Effect of mechanical mixing and dung concentration on biogas generation

Abstract

This study investigates the effect of mixing and cow dung concentration on biogas production in batch scale study. Mixing of slurry is one of the basic requirements for better performance of a digester, But the existing models of digesters have either a little or no arrangement for proper mixing. Five numbers of nonmixing and five numbers of mixing type digester are fabricated to investigate the difference in gas generation, The dung concentration in each type of digester. are varied from 40-60% gobar by weight with an incremental value of 5%. A stirrer type of mixing arrangements consisting of fins fixed on a shaft and water seal tightening fixture at ends are fitted in case of mixing type digester. The mixing arrangements were completely manual and controlled from outside the digester. The operating temperature of the slurry were 29i3'C. The experimental results reveal that the mixing significantly increases the biogas generation irrespective of dung concentration. The increase was from 20% to as high as 60% depending on gobar concentration. The total gas generation is directly related to the amount of gobar present in the mother slurry, But the gas generation per kg gobar was maximum at 50% dung concentration which is slightly less than 1:1 ratio by volume. The net gas generation were .025 to .044 cu m per kg gobar and the volume of gas production per • 3 unit volume of digester varied from .15 to .26 m'/m per day.