Dynamics of Granule Formation and Destruction

The granules were retained in the SBR while the flocs were washed out with the effluent. Concentration of granular biomass (VSS) during 6 days of experimental period was stable, at 6.5 ± 0.2gL-1. Concentration of floc biomass (VSS) was 0.15 ± 0.02gL-1. Stable concentration of granular biomass can be due to the balanced attachment and detachment of the flocs to granules or balanced growth and destruction of the granules. The hydraulic residence time was 0.33d, which corresponded to a daily exchange of three reactor volumes. Therefore, the ratio of produced granular biomass to produced floccular biomass was 14.5.

This ratio was close to 18.3, the initial ratio of granular labeled biomass to the flocculent labeled biomass after 4 h of labeling with lipophilic tracer (one growth cycle in SBR). Content of lipophilic tracer in granular biomass was stable for 6 days of study and was thought to be attributed to balanced attachment and detachment of the flocs to granules or balanced growth and destruction of the granules. It cannot be regarded as the result of negligible degradation of granules because the labeled biomass was permanently released as the labeled flocs. The tracer content could decrease if the rate of granule growth is higher than the rate of granule degradation.

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