| Artificial wastewater was commonly used for cultivation of aerobic granular sludge in sequencing batch reactor(SBR),which led to few studies for protozoa.In addition, the out growth of filamentous bacteria in or on aerobic granular sludge caused poor settleability and instability of aerobic granular sludge. Consequently,the objective of this work was to study the effect on the forming process and structural characteristics of aerobic granular sludge with protozoa and filamentous bacteria.After the inoculation of activated sludge from a municipal sewage treatment plant, the aerobic granular sludge with a number of Epistylis adhering to the surface was cultivated in an SBR which was used to treat domestic wastewater. Running for 120 d, the concentration of the aerobic granular sludge reached 4482 mg/L. The value of SVI was around 55 mL/g. The diameters of the granules mainly ranged from 1.6 to 2.4 mm. The average settling velocity was 55.4 m/h. Meanwhile, the density of Epistylis reached 30450 ind/mL. The average removal rates of CODCr and NH4+-N were 87.9% and 91.8%, respectively. The direct immunoflluorescence method confirmed that the FITC(Fluorescein Isothiocyanate)-labeled free bacteria could be ingested by Epistylis. The suspended solids(SS) of the effluent decreased accordingly. The structure analysis indicated that Epistylis rooted in the surface of the granules and the stalks served as the “skeleton” of the granular sludge, which was beneficial to the structure strength and stability of aerobic granular sludge.Low organic loading and height-diameter ratio of SBR led to excessive growth of extended filamentous bacteria on the surface of aerobic granular sludge. Results showed that aerobic granular sludge recovered better stability quickly in the reactor added sludge micropowder(20~200 μm) which made of grinded dry waste sludge from a municipal sewage treatment plant. Through the conventional staining reactions, the out growth of filamentous bacteria in the aerobic granular sludge system was mainly caused by Eikelboom Type 021 N filamentous bacteria. Mechanism hypotheses by adding micropowder was put forward, sludge micropowder suddenly increases the organic load and shear force to prevent the extensive growth of extended filamentous bacteria. Meanwhile, as the crystal nucleus, sludge micropowder can combine with filamentous bacteria and extracellular polymeric substances to clustering again. |
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