Influence of sugar content of wastewater on the microbial characteristics of granular sludge developed at 20C in the anaerobic granular sludge bed reactor

The influence of the sugar content of wastewater on changes in the characteristics of the retained sludge was investigated by using two lab-scale granular sludge bed reactors at 20C. Both reactors were inoculated with granular sludge grown at 20C and were fed with synthetic wastewater containing sucrose and volatile fatty acids (VFAs). On day 70, the sucrose content of the wastewater was changed to 90% (based on wastewater COD value) for the first reactor and 0% (VFA 90%) for the second. After this change in feed composition, the COD removal efficiency became about 91% for the sucrose-fed reactor and 95% for the VFA-fed reactor. The growth yield (Yg) of the sucrose-fed sludge increased more than that of the VFA-fed sludge. Consequently, deterioration of the settleability of the sucrose-fed sludge was observed. The sucrose-degrading activity of the retained sludge obtained from the sucrose-fed reactor increased significantly from 3.7 g COD g VSS- 1 day- 1 on day 62 to 36.8 g COD g VSS- 1 day- 1 on day 230, in accordance with the predominant growth of sugar-degrading bacteria - namely, Lactococcus, Clostridium and Chloroflexi - in the retained sludge. The excessive growth of these sugar-degrading bacteria in the retained sludge caused unstable process performance in the sucrose-fed reactor at 20C.