Protease and xylanase activities and thermophilic populations as potential process monitoring tools during thermophilic aerobic digestion

Abstract

AbstractThermophilic aerobic digestion (TAD) of potato process waste slurry was carried out in a batch process in a continuously stirred tank reactor at 55 °C for a total of 156 h. The pH of the slurry was either unregulated, or regulated at 6.0, 7.0, 8.0, 9.0 and 9.5, and aeration rate was 0.5 vvm. The effect of aeration rate on the digestion process was studied at 0.1, 0.25, 0.5 and 1.0 vvm at pH 7.0 and 55 °C. The development of thermophiles (55 and 65 °C populations) and hydrolytic enzyme activities (protease and xylanase) in the process were monitored. Thermophiles developed rapidly to reach peak populations in 24h or earlier, and remained stable at all fixed pH reactions. The thermophile population was only minimally affected by the aeration rate, and they were present mostly as spores after 96h of digestion. Xylanase enzyme appeared rapidly, reached a peak in approximately 60h, and declined rapidly thereafter. Highest activities were produced in neutral reactions and higher aeration rates. Aeration rates affected protease activity profoundly. The profile of both enzymes closely reflected the development of microbial activity and the overall progress of TAD, in a medium where their substrates were not predominant and not the preferred carbon sources. The relatively simple process of measuring the activities of these enzymes is potentially a more direct measure of the progress of TAD than enumeration of the microbial populations and thus, has greater potential in process monitoring. Copyright © 2003 Society of Chemical Industry