Bulking agents enhance humification and mitigate odor during kitchen waste composting by modulating bacterial dynamics

Aerobic composting is a promising strategy for kitchen waste valorization, yet inadequate humification and odor emissions hinder its efficiency and sustainability. This study investigated the effects of corn straw (CS) as a bulking agent in kitchen waste composting, employing watermelon seedlings (WS) with varying attributes to assess the influence of its physicochemical characteristics. CS addition markedly enhanced humification (HA/FA ratio increased from 0.76 to 3.11) and reduced emissions of key odorants like methyl mercaptan (MM) and H₂S by 68.12% and 43.64%, respectively, leading to a 62.81% decrease in overall odor intensity. In contrast, WS addition increased the overall odor intensity by 84.42%. Analysis of bacterial community dynamics in the CS treatment elucidated the underlying microbial mechanisms. The enhanced efficacy stems from its bidirectional microbial regulation: it propelled diversity and selectively enriched key functional guilds (e.g., Bacillus , Thermobifida , and Flavobacterium ) critical for the mineralization of recalcitrant organics and humification. Concurrently, CS suppressed proliferation of taxa linked to anaerobic fermentation and sulfur reduction (e.g., Pseudomonas , Thermobacillus ), thereby disrupting core malodorous metabolic pathways. These findings reveal the microbial basis for how lignocellulosic bulking agents improve compost quality and provide a practical strategy for the sustainable management of kitchen waste. • Corn straw concurrently enhances humification and mitigates odor in kitchen waste compost • Corn straw enhances the HA/FA ratio and reduces odor intensity by suppressing multiple volatile sulfur compounds • High moisture and protein in watermelon seedlings exacerbate odor emissions. • Corn straw drives microbial succession toward humification and deodorization pathways