Effect of mixing digested slurry on the rate of biogas production from dairy manure in batch fermenter

Forty kilograms of pure cattle dung and cattle dung mixed with 10% digested slurry obtained from a Weld biogas plant was batch fermented in horizontal biogas digesters for 15 weeks under Weld conditions with mean ambient temp erature 20-23 degreesC. Compared to 821 l of biogas from digester I, contai ning cattle dung alone, 1457 l of biogas was obtained from digester II, con taining cattle dung mixed with 10% digested slurry. Mixing of slurry not on ly speed up the gas production but also enhanced its rate from 108 l/kg dry matter to 158 l/kg dry matter. It also resulted in 36.1% distraction of to tal volatile solid in digester II, compared to 23.93% observed in digester I. Mixing digested slurry is recommended for raising biogas production from cattle dung in dry fermenters.