Field-validated microbial deodorant reduces hazardous gas exposure and improves air quality in rural household toilets.

Malodorous emissions from rural sanitation systems pose a direct environmental health concern. This study developed a composite microbial deodorant (CMD) using five bacterial strains isolated from activated sludge, combined in an optimal 1:1:1:1:1 ratio determined by orthogonal testing, to mitigate emissions of NH₃ and H₂S-key hazardous and odorous pollutants. In laboratory simulations, the CMD reduced NH₃ and H₂S by 82.1% and 86.1%, respectively. A pivotal 6-month field evaluation in three common types of rural household toilets demonstrated sustained, real-world efficacy, with peak removal rates of 79.43% for NH₃ and 80.83% for H₂S. The intervention also conserved nitrogen, reducing total nitrogen loss by 14.8%. Metagenomic analysis revealed the mechanistic basis: the CMD reshaped microbial metabolic pathways by upregulating genes for nitrification (hao) and sulfur oxidation (sqr), while suppressing reductive genes (nif, aprA), thus curbing emissions at source. This work provides robust field evidence that an in situ microbial strategy can effectively and sustainably improve household air quality in rural settings, offering a practical, low-cost, and eco-friendly solution for in situ odor control in rural sanitation- a critical step for sustaining the health benefits of the ''Toilet Revolution'' and improving rural living environments. One-Sentence Summary A composite microbial deodorant effectively reduces ammonia and hydrogen sulfide emissions and improves air quality in rural household toilets through 6-month field validation, providing an eco-friendly and low-cost odor control solution for rural sanitation.