6.5.10 Volumetric Exchange Ratio
Volumetric exchange ratio defines the volume of the effluent withdrawn in every
cycle of the sequencing batch reactor. An exchange ratio of 40%, 50% or 80% was
found favourable for granulation. Wang et al. (2006b) observed that rapid granulation was possible in aerobic granular reactors having high volumetric exchange
ratios and good settling properties. If settling velocity was less, high volumetric
exchange ratio caused excessive biomass washout causing poor granulation.
6.5.11 Substrate Composition
Aerobic granulation occurred in wide varieties of simple carbon substrates like
glucose, sucrose, acetate, molasses and ethanol (Adav et al. 2008). Granulation
was also observed with recalcitrant compounds like phenol (Tomar and Chakraborty
2018a), thiocyanate (Tomar and Chakraborty 2018b), hydrocarbons (Zhang et al.
2011; Ghosh and Chakraborty 2019) and aniline (Winkler et al. 2018). Granules
cultivated in inorganic carbon source with nitrifying bacteria exhibited excellent
nitrification efficiencies (Tay et al. 2002; Tsuneda et al. 2003). Aerobic granulation
was successfully employed in treating low-strength to high-strength real domestic
and industrial effluents generated from municipal, petrochemical, brewery, textile,
paper mill, dairy products, seafood, manure and pharmaceutical sectors (Winkler
et al. 2018).
However, granule microscopic structure and bacterial community are largely
dependent upon the types of substrates in which they are cultivated. Literature
evidences proved that glucose-fed granules obtained loosely bound and filamentous
structures, whereas acetate-fed granules achieved compact and non-filamentous
structures with more stability (Liu and Tay 2004; Tay et al. 2002b).
6.5.12 Environmental Factors
pH
According to Hailei et al. (2006), approximately pH 7.5, which is slightly alkaline, is
essential for matured granule formation. However, granulation might be hindered at
pH values above 8.5. Acidic pH is favourable for fungi growth inside the granules,
whereas an alkaline pH produces bacteria dominating granules ensuring compact
microbial structure (Yang et al. 2008).
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S. Ghosh and S. Chakraborty
Volumetric exchange ratio defines the volume of the effluent withdrawn in every
cycle of the sequencing batch reactor. An exchange ratio of 40%, 50% or 80% was
found favourable for granulation. Wang et al. (2006b) observed that rapid granulation was possible in aerobic granular reactors having high volumetric exchange
ratios and good settling properties. If settling velocity was less, high volumetric
exchange ratio caused excessive biomass washout causing poor granulation.
6.5.11 Substrate Composition
Aerobic granulation occurred in wide varieties of simple carbon substrates like
glucose, sucrose, acetate, molasses and ethanol (Adav et al. 2008). Granulation
was also observed with recalcitrant compounds like phenol (Tomar and Chakraborty
2018a), thiocyanate (Tomar and Chakraborty 2018b), hydrocarbons (Zhang et al.
2011; Ghosh and Chakraborty 2019) and aniline (Winkler et al. 2018). Granules
cultivated in inorganic carbon source with nitrifying bacteria exhibited excellent
nitrification efficiencies (Tay et al. 2002; Tsuneda et al. 2003). Aerobic granulation
was successfully employed in treating low-strength to high-strength real domestic
and industrial effluents generated from municipal, petrochemical, brewery, textile,
paper mill, dairy products, seafood, manure and pharmaceutical sectors (Winkler
et al. 2018).
However, granule microscopic structure and bacterial community are largely
dependent upon the types of substrates in which they are cultivated. Literature
evidences proved that glucose-fed granules obtained loosely bound and filamentous
structures, whereas acetate-fed granules achieved compact and non-filamentous
structures with more stability (Liu and Tay 2004; Tay et al. 2002b).
6.5.12 Environmental Factors
pH
According to Hailei et al. (2006), approximately pH 7.5, which is slightly alkaline, is
essential for matured granule formation. However, granulation might be hindered at
pH values above 8.5. Acidic pH is favourable for fungi growth inside the granules,
whereas an alkaline pH produces bacteria dominating granules ensuring compact
microbial structure (Yang et al. 2008).
184
S. Ghosh and S. Chakraborty