The purpose of this chapter is to present a generalized model for the construction of inventories for the production of electricity through biogas. This general framework can be adjusted to any power plant that uses biogas, since it complies with the main material and energy balances. This chapter describes the main technologies used in biogas power energy production, separating them into five main subsystems that integrate the general life cycle inventory, as well as the inputs and outputs considered in the development of the inventories. The life cycle assessment (LCA) of two types of plants is presented as study cases: (i) the biogas power energy generation with organic waste in landfills as substrate and (ii) the biogas power energy generation using dairy cattle manure as substrate. Both systems, in addition to using different types of substrate, present differences in their substages. It is concluded that the generation of studies of life cycle analysis of technologies facilitates decision makers, producers, and government agencies to develop and identify areas of opportunity from life cycle thinking.

The main goal of this study was to compare energy consumption scenarios at a small-scale barn with an in situ biogas plant. Five life cycle assessment scenarios of dairy manure management were assessed. A real small-scale manure biogas power plant in Mexico (S-BPP) was used as case study. Five scenarios were modeled: (1.1) electricity consumption from the national grid; (1.2) electricity consumption considering a natural gas combined cycle power plant (CCPP); (2.1) partial use of electricity from the national grid and the electricity produced by the S-BPP; (2.2) partial use of electricity from the CCPP and the S-BPP, and (3) a dry anaerobic digestion S-BPP. A Monte Carlo simulation was carried out to manage the uncertainty with 95 % of confidence. A reduction of emissions in the combined cycle power grid by exploiting the manure to produce biogas, was established. Specifically, in the climate change category, there is an impact reduction by up to 70 %, which corroborates that the choice of small-scale biogas in agriculture systems is environmentally feasible. It is confirmed that using S-BPP produces a significant decrease of impacts when compared to CCPP. The results of the modeling scenarios, such as dry anaerobic digestion and/or combined cycle power plants, show a significant reduction in the emissions of the selected impact categories. This study confirms the need to develop more accurate databases of life cycle inventories regarding the Mexican electricity grid, in order to perform more reliable studies.