higher particle size, lower energy requirement and reduced physical stress on the
microbial cells. In view of eliminating the crushing step to achieve size reduction,
coarsely ground e-waste can be used in this type of bioreactor [65].
3.3.3 Packed Bed Column
Most of the column bioreactors are set up in series to achieve growth in one column
followed by bioleaching in another column/any other reactor. Packed bed reactors
have a packed bed of e-waste material providing higher e-waste loading capacities as
illustrated in Fig. 3. Ilyas et al. [66] have reported a load of 10 kg e-waste for
bioleaching in a packed bed reactor. The temperature control is maintained by water
jackets. The efficiency of packed bed reactor in bioleaching depends on the temperature, redox potential, pH, and Fe
2+ /Fe
3+ concentrations and allows the leaching
media to pass through the bed of solids which limits the mass transfer in the system
[22]. The major limitation with the packed bed column for multiphase bioprocess is
the bed loading wherein the gaseous and liquid phases contact the solids only
through the void spaces. These spaces may be clogged by the growing biomass
(cell aggregates or biofilms). This might hinder the air and liquid flow through the
packed bed, and a uniform mixing of the solid, liquid, and gaseous phases would not
be achieved [67].
3.3.4 Pulsed Plate Bioreactor
In pulsed plate column, the solids are loaded between the reciprocating perforated
plates as represented in Fig. 4. The liquid and gas phases contact the solids through
the perforations in the plates. Our previous studies have found that in pulsed plate
column, higher particle loading resembles the tightly packed bed and consequently
reduced the recovery. Lower particle loading has resulted in movement of the
particles in the bed and thus improving the phase contacts resulting in higher
metal recovery. The significant functional parameters to be considered in this
bioreactor are the frequency of pulsation, amplitude, number of plates, and space
Fig. 2 Rotating drum bioreactor
36
M. Minimol et al.
microbial cells. In view of eliminating the crushing step to achieve size reduction,
coarsely ground e-waste can be used in this type of bioreactor [65].
3.3.3 Packed Bed Column
Most of the column bioreactors are set up in series to achieve growth in one column
followed by bioleaching in another column/any other reactor. Packed bed reactors
have a packed bed of e-waste material providing higher e-waste loading capacities as
illustrated in Fig. 3. Ilyas et al. [66] have reported a load of 10 kg e-waste for
bioleaching in a packed bed reactor. The temperature control is maintained by water
jackets. The efficiency of packed bed reactor in bioleaching depends on the temperature, redox potential, pH, and Fe
2+ /Fe
3+ concentrations and allows the leaching
media to pass through the bed of solids which limits the mass transfer in the system
[22]. The major limitation with the packed bed column for multiphase bioprocess is
the bed loading wherein the gaseous and liquid phases contact the solids only
through the void spaces. These spaces may be clogged by the growing biomass
(cell aggregates or biofilms). This might hinder the air and liquid flow through the
packed bed, and a uniform mixing of the solid, liquid, and gaseous phases would not
be achieved [67].
3.3.4 Pulsed Plate Bioreactor
In pulsed plate column, the solids are loaded between the reciprocating perforated
plates as represented in Fig. 4. The liquid and gas phases contact the solids through
the perforations in the plates. Our previous studies have found that in pulsed plate
column, higher particle loading resembles the tightly packed bed and consequently
reduced the recovery. Lower particle loading has resulted in movement of the
particles in the bed and thus improving the phase contacts resulting in higher
metal recovery. The significant functional parameters to be considered in this
bioreactor are the frequency of pulsation, amplitude, number of plates, and space
Fig. 2 Rotating drum bioreactor
36
M. Minimol et al.