The Effect of Aeration Basin Reactor Configuration on Anaerobic Digestion and Sludge Properties

The effect of wastewater treatment aeration basin hydraulics on sludge properties, extractable extracellular polymeric substances (EPS), and anaerobic digestibility was studied by operating six pairs of bench scale activated sludge reactors. The reactors mimicked plug flow reactor (PFR) and continuously stirred-tank reactor (CSTR) substrate gradients while keeping all other conditions constant relative to each other. Sludge taken from each reactor was anaerobically digested and characterized in terms of SVI, extractable extracellular polymeric substances (EPS), and other characteristics. The EPS and SVI species of one reactor pair were tracked for 12 days (3 retention times) from startup. Within one day of operation SVI and extractable EPS from the CSTR started to increase while remaining constant in the PFR. After 12 days extractable EPS and SVI of sludge taken from the CSTR was found to be significantly higher than that taken from the paired PFR, a result reflected in all other reactor pairs at 12 days of operation. Sludge generated in CSTRs was found to digest less completely then the paired PFR generated sludge in all cases. Correlations were found between extracted EPS and both SVI and anaerobic digestibility. These results lead us to conclude that reactor hydraulics plays a strong role in determining the quantity and type of EPS generated which in turn governs anaerobic digestibility and other sludge properties.