| China is one of the largest agricultural countries in the world with about 0.7 billion tons of agricultural stalks being generated annually, and rice straw is one kind of these major crops. Rice straw contains high percentage of lignocellulose, which is not biodegradable to anaerobic bacteria, leading to low digestion rate and biogas yield.The effluent from anaerobic digestion was used in this experiment for the rice straw pretreatment. An orthogonal experiment program was carried out to determine the effects of temperature, moisture, time and MLSS (Mixed liquid suspended solid ) during pretreatment. The untreated and retting-treated rice straws were then anaerobically digested at mesophilic temperature (35℃) in batch reactors. The result showed the best conditions were 30℃, 90% moisture, 10d and MLSS at 1500mg/L.The lignocellulose content of untreated and retting-treated rice straws was determined. Water and organic extractives content were measured and the infrared spectrums of them were investigated. The results showed that retting pretreatment can destroy the chemical bonds between lingnin and carbohydrate in some degrees, and generate more soluble lingnin. It was found that much more small molecules or soluble carbohydrates were generated and also removed some resin, wax and fat which was not conducive to the anaerobic digestion through the retting pretreatment.The analysis of the feasibility of retting pretreatment was carried out which contained cost estimates, biogas yield, economic and environmental benefits, and other aspects of comparative analysis. The analysis showed that the technology of using the pretreated straw as the main raw materials for large-scale biogas production is economical and feasible, and retting pretreatment with a better sense of reality to promote.
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