3.3.6 Airlift Reactors
Airlift reactors [68, 70] are pneumatically agitated reactors. Airlift reactors are
distinguished from bubble column reactors by fluid circulation. They provide welldefined fluid circulation with a cyclic pattern that provide a loop liquid recycle.
These reactors consist of (1) riser, to which the gas is injected at the bottom and
upward flow of the gas and liquid occurs in this section, (2) gas separator wherein
gas disengages from the liquid, and (3) downcomer in which the liquid flows down
from the top to the reactor bottom [71, 72]. The liquid circulation is determined by a
pressure difference created between the riser and downcomer due to difference in the
gas volumes retained in them. Conventional airlift reactors may provide internal loop
configuration as in the concentric (draft) tube and the split vessel reactors or external
loop configuration [71, 73]. A schematic of the airlift reactor that can be used for
bioleaching of metals from e-waste is shown in Fig. 6.
Airlift reactors have been used in the bacterial leaching of metals from sewage
sludge [74, 75], bioleaching of heavy metals from the sediment by sulfur-oxidizing
bacteria [76], and copper recovery from chalcopyrite by Acidithiobacillus
ferrooxidans [77].
These reactors provide high gas dispersion, good mixing efficiency, better heat
transfer characteristics, simple in construction, and easier control over sterility [70,
71, 78, 79]. In stirred tank or bubble column reactors, energy dissipation is localized
producing heterogeneous shear field, whereas airlift reactors are advantageous as
Fig. 6 Airlift bioreactor
Process Engineering Aspects in Bioleaching of Metals from Electronic Waste
39
Airlift reactors [68, 70] are pneumatically agitated reactors. Airlift reactors are
distinguished from bubble column reactors by fluid circulation. They provide welldefined fluid circulation with a cyclic pattern that provide a loop liquid recycle.
These reactors consist of (1) riser, to which the gas is injected at the bottom and
upward flow of the gas and liquid occurs in this section, (2) gas separator wherein
gas disengages from the liquid, and (3) downcomer in which the liquid flows down
from the top to the reactor bottom [71, 72]. The liquid circulation is determined by a
pressure difference created between the riser and downcomer due to difference in the
gas volumes retained in them. Conventional airlift reactors may provide internal loop
configuration as in the concentric (draft) tube and the split vessel reactors or external
loop configuration [71, 73]. A schematic of the airlift reactor that can be used for
bioleaching of metals from e-waste is shown in Fig. 6.
Airlift reactors have been used in the bacterial leaching of metals from sewage
sludge [74, 75], bioleaching of heavy metals from the sediment by sulfur-oxidizing
bacteria [76], and copper recovery from chalcopyrite by Acidithiobacillus
ferrooxidans [77].
These reactors provide high gas dispersion, good mixing efficiency, better heat
transfer characteristics, simple in construction, and easier control over sterility [70,
71, 78, 79]. In stirred tank or bubble column reactors, energy dissipation is localized
producing heterogeneous shear field, whereas airlift reactors are advantageous as
Fig. 6 Airlift bioreactor
Process Engineering Aspects in Bioleaching of Metals from Electronic Waste
39