Livestock manure refers to animal dung and waste which has been used for centuries as a fertilizer for farming. According to the Renewable Energy Development Project (REDP, 2005), nearly 80 billion cubic meters of biogas, which equals 57 million tonnes of standard coal equivalent are generated from farming and the agriculture industry in China (Li et al., 2001).

With the great change of food choice on Chinese people’s tables, livestock production has been expanded to meet increasing demand for meat, egg and dairy products. Due to N2O and CH4 emission from ammonia utilization and untreated manure, as well as CO2 emission from a large reliance on fossil fuels and traditional biomass, and anaerobic digestion as a biological waste treatment, technology to integrate the energy system and agricultural system into a manure management system has now attracted attention from the public. Of special concern in this task is the setting up of a manure-biogas-digestate model and evaluating its greenhouse gas (GHG) emission abatement compared to a reference system. Due to differences in livestock production, energy consumption pattern and agricultural land distribution, household biogas systems and livestock farm-based biogas systems are encouraged strongly in suburban and rural areas in China, respectively (Liu, 2010).

The aims of this chapter are to assess the environmental benefits from a manure treatment per­spective, energy perspective and agricultural perspective ofthe entire biogas system and to analyze whether biogas system implementation is a good choice to achieve sustainability. Three steps are in focus to achieve the research aim: (1) Calculating GHG emission abatement from household biogas systems in rural areas and assessing which contributes to environmental impacts; (2) Assessment of environmental impact made through comparison between energy-environmental biogas systems and energy-ecological biogas systems; (3) Comparisons of these two types of manure-biogas-digestate systems with changes of energy consumption pattern and agricultural land area are then made. Through investigation of a household biogas project in western China and a livestock farm-based biogas project in east, the basic data used for assessing environmental benefits ofthe two systems were collected. In the household biogas system, CO2 emission abate­ment is the largest in biogas substitution but CH4 is produced in large amount from an uncovered anaerobic lagoon after anaerobic digestion (AD). As for livestock farm-based biogas systems, AD selection and manure treatment process design play an important role in the GHG emission mitigation potential, which are based on the main purpose of project implementation. Both energy substitution and agricultural land acceptable capacity are considered as constraint conditions of large-scale biogas system development (Liu, 2010).