reactors, and airlift bioreactors. The operational factors like pattern of mixing, air
distribution, packing of solids, etc. are specific to each type of reactor.
3.3.1 Mechanically Agitated Stirred Tank Reactors
In mechanically agitated stirred tank reactors, the internal moving components as
illustrated in Fig. 1 bring about contact between the phases [31, 61]. In this type of
reactors, the air distribution is provided from the bottom of the cylindrical vessel
[62]. The speed (as revolutions per minute) of the mechanical stirrer plays a
significant role in homogeneous mixing of the phases. The temperature is maintained
by suitable heat regulatory system [61, 63]. E-waste loaded and the particle size used
is relatively high, as the mixing is brought about by an external stirrer and can be
controlled for its efficient bioleaching. The reactor can be employed by itself or in
combination with other type of reactors for leaching and growth separately [64]. One
of the major limitations in the bioreactor is the moving components causing cell
disintegration due to attrition of the cells with moving parts in one-step or two-step
bioleaching process. The colonization of the organism in the baffles may also occur.
3.3.2 Rotating Drum Bioreactor
Limited studies exist on the efficiency of rotating drum contactors for bioleaching of
metals. The rotating drum bioreactor as a whole rotates in the leaching liquor
wherein the perforations in the solid containing drum allow solid-liquid contact as
shown in Fig. 2. The rotations of the drum establish uniform mixing. It is an efficient
alternative to stirred tank reactors with the advantages of using high solid loading,
Fig. 1 Stirred tank bioreactor
Process Engineering Aspects in Bioleaching of Metals from Electronic Waste
35
distribution, packing of solids, etc. are specific to each type of reactor.
3.3.1 Mechanically Agitated Stirred Tank Reactors
In mechanically agitated stirred tank reactors, the internal moving components as
illustrated in Fig. 1 bring about contact between the phases [31, 61]. In this type of
reactors, the air distribution is provided from the bottom of the cylindrical vessel
[62]. The speed (as revolutions per minute) of the mechanical stirrer plays a
significant role in homogeneous mixing of the phases. The temperature is maintained
by suitable heat regulatory system [61, 63]. E-waste loaded and the particle size used
is relatively high, as the mixing is brought about by an external stirrer and can be
controlled for its efficient bioleaching. The reactor can be employed by itself or in
combination with other type of reactors for leaching and growth separately [64]. One
of the major limitations in the bioreactor is the moving components causing cell
disintegration due to attrition of the cells with moving parts in one-step or two-step
bioleaching process. The colonization of the organism in the baffles may also occur.
3.3.2 Rotating Drum Bioreactor
Limited studies exist on the efficiency of rotating drum contactors for bioleaching of
metals. The rotating drum bioreactor as a whole rotates in the leaching liquor
wherein the perforations in the solid containing drum allow solid-liquid contact as
shown in Fig. 2. The rotations of the drum establish uniform mixing. It is an efficient
alternative to stirred tank reactors with the advantages of using high solid loading,
Fig. 1 Stirred tank bioreactor
Process Engineering Aspects in Bioleaching of Metals from Electronic Waste
35