Mechanistic insights into the viral microorganism inactivation during lime stabilization for wastewater sludges

The pathogens inactivation in wastewater sludges is vitally important for safely managing solid wastes and protecting public and environmental health especially in the emergency. Reports have shown the effectiveness of lime to kill virus pathogens in sludges, but mechanism of virus inactivation and related human diseases is unclear. This study evaluated representative limes of CaO/CaO₂ on actual viral microorganism inactivation by viral metagenomic sequencing technology. As results, the CaO₂ treatment enhanced the sludge hydrolysis and enveloped viral pathogens suppression via EPS structure destruction by oxidative radical generations; while CaO suppressed most of none-enveloped plant related viral pathogens. Most of the viromes of plant virus including Virgaviridae and Nodaviridae were inactivated by CaO, but the human virus-Feirsviridae and plant virus-Solemoviridae were occurred after lime stabilization compared to untreated sludge, with abundances of 1%-37% and 21%-32% in CaO-treated (CaO-T) and CaO₂-treated (CaO₂-T) samples, respectively. In addition, metatranscriptome analysis revealed distinct gene expression patterns between the CaO-T and CaO₂-T sludges, in which lipopolysaccharide biosynthesis (LPS) and aminoacyl-tRNA synthetases (ARSs) in CaO-T, the formation of ribosome in CaO₂-T were crucial to RNA virus regrowth in sludge. These findings suggested neither of CaO and CaO₂ could completely suppress pathogens in sludge, and the effect of representative limes of CaO and CaO₂ on the viral pathogen diversity, abundance, and metabolic function of the core microbiome on virus suppression and regrowth were ignored. Therefore, combined processes were recommended to provide possible alternatives for sludge safe management in pandemic emergencies.