Effect of Digestion Temperature and Stirring Time on Biogas Properties Using Vertical and Horizontal Units

Abstract

This work was carried out in order to compare the performance of two digesters types (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 determination 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 indicated that, biogas production from vertical digester is more than that from horizontal one. It is recommended to use temperature of 40 ºC with stirring time 15 minutes every 3 hours at total solid of 12% and stirring speed of 120 rpm. According to 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 give higher crop yield and soil microbial activities.