Dry Anerobic Digestion Process Rearch For Pig Slurry And Its Benefits Analysis

With the development of social production and improvement of people's living standards, the waste, without appropriate treatment, increases fast, and the organic pollution is becoming increasingly serious. With technology of dry anaerobic digestion, which is an important method for waste processing and has many advantage, including high rate of gas production, capacity utilization of pools and saving water, management time, and the cost of waste disposal rate, etc., the organic waste can be used as fermentation material for biogas and organic fertilizer, and it may benefit both energy and environment for solving the pollution and the energy problem effectively. The technology of dry anaerobic fermentation on processing pig manure for biogas had been studied with possible recommendations in this thesis, and the economic benefits of the technology had been analyzed.the test of dry anaerobic digestion on pig manure studied the effect of retting time, TS ratio of manure to straw, inoculation rate and fermentation time on anaerobic digestion process by an L₂₅ (6⁴) orthogonal test and optimized the parameters. There were five levels for each factor, 2d, 3d, 4d, 5d and 6d for retting time, 8:2, 7:3, 6:4, 5:5 and 4:4 for TS ratio, 10%, 15%, 20%, 25% and 30% for inoculation rate, and 10d,15d,20d,25d and 30d for fermentation time. The result showed that the optimal process parameters were retting time at 3d, TS ratio at 5:5, inoculation rate at 30%, and fermentation time at 30d.At the basis of optimal process, a magnified 10 times test was carried out to investigate the stability of the process routes and the gas production at magnified status. The teat showed that when the dry anaerobic digestion operated for 20 to 22 days, the methane production could reach to the highest at 1600 ml·Kg^-1·d^-1. Throughout the fermentation process, the average methane production was 1157.5 ml·Kg^-1·d^-1, the period for methane content of biogas above 45% was 24 days (80% of the total fermentation time), and the period for daily methane production above 90% of the average methane production was 20 days (66.7% of the total fermentation time).Comprehensive benefits of the optimal process on treating pig manure and rice straw were analyzed in this thesis. The result indicated that the fixed assets investment of a dry anaerobic project for a pig farm with 10,000 hog/a was 400 million Yuan, and the investment recovery period was 11.6 a with little investment risk and internal rate of return at 4.5%. Moreover, the process could get removal rates of BOD5 and COD at 259.8t/a and 266.1t/a, produce organic fertilizer 5235.4t/a, reduce CH₄ 40t/a and stench significantly, and create 2880 d/a employment opportunities as well. The process technology could promote the harmonious relationship between breeding enterprises and residents with high environmental, social benefits, and low economic benefits, but from the perspective of environment protection and sustainable development, it is worthy to apply the optimal process at appropriate farms.