Most of the odorous substances generated in public environment facilities are treated using a local exhaust ventilation system. This study assessed the leakage of odorous substances by measuring design criteria, collected air volume, and complex odor in the unit process of sewage treatment facilities. The closer the guideline/design operation airflow ratio of each odor source is to 1.0, the more identical the guideline:design:operation airflow. The average air volume ratio of the facilities under the study was 0.95~0.99 for the MBR process and 0.29~0.68 for the BNR process. As a result of comparing the types of wastewater treatment processes, the leakage of odorous substances was about 9.7 times higher in the BNR process (192,732 m3/min) than in the MBR process (19,838 m3/ min). In this study, it was found that the following two means are important for the proper collection and prevention of odorous substances. The first is the estimation of collection air volume with consideration to the characteristics of the odor source (temperature, odor generation condition, etc.). The second is the design and operation of the local exhaust ventilation system.