they provide homogeneity of the stress forces [80–83]. The hydrodynamic environment in stirred tank reactors, bubble column reactors, or pulsed plate reactors may
lead to physical damage of the cells caused by moving mechanical parts or fluid
turbulence. But the hydrodynamic environment developed in ALR is favorable to
prevent such cells damage by agitation or turbulence [71]. Shear stress being lower
in airlift reactors, biofilm growth is facilitated [71], and thus rate of reaction
occurring during leaching process can be improved [84].
ALRs require less power than STRs to attain a given rate of gas-liquid mass
transfer. The investment costs are lower, and operation cost is lower or similar
compared to STRs [85]. The ALRs provide better heat and mass transfer characteristics, lower energy consumption for mixing [86] compared to BCRs.
However, ALRs are less flexible to changes in process requirements [86], as they
do not have such modifiable features [71]. ALRs offer limitations in handling highviscosity fluids because wall friction causes high energy dissipation leading to low
circulation velocity and reduced mixing [72].
4 Conclusion
To apply bioleaching in an industrial scale for the recovery of metals from e-waste,
(a) a suitable microorganism may be chosen; (b) a suitable reactor may be chosen
based on (1) the type of microorganism, its oxygen requirements, its shear sensitiveness considering the rheological behavior of the media during the growth;
(2) number of phases to be contacted, mixing and mass transfer characteristics;
(3) ease of control of temperature, sterility, etc.; and (4) simplicity of construction,
operating costs involved along with ease of maintenance; and (c) a suitable mode of
operation such as one step, two-step, or spent medium bioleaching may be chosen.
The bioleaching efficiency can be maximized by adequate optimization of the
process conditions. Thus, the bioreactor type, its components, and operational
parameters play a significant role in the process engineering of e-waste bioleaching.
All biotic and abiotic factors based on the bioreactor type should be considered. The
operational parameters vary with reactor type. An optimization of all these features
will give an effective implication of bioprocess engineering in bioleaching of metals
from electronic wastes. The benefits of engineered systems for bioleaching reduce
energy and cost, operational conditions can be controlled, and recovery is efficient.
On selection of appropriate systems, the bioleaching can be established as a bioremediation strategy in an eco-friendly manner.
40
M. Minimol et al.
lead to physical damage of the cells caused by moving mechanical parts or fluid
turbulence. But the hydrodynamic environment developed in ALR is favorable to
prevent such cells damage by agitation or turbulence [71]. Shear stress being lower
in airlift reactors, biofilm growth is facilitated [71], and thus rate of reaction
occurring during leaching process can be improved [84].
ALRs require less power than STRs to attain a given rate of gas-liquid mass
transfer. The investment costs are lower, and operation cost is lower or similar
compared to STRs [85]. The ALRs provide better heat and mass transfer characteristics, lower energy consumption for mixing [86] compared to BCRs.
However, ALRs are less flexible to changes in process requirements [86], as they
do not have such modifiable features [71]. ALRs offer limitations in handling highviscosity fluids because wall friction causes high energy dissipation leading to low
circulation velocity and reduced mixing [72].
4 Conclusion
To apply bioleaching in an industrial scale for the recovery of metals from e-waste,
(a) a suitable microorganism may be chosen; (b) a suitable reactor may be chosen
based on (1) the type of microorganism, its oxygen requirements, its shear sensitiveness considering the rheological behavior of the media during the growth;
(2) number of phases to be contacted, mixing and mass transfer characteristics;
(3) ease of control of temperature, sterility, etc.; and (4) simplicity of construction,
operating costs involved along with ease of maintenance; and (c) a suitable mode of
operation such as one step, two-step, or spent medium bioleaching may be chosen.
The bioleaching efficiency can be maximized by adequate optimization of the
process conditions. Thus, the bioreactor type, its components, and operational
parameters play a significant role in the process engineering of e-waste bioleaching.
All biotic and abiotic factors based on the bioreactor type should be considered. The
operational parameters vary with reactor type. An optimization of all these features
will give an effective implication of bioprocess engineering in bioleaching of metals
from electronic wastes. The benefits of engineered systems for bioleaching reduce
energy and cost, operational conditions can be controlled, and recovery is efficient.
On selection of appropriate systems, the bioleaching can be established as a bioremediation strategy in an eco-friendly manner.
40
M. Minimol et al.