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Study On The Stability And The Effect Of Nitrogen Removal Of Aerobic Granular Sludge Under Different C/N Ratios

Posted on:2017-01-25Degree:MasterType:Thesis
Country:ChinaCandidate:G YanFull Text:PDF
GTID:2271330488495216Subject:Municipal engineering
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Aerobic granular sludge was cultivated in sequencing batch reactor (SBR) by using synthetic wastewater of different C/N (COD/NH4+-N) ratios, which had good denitrification and carbon removal performance. The cultivation process,operation stability and removal efficiency of COD and NH4+-N were studied and the nitrification bacteria was enriched by adding activated sludge. The static experiments of single cycle were made at different stages of the operation to further clarify the specific removal mechanism and ammonia nitrogen removal effect of aerobic granular sludge at different C/N ratios, which was in order to provide a theoretical reference for the practical application of aerobic granular sludge in different waste water.Through these studies, some main conclusions were drawn as follows:(1)From the formation process of granular sludge, adding a small amount of primary aerobic granular sludge and Ca2+could culture aerobic granular sludge in 11d; from the color changes of granular sludge, when sludge was in the mature stage, the color showed light yellow or khaki; from the photos of electron microscopy, internal superiority bacteria was different at different C/N ratios, it was heterotrophic bacteria in filamentous form when C/N was high. The filamentous bacteria was distributed in the outer layer of granular sludge and the ball and claviform bacteria were distributed in the interior of the particles.(2)The increase of MLSS leading to the decrease of F/M and the increase of particle size leading to lack of DO and nutrition were the two main reasons for the instability of morphology, filamentous bulking was also an important factor affecting the stability of the particles.When C/N ratio was high, the average size of aerobic granular sludge increased by increasing C/N ratio; after reducing C/N ratio, particle size distribution moved to smaller size interval and the average particle diameter also decreased. When the granular sludge was in stable operation period, regardless of C/N ratio, the particle size was tend to be the same and the distribution moved to a larger particle size range. Therefore, controlling the particle size in 2-3mm was more helpful to maintain the stability of the reactorIn the stable stage, the MLSS was tend to be lager and it was much larger at high C/N ratio. At low C/N ratio, the variation range of MLSS was less and the reactor was more stable. At the disintegration of granular sludge, when C/N ratio was high, filamentous bacteria bloomed, MLSS rapidly increased but when C/N ratio was low, the debris were discharged with effluent, MLSS decreased. Therefore, when C/N ratio was high, it should discharge sludge regularly to control MLSS, but when C/N ratio was high,there was no need to consider SRT.When C/N ratio was high, after the disintegration of granular sludge, filamentous bacteria became short filamentous or claviform particle, gradually turned into a nearly spherical particle by the effect of settling time and hydraulic shear force; When C/N ratio was low, granular sludge has two different disintegration ways, one was a rupture from the inside out, the other was the spalling of the outer layer of the granular sludge, the fragments of sludge could be a new second nuclear to forming granular sludge. Changing the influent mode from aerobic to anaerobic was restrain the filamentous bulking effectively.(3)Aerobic granular sludge achieved good NH4+-N removal efficiency in the stable period at different C/N ratios, but it had different removal mechanisms. NH4+-N were assimilated as nutrients by heterotrophic bacteria when C/N ratio was high, at this moment, nitrifier were washed out, After reducing C/N ratio, Aerobic granular sludge could achieve enrichment of nitrifier by adding nitrifying activated sludge and NH4+-N were removed by nitrification.When C/N ratio was high, the higher influent C/N ratio, the greater assimilation and the better NH4+-N removal efficiency, the efficiency was greater than 93% when C/N ratio was 30. When C/N ratio was low, at the moment the lower influent C/N ratio, the better activity of nitrifier and the better NH4+-N removal efficiency. The efficiency was greater than 98% when C/N ratio was 4.The NH4+-N degradation rate existed two different phases in a single cycle at different C/N ratios. When C/N ratio was high, the rate increased faster initial and grow slower after due to the granular sludge absorption and assimilation at the beginning of aeration. When C/N ratio was low, the rate appeared slowly first and fast afterwards due to the activity of nitrifying bacteria decreased by influent COD.pH firstly increased and then decreased and increased at last during the single period at different C/N conditions, but the change for different reasons. It could monitor pH value and DO to determine COD and ammonia nitrogen removal.In the high C/N ratio of single cycle, the greater the C/N ratio, the greater the initial degradation rate of the ammonia nitrogen. When C/N was 26, the initial degradation rate of NH4+-N was 0.3907 mg·(L·min)-1; when C/N was 29, the initial degradation rate of NH4+-N was 0.4503 mg·(L·min)-1. Under the condition of low C/N ratio, the lower the C/N ratio, the greater the degradation rate of ammonia nitrogen. When C/N was 5.8, the degradation rate of NH4+-Nwas 0.1061 mg·(L·min)-1; when C/N was 3.7, the degradation rate of NH4+-N was 0.1196 mg·(L·min)-1.
Keywords/Search Tags:aerobic granular sludge, C/N ratio, stability, particle size distribution, MLSS, assimilation, nitrification, enrichment of nitrifier, NH4+-N degradation rate
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