy of monochloramine (NH₂Cl) has been less well researched. This study aimed to determine the effectiveness of pre-formed monochloramine for disinfection of human coronavirus 229E (HCoV-229E) in both phosphate-buffered saline (PBS) and reclaimed water from a water reclamation plant in Tucson, Arizona. Reclaimed water was sampled over the course of six months (August 2020 to November 2020), and dosed with monochloramine at 3 mg/L. An additional 1 mg/L free ammonia was added to simulate the operational conditions of the treatment plant. Viability was determined using MRC-5 host cell monolayers, using the TCID₅₀ assay method. An average Ct_99.9 (concentration of disinfectant multiplied by the contact time to achieve a 99.9 % reduction of the target organism) of 176 mg*min/L monochloramine was determined. No significant difference in inactivation rate was observed between the dosed reclaimed water and phosphate buffered saline (PBS). These data indicate that monochloramine is an effective disinfectant for coronaviruses. They also indicate that the water matrix type did not significantly impact the disinfection efficacy of monochloramine against HCoV-229E in reclaimed wastewater compared to PBS.