| Aerobic granular sludge have many advantages, cloud improve the biomass also the nitrogen and carbon removal efficiency of the reactor. One new type strain possesses flocculant producing function and heterotrophic nitrification-aerobic denitrifying bacteria TN-14 was isolated from environment, and vaccinated in ordinary flocculent sludge in a continuous flow reactor to cultivating aerobic granular sludge.In view of the difficulty that aerobic granular sludge in the low substrate continuous flow is not easy to form and the traditional nitrogen removal efficiency was low.The forming process and its mechanism as well as the characteristics of continuous operation were discussed in this paper, mainly draws the following conclusion:(1) The flocculant produced heterotrophic nitrification-aerobic denitrifying bacteria TN-14 was identified as Acinetobacte sp..The strain was preserved in China Center For Type Culture Collection on June 5,2013, and the preservation Number is CCTCCNO M2013247. Within 24 h, TN and NH4+-N removal rates reached 93.53% and 93.53% respectively in heterotrophic nitrification system; NO3--N and NO2--N removal rates were 58.27% and 72.25% respectively in denitrification system.TN-14 also showed good flocculation ability, flocculation efficiency of 0.4% kaolin suspensions maximum reached 95%. It has excellent adaptability in dealing with real life sewage, can largely offset the poor denitrification ability of activated sludge system, and improve the system ability of nitrogen.(2) Inoculated 80%(MLSS) of TN-14 bacteria mud to ordinary active sludge could appear aerobic granular sludge in 25 d, and became mature in the 40 d.While in the same condition of unvaccinated TN-14 normal activated sludge were not. The removal rate of COD, NH4+-N, TN were 85%,95.5% and 65.56% respectively in the process of AGS formation.TN-14 gradually adapt and become advantage species in AGS, secreted a large number of EPS changed the surface characteristic of the sludge, and improved the relative hydrophobicity on the surface of the sludge, make it easier for sludge agglomeration.(3) The AGS formation mechanism in continuous flow has been preliminary carried out: The form of the calcium ions deposition which was added in the flooding water mainly combined with C、O、P elements and generated CaCO3, K2CaP2O7, Ca2?207 and Ca4O (PO4) 2, all within the granular sludge. These inorganic substances as the initial crystal nucleus of AGS formed small particles, the hydrophobic property and charge on the surface were changed under the Winding effect of EPS secreted by TN-14, and promote small particles growing to larger particles. In addition, the negatively charged functional groups on EPS combined with Ca in the form of chemical bonds reduced the electrostatic repulsion between the sludge, so that the AGS cloud rapid formation.(4) The mature AGS is yellow round or oval, particle size in 0.6-1.5 mm, SVI value between 40-50 mL/g, rich microbial phase which mainly composed of coccus and bacillus. It has an obvious advantage on physical properties compared with activated sludge. The denitrification rate of mature AGS was 5.75 (mgNO3--N/L·h) under the aerobic condition, meanwhile the denitrification of nitrate nitrogen efficiency was 77.07%;SND efficiency was reached 5.78(mgNH4+-N/L-h) and denitrification rate was 4.90 (mgNOx-N/L·h), SND fitting equation is: (dW/dt)SND=2.91×W/W+8.12-1.90×N/N+0.57(5) In continuous flow operation, the removal rate of COD, NH4+-N, TN and TP cloud reach 83.48%、91.44%、68.89%、65.11%, respectively. While, reduced to 75.47%、 76.88%、65.84%、55.74%, respectively, due to the lower temperature lead nitrification been restrained. Sludge morphology has larger changes along with the continuous operation, Later the granular sludge internal fostered by filamentous fungi, the structure became loose, MLSS reduced to 2.74 g/L, SVI value also goes up to 94.18 mL/g. But the TN-14 could be reserved in the granular sludge stability, and maintain a higher denitrification effect.The mechanism and optimization control of technical conditions of the long-term operation stability of AGS under low temperature operation need to further explore. |
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