You should certainly look at ...
Published by Richard Bleam, Director of Technical Services
You should certainly look at the biomass under microscope to determine if filamentous bacteria are the cause as well as determining the floc structure. What DO level is maintained in the digester? What is the TSS concentration in digester? Rising sludge usually is associated with denitrification which should not occur in aerobic conditions, but if the DO is low and the TSS is high, anoxia may be contributing.