The role of small-scale biodigesters in the energy, health, and climate change baseline in Mexico

This thesis addresses aspects of the technical, economic, and social challenges to the implementation of small-scale biodigester systems at small pig farms in Mexico. I outline the development and testing of an improved biodigester design aimed at addressing weaknesses in traditional low-cost systems. The improved biodigester design has technical advantages over the traditional bag biodigester, including durability, repairability, and ease of installation. The life cycle cost over 15 years is estimated to be 40% less than the traditional low-cost system. Among the benefits of biodigesters are renewable energy production, waste treatment, greenhouse gas emissions reduction, and human and environmental health improvements. Many of these benefits can be converted into monetary values using current markets and valuation techniques. Using these values I have estimated a cost/benefit relationship for the installation of biodigesters, expressed in terms of payback rates (years). A 10-meter biodigester for a small farm has a 2.8 year payback rate based only on energy services (displacing fuelwood); a 1.5 year payback including energy services and emissions reductions; and a 0.9 year payback when energy services, emissions reductions, and avoided health risks are considered. Biodigesters may also have additional positive externalities such as improved environmental health and socioeconomic indicators. Given this wide range of benefits, distributed in many distinct areas, it is reasonable to consider a wide range of potential funders for a broad-scale biodigester deployment project.