Effects of Feeding Patterns on Activated Sludge Characteristics and Its Digestibility in Anaerobic Digestion

The effect of reactor configurations on activated sludge characteristics and its subsequent influence on anaerobic digestion have been investigated using the laboratory reactor study. Activated sludge was generated in two types of reactors that mimic plug flow reactors (PFR) and continuously-fed-stirred-tank reactors (CSTR). All operational conditions (seed sludge, influent, HRT, SRT, etc.) were the same, with reactor configuration being only the difference between the two systems. The results showed that sludges generated from PFR activated sludge systems digest much more favorably than the CSTR sludges under anaerobic conditions, regardless of sludge age of activated sludge. The volatile solids reduction (VSR) efficiency was about 10% more for the PFR-activated sludge. The sonication extraction data, however, showed that CSTR sludge was much more susceptible to sonication and released much more extracellular polymeric substances (EPS) and active proteolytic enzymes into the extract. It is currently hypothesized that substrate level differences in the two activated sludge systems lead to different physiological adaptations of microflora, which further leads to different EPS makeup and different sludge digestibility in anaerobic digestion. The study shows that the configuration of activated sludge reactor plays a very important role in determining the digestibility of sludge. Further investigation is needed for more effectively assessing the role of activated sludge reactor in sludge characteristics and digestion.