In this study, a lab-scale bioreactor experiment was conducted to investigate the fates of three aromatic hydrocarbons (benzene, toluene, and xylenes) in wastewater treatment processes, with respect to the differences among the species, together with the effects of aeration and the presence of activated sludge. The concentrations of the volatile organic compounds (VOCs) in the phases of air, water, and activated sludge in the bioreactor were analyzed to determine the respective chemical activities and to predict the possible transferring potentials of the VOCs among the three phases. Given appreciable levels of the VOCs being absorbed from the wastewater treatment plants (WWTPs) and their volatility, the directions of the transfers for these VOCs were from activated sludge to water and from water to air, indicating the importance of volatilization for the fates of VOCs in this reactor. The presence of activated sludge in the bioreactor had a positive effect on the transfers of the VOCs from air to water and from water to sludge, particularly for those VOCs with large octanol-water partition coefficients (KOW). The effect of aeration on the fates of the VOCs was affected by factors including the Henry’s law coefficients and KOW values of the VOCs, and the presence of activated sludge in the system. For the VOCs with large Henry’s law coefficients and small KOW values, aeration reduced the concentration of the VOCs in the air and water phases more significantly, resulting in positive and negative impacts on the volatilization and biosorption/biodegradation of the VOCs in WWTPs, respectively, which was unexpected based on the design of the WWTPs for VOC removal.