EFFECT OF MECHANICAL STIRRING ON BIOGAS PRODUCTION EFFICIENCY IN LARGE SCALE DIGESTERS

Abstract

This research work aims to study the effect of mechanical stirring at different speeds and interval stirring periods on the biogas production yield and productivity and the energy balance in large scale biogas digesters. This investigation was conducted on two fixed dome digesters with 20 m3 total volume. The study includes three speeds of stirring (30, 45 and 60 rpm) and four stirring periods (15 min/hr, 15 min/2 hr, 15 min./3 hr and 15 min./4hr) ‘which equal to 6, 3, 2 and 1.5 hr/day, respectively. The obtained results showed that the stirring speed of 60 rpm was gave the high values of biogas production rate( 0.423 m3/m3/day), biogas productivity (0.423 m3/m3/day, 0.106 m3/kg TS add and 0.707 m3/kg VS consumed), energy production (9.379 MJ/m3/day), energy consumption in the stirring process (3.430 MJ/m3/day) and net energy gained (8.448 MJ/m3/day). However, the stirring period of 15 min./2 hr (3 hr/day) was gave the maximum biogas production rate and energy production at different stirring speeds and net energy gained at stirring speeds of 30 and 45 rpm. Meanwhile, the stirring period of 15 min./4 hr (1.5 hr/day) was gave the lowest energy consumption at different speeds and high net energy gained at stirring speeds of 60 rpm.