| Biogas is a clean renewable biological energy produced by anaerobic methanogenic bacteria decomposing organic matter and one of the renewable energy sources extensively used in our countryside. It does not only convert organic waste to resource and protect our natural environment, but also remain low-production cost and high yield to substrate. However, scums produced can be attached by many bubbles and float up to the liquid level,then surface crusting will be formed due to evaporation of water. It will affect the complete decomposition of substrate,gas-liquid diffusion separation of biogas produced and decrease the fermentation rate, low production rate and content of methane also combustion calorific value. Inaddition, these problems such as bad heat insulation performance, and low fermentation temperature and lack of nutrients in the household-digester can result in extended start-up time of anaerobic fermentation, low utilization rate of substrate and low gas production rate during biogas production. Therefore, the wide application of biogas technology will be affected.According to the principles of surface crusting, a device with the performance of anti-crusting and gas-collecting was designed. The performance of anti-crusting and biogas production, as well as the effect of total solids substrate concentration and exogenous supplements performance of biogas fermentation were respectively investigated. In this thesis, the characteristicses of machinery and heat transfer of glass fiber reinforced plastics were also investigated and the fermentation performance of biodigester made of glass fiber reinforced plastics with anti-scrusting and temperature-holding was tested in pilot scale. The following conclusions are obtained in the thesis:1. The research result indicates that the prepared glass fiber reinforced plastics had high mechanical strength and heat insulation. When the thickness of glass fiber reinforced plastics was 6 mm, the compression strength and bending strength were respectively achieved above 140 MPa and 120 MPa. The thermal conductivity coefficient of biodigester wall covered with polyethylene foamed insulation board was decreased to 0.099 W/(m·K ), which can be beneficial to maintain the fermentation temperature and improve the utilization rate of substrate. Moreover, the prepared digester wall made from glass fiber material could anti acid rather than alkali. 2. The designed anti-crusting device could effectively prevent scum floating up. It resulted in more completely fermentative process and high substrate utilization rate, and improved the capacity of biogas production by the degister with the anti-scrusting device. In addition, the anti-scrusting device in the degister was beneficial to maintain the netral liquid environment by the effective gas-liquid separation and the high metabolic activities of methanogenic bacteria. Therefore, the production rate of methan was significantly increased in the biodegister.3. The biogas production of the degister with the anti-scrusting device was obviously effected by total solid substrate concentration. Especially, when the total solid substrate concentration of potato peeling was set at 4%, the fermentation material was fully utilized and the more menthan was produced in the biodegister with 27(±3)℃fermentation temperature. As a result, the maximal daily gas yield of 11.2 L, biogas production rate of 600.0 L/(kg·TS) and COD remocal rate of 69.7% were achieved, respectively. And the obtained methane concentration in biogas was kept about 62%. However, too low or too high total solid substrate concentration could decrease the abilities of biogas prpduction and anaerobic fermentation.4. In the present study urea, compound phosphates and multivitamins were chosen as the supplements. The results indicate that the supplements shortened the startup time and significantly improved the daily biogas production and methane concentration of the anaerobic digester. The optimal supplement amounts of urea, compound phosphates and multivitamins were 1.0, 1.20, 0.015 g/L, respectively. Correspondingly, the highest volumetric production rate of biogas reached to 0.869, 0.659, 0.843 m~3/(m~3·d), and the methane concentration in biogas maintained at about 65%, 68%, 70% at the end of the biogas fermentation, respectively. Compared to the control, the cumulative total amounts of biogas were enhanced by 52.9%, 28.9%,48.4%.5. The effects of magnesium sulfate on biogas production performances were conducted in an anaerobic digester with anti-crusting device using asparagus lettuce peelings and potato peelings. The results reveal that the magnesium ions shortened the startup time and significantly improved the daily biogas production and methane concentration of the anaerobic digester. The optimal magnesium ions concentration for the asparagus lettuce peelings and potato peelings were 0.30, 0.10 g/L, respectively. Correspondingly, the highest volumetric production rate of biogas reached to 0.398, 0.804 m~3/(m~3·d), and the methane concentration in biogas maintained at about 70%, 68% at the end of the biogas fermentation, respectively. The cumulative total amounts of biogas were enhanced by 71.4%, 41.6%, compared to the control.6. The results of pilot test of digerter with anti-crusting device (8 m~3) indicate that the degister kept a stable biogas production after 15-day anaerobic fermentation period, and the maximal daily production rate and the average volumetric production rate of biogas in the digester reach to 2.688 m~3, 0.215 m~3/ (m~3·d) in the winter with arverage atmosphere temperature 8℃, and the highest pressure of biogas achieved 12 kPa, no scum crusting was observed on the liquid surface. Moreover, the liquid temperature in the biodegister covered with heat preservation material was higher 3-4℃than that in the traditional degister in the winter. It demonstrates that the heat insulation performance of the designed biodegister wall met the requirement of anaerobic fermentation for biogas production in low atmosphere temperature. Therefore, the metabolic heat produced by anaerobic fermentation could be utilized to maintain the relatively high fermentation temperature of liquid and improve the biogas production in the degister.
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