The role of ammonia in virus inactivation: A systematic and meta-analysis review

Ammonia (NH₃), a naturally occurring disinfectant in wastewater, plays an important role in inactivating pathogens, including viruses. Despite its importance in non-sewered sanitation systems, the inactivation rate constant attributed solely to ammonia ( [Formula: see text] ) remains unclear, owing to the diverse range of disinfection conditions in existing studies. Determining [Formula: see text] is critical for quantifying the contribution of ammonia to viral inactivation and distinguishing it from other environmental factors. Therefore, this study aimed to estimate [Formula: see text] and provide a model to understand the impact of environmental factors on virus inactivation. Literature data were collected using Google Scholar (last search: April 12, 2024). Only peer-reviewed articles with ammonia concentration and viral decay were included for data extraction. A dataset of 320 data points was clustered by pH using k-means clustering and then analyzed with a linear mixed model. The results showed that ammonia significantly enhanced inactivation above pH 9.2 (cluster 2 [Formula: see text] = 0.486; cluster 3 [Formula: see text] = 0.527), with environmental matrices being the most influential factor. Although temperature had the smallest effect, it remained statistically significant across all the clusters. The overall inactivation rate constant (k_obs) was assessed against 4-log virus reduction requirement of the United States Environmental Protection Agency (US EPA) under reference conditions. For single-stranded RNA (ssRNA) viruses, k_obs consistently met this requirement, whereas inactivation for other viruses required a higher pH or prolonged storage. These findings provide a basis for quantifying the role of ammonia in virus inactivation and optimizing ammonia-based sanitation strategies, especially those targeting non-sewered sanitation systems.