There has been a considerable effort to accomplish simultaneous denitrification and methanogenesis (SMD) in a single bioreactor since the late 80s. SDM is thermodynamically and kinetically a very complicated process. This literature review shows that the influence of various operational parameters resulted in various performances of either denitrification or methanogenesis. Each published report or paper in this regard focuses on a specific cause and effect such as: the effect of C/N ratio, type of substrate, oxidation reduction potential, inhibitory effect of nitrogen oxides and the nitrogen cycle in SDM processes. Therefore, a thorough literature review seemed necessary to compare all the reports and results in a global manner to identify the major causes of inhibition and feasibility of integrating denitrification and methanogenic processes by comparing the operational conditions of different proposed systems that target SDM as well as experimental data that were designed to reveal the science behind this process. (C) 2011 Elsevier B.V. All rights reserved.