A two-stage Moving Bed Biofilm Reactor (MBBR) system consisting of a methanogenic and an aerobic reactor in series was used for medium strength dairy wastewater treatment. An energy analysis was conducted for the methanogenic MBBR to investigate its autonomy and its potential to act as a pretreatment step for dairy wastewater treatment under ambient conditions. According to the results, the operation of the methanogenic reactor under ambient conditions achieves partial removal of COD and important biogas production for having energy autonomy. A total energy production of 0.538 kWh m-3 was estimated in this reactor, whereas its energy consumption was equal to 0.025 kWh m-3. Its coupling with the aerobic MBBR results to total removal of COD, NH4-N TKN, and PO4-P equal to 93, 97, 99 and 49%, respectively.