6.2 Mechanism of Granulation
Granulation mechanisms have been hypothesized by many researchers. But the
process is not well defined so far. Some of the proposed mechanisms are described
below.
6.2.1 Triggering Forces in Aerobic Granules
Liu and Tay (2002) proposed that granulation takes place in four steps:
• Bacterium to bacterium interaction mediated by physical processes such as
diffusion, gravity, and hydrodynamic and/or thermodynamic forces;
• Bacterial aggregation by either physical forces like thermodynamic forces and
Van der Waals or by chemical forces like inter-particulate bridging, ionic bonding
or by biochemical forces such as cell surface dehydration, fusion of the cell
membranes, cell to receptor attraction and so on;
• Cell aggregation by cellular forces like cell clustering or extracellular polymeric
substances production;
• Granule structure stabilization by hydrodynamic shear force. This shear force was
found to be responsible to provide a final three-dimensional granular structure to
the microbial community.
Fig. 6.1 Aerobic granulation technology is given in a nutshell. Granule formation and its subsequent scale-up implementation are described in laboratory scale, pilot scale and in full scale for
treating pulp and paper mill wastewater (Sengar et al. 2018)
176
S. Ghosh and S. Chakraborty
Granulation mechanisms have been hypothesized by many researchers. But the
process is not well defined so far. Some of the proposed mechanisms are described
below.
6.2.1 Triggering Forces in Aerobic Granules
Liu and Tay (2002) proposed that granulation takes place in four steps:
• Bacterium to bacterium interaction mediated by physical processes such as
diffusion, gravity, and hydrodynamic and/or thermodynamic forces;
• Bacterial aggregation by either physical forces like thermodynamic forces and
Van der Waals or by chemical forces like inter-particulate bridging, ionic bonding
or by biochemical forces such as cell surface dehydration, fusion of the cell
membranes, cell to receptor attraction and so on;
• Cell aggregation by cellular forces like cell clustering or extracellular polymeric
substances production;
• Granule structure stabilization by hydrodynamic shear force. This shear force was
found to be responsible to provide a final three-dimensional granular structure to
the microbial community.
Fig. 6.1 Aerobic granulation technology is given in a nutshell. Granule formation and its subsequent scale-up implementation are described in laboratory scale, pilot scale and in full scale for
treating pulp and paper mill wastewater (Sengar et al. 2018)
176
S. Ghosh and S. Chakraborty