| Aerobic granule is microbial self-aggregate cultivated in aerobic wastewater system.Compared with conventional activated sludge system, the granules character with highmicrobial density, excellent settleability, little surplus sludge and simple separation processfor effluent. Meanwhile, the reactor with aerobic granules performs compact structure andwithout the secondary sendimentation tank and refluxing equipment, which lead to thetechnology of aerobic granules for wastewater to present many advantages, such as simpleprocess, flexible operation, small occupation area and low cost of investment and operation.So it is a potential technology for wastewater treatment.This study investiged the startup of aerobic granular system by stepwise increasingsubstrate N/COD ratio and shortening settling time, which is suitable way to reinforcemicrobial selection pressure and hydraulic selection pressure so as to select slow-growingnitrifying bacteria and to form aerobic nitrifying granules. The physical characteristics and theability to remove substrates were investigated during the period of granulation. Takingaccount of economizing cost in practical application, the physical characteristics, stability ofaerobic granules and the ability to nitrification and denitrification were also investigated attwo different aeration rates. Finally, denitrification was mainly invedtigated at the operationof the anoxic-oxic style by anoxic influent without mix. Conclusions are maily following as,1. The activities of ammonium oxidizing bacteria, nitrite oxidizing bacteria and.heterotrophs are all enhanced by the increase of N/COD ratio. The ability of heterotrophsdevelops slower than nitrifying bacteria. The mean size of aerobic granules increases by thespeed of 9.3μm·d-1. The density of granular structure becomes much compact with sludgegranulation process.2. The value of sludge volume index (SVI) is below 20mL·g(-1). The superficial sludgeyield is in the range of 0.17 gVSS·g-1COD to 0.25 gVSS·g-1COD when the sludge loading rateis about from 0.2gCOD·g-1VSS·d-1 to 0.4 gCOD·g-1VSS·d-1.3. The reactor performs excellent ability to remove COD with removal efficiency of over80% and ammonium removal efficiency is over 98%. But the total nitrogen removalefficiency is below 15% during the startup of reactor.4. The granular surface is more irregular at the low aeration rate than that at the highaeration rate and granular interstice performed increasing with it. In 55 days, comparing with high aeration rate, superficial sludge yield and the mean size of aerobic granules at the lowaeration rate is increased by 33% and 25%, respectively, while the granular relative strengthand EPS were reduced by 6% and 12%, respectively. The sludge volume index (SVI) at twoaeration rates is about between 10mL·g-1 and 15mL·g-1, which implied that granules at bothaerations behaved well settling ability.5. The reactor at low aeration rate performs better COD removal efficiency and TNremoval efficiency than high aeration rate, while ammonium removal efficiency is notindluent by aeration rate. TN removal efficiency is noly from 15% to 33% because highdissolved oxygen (DO).6. The contribution of granular size for denitrification is extremely little underuncontrolled DO. The TN removal efficiency increases to 35% at the operation of theanoxic-oxic style by anoxic influent without mix, and ammonium removal efficiency still liesover 98%. The TN removal efficiency reaches 54% when COD is increased to 750 mg·L-1,and it further increase to 60% when COD reaches 1000 mg·L-1.
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