presents the critical analysis of various process engineering aspects in the
bioleaching of metals from e-waste. To engineer a bioleaching process, (1) various
biological, nutritional, and physicochemical factors, such as media composition, pH,
e-waste loading, particle size, oxygen requirement, inoculum size, etc., should be
optimized and (2) suitable bioreactor choice considering the microbial type, phases
to be contacted, and the pattern of contacting followed by optimization of bioreactor
operational parameters. This paper brings out a critical review of these bioprocess
engineering aspects in bioleaching of metals from e-waste, directing the reader to the
future scope of research on bioleaching, a bioremediation strategy to save and
conserve environment for sustainable development.
Keywords Abiotic factors, Bioleaching, Bioreactors, Biotic factors, E-waste,
Optimization
1 E-Waste Management
Rapid evolution in the quality of living has imparted several technological innovations, especially in the use of electronic gadgets. Consequently, these gadgets have a
short life span, and the obsolete ones are disposed of as e-wastes. The composition of
e-wastes includes non-hazardous and hazardous constituents like plastics, glass,
ceramics, and metals. Informal handling of these constituents causes environmental
issues by the release of noxious gases, toxic leachate, and effluents posing health
risks to the ecological niche [1]. Vaccari et al. [2] has presented a detailed statistics
on the generation and collection of both electrical and electronic wastes, according to
which Asia produces the highest amount of e-waste. Only one-third of the waste
generated is collected for recycling. The challenges in e-waste treatment are due to
the lack of infrastructure to recycle the large quantities of waste generated, the flow
of e-wastes from the developed to the developing countries, inadequate knowledge
about the toxicity and impact of the e-waste, improper segregation of e-waste from
municipal solid waste, etc.
A major portion of the computer and mobile phone e-wastes are printed circuit
boards (PCBs). The metallic fraction of PCBs contains substantial quantities of
precious metals, base metals, and heavy metals, making it a suitable secondary ore
for urban mining. The most common strategies for the recovery of these metals is
through (1) mechanical separation by dismantling, pulverization followed by magnetic or electrostatic separation techniques resulting in a poor quality yield [3],
(2) pyrolysis at high temperatures which releases hazardous emissions and is not
an economically feasible technique [4, 5], and (3) hydrometallurgical methods by the
use of chemical leaching agents with complete dissolution of metals [6]. The
drawbacks of these techniques, like natural resource pollution, low purity, and the
use of high-cost operations and energy, necessitate an eco-friendly and cost-efficient
recovery strategy [7]. A green technology to confront the shortcomings of the
conventional strategies is the alternative use of biological leaching agents in
28
M. Minimol et al.
bioleaching of metals from e-waste. To engineer a bioleaching process, (1) various
biological, nutritional, and physicochemical factors, such as media composition, pH,
e-waste loading, particle size, oxygen requirement, inoculum size, etc., should be
optimized and (2) suitable bioreactor choice considering the microbial type, phases
to be contacted, and the pattern of contacting followed by optimization of bioreactor
operational parameters. This paper brings out a critical review of these bioprocess
engineering aspects in bioleaching of metals from e-waste, directing the reader to the
future scope of research on bioleaching, a bioremediation strategy to save and
conserve environment for sustainable development.
Keywords Abiotic factors, Bioleaching, Bioreactors, Biotic factors, E-waste,
Optimization
1 E-Waste Management
Rapid evolution in the quality of living has imparted several technological innovations, especially in the use of electronic gadgets. Consequently, these gadgets have a
short life span, and the obsolete ones are disposed of as e-wastes. The composition of
e-wastes includes non-hazardous and hazardous constituents like plastics, glass,
ceramics, and metals. Informal handling of these constituents causes environmental
issues by the release of noxious gases, toxic leachate, and effluents posing health
risks to the ecological niche [1]. Vaccari et al. [2] has presented a detailed statistics
on the generation and collection of both electrical and electronic wastes, according to
which Asia produces the highest amount of e-waste. Only one-third of the waste
generated is collected for recycling. The challenges in e-waste treatment are due to
the lack of infrastructure to recycle the large quantities of waste generated, the flow
of e-wastes from the developed to the developing countries, inadequate knowledge
about the toxicity and impact of the e-waste, improper segregation of e-waste from
municipal solid waste, etc.
A major portion of the computer and mobile phone e-wastes are printed circuit
boards (PCBs). The metallic fraction of PCBs contains substantial quantities of
precious metals, base metals, and heavy metals, making it a suitable secondary ore
for urban mining. The most common strategies for the recovery of these metals is
through (1) mechanical separation by dismantling, pulverization followed by magnetic or electrostatic separation techniques resulting in a poor quality yield [3],
(2) pyrolysis at high temperatures which releases hazardous emissions and is not
an economically feasible technique [4, 5], and (3) hydrometallurgical methods by the
use of chemical leaching agents with complete dissolution of metals [6]. The
drawbacks of these techniques, like natural resource pollution, low purity, and the
use of high-cost operations and energy, necessitate an eco-friendly and cost-efficient
recovery strategy [7]. A green technology to confront the shortcomings of the
conventional strategies is the alternative use of biological leaching agents in
28
M. Minimol et al.