Assessment of ecological environment benefit for household biogas in areas of returning farmland to forest

In order to evaluate ecological environment benefits of household biogas in land conversion area, based on the household biogas project in land conversion area of Shaanxi province, the methods of carbon fixation and oxygen release services of Specifications for Assessment of Forest Ecosystem Services in China, methodologies (AMS-III.R) proclaimed by Executive Board of clean develop mechanism(CDM) and international commonly calculation method of emission reduction were used to evaluate the ecological environment benefits of installing household biogas digesters of 2 543 households in 6 towns of land conversion area by calculating the indexes of protected forest area, greenhouse gas and SO2 emission reduction. The results indicated that installing biogas digesters not only protected and increased the forest area, but also reduced greenhouse gas and SO2 emission in land conversion area. After the implementation of the household biogas project, forest area of 507.77 hm2 was protected annually, and greenhouse gas emissions of 7 428.40 t CO2 equivalent and SO2 emissions of 1 594.57 kg were reduced annually. The research provides a reference for rural renewable energy development and evaluation of ecological environment.