EFFECT OF DIFFERENT STIRRING SPEEDS AND DIGESTION MIXTURES ON BIOGAS PRODUCTION

A stainless steel horizontal digester for biogas production was designed, constructed and installed in the biogas laboratory of the Agricultural Engineering Department, Faculty of Agriculture, Mansoura University to investigate the effect of different digestion mixtures (mixture 1(100% cow manure), mixture 2 (75% cow manure + 25% poultry droppings), mixture 3(50% cow manure + 50% poultry droppings), and mixture 4 (25% cow manure + 75% poultry droppings)) under different stirring speeds (40, 60, and 80 rpm) on biogas production as a source of renewable energy. Digestion temperature, stirring time and influent total solids were adjusted at 40 o C and 15 minutes / 4 hours, 10% respectively. The hydraulic retention time (HRT) was 45 days. During batch process anaerobic digestion of all digestion mixtures, daily biogas production and methane content were measured. The biogas calorific value were determined. Biochemical oxygen demand (BOD) of influent and effluent slurries was determined to calculate the digestion process efficiency. Chemical analysis for different influents and effluents was also carried out. Conclusively, the obtained results indicated that, biogas production of mixture 3 is more than other mixtures. It is advised to use stirring speed of 80 rpm with stirring time 15 minutes every 4 hours at total solid of 10%, digestion temperature 40 o C and 45 HRT. According to chemical analysis, the effluent slurry could be used as a good organic fertilizer.