Operation of sludge treatment processes mainly relies on manual control, which is far from ideal. There is a need for new approaches to optimize the design and operation of sludge treatment processes and wastewater plants. This research aims to identify new tools and methods that can be used for in-line and real-time characterization and monitoring of sludge. Two methods that were examined in this thesis that have potential to be used as monitoring technologies were ultraviolet/visible spectrophotometry and torque rheology. Effluent and filtrate absorbance measurements in the ultraviolet/visible range were successful in monitoring the progress of aerobic digestion. Torque rheology was not found to be sensitive enough for monitoring aerobic digestion of sludge. Torque rheology detected significant changes in anaerobically digested sludge when trivalent cations were added, but not when divalent cations were added.