The Formation And Analysis Of Aerobic Granules In A Reverse Flow Baffled Reactor (RFBR) Operated In Continuous Flow Mode

Until now, most of the aerobic granular sludge was cultivated in sequential batch reactor (SBR). However, in continuous-flow reactor, simultaneous maintenance of periodic Feast-famine condition, selective pressure and high height/diameter (H/D) ratio is difficult, thus aerobic granulation could not be successfully achieved. In addition, conventional continuous flow process requires sludge recycle pump, which destroys the formed aerobic granules. Continuous flow operation is commonly used in worldwide, therefore, research on achieving aerobic granules in continuous flow process has significant importance.A novel Reverse Flow Baffled Reactor (RFBR) was designed and operated in a continuous mode using real municipal wastewater, which could overcome the problems mentioned above. Further, the flow direction could be reversed periodically, the reactor was divided into several cells by baffles, and settling time was controlled, which maintains periodic Feast-famine condition, effective selection pressure, high H/D ratio and without sludge recycle step, thus the RFBR was good for granulation. The stable aerobic granular sludge with excellent settling properties was successfully produced in this RFBR which operated steadily135days. The SVI was down to34-35mL/g and mean diameter of granule was220μm. RFBR had good performance of BOD5and ammonia removal. Compared to SBR, longer time for granule formation and development was required in RFBR, however, the granules with good settling properties could be achieved in RFBR after further cultivated. The extracellular polymeric substances (EPS) content of granules from RFBR and SBR were higher than seed sludge. The protein/polysaccharide (PN/PS) ratio in EPS was about10. Bacterial community analysis revealed that most species from seed sludge were preserved in both RFBR and SBR except bacteria (Pedobacter sp.) might be easily washed out during granulation. Presence of Fe, Ca, Al, Si and P in wastewater were aggregated in granules and acted as a core to enhance the granulation. Further, the characteristics of granules taken from both RFBR and A/O were compared and the aerobic granulation only can be achieved in RFBR although the both processes used the same raw wastewater as influent. Further, the unique structure and operation mode of RFBR played an important role in granular formation.