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Photosynthetic green microalgal bio-electrochemical system for self-sustainable bioelectricity generation

Authors:

Abstract

Microalgal bioelectrochemical systems have received substantial interest among the developing technologies for bioenergy. It is based on the interaction of two major components, i.e., microalgae and electrochemical processes. Microalgal photosynthesis and electrochemical reactions integrate the microalgae bioelectrochemical systems for a sustainable and efficient technique of bioelectricity generation. In this work, we have deliberated on the critical biological component of microalgae, which captures solar energy and transform it into chemical energy via photosynthesis. This includes selecting optimal microalgal strains with high photosynthetic efficiency , optimal nutrition, and availability of carbon dioxide and designing electrodes and membrane materials to improve electron transmission and reduce energy losses. Also, we have presented microalgal bioelectrochemical systems as a promising technique for generating bioelectric energy. In addition, this system also provides an innovative method for wastewater treatment, carbon dioxide mitigation, and direct solar energy conversion by involving microalgae with elec-trochemical processes. We have explored the ability to address environmental concerns while producing bioelectricity, making microalgal bioelectrochemical an appealing alternative for a cleaner future. Therefore, continuous research and technological developments of revolutionary bioenergy generation platforms pave the way for a more sustainable and green energy landscape.
143
Review Article
Photosynthetic green microalgal bio-electrochemical system for self-sustainable
bioelectricity generation
Md. Sourav Talukder 1, #, Gokul G 1, #, Boggavarapu Veera Venkata Kiran Krishna 1, Neha
Gupta 2, Naveen Kumar 3, Binny M. Marwein 3, Bittesh Barman 4, Krishna Kumar Jaiswal 1,*
1 Department of Green Energy Technology, Pondicherry University, Puducherry 605014, India
2 Department of Environmental Science, Babasaheb Bhimrao Ambedkar University, Lucknow, Uttar Pradesh
226025, India
3 Department of Ecology and Environmental Sciences, Pondicherry University, Puducherry 605014, India
4 Department of Chemistry, Pondicherry University, Puducherry 605014, India
#These authors contributed equally to this work
*corresponding author e-mail address: kkjindia@gmail.com
Abstract: Microalgal bioelectrochemical systems have received substantial interest among the
developing technologies for bioenergy. It is based on the interaction of two major components,
i.e., microalgae and electrochemical processes. Microalgal photosynthesis and electrochemical
reactions integrate the microalgae bioelectrochemical systems for a sustainable and efficient tech-
nique of bioelectricity generation. In this work, we have deliberated on the critical biological
component of microalgae, which captures solar energy and transform it into chemical energy via
photosynthesis. This includes selecting optimal microalgal strains with high photosynthetic effi-
ciency, optimal nutrition, and availability of carbon dioxide and designing electrodes and mem-
brane materials to improve electron transmission and reduce energy losses. Also, we have pre-
sented microalgal bioelectrochemical systems as a promising technique for generating bioelectric
energy. In addition, this system also provides an innovative method for wastewater treatment,
carbon dioxide mitigation, and direct solar energy conversion by involving microalgae with elec-
trochemical processes. We have explored the ability to address environmental concerns while
producing bioelectricity, making microalgal bioelectrochemical an appealing alternative for a
cleaner future. Therefore, continuous research and technological developments of revolutionary
bioenergy generation platforms pave the way for a more sustainable and green energy landscape.
Keywords: Microalgae; Bioelectrochemical systems; Anode; Cathode; Bioelectricity generation
1. Introduction
The increasing demand for clean and sustainable energy sources has led to a
growing interest in exploring alternative methods for renewable energy generation. Mi-
croalgal bioelectrochemical systems have gained considerable attention among these
emerging technologies (Elshobary et al., 2021). Microalgae, tiny photosynthetic organ-
isms capable of converting light energy into chemical energy through photosynthesis,
offer a promising avenue for harnessing renewable energy. Integrating microalgae with
bioelectrochemical systems can provide a sustainable and efficient means of generating
electricity, biofuels, and other value-added products (Saratale et al., 2022).
Citation: Md. Sourav Talukder ,
Gokul G, Boggavarapu Veera Venkata
Kiran Krishna, Neha Gupta, Naveen
Kumar, Binny M. Marwein, Bittesh
Barman, Krishna Kumar Jaiswal.
Photosynthetic green microalgal
bio-electrochemical system for
self-sustainable bioelectricity genera-
tion. Octa J. Biosci. Vol. 10
(2):143-153
Received: 24/07/2022
Revised: 18/11/2022
Accepted: 25/12/2022
Published: 30/12/2022
Publisher’s Note: SPS stays neutral
with regard to jurisdictional claims in
published maps and institutional affili-
ations.
Copyright: © 2022 by the authors.
Submitted for possible open access
publication under the terms and condi-
tions of the Creative Commons Attrib-
ution (CC BY) license
(https://creativecommons.org/licenses/
by/4.0/).
Octa Journal of Biosciences 2022
144
The concept of microalgal bioelectrochemical systems revolves around combining
two key components, i.e., the microalgae and the electrochemical processes. Microalgae
serve as the main biological component, harnessing solar energy and converting it into
chemical energy through photosynthesis. The electrochemical component, formed by
anode and cathode electrodes, facilitates the conversion of chemical energy produced by
microalgae into electrical energy. This integration enables directly harvesting electricity
from photosynthetic organisms, making microalgal bioelectrochemical systems an ex-
citing pathway for sustainable energy generation (ElMekawy et al., 2014). One of the
key advantages of microalgae bioelectrochemical systems is their ability to use
wastewater or other organic waste streams as a nutrient source for microalgae cultiva-
tion (Rajput et al., 2022). This aspect presents an attractive solution to two critical chal-
lenges: wastewater treatment and sustainable energy production. Integrating microalgal
bioelectrochemical systems with wastewater treatment systems allows organic contam-
inants to be effectively removed while simultaneously producing renewable energy.
This symbiotic relationship between microalgae and electrochemical processes has the
potential to transform wastewater treatment plants into self-sufficient power generation
facilities. A microalgal bioelectrochemical system also holds promise for carbon diox-
ide mitigation (Das et al., 2019).
Microalgae are remarkably able to absorb and use environmental carbon dioxide as
a carbon source for photosynthesis. Integrating microalgae with electrochemical sys-
tems can convert the captured carbon dioxide into valuable products such as biofuels or
high-value chemicals (Kumar et al., 2021; Jaiswal et al., 2021). This mitigates carbon
dioxide emissions and provides a pathway for producing sustainable fuels and chemi-
cals that can replace their fossil-based counterparts (Sheldon, 2018). In addition, micro-
algae bioelectrochemical systems can be used to generate electricity directly from sun-
light, eliminating the need for complex and expensive infrastructure typically associated
with conventional solar power systems. Microalgae's ability to use solar energy effi-
ciently makes them ideal candidates for this purpose. Microalgae transform captured
solar energy into chemical energy, which can then be collected as electrical energy
through electrochemical reactions at the anode and cathode electrodes (Mekuto et al.,
2020).
Research and development efforts in microalgae bioelectrochemical systems have
been directed at improving the efficiency, scalability, and overall performance of these
systems. Advances in electrode materials, reactor design, and culture techniques have
improved microalgae bioelectrochemical systems' energy production and stability. In
addition, genetic engineering approaches have been explored to enhance the productiv-
ity of microalgae and adapt their metabolic pathways to optimize energy generation
(Bharadwaj et al., 2020). In this work, microalgal bioelectrochemical systems represent
a promising technology for sustainable energy generation. By integrating microalgae
with electrochemical processes, these systems offer a novel approach to wastewater
treatment, carbon dioxide mitigation, and direct solar energy conversion. Also, we have
deliberated the potential to address environmental challenges and produce renewable
energy simultaneously, making microalgal bioelectrochemical an attractive solution for
a greener future. Ongoing research and technological advancements continue to unlock
Octa Journal of Biosciences 2022
145
the full potential of this innovative bioelectricity generation platform, opening the doors
to a more sustainable and environmentally friendly energy landscape.
2. Bioelectrochemical system
Bioelectrochemical systems have emerged as a promising technology that com-
bines biology and electrochemistry to convert organic matter into valuable energy. By
utilizing the metabolic activities of microorganisms, bioelectrochemical systems allow
the direct extraction of electrical current from the degradation of organic compounds.
This innovative approach has gained significant attention due to its potential applica-
tions in renewable energy generation, waste treatment, and resource recovery (Bajra-
charya et al., 2016). At the heart, the bioelectrochemical system is the concept of extra-
cellular electron transfer, which involves the exchange of electrons between microor-
ganisms and solid-state electrodes. Bacteria and archaea possess unique electron trans-
fer mechanisms, allowing them to oxidize organic matter and transfer the released elec-
trons to an electrode, creating an electrical current. This electrochemical connection al-
lows the direct harnessing of microbial electricity. One of the most explored applica-
tions of bioelectrochemical systems is wastewater treatment. Traditional wastewater
treatment processes consume substantial energy for aeration and other treatment steps
(Pant et al., 2011). The bioelectrochemical system offers an energy-efficient alternative
using microorganisms to treat wastewater and simultaneously generate bioelectricity. In
microbial fuel cells, microorganisms in the anode chamber oxidize organic matter while
the produced electrons are transferred to the cathode through an external circuit, gener-
ating electrical power.
This integration of wastewater treatment and energy production makes bioelectro-
chemical systems a sustainable solution for the water-energy nexus. In addition, the bi-
oelectrochemical system promises in the field of resource recovery. Organic matter in
wastewater or other waste streams can serve as a valuable source for producing
high-value chemicals, biofuels, and other bioproducts (Ashokkumar et al., 2022). The
bioelectrochemical system enables the selective production of target compounds by re-
directing the flow of electrons toward desired chemical reactions. This concept, known
as microbial electrosynthesis, transforms waste into valuable resources, promoting a
circular economy and reducing dependence on fossil fuels. Another exciting application
of bioelectrochemical systems is environmental remediation, specifically removing
contaminants (Dutta et al., 2020). Certain microorganisms can degrade or immobilize
various pollutants, such as heavy metals, hydrocarbons, and emerging pollutants (Fati-
ma et al., 2020; Jaiswal et al., 2020; Jaiswal et al., 2021; Nanda et al., 2021). By com-
bining these microbial capabilities with the electrochemical interface provided by bioe-
lectrochemical systems, researchers have explored the use of bioelectrochemical sys-
tems for efficient and sustainable remediation strategies. Microbe-driven reactions in
bioelectrochemical systems can enhance contaminants' degradation or immobilization,
providing a greener approach to environmental cleanup (Mohapatra and Phale, 2022).
Beyond wastewater treatment and environmental remediation, the bioelectrochemical
system has also shown potential in other areas. For example, bioelectrochemical system
can be used in biosensors to detect and quantify target analysts by monitoring electrical
signals generated by microorganisms in response to specific stimuli.
Octa Journal of Biosciences 2022
146
This potential application opens up possibilities in various fields, including
healthcare, environmental monitoring, and food safety. Advances in electrode materials,
reactor design, and microbial engineering have driven the development and optimiza-
tion of bioelectrochemical system technologies (Mier et al., 2021). The researchers are
exploring novel electrode materials that improve system performance and stability,
while reactor design improvements aim to maximize contact between microorganisms
and electrodes for efficient electron transfer. Microbial engineering approaches, such as
genetic modification or synthetic biology, allow the optimization of microbial strains to
improve their electrochemical activities and increase overall system performance. Bioe-
lectrochemical systems represent an innovative approach integrating biology and elec-
trochemistry for sustainable energy generation, wastewater treatment, and resource re-
covery (Marami et al., 2022). By harnessing the bioenergy of microbial electricity, the
bioelectrochemical system offers solutions to environmental challenges while providing
an opportunity to produce valuable products (Jaiswal et al., 2022). The bioelectrochem-
ical system's ongoing research and development efforts have great potential to unlock
its full capabilities, driving the transition toward a cleaner and more sustainable future.
3. Microalgae in a bioelectrochemical system
Microalgal bioelectrochemical systems are a promising technology that integrates
biological processes with electrochemical reactions to convert organic matter into ener-
gy or valuable chemicals. An exciting application of bioelectrochemical systems in-
volves using microalgae, microscopic photosynthetic microorganisms capable of con-
verting sunlight and carbon dioxide into biomass. The role of microalgae in bioelectro-
chemical systems, their benefits, and their potential applications have been assessed ef-
ficiently. Microalgae offer several advantages in bioelectrochemical systems (Wang et
al., 2022). First, they have high photosynthetic efficiency, which allows them to capture
solar energy and convert it into chemical energy through photosynthesis. This charac-
teristic makes them an excellent candidate for the use of renewable energy. Additionally,
microalgae can proliferate and produce large amounts of biomass quickly, making them
highly productive organisms. Further, microalgae can be grown in various environments,
including freshwater, seawater, and wastewater, providing flexibility in their application
(Leu and Boussiba, 2014).
In typical bioelectrochemical systems, microalgae are integrated into the system
differently. A common approach is to immobilize the microalgae on the surface of an
electrode. The electrode acts as a support structure and electron acceptor. As the micro-
algae photosynthesize, they release electrons the electrode captures, generating an elec-
trical current (Jaiswal et al., 2020). This phenomenon is known as microbial photosyn-
thetic cathodic current. The induced current can be used for various applications, such
as powering devices or feeding into the grid. Another approach is to couple microalgae
with other electrochemically active microorganisms, such as bacteria, in what is known
as a microbial fuel cell. In a microbial fuel cell, the microalgae provide the primary
source of electrons through photosynthesis, while the bacteria in the system facilitate
the transfer of electrons to the electrode (Mekuto et al., 2020). This synergy between
microalgae and bacteria increases energy production and provides a platform for simul-
taneous wastewater treatment. The integration of microalgae in bioelectrochemical sys-
Octa Journal of Biosciences 2022
147
tems has several benefits. First, it enables the production of renewable energy from sun-
light and carbon dioxide. This is crucial in fighting climate change and reducing de-
pendence on fossil fuels. Additionally, using microalgae in bioelectrochemical systems
can help mitigate carbon dioxide emissions by capturing and using this greenhouse gas
(Pahunang et al., 2021).
Additionally, microalgae-based bioelectrochemical systems can be used for
wastewater treatment, as the organisms can remove nutrients and contaminants from the
water. This dual functionality of energy production and wastewater treatment makes
microalgae attractive for sustainable applications. The potential applications of micro-
algae in bioelectrochemical systems are diverse. One notable area is bioenergy produc-
tion. The electrical current generated can be used to power small devices or stored in
batteries for later use (Kumar et al., 2019). Furthermore, the biomass produced by mi-
croalgae can be converted into biofuels such as biodiesel, bioethanol, etc., offering an
alternative to traditional fossil fuels (Jaiswal and Pandey, 2014). This can contribute to a
more sustainable and environment-friendly energy sector. The microalgae in bioelec-
trochemical systems also have implications for agriculture and aquaculture. The gener-
ated electrical current can be used to power sensors or actuators in precision agriculture,
optimizing resource management and crop yields (Maraveas et al., 2022). Additionally,
microalgae can be grown in wastewater or nutrient-rich streams, providing a
cost-effective, renewable feed source for aquaculture.
4. Anode and cathode in a microalgal bioelectrochemical system
Bioelectrochemical systems represent a revolutionary approach to sustainable en-
ergy generation, drawing inspiration from nature's inherent ability to harness the power
of microorganisms. The anode and cathode are central components to the operation of
bioelectrochemical systems (Figure 1). This may play a critical role in facilitating elec-
tron transfer and achieving efficient energy conversion (Gong et al., 2020). This work
explores the intricate workings of the anode and cathode in bioelectrochemical systems,
exploring their significance and potential applications for a greener future. A bioelec-
trochemical system is an electrochemical system in which microorganisms are used as
catalysts for various electrochemical reactions. These systems are designed to harness
the metabolic capabilities of microbes, particularly electroactive microorganisms, to
promote the conversion of organic matter into electricity or valuable chemicals. The
central components of a bioelectrochemical system are the anode and cathode, where
vital redox reactions occur (Ivase et al., 2020).
4.1 The anode: microbial oxidation
The anode is the electrode in a bioelectrochemical system where microbial oxida-
tion occurs. This electrode acts as an electron donor and provides an interface for the
microbial community to transfer electrons from the oxidation of organic compounds to
the external circuit. Microbial oxidation at the anode generally involves decomposing
complex organic matter by microorganisms, such as bacteria, using extracellular en-
zymes (Rabaey et al., 2009). This process releases electrons, protons, and other by-
products. Microorganisms with the capacity to transfer electrons extracellularly, known
as exoelectrogens, are essential for the functioning of the anode. These exoelectrogens
use specialized proteins, such as cytochromes and conductive pili, to facilitate the
Octa Journal of Biosciences 2022
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transfer of electrons to the anode surface. Notable exoelectrogens include Geobacter,
Shewanella, and Rhodoferax species (Kumar et al., 2015). In addition, some microor-
ganisms can perform direct electron transfer, eliminating the need for extracellular elec-
tron transfer mediators.
4.2 The cathode: microbial reduction
The cathode is the electrode in a bioelectrochemical system where microbial re-
duction occurs. It acts as an electron acceptor, capturing electrons from the external
circuit and facilitating the removal of specific compounds. The cathode can be designed
to promote the reduction of various compounds, such as oxygen, nitrates, sulfates, or
even carbon dioxide, depending on the intended application of the bioelectrochemical
system. Microorganisms involved in the cathodic process are known as electrotrophs.
Electrotrophic microorganisms can use cathode electrons to reduce different compounds,
driving essential bioremediation processes or producing valuable chemicals (Lovley,
2011; Nanda et al., 2021). For example, oxygen reduction at the cathode can be har-
nessed for microbial fuel cells to generate electricity. In contrast, carbon dioxide reduc-
tion can produce valuable chemicals such as methane or acetate.
4.3 Electron transfer mechanisms
Electron transfer in bioelectrochemical systems can occur via two main mecha-
nisms, i.e., direct and mediated electron transfer. In direct electron transfer, direct elec-
trical connections involve between the microbial cells and the electrode surface. In this
process, proteins on the outer membrane of microbial cells, such as cytochromes or
conductive hairs, facilitate the direct transfer of electrons to the anode or from the cath-
ode. Direct electron transfer is considered more efficient as it eliminates the need for
extracellular mediators, which can be expensive and unstable (Mohan et al., 2014). An-
other, in mediated electron transfer, the use of extracellular electron carriers or media-
tors involves facilitating the transfer of electrons between microbial cells and the elec-
trode surface. These mediators can be soluble redox molecules or solid-state conductive
materials that act as intermediates for electron transport. However, mediated electron
transfer is more widespread in bioelectrochemical systems; it often represents additional
complexity and cost due to reliance on mediator compounds (Schröder, 2007).
Figure 1 Schematic representation of microalgal bioelectrochemical cell
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5. Energy generation in microalgal bioelectrochemical system
Microalgal bioelectrochemical systems are a promising technology that combines
microalgae and electrochemical processes to generate energy. These systems take ad-
vantage of the unique abilities of microalgae to convert sunlight and carbon dioxide into
biomass while also using the electrochemical reactions that occur at the anode and
cathode to produce bioelectricity. Integrating photosynthesis and electrochemical reac-
tions makes microalgae bioelectrochemical systems a sustainable and efficient approach
to bioelectricity generation. Microalgae play a central role in these systems since they
serve as the primary source of biomass production. They are photosynthetic microor-
ganisms that use sunlight, carbon dioxide, and nutrients to carry out photosynthesis.
During photosynthesis, microalgae convert solar energy into chemical energy by cap-
turing light energy through pigments such as chlorophyll and using it to convert carbon
dioxide and water into organic molecules, mainly carbohydrates (Sun et al., 2018). This
process releases oxygen as a byproduct. The biomass produced by microalgae can be
harvested and processed to extract valuable products such as biofuels, bioplastics, or
high-value chemicals.
In microalgae bioelectrochemical systems, the anode and cathode compartments
are separated by an ion exchange membrane, creating a two-chamber system (Figure 2).
The anode compartment contains the microalgae and acts as a site for photosynthetic
activity. In contrast, the cathode compartment has a suitable electron acceptor, such as
oxygen or a metal catalyst, for electrochemical reactions. The anode and cathode are
connected by an external circuit, allowing the flow of electrons generated during pho-
tosynthesis to be used to produce electricity (Zhou et al., 2013). At the anode, the mi-
croalgae undergo photosynthesis and release electrons. These electrons are transferred
to the anode electrode, which acts as an electron acceptor. The anode electrode is usu-
ally made of a conductive material, such as carbon cloth or graphite, which provides a
surface for microalgae to attach to and facilitates electron transfer. The electrons gener-
ated at the anode are then transported through the external circuit to the cathode. At the
cathode, the electrons received from the anode combine with an electron acceptor,
which may be oxygen or a metallic catalyst such as platinum. This reaction generates
electrical current and produces water as a byproduct. The cathode electrode is designed
to have a large surface area and good electrical conductivity to enhance electrochemical
reactions and maximize electricity production (Zou et al., 2008). Further, the ion ex-
change membrane between the anode and cathode compartments allows for ion
transport and prevents the mixing of microalgae and the electron acceptor. This separa-
tion is crucial to maintain the photosynthetic activity of the microalgae while facilitating
electrochemical reactions at the cathode.
To optimize energy generation in microalgae bioelectrochemical systems, several
factors must be considered. These include selecting suitable microalgae strains with
high photosynthetic efficiency, optimizing nutrient and carbon dioxide availability, and
designing electrodes and membrane materials to enhance electron transfer and minimize
energy losses (Gao et al., 2014). In addition, control of environmental factors, such as
light intensity, temperature, and pH, is essential to ensure optimal growth and perfor-
mance of microalgae. Microalgae bioelectrochemical systems have the potential to pro-
vide a sustainable and renewable energy source by harnessing the power of microalgae
Octa Journal of Biosciences 2022
150
and electrochemical reactions (Kusmayadi et al., 2020). They offer advantages such as
carbon dioxide sequestration, wastewater treatment, and biomass production, making
them versatile technology for power generation. Ongoing research and development ef-
forts aim to improve the efficiency and scalability of microalgae bioelectrochemical
systems to realize their full potential as a clean energy solution for the future.
Figure 2 Bioelectricity generation using microalgal bioelectrochemical system
6. Conclusion
Microalgae have an extraordinary ability to capture and use atmospheric carbon
dioxide as a carbon source for photosynthesis. The captured carbon dioxide can be
transformed into valuable products such as biofuels or high-value compounds by merg-
ing microalgae with electrochemical apparatus. Research and development activities in
microalgae bioelectrochemical systems have focused on enhancing the efficiency,
scalability, and overall performance of bioelectrochemical systems. Advances in elec-
trode materials, reactor design, and growth techniques have all led to the improved en-
ergy generation and stability of microalgae bioelectrochemical systems. Also, genetic
engineering approaches have been investigated to boost microalgae productivity and al-
ter their metabolic pathways to optimize energy generation. Several aspects must be
considered to maximize energy generation in microalgae bioelectrochemical systems.
Selection of suitable microalgae strains with high photosynthetic efficiency, optimiza-
tion of nutrition and carbon dioxide availability, and design of electrodes and membrane
materials to promote electron transport and minimize energy losses are all part of this.
By combining the power of microalgae and electrochemical processes, microalgae bio-
electrochemical systems have the potential to create a sustainable and renewable energy
source. Microalgae bioelectrochemical systems provide carbon dioxide sequestration,
wastewater treatment, and biomass production benefits, making them a versatile bioen-
ergy generation technology.
ACKNOWLEDGEMENTS
The authors express gratitude to the Pondicherry University, Puducherry, India.
Octa Journal of Biosciences 2022
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