A transient model considering the emission rate of volatile and semivolatile organic compounds from an intermittently aerated bioreactor is developed and solved analytically. If the aeration time is relatively short, and/or the overall mass transfer resistance is high, a large deviation can occur from the pseudo-steady-state mass transfer model by Chern and Yu (Chern, J.-M.; Yu, C.-F. Ind. Eng. Chem. Res. 1995, 34, 2634) or from the conventional ASCE standard model by Matter-Muller et al. (Matter-Muller, C.; Gujer, W.; Giger, W. Water Res. 1981, 15, 1271).