Performance of microbial deodorization on anaerobically digested biosolids and odor rebound under rewetting conditions.

Odor control is a critical bottleneck in the quality upgrade of anaerobically digested biosolids for land application. The efficacy of microbial deodorization on biosolids has been scarcely evaluated and the mechanisms behind remain unclear. This study applied a sensory-instrumental combined analysis approach to evaluate the deodorization efficiency of two microbial agents on biosolids and odor recurrence upon rewetting. Results show that treatment with microbial agent could reduce the odor intensity and mitigate ammonia emission, yet it failed to completely eliminate the odor. The volatile profile of biosolids is complex, including various N-, S-, O-containing organic and inorganic compounds that collectively contribute to the malodor of biosolids. Rewetting of biosolids induced a rapid odor rebound to varying degrees depending on the maturity of biosolids. Deodorization treatment enhanced the solubility, transformation of biosolids organic matter and increased the humic-like characteristics of WEOM and reshaped the bacterial community showing enrichment of functional taxa (e.g., Actinobacteriota and Chloroflexi). Metagenomic analysis revealed that the key nitrogen-cycling genes (ureC, narG) were suppressed, thereby limiting the generation of NH3 and other related odorants. These findings elucidate a mechanistic linkage between microbial dynamics and the odor generation potential of biosolids, and highlight the critical role of moisture management in governing odor generation and post-deodorization biological stability of biosolids.