Mixing performance of gas sparging system in a model anaerobic digester

Mixing performance of a gas sparging system in a model anaerobic digester was investigated using XGKT (xanthan gum) solution, a transparent liquid, to simulate the flow behaviour of digested sludge. The effect of specific power input on mixing performance was studied with 0.15% and 0.4 wt% XGKT solutions using upward and downward gas sparging arrangements.A flow visualisation technique was used to observe the mixing patterns and the inactive volume in the vessel. Experimental results show that the specific power input has no significant effect on inactive volume reduction in both 0.15 and 0.4 wt% solutions. Both gas sparging arrangements led to homogeneous mixing in 0.15 wt% solution. However, a significantly large volume of inactive region occurred in 0.4 wt% solution and remained undestroyed even after a long period of mixing. The effect of sparging arrangement was significant only in 0.4 wt% solution. Downward sparging led to smaller inactive volumes compared to upward sparging in both solutions.