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Although activated sludge (AS) diffusion is promising for odor control, disagreement still exists on its treatment efficiency of varying odorants, and its microbiological mechanisms remain largely unknown. Herein, we investigated the deodorization efficiency, wastewater treatment performance, and microbiological and ecological effects of AS diffusion in two in situ membrane bioreactors (MBRs). AS diffusion removed ≥ 94.7% of H2S and 100% of NH3, while other odorants were released at low concentrations. The odor-diffused system also achieved appreciable wastewater treatment performance (effluent phosphate at 0.13 ± 0.12 mg/L, COD at 12.1 ± 1.8 mg/L, and total nitrogen at 5.9 ± 1.8 mg-N/L), while membrane fouling was mitigated. Notably, influent wastewater substrates and nutrients, other than MBR system settings, significantly affected system performance, main functional taxa and bacterial community dynamics. Ecological null model and network analysis revealed that odor diffusion strengthened the niche-based deterministic processes (i.e., environmental selection) and caused more negative and intense microbial interactions. Organics competition was enhanced, and some hydrolytic bacteria correspondingly became keystone taxa in the odor-diffused system. The findings provide valuable guidance in establishing efficient AS systems for integrated wastewater and odor treatment.