| The shortcomings of aerobic granular sludge, such as the harsh conditions to form granular, high energy consumption and poor stability, hindered its application. The three parts works were conducted in order to overcome these shortcomings, studying the process of granulation, the influence of aeration conditions and the sludge stability.The first part presents the process of granulation. The physicochemical characteristics and denitrogenation characteristics of the sludge during the granulation were investigated in a SBR. It was revealed that the process of granulation could be divided into three stages, including formation, growth and mature stage. In the first stage, the settling ability of sludge was improved obviously, and SVI decreased from 110ml/g to 23ml/g during the first 30 days. In the second phase, the aerobic granules grew rapidly in the following 15 days, and the mean diameter increased to 0.82mm from 0.25mm. At the same time the value of SOURh decreased from 80mg /(g·h) to 35 mg/(g·h). The denitrification rate was highly improved and the removal rate of TN was increased to 80% from 55%. In the last stage, the physicochemical characteristics of sludge and denitrogenation became stable, and the removal efficiency of TN could achieve 85%, indicting that simultaneous nitrification and denitrification was realized. The second part has investigated the influence of aeration intensity and aeration mode. Firstly, effects of aeration intensity on organic removal capacity and denitrogenation of aerobic granules and cyclical variation of DO in one operating cycle were studied in two SBRs with different mean diameter, 0.38mm and 0.96mm separately.The four group of aeration intensity were 0.5cm/s, 1.5cm/s, 2.5cm/s and 3.5cm/s. The structure model was established on the basis of experiment results. It was revealed that the organic removal capacity and denitrogenation were influenced by both aeration and granule diameter. Aeration intensity could decide the depth of oxygen transferring directly in the internal of granule, which could play a positive role to improve removal efficiency of COD and NH3-N while the aeration intensity was between 0.5cm/s and 2.5cm/s. The diameter has little impact to removal efficiency of NH3-N but influence obviously to COD removal especially while the aeration intensity was in the mild range.The accumulation of NOx--N was also effected by both aeration and diameter simultaneously. To those big aerobic granules, providing more aeration can contribute more to denitrification. In actual application, the aeration strength and granule diameter should be considered comprehensively. Secondly, the effect of aeration mode has been studied in one SBR. The results demonstrated that large aeration intensity in the first phase of the operation cycle and smaller aeration intensity in the latter stage can be benefit to total nitrogen removal.The stability of aerobic granular sludge was analyzed in the third part. There are two reasons resulting in the instability of granular sludge. The first one is the larger mass transfer resistance which hinders the transfer of nutrients and dissolved oxygen, and the second one is the granular aging. This paper proposed two solutions, one is to cultivate aeration granules with small size of the sludge with suitable aeration intensity, and the other is to rule out the granules of large size timely during the operation. |
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