The emission of volatile organic compounds (VOCs) during equalization in wastewater treatment plants (WWTPs) is a particular source of concern. In this study, VOC emissions during equalization in three industrial WWTPs were analyzed by two different approaches. The flux-chamber method is a standard method used in many countries including Taiwan, as the theory behind the mass-transfer method is well-established. The objective was to investigate whether different outcomes were generated between two estimation methods and to determine potential overestimation of VOC, chemical oxygen demand (COD), or total organic carbon (TOC) removals in the WWTPs due to VOC emission during equalization. In the results, the estimated VOC fluxes during equalization were similar between two approaches. Recognizable amounts of VOCs were emitted during equalization (up to 28.2%, 13.6%, and 7.6% in three WWTPs). Their impacts on the COD (e.g., less than 0.1% in three WWTPs) or TOC removals (e.g., less than 11.4% in three WWTPs) were rather limited. Through the correlation analysis, the estimated VOC emission flux was not dependent upon individual but on co-influence of the compound's physicochemical characteristics, water quality, and operation during equalization. Although two approaches generated similar outcomes, the results by the flux-chamber method seemed to be more relevant to the operation during equalization, while the water quality were more important to the results by the mass-transfer method. Both methods were effective to quantify VOC emission during wastewater equalization, as the flux-chamber method is possibly a preferable option given their applicability and economic comparison. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.