Size effect of anaerobic granular sludge on biogas production: A micro scale study.

This study investigated the influence of anaerobic granular sludge size on its bioactivity at COD concentration of 1000, 3000 and 6000 mg/L. Based on size, granules were categorized as large (3-3.5 mm), medium (1.5-2 mm) and small (0.5-1 mm). A positive relationship was obtained between granule size and biogas production rate. For instance, at COD 6000 mg/L, large granules had highest biogas production rate of 0.031 m(3)/kgVSS/d while medium and small granules had 0.016 and 0.006 m(3)/kgVSS/d respectively. The results were reaffirmed by applying modified Fick's law of diffusion. Diffusion rates of substrate for large, medium and small granules were 1.67×10(-3), 6.1×10(-4)and 1.8×10(-4) mg/s respectively at that COD. Large granules were highly bio-active due to their internal structure, i.e. big pore size, high porosity and short diffusion distance as compared to medium and small granules, thus large granules could improve the performance of reactor.