| Through the two years of rice straw dry-fermentation experiments, we had research the effects of Dry-fermentation to produce biogas with different particle size of the straw, inoculation amount, substrate concentration, C/N, nature of retting, temperature and the number of spray in batch reactor. Explored the best process conditions of the rice straw Dry-fermentation by using the Design-Expert software in the response surface optimization methods to produce biogas, The principal results were shown as follows:1. The particle size of straw has a significant effect on rice straw Dry-fermentation to produce biogas. Between the three different particle size of straw in 1cm,3cm,5cm, the effect of gas in 3cm length of straw is better than 1cm,5cm. The biogas accumulation production in 3cm particle size of straw is 10.12% higher than 1cm,11.39% higher than 5cm. The methane accumulation production in 3cm particle size of straw is 10.06% higher than 1m,5.96% higher than 5cm.2. The inoculation amounts have significant effects on rice straw Dry-fermentation to produce biogas. The more inoculation amounts, the higher biogas accumulation production and methane accumulation production between the four contrast experiments with different inoculation amounts in 25%,30%,35%,40%. The biogas accumulation production in 40% inoculation amounts is 30.04% higher than 25% inoculation amounts,25.35% higher than 30% inoculation amounts,17.83% higher than 35% inoculation amounts. The methane accumulation production in 40% inoculation amounts is 34.97% higher than 25% inoculation amounts,19.15% higher than 30% inoculation amounts,8.83% higher than35% inoculation amounts.3. The substrate concentration has a significant effect on rice straw Dry-fermentation to produce biogas. The higher substrate concentration, the lower biogas accumulation production and methane accumulation production between the four contrast experiments with different substrate concentration in 20%,25%,30%,35%.The biogas accumulation production in 20% substrate concentration is 24.94% higher than 25% substrate concentration,41.05% higher than 30% substrate concentration,52.85% higher than 35% substrate concentration. The methane accumulation production in 20% substrate concentration is 28.52% higher than 25% substrate concentration,46.65% higher than 30% substrate concentration,56.60% higher than 35% substrate concentration.4. The C/N has a smaller effect on rice straw Dry-fermentation to produce biogas. The C/N has a smaller effect on the biogas accumulation production and methane accumulation production between the three contrast experiments with different C/N in 15:1,25:1,34:1. The effect of straw producing gas in 25:1 C/N is higher than 15:1 C/N and 34:1 C/N. The biogas accumulation productions are basically the same between 25:1 C/N and 34:1 C/N. The biogas accumulation production in 25:1 C/N is 15.02% higher than 15:1 C/N,2.58% higher than 34:1 C/N. The methane accumulation production in 25:1 C/N is 9.59% higher than 15:1 C/N,4.92%higher than 34:1 C/N.5. The nature of retting has a significant effect on rice straw Dry-fermentation to produce biogas. The biogas accumulation production of the experimental group pretreated by the nature of retting than the without any pretreatment group increased 3.92%. The methane accumulation production of the experimental group pretreated by the nature of retting than the without any pretreatment group increased 1.11%. Found in the fermentation process, the experimental group pretreated by the nature of retting is faster producing fermentation gas and shorter the fermentation time than the without any pretreatment group. The result shows that nature of retting can decompose the various component of rice straw, undermining the straw structure, increasing the specific surface area.6. The temperature has a smaller effect on rice straw Dry-fermentation to produce biogas. Between the four contrast experiments with different temperature in 30° C,35° C, 40° C,45° C, the biogas accumulation production in the temperature 40° C is 37.54% higher than the temperature 30° C,16.01% higher than the temperature 35° C,81.22% higher than the temperature 45° C. The methane accumulation production in the temperature 40° C is 39.66% higher than the temperature 30° C,15.49% higher than the temperature 35° C, and 90.33% higher than the temperature 45° C. Early stage of the fermentation, the temperature 40°C fermentation rate is significantly higher than the other three groups. But in the middle of the fermentation, the gas reduces gradually even to zero. Maybe due to the higher fermentation temperature can shorten the fermentation period, but the methanogens couldn’t keep up with the fermentation rate, caused the acidification.7. In the experiment by using the Design-Expert software in the response surface optimization methods to produce biogas, the results show that the most obvious of factors to impact the dry-fermentation produce biogas are temperature, inoculation amount, and substrate concentration. Through the six single factor experiments single out temperature, substrate concentration, C/N, analysis three factors three levels of response surface by using the Design-Expert software in the application of response surface optimization method. The result shows that the optimum process conditions are 20% of the substrate concentration, the temperature of 35.59°C, the C/N 30.24:1.8. The number of spray in batch reactor has a significant effect on rice straw Dry-fermentation to produce biogas. We explored the effects of biogas production with different number of spray in self-developed 42.4L batch reactor. We selected three different numbers of sprays of 0 times per day,3 times per day,6 times per day. The result showed: the more number of spray, the more biogas accumulation production and methane accumulation production. The biogas accumulation production in 6 times per day is 21.80% higher than 0 times per day,14.10% higher than 3 times per day. The methane accumulation production in 6 times per day is 25.91% higher than 0 times per day,16.12% higher than 3 times per day. |
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