Aeration and Mixing
In addition to organic carbon supplement, constant aeration and good mixing of
water are essential for maintenance of bioflocs technology systems. Bioflocs
technology ponds could be considered as biological completely mixed reactors. Under
sufficient oxygenation and mixing, heterotrophic bacteria are able to assimilate as much
as 40 to 60% of the total organic matters added. Inadequate aeration and mixing result
in excessive organic loading in water and quick solid sedimentation at bottom of the
pond that could easily develop into anaerobic conditions (Avnimelech, 1999; and
Avnimelech and Ritvo, 2003). As a result, aeration is normally provided 24 hours a day
and is typically achieved via mechanical aeration devices to maintain DO concentrations
above 4.0 mg/L (Boyd and Clay, 2002). Malfunction of aeration equipments in bioflocs
technology systems could lead to a rapid decrease of oxygen inventory to reach critical
levels within 3 hours. The availability of dissolved oxygen in water may determine
bioflocs structures. Filamentous bacteria tends to dominate at DO < 2 mg/L whereas
larger and more compact bacteria flocs are more abundant at higher DO levels (i.e., DO
= 2.0 – 5.0 mg/L) (Martin et al., 2004). Schryver et al. (2008) recommended operating
bioflocs technology ponds at high DO levels to produce the flocs volume index (FVI)
greater than 200 mL/g to avoid bioflocs settling too quickly in the dead zone region of
ponds
Aeration and MixingIn addition to organic carbon supplement, constant aeration and good mixing ofwater are essential for maintenance of bioflocs technology systems. Bioflocstechnology ponds could be considered as biological completely mixed reactors. Undersufficient oxygenation and mixing, heterotrophic bacteria are able to assimilate as muchas 40 to 60% of the total organic matters added. Inadequate aeration and mixing resultin excessive organic loading in water and quick solid sedimentation at bottom of thepond that could easily develop into anaerobic conditions (Avnimelech, 1999; andAvnimelech and Ritvo, 2003). As a result, aeration is normally provided 24 hours a dayand is typically achieved via mechanical aeration devices to maintain DO concentrationsabove 4.0 mg/L (Boyd and Clay, 2002). Malfunction of aeration equipments in bioflocstechnology systems could lead to a rapid decrease of oxygen inventory to reach criticallevels within 3 hours. The availability of dissolved oxygen in water may determinebioflocs structures. Filamentous bacteria tends to dominate at DO < 2 mg/L whereaslarger and more compact bacteria flocs are more abundant at higher DO levels (i.e., DO= 2.0 – 5.0 mg/L) (Martin et al., 2004). Schryver et al. (2008) recommended operatingbioflocs technology ponds at high DO levels to produce the flocs volume index (FVI)greater than 200 mL/g to avoid bioflocs settling too quickly in the dead zone region ofponds
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