Research On The Formation And The Operating Stability Of Aerobic Granular Sludge

Sludge granulation technology was a promising method of sewage treatment. However, the technology have some problems such as the slowly granulation process, filamentous bulking, and it was easy to disintegrate for mature sludge so as to no recovery for the system timely, and so on, eventually these will cause the entire run crash. Therefore, a promotion and industrial application of the technology can be limited. The aerobic granular sludge were cultivated successfully and the performance of the different forms of sludge and the role of filamentous microorganisms in the granulation process and the general methods of control expansion were studied further in this project. Meantime, the influence on influent carbon-nitrogen ratio to the granular sludge formation and stability were investigated. The kinetics of substrate degradation and biomass growth were also researched, and then aerobic granular sludge technology was applicated in treatment of soybean wastewater. The research of this project would provide a theoretical basis for long-term stable operation of the aerobic granular sludge reactor in practical industrial application.Firstly, flocculent activated sludge was inoculated through the SBR reactors, filiform expansion phenomena to be effectively controlled through the regulation of various process conditions. At last, aerobic granular sludge was cultivated. The results showed that filamentous microorganism plays an important role in formation and maintain stability of aerobic granular sludge, settleability of aerobic granules and the removal efficiency of organic pollution becomes poor in filamentous bulking, but whether filamentous bulking or not, the reactor had little impact on the removal rate of phosphorous and ammonia nitrogen, and they all show high and stable removal efficiency. Studies have shown that, increased the hydrodynamic shear force on the controlling of filamentous bulking has certain effects and declined the C/N ratio in seed water, balanced nutrition can fundamentally resolve the problem of filamentous bulking.By changing the influent C/N ratio, the effect on C/N ratio of granular sludge was studied. The results indicated C/N ratio with too high or too low all affects the sludge granulation process. It would not be conducive to the stability of the system. The influent C/N ratio had little influence on the removal of organism, and the CODcr removal remained at about87.00%after sludge particles formed preliminarily. The average phosphorus removal efficiency remained above80.00%when C/N ratio was between6.67and2.86. While the lower or higher C/N ratio could result in poor granulation and the lack of micro-environment, these were not useful for the phosphorus removal. On the other hand, the influence of influent C/N ratio on the ammonia nitrogen removal efficiency was obvious. Aerobic granular sludge had good simultaneous nitrification and denitrification performances, and the average NH3-N removal could reach90.59%when C/N ratio was10. However, when influent C/N ratio was decreased from5to2in the reactor, the activities of nitrifying bacteria and denitrifying bacteria were inhibited obviously, the NH3-N removal rate reduced from65.23%to38.77%.The reactor was operated at22±3℃, the superficial gas velocity was1.6cm/s, the influent organism concentration was1300mg/L, and retained C:N:P was100:10:2. After35days operation, the sludge floe in the reactor was completely granulized. Mature granular sludge with good settling ability and decontamination effect and average settling rate from70m/h to80m/h, The removal rate of CODcr, NH3-N and TP come up to94%,96%and97%, respectively.The synthetic wastewater was gradually replaced by the diluted soybean wastewater which acclimated aerobic granular sludge. In early operation period, the change of substrate caused certain impact to reaction systems. As aerobic granular sludge gradually adjust to the new culture environment, the acclimatization of sludge was achieved finally. The SVI and MLSS in the reactor were stable at50mL/g and4200mg/L, the removal rate of CODCr, NH3-N and TP reached88%,75%, and94%, respectively.The sequencing batch test that using sludge degraded organic substance in the different concentration of organic matter. The content of the substrate utilization and volatile organic compounds were monitored during the process of degradation. For the aerobic granular sludge and activated sludge, the kinetics of substate degradation and biomass growth were discussed by graphic methods. The result shown that the half-saturation constant (Ks) and maximum specific degradation rate (Vmax) of aerobic granular sludge was 3.4times and8.2times than activated sludge. But yield coefficient (Y) lower than activated sludge, contrary to decomposition coefficient (b). it theoretically explained that aerobic granular sludge technology was superior to traditional activated sludge.