Potentials of biogas production and GHG mitigation in Guatemalan dairy farms

This work presents results of a survey of case studies to quantify the potential energy production and GHG emission changes of anaerobically digesting (AD) cattle manure in three Guatemalan dairy farms. Livestock inventory and energy consumption data were collected and used to define three scenarios for each farm: baseline, AD with condensing boiler (AD-boiler) and AD with combined heat and power unit (AD-CHP). The estimated emissions account for enteric fermentation, manure/digestate handling, import/export of thermal energy and electricity and use of fossil fuels for transport. The AD systems result in a production of 100±37 kg_CH4 · head^-1 · yr^-1. If this CH₄ is combusted in the AD-boiler scenarios, 5.00±1.59 GJ · head^-1 · yr^-1 of thermal energy is generated and emissions from baseline scenarios are offset by 600±280 kg_CO2e · head^-1 · yr^-1. The generated heat is sufficient to operate digesters (308 K) and export 2.90±0.62 GJ · head^-1 · yr^-1. Challenges are found to use that thermal power because domestic heating is inessential. ADCHP is found to be more suitable because it produces sufficient thermal energy for the digesters (2.50±0.80 GJ · head^-1 · yr^-1) while generating electric power (1.80±0.57 GJ · head^-1 · yr^-1). This scenario could promote the welfare of neighboring communities by making sustainable electricity available. AD-CHP could offset 400±320 kg_CO2e ·head^-1 · yr^-1 from the baselines.