Potential of biogas production from livestock manure in China

Abstract: With great change of food pattern on Chinese people‘s table, livestock production has been expanded to meet increasing demand of meat, egg and dairy products. Due to N2O and CH4 emission from ammonia utilization and untreated manure as well as CO2 emission from large reliance on fossil fuels and traditional biomass, anaerobic digestion as a biological waste treatment technology to integrate energy system and agricultural system into manure management system, has attracted attention from public. Of special concern in this thesis is the setting up of manure-biogas-digestate‘ model and evaluating its GHG emission abatement compared to reference system.Due to differences in livestock production, energy consumption pattern and agricultural land distribution, household biogas system and livestock farm-based biogas system are encouraged strongly in rural and suburb areas in China respectively. Aims of this thesis are to assess environmental benefits from manure treatment perspective, energy perspective and agricultural perspective of entire biogas system and to analyze whether biogas system implemented is a good choice to achieve the sustainability. Three steps are in focus to achieve the research aim:Calculating GHG emission abatement from household biogas system in rural areas and assessing which phase contributes to the most environmental impact;Assessing environmental impact through comparison between energy-environmental‘ biogas system and energy-ecological‘ biogas system.Doing future estimation of these two types of manure-biogas-digestate‘ systems with changes of energy consumption pattern and agricultural land area.Through investigation of household biogas project in western China and livestock farm-based biogas project in east, the basic data used for assessing environmental benefits of two systems were collected. In household biogas system, CO2 emission abatement is the largest in biogas substitution part but CH4 is produced in large amount from uncovered anaerobic lagoon after anaerobic digestion (AD); As for livestock farm-based biogas system, AD selection and manure treatment process design play important role in the GHG emission mitigation potential, which are based on main purpose of project implement. Both energy substitution and agricultural land acceptable capacity are considered as constraint conditions of large-scale biogas system development.