Anaerobic hydrolysis kinetics of particulate substrates

A mathematical description of the surface related hydrolysis kinetics for spherical particles in a batch digestion is presented as well as a verification of this model with particulate starch as a substrate. Three substrates containing starch with different particle size distributions (PSD) were used. Two were obtained from fresh potatoes by wet sieving and for the third substrate a commercially available starch was used. The substrates were batch digested at 30 degrees C with granular sludge as inoculum and the hydrolysis efficiency was measured and fitted with the model. The results revealed that the hydrolysis rates for the three substrates were equal, viz. 0.4 +/- 0.1 g starch/m2/hour. Moreover, for the commercial starch not only the hydrolysis efficiency but also the changes within the PSD of the starch was determined several times with the use of light microscopy and image analysis. The obtained experimental PSD showed good similarity with the theoretical PSD from model calculations. This shows that the surface of the particulate substrate is the key factor for the hydrolysis process.