الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 154 |  |  |
| | | from | 154 | | |
Abstract
This work was carried out in order to compare the performance of two digesters type (horizontal and vertical) for biogas production from animal wastes as a source of renewable energy at the biogas laboratory of the Agricultural Engineering Department, Faculty of Agriculture, Mansoura University. Daily biogas production and its content of methane was recorded. The biogas production rate, productivity and the calorific value were determined during batch process anaerobic digestion of buffalo dung. Three different digestion temperatures (35 ºC, 40 ºC and 45 ºC) with stirring time of 15 minutes every 2 hours and total solid of 12% were investigated to identify the optimal digestion temperature (O.D.T). The optimal digestion temperature was used with two different stirring times (15 minutes every 3 hours and 15 minutes every 4 hours daily) to define the optimal condition for biogas productivity. The stirring speed for all experiments was adjusted at 120 rpm and hydraulic retention time of 60 days. Chemical analysis and biochemical oxygen demand (BOD) of influent and effluent slurries were also carried out. The obtained results showed that biogas production from the vertical digester is more than that from horizontal one at all experimental conditions, the main results were recorded: The total biogas production for the vertical digester was 361.0, 503.3 and 505.9 liters at digestion temperatures of 35 ºC, 40 ºC and 45 ºC, respectively, at stirring time of 15 minutes every 2 hours, while it was 578.1 and 434.4 liters at digestion temperature of 40 ºC with stirring time 15 minutes every 3 hours and 15 minutes every 4 hours, respectively. The total biogas production for the horizontal digester was 281.8, 383.0 and 428.5 liters at digestion temperatures of 35 ºC, 40 ºC and 45 ºC, respectively, at stirring time of 15 minutes every 2 hours, while it was 541.4 and 339.7 liters at digestion temperature of 40 ºC with stirring time 15 minutes every 3 hours and 15 minutes every 4 hours, respectively. The calorific value of biogas production for the vertical digester was 7.20, 9.60 and 9.49 MJ at digestion temperatures of 35 ºC, 40 ºC and 45 ºC, respectively, at stirring time of 15 minutes every 2 hours, while it was 10.73 and 7.23 MJ at digestion temperature of 40 ºC with stirring time 15 minutes every 3 hours and 15 minutes every 4 hours, respectively. The calorific value of biogas production for the horizontal digester was 5.20, 7.80 and 7.90 MJ at digestion temperatures of 35 ºC, 40 ºC and 45 ºC, respectively, at stirring time of 15 minutes every 2 hours, while it was 9.50 and 6.61 MJ at digestion temperature of 40 ºC with stirring time 15 minutes every 3 hours and 15 minutes every 4 hours, respectively. Temperature is considered to be the main factor for survival of microorganisms which affects the biogas production during anaerobic digestion. Therefore the variation in biogas production between the horizontal and the vertical digesters for all experiments was attributed to the regular temperature distribution and varied by different stirring time. According to the chemical analysis, the effluent slurry of different experiments could be used as a good organic fertilizer. It contains high concentration of plant nutrients and organic matter and it had tendency to gives higher crop yield and soil microbial activities. The efficiency of the digestion process for the vertical digester was 88.75, 92.0 and 94.37 (%) at digestion temperatures of 35 ºC, 40 ºC and 45 ºC, respectively, at stirring time of 15 minutes every 2 hours, while it was 95.24 and 89.54 (%) at digestion temperature of 40 ºC with stirring time 15 minutes every 3 hours and 15 minutes every 4 hours, respectively. The efficiency of the digestion process for the horizontal digester was 80.0, 85.0 and 91.54 (%) at digestion temperatures of 35 ºC, 40 ºC and 45 ºC, respectively, at stirring time of 15 minutes every 2 hours, while it was 93.65 and 84.51 (%) at digestion temperature of 40 ºC with stirring time 15 minutes every 3 hours and 15 minutes every 4 hours, respectively. The efficiency of the digestion process for the vertical digester was always higher than the horizontal digester for all experiments. The efficiency of the digestion process was increased by increasing the digestion temperature and varied by different stirring time.