6.3.1 Physical Parameters
Size of Granules
The approximate average granule diameter range lies between 0.2 μm to 16 mm
(Beun et al. 1999; Toh et al. 2003; Zheng et al. 2006). High organic loading rate
promotes larger granules whereas, smaller granules can be formed under high shear
forces (Li et al. 2008; Gao et al. 2011).
Granule Settling Velocity
Granule settling velocity corresponds with granule size and structure which lies
between 30 to 70 m/h, which is three times greater than the settling velocity of
conventional activated sludge (Liu and Tay 2004). Aerobic granulation is also
achievable at settling velocity below 9.5 m/h (Val del Río et al. 2013).
Sludge Volume Index
Sludge volume index determines the volume (in milliliters) required for 1 g of settled
sludge after a specific settling time such as 5, 10 or 30 min. Granule settleability is
generally represented by sludge volume index. Shorter sludge volume index denotes
more compact and stable granular structure. Liu et al. (2003b) observed excellent
granule hydrophobicity at sludge volume index values lower than 50 mL/g.
Physical Strength and Density
According to literature, approximately 1 g/mL granule density is observed for
matured aerobic granules (Etterer and Wilderer 2001).
Physical Structure
Aerobic granules are either spherical or rod-shaped. They are mainly yellow, brown
and black in colour (Zheng et al. 2006) which is dependent on type of carbon source,
feed composition and microbial population.
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Size of Granules
The approximate average granule diameter range lies between 0.2 μm to 16 mm
(Beun et al. 1999; Toh et al. 2003; Zheng et al. 2006). High organic loading rate
promotes larger granules whereas, smaller granules can be formed under high shear
forces (Li et al. 2008; Gao et al. 2011).
Granule Settling Velocity
Granule settling velocity corresponds with granule size and structure which lies
between 30 to 70 m/h, which is three times greater than the settling velocity of
conventional activated sludge (Liu and Tay 2004). Aerobic granulation is also
achievable at settling velocity below 9.5 m/h (Val del Río et al. 2013).
Sludge Volume Index
Sludge volume index determines the volume (in milliliters) required for 1 g of settled
sludge after a specific settling time such as 5, 10 or 30 min. Granule settleability is
generally represented by sludge volume index. Shorter sludge volume index denotes
more compact and stable granular structure. Liu et al. (2003b) observed excellent
granule hydrophobicity at sludge volume index values lower than 50 mL/g.
Physical Strength and Density
According to literature, approximately 1 g/mL granule density is observed for
matured aerobic granules (Etterer and Wilderer 2001).
Physical Structure
Aerobic granules are either spherical or rod-shaped. They are mainly yellow, brown
and black in colour (Zheng et al. 2006) which is dependent on type of carbon source,
feed composition and microbial population.
6 Aerobic Granulation in Hydrocarbon-Rich Wastewater Treatment
179