This study shows that a proper assessment of granule morphology is fundamental before applying any mathematical derivation or empirical formula based on the shape factor of anaerobic-granular particles to determine granular characteristics. The granular images and size distribution
of samples observed in this study revealed two different dimensions along two axes, which characterize these particles as ellipsoids. In the literature, theoretical-settling velocities and particle-size distribution of anaerobic granules have been calculated by assuming granules as spherical-shaped
and using the numerical correlation between the size and settling velocity. This resulted in large deviations in results reported for settling velocities and size distribution calculated by using empirical equations when compared with experimentally measured values. It is believed that, because
of the nonspherical nature of these particles, errors have been made in the earlier studies (which considered these particles as spherical), while evaluating granular-physical properties.
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