Effects of anaerobic digestion on the dewaterability of sonicated biosludge

Studies on the impact of anaerobic digestion on biosludge dewatering are conflicting and mechanisms are poorly understood, with significant implications to both wastewater costs and environmental impact. To identify the mechanisms that improve dewaterability and to amplify the impacts of anaerobic digestion, biosludge was first sonicated to deteriorate dewaterability. Sonicated biosludge was next anaerobically digested under mesophilic conditions in three experiments, and the roles of extracellular polymeric substances (EPS) and supracolloidal particles on dewaterability were explored. Dewaterability, as measured by capillary suction time, improved with anaerobic digestion from 84.7 ± 11.3 s-L/g to 31.6 ± 3.2 s-L/g. The loosely-bound fraction of EPS saw only a minor decrease from 6.4 % ± 1.1 %-1.2 % ± 0.3 % and total EPS protein did not change significantly. On the other hand, in a separate experiment, significant removal of supracolloidal particles under 10 μm was observed within 6 days of anaerobic digestion, coinciding with an improvement in a capillary suction time from 116.0 ± 6.7 s-L/g to 69.8 ± 1.1 s-L/g and Crown Press filtrate total solids from 13.7 ± 0.2 g/L to 8.4 ± 0.5 g/L. In addition, in a third experiment, raw biosludge as well as sonicated at five different intensities, saw significantly faster capillary suction time and decreased Crown Press filtrate total solids which coincided with a decrease in the volume % of particles under 16 μm. The results suggest the net removal of small supracolloidal particles is a mechanism that occurs during anaerobic digestion to improve biosludge dewaterability.