polysaccharides to the cell proteins and a rise in granule hydrophobicity (Qin et al.
2004).
6.5.3 Intermittent Feeding Strategy
According to the literature, aerobic granules had been mostly reported in sequencing
batch reactors. Sequencing batch reactor operation mode consists of feeding, aeration, sludge settling and effluent decanting in each cycle. In a cycle, the settling time
and volume exchange ratio provide a specific pressure to washout loose and
non-granular biomass from the reactor eliciting mature granulation (Liu et al. 2007).
6.5.4 Hydrodynamic Force
High hydrodynamic shear force enhances stable and compact granule formation
(Khan et al. 2009). Superficial air velocity above 1.2 cm/s is required for aerobic
granulation inside a sequencing batch reactor (Liu and Tay 2004). Hence, high shear
force promotes faster microbial aggregation leading to rapid biogranulation (Beun
et al. 1999).
6.5.5 Augmentation
A study conducted by Jiang et al. (2003) showed that external augmentation of
100 mg Ca
2+ /L promoted more regular and compact granule morphology as compared to control which was without Ca
2+ . Liu et al. (2014) observed that augmentation of 500 mg/L of poly aluminum chloride in sequencing batch reactor decreased
granulation time from 17 to 7 days. The average size of poly aluminum chloride-fed
granules was found to be 3.2 mm having more extracellular polymeric substances
content and better settling properties than control reactor.
6.5.6 Seed Sludge
The properties of the initial seed sludge affects aerobic granule formation. Two
sequencing batch reactors were seeded with two different types of sludge. One was
inoculated with 100% flocculent sludge and another one was added with 10%
crushed granules (and 90% flocculent sludge) for studying the aerobic granulation
enhancement. Aerobic granules developed faster in 90%-floc sequencing batch
reactor and were fully granulated than 100% floc sequencing batch reactor.
182
S. Ghosh and S. Chakraborty
2004).
6.5.3 Intermittent Feeding Strategy
According to the literature, aerobic granules had been mostly reported in sequencing
batch reactors. Sequencing batch reactor operation mode consists of feeding, aeration, sludge settling and effluent decanting in each cycle. In a cycle, the settling time
and volume exchange ratio provide a specific pressure to washout loose and
non-granular biomass from the reactor eliciting mature granulation (Liu et al. 2007).
6.5.4 Hydrodynamic Force
High hydrodynamic shear force enhances stable and compact granule formation
(Khan et al. 2009). Superficial air velocity above 1.2 cm/s is required for aerobic
granulation inside a sequencing batch reactor (Liu and Tay 2004). Hence, high shear
force promotes faster microbial aggregation leading to rapid biogranulation (Beun
et al. 1999).
6.5.5 Augmentation
A study conducted by Jiang et al. (2003) showed that external augmentation of
100 mg Ca
2+ /L promoted more regular and compact granule morphology as compared to control which was without Ca
2+ . Liu et al. (2014) observed that augmentation of 500 mg/L of poly aluminum chloride in sequencing batch reactor decreased
granulation time from 17 to 7 days. The average size of poly aluminum chloride-fed
granules was found to be 3.2 mm having more extracellular polymeric substances
content and better settling properties than control reactor.
6.5.6 Seed Sludge
The properties of the initial seed sludge affects aerobic granule formation. Two
sequencing batch reactors were seeded with two different types of sludge. One was
inoculated with 100% flocculent sludge and another one was added with 10%
crushed granules (and 90% flocculent sludge) for studying the aerobic granulation
enhancement. Aerobic granules developed faster in 90%-floc sequencing batch
reactor and were fully granulated than 100% floc sequencing batch reactor.
182
S. Ghosh and S. Chakraborty