The energetic investment is embodied energy for the construction of an anaerobic digestion treatment plant. The energetic investment can be related to the capital cost. According to the cost of the AD plant, a plant with a capacity of 289 kW electricity generations requires an energetic investment of V786,980. The energetic pay-back time in year (EPBT) was used to evaluate the energetic aspect and represents the number of years required to pay-back the energetic investment according to the energy balance of the process.