Effects of Activated Sludge Reactor and EPS on Anaerobic digestion and Sludge Pretreatment

The impact of reactor configuration on extracellular polymeric substances (EPS) and subsequent anaerobic digestion and sludge pretreatment have been studied. Activated sludge (AS) was generated in fast feeding and slow feeding sequencing batch reactors (SBR), which were designed to mimic the substrate concentration gradients in plug flow reactor (PFR) and continuous stirred tank reactor (CSTR), respectively. The solids retention times (SRT) of these two reactors were 6 days. The influent was composed of both synthetic wastewater and primary effluent collected from a local wastewater treatment plant. Mixed liquor from both reactors were thickened and fed into semi-continuous mesophilic anaerobic digesters daily. Batch anaerobic digestions with thickened sludge and sonication pretreated sludge were also investigated during this study. The results showed that the fast feeding system (i.e., PFR) generated a better sludge settling and better effluent quality than CSTR. Sludge generated from both the CSTR and PFR reactors showed similar anaerobic digestibility. However, after sonication pretreatment, only CSTR-generated sludge showed improved digestibility. A total of 7% more volatile solids reduction (VSR) was achieved after sonication pretreatment of CSTR sludge as compared to little change for PFR-generated sludge. The expected variation of anaerobic digestibility between CSTR and PFR sludge without sonication pretreatment might have been masked by the high iron content in the influent for the current study. EPS extracted by sonication, base, and blender methods from the two reactors showed that more EPS was generated by the CSTR system. The reactor configuration was also associated with anaerobic pretreatment. Protein analyzed by sodium dodecyl sulfate polyacrylamide gel electroresis (SDS-PAGE) showed more diverse protein bands from CSTR-generated sludge. More complete study on the impact of reactor configuration and feeing composition on anaerobic digestion and sludge pretreatment is currently undertaken.