Algal Biorefinery Towards Decarbonization: Economics and Environment

Bioresource Technology 364 (2022) 128103
Available online 13 October 2022
0960-8524/© 2022 Elsevier Ltd. All rights reserved.
Algal biorenery towards decarbonization: Economic and
environmental consideration
V. Godvin Sharmila
a
, J. Rajesh Banu
b
, M. Dinesh Kumar
c
, S. Adish Kumar
d
,
Gopalakrishnan Kumar
e , *
a
Department of Civil Engineering, Rohini College of Engineering and Technology, Kanyakumari, Tamil Nadu, India
b
Department of Biotechnology, Central University of Tamil Nadu, Neelakudi, Thiruvarur, Tamil Nadu 610005, India
c
Department of Civil Engineering, Saveetha School of Engineering, Saveetha Institute of Medical and Technical Sciences (SIMATS), Chennai, Tamil Nadu, India
d
Department of Civil Engineering, Anna University Regional Campus, Tirunelveli, Tamilnadu, India
e
School of Civil and Environmental Engineering, Yonsei University, Seoul 03722, Republic of Korea
HIGHLIGHTS GRAPHICAL ABSTRACT
•This review emphases on algal bio-
renery on biofuel & bioproducts.
•Technoeconomic assessment of algal
biorenery is elaborated.
•Decarbonisation aspect of algal bio-
renery has been presented.
•Commercialization perspectives & envi-
ronmental concerns are deeply
discussed.
ARTICLE INFO
Keywords:
Microalgae
Macroalgae
Biorenery
Carbon dioxide emission
Commercialization
ABSTRACT
Algae biomass contains various biological elements, including lipids, proteins, and carbohydrates, making it a
viable feedstock for manufacturing biofuels. However, the biggest obstacle to commercializing algal biofuels is
their high production costs, primarily related to an algae culture. The extraction of additional high value added
bioproducts from algal biomass is thus required to increase the economic viability of producing algae biofuel.
This study aims to discuss the economic benets of a zero-carbon economy and an environmentally sustainable
algae resource in decarbonizing the environment through the manufacture of algal-based biofuels from algae
biomass for a range of potential uses. In addition, research on the algae bioreneries, with an emphasis on case
studies for various cultivation methods, as well as the commercialization of biofuel and bioenergy. Overall, the
algal biorenery offers fresh potential for synthesizing various products.
* Corresponding author.
E-mail address: [email protected] (G. Kumar).
Contents lists available at ScienceDirect
Bioresource Technology
journal homepage: www.elsevier.com/locate/biortech
https://doi.org/10.1016/j.biortech.2022.128103
Received 31 August 2022; Received in revised form 5 October 2022; Accepted 7 October 2022

Bioresource Technology 364 (2022) 128103
2
1. Introduction
Modern industrialized zones across the globe face the challenges of
excessive generation of CO
2
, which intensies climate change, and high
levels of contaminants. Now more individuals lose consistent access to
food, clean air, and pleasant lands as the wealth gap between the
afuent and poor get widens (Kaur et al., 2021). Although there is a
growing need for energy on a broader scale, fossil fuels remain to have
limitations and pose a serious environmental concern. The global
mandate for fuel consumption has grown dramatically, and the usage of
fossil fuels has a seriously detrimental effect on the biosphere. In 2020,
the amount of CO
2
emitted globally decreased by 5.8 %, or about 2 Gt
CO
2
– the most signicant decrease ever. Despite of CO
2
emissions
reduction of about 2 billion tons in 2020, global energy related CO
2
emissions remained at 31.5 Gt, which helped CO
2
achieve its highest
annual average concentration in the atmosphere in 2020 of 412.5 parts
per million, or over 50 % more than the start of the industrial revolution.
The demand for coal, oil, and gas is expected to increase by 4.8 percent
in 2021 as the economy recovers, leading to a rise in global energy-
related CO
2
emissions. With global emissions expected to reach
approximately 400 Mt CO
2
in 2021, the surge of much more than 1500
Mt CO
2
might be the highest single increase since the carbon-intensive
economic growth from the economic recession more than ten years
ago (Liu et al., 2022). The emission of CO
2
from various countries is
provided in Fig. 1. The present global energy problem has received a
great deal of attention. In order to handle current global constraints
towards the domains of environmental protection, process biotech-
nology will play a prominent role. Technologies used in bioreneries are
rooted in the notion of rening biomass sustainably to generate a wide
range of products that can be commercialized (see Table 1).
Mainly in the current milieu, the product portfolio concept has now
become highly signicant for algae as it is the ideal feedstock for a
biorenery concept. Algal biomass is a potential third generation feed-
stock for biofuel. The diversity of available varieties and the range of
products that might have been produced from algal biomass are two
distinctive features of algal feedstocks, which makes it an ideal choice
for upcoming treatment in biofuel production. Using production systems
such as anaerobic digestion, pyrolysis, gasication, catalytic cracking,
and enzymatic or chemical transesterication, whole algae or algal oil
derivatives may be transformed into various fuel types such as biogas,
liquid and gaseous transportation fuel, kerosene, ethanol, aviation fuel,
and biohydrogen (Khoo et al., 2019). Financial sustainability for the
biofuel manufacturing unit may be achieved by synchronizing the
sequential processing of algal biomass to produce various products
(Chang et al., 2022; Kumar et al., 2022). An appealing contribution to
the variety of initiatives to reduce the existing dependency on fossil fuels
seems to be the potential for producing fuel affordably from growing
algal biomass. Algae are a potential substitute for biofuel production due
to the relatively low space requirements, the endurance of dire cir-
cumstances, and the capacity to reduce carbon dioxide (Singh et al.,
2022). Algae grow 20–30 times quicker than nutritional crops, and its oil
content is roughly 30 times higher than typical rst- and second-
generation feedstocks (Ullah et al., 2014; Zhou et al., 2022). Algae are
also utilized in wastewater bioremediation which is protable in the
long run (Moshood et al., 2021). Additionally, researchers may combine
the generation of CO
2
neutral fuel with CO
2
sequestration from other
power sectors to produce carbon credits.
In Istanbul, the rst carbon-negative biorenery in Europe was
launched using algae to produce an array of products for various Turkish
industries. The biorenery transforms biodegradable substances into
usable products and fuel. Also, Turkey hopes to employ microalgae and
macroalgae in its newest biorenery approach to create an array of
products like biofuel, nutritional supplements, and fertilizers. Moreover,
sustainability and relevant technological and nancial challenges
should be resolved for such an established commercial sector to grow.
According to studies, the market for algal biofuel would increase from
US$5.022 billion in 2020 to US$9.033 billion in 2027. Demand for
algae-based biofuel as a primary energy source is increasing as the price
of petrol and gasoline is continued to rise (Ullah et al., 2014). This re-
view provided an outline of algal biorenery, its inuence on a zero-
carbon economy, and economic and environmental assessments.
Various techniques of cultivation with their economic evaluation were
discussed. In addition, this review will discuss the aspects that empha-
size the commercialization, scaleup and limitations of biofuel produc-
tion with advantages, obstacles, and future prospects.
2. Economic benets of zero carbon economy
Every country pledged to reduce its carbon footprint owing to the
severe warning issued by the Intergovernmental Panel on Climate
Change (IPCC) which causes temperature increments. But, the signi-
cant reductions in CO
2
and other greenhouse gas emissions are mandates
Fig. 1. Carbon dioxide emissions from various countries.
V.G. Sharmila et al.

Bioresource Technology 364 (2022) 128103
3
and were accomplished through a Nationally Determined Contributions
(NDCs) system which is linked to Green Energy, an intrinsic and critical
component of reducing carbon emissions and the decarbonizing in-
dustry must be prioritized (Arun et al., 2020). Efforts to decarbonize
industry must therefore be founded on four pillars which were provided
in Fig. 2. The rst step is to identify carbon-free or low-carbon energy
sources capable of producing the intense heat and energy required for
industrial production. The second step is to transition, wherever
Table 1
Algal biorenery for biofuel production.
Feedstock Experiment/reactor Biorenery type Conditions Product Yield/
production
References
Microalgal Biorenery
Scenedesmus dimorphus Fungal treatment Ethanol fermentation pH: 5;
Temperature: 36 ◦C;
Yeast loading: 3 g/L
Bioethanol 0.26 g/g Chng et al. (2016)
Nannchloropsis gaditana High-pressure homogenization Direct
transesterication
Feed rate: 9 L/h
Pressure: 140 MPa
FAME/Biodiesel
99.5 wt%
Lopez et al.
(2016)
Isochrysis galbana – Transestercation Catalyst: H
2
SO
4
catalyst/solvent/oil ratio:
1.74/15/1
FAME/Biodiesel
75.9 wt%
S´ anchez-Bayo
et al. (2019)
Isochrysis galbana – Anaerobic digestion – Methane
310 mL CH
4
/g
volatile
S´ anchez-Bayo
et al. 2019
Scenedesmus abundans Lab-scale hybrid loop airlift photo
bioreactor
Catalytic hydrothermal
liquefaction
Temperature: 300 ◦C;
Pressure: 5 Mpa
Solid/Liquid: 15 g/200 mL;
Retention Time: 60 min
Bio oil
0.963 g/g algae
SundarRajan et al.
(2019)
Microcystis wesenbergii and
Microcystis aeruginosaare
Hydrothermal acid pretreatment Dark fermentation Temperature: 135 ◦C;
Time: 15 min;
Acid: 2 % H
2
SO
4
Biohydrogen
24.96 mL H
2
/g total
volatile solids
Cheng et al.
(2019)
Chlorella sp Thermal pretreatment Two-stage anaerobic
fermentation
Temperature: 150 ◦C Biohydrogen
5.15 mL H2/g VS
Wu et al. (2020)
Chlorella sp Thermal pretreatment Two-stage anaerobic
fermentation
Temperature: 150 ◦C Biomethane
434.38 mLCH4/gVS.
Wu et al. (2020)
Scenedesmus obliquus – Catalytic hydrothermal
liquefaction
Temperature: 240–300 ◦C;
Pressure: 5 Mpa
Solid/Liquid: 15 g/200 mL;
Retention Time:60 min
Bio oil
39.6 wt%
Arun et al. (2020)
Hydrodictyon reticulatum – Ethanol fermentation Fermentation strain:
Saccharomyces cerevisiae
KCTC7017
Bioethanol
93.5 %
Min et al. (2021)
Macroalgal Biorenery
Saccharina japonica Heat-Base treatment Anaerobic fermentation Temperature: 121 ◦C;
Base: 2 % NaOH;
Time: 30 mim
Biohydrogen
17.5 mL/g TS
added
Yin and Wang
(2018)
Chaetomorpha antennina Thermo-chemo disperser liquefaction Anaerobic digestion Disperser g-force: 1613 g;
Temperature: 80 ℃; pH: 11;
Biomethane
215 mL/g VS
Tamilarasan et al.
(2018)
Saccharina latissima Hydrothermal pretreatment Anaerobic fermentation Temperature =100–180 ◦C;
Time =10 min
Biohydrogen
6.9–13.7 mL H
2
/g
VS
Lin et al. (2019)
Saccharina latissima Hydrothermal pretreatment Anaerobic digestion Temperature =100–180 ◦C;
Time =10 min
Biomethane
278.7–345.1 mL
CH
4
/g VS
Lin et al. (2019)
Ulva prolifera Hydrothermal liquefaction Liquefaction Temperature: 290 ℃;
Catalyst: KOH – 0.1 g;
Reaction time: 10 mins
Bio oil
26.7 wt%
Yan et al. (2019)
Laminaria digitata Hydrothermal pretreatment Two-stage dark
fermentation
Temperature: 140 ◦C;
Time: 20 min
Biohydrogen
44.8 mL/gVS
Ding et al. (2019)
Laminaria digitata Hydrothermal pretreatment Anaerobic digestion Temperature: 140 ◦C;
Time: 20 min
Biomethane
282.2 mL/gVS
Ding et al. (2019)
Ulva fasciata Chemo thermal coupled sonic
homogenization
Anaerobic fermentation Sonic power: 140 W;
Treatment time: 14 min;
Temperature: 80 ℃
Volatile Fatty Acid
2172.09 mg/L
Banu et al. (2020)
Ulva reticulate Microwave with hydrogen peroxide
(H
2
O
2
) pretreatment under alkaline
condition
Anaerobic fermentation Pretreatment conditions:
Power: 360 W;
H
2
O
2
dosage: 0.024 g/g TS;
pH: 10;
Time: 8 min.
Biohydrogen
87.5 mL H
2
/g COD
Kumar et al. 2020
Kappaphycus alvarezii Fungal pretreatment Ethanol fermentation Fungus: T. harzianum;
Yeast: Saccharomyces
cerevisiae
Bioethanol
38.23 %
Sulfahri et al.
(2020)
Ulva lactuca Microwave-assisted pyrolysis pyrolysis Temperature: 500 ◦C Biooil
18.4 wt%
Wang et al.
(2021)
Ulva reticulate Surfactant induced microwave
disintegration
Anaerobic fermentation Pretreatment conditions:
Power: 360 W;
Surfactant dosage: 0.021 g/g
TS; Time: 8 min.
Biohydrogen
54.9 mL H
2
/g COD
Kumar et al.
(2022)
V.G. Sharmila et al.

Bioresource Technology 364 (2022) 128103
4
possible, to carbon-free processes or to upgrade processes to use low-
carbon energy. The third pillar, where CO
2
emissions are unavoidable
based on current technology, is carbon dioxide capture, utilization, or
storage (CCUS). The nal and slightly more contentious option is to
create carbon offsets by planting and growing trees. The potential
reduction in GHG emissions is between 18 and 38 %, according to
preliminary results of using green hydrogen to reduce iron in blast fur-
naces directly. However, CO
2
emissions appear to be unavoidable for the
foreseeable future. Therefore, it unavoidably leads us to the next
decarbonization pillar for industry: CCUS.
CCUS is the capture and storage of CO
2
emissions in deep geological
formations. Shaw and Mukherjee et al. (2022) which is now the most
economically viable method of aiding the industry in its decarbonization
until the establishment of alternative technologies i.e., Green Hydrogen
or process modications. This captured CO
2
was used to create the Blue
Ammonia usually transported from Saudi Arabia to Japan. Different
carbon offset programs offer the chance to reduce emissions. The gov-
ernments must intervene and take an active part in facilitating this
process to minimize CO
2
emissions by utilizing various strategies,
including incentives, their clout as sizable consumers of industrial
goods, and the introduction of regulatory acts. It will be necessary to
adapt existing industrial facilities to employ cleaner energy sources like
Green Hydrogen. Another regulatory approach to compel the industry to
speed up decarbonization and inform customers of the environmental
consequences of their purchasing decisions is the “Green Tax. Govern-
ments can also compel the industry to go greener and more sustainable
by using the regulatory authority (Kolcava and Bernauer et al., 2021).
For instance, the E.U. has stated that it intends to impose a carbon tax at
its borders to reduce GHG emissions. However, experts have noted that
calculating and enforcing such a tax would be incredibly challenging. It
is important for all stakeholders governments, industry, and nal con-
sumers must take part in minimizing the carbon emission to decarbonize
in the upcoming days and years.
3. Algae an environmentally sustainable resource for
decarbonization
An extensive and diverse species of biota known as algae were indeed
able to produce O
2
through a process called photosynthesis, which al-
lows algae to use the solar energy into chemical energy to expand and
create a variety of biochemicals (Bar-Shai et al., 2021). These potential
and associated traits may offer algae as a valuable resource in creating
cutting-edge technologies for resourcefully treating wastewater, gener-
ating greener fuels and renewable biofuels, minimizing hazardous car-
bon dioxide emissions, and enhancing decontamination and pollution
control approaches (Chiarathanakrit et al.,2019). Algal biomass is
currently the subject of extensive research to determine its viability as a
substitute biofuel feedstock, consequently resolving the concerns of the
food versus fuel conict (Ubando et al., 2022). Algae are efcient carbon
sinks and supply 50 % of the oxygen in the globe. Although algae need a
lot of water and carbon dioxide (CO
2
) to ourish, algae also have the
potency to provide 10 to 100 times more fuel per acre of land than other
crops. The feedstocks generated by algae and municipal solid waste
(MSW) streams were transformed into low-carbon fuels that can sub-
stantially aid in the decarbonization of transportation sectors that face
challenges with electrication (Hoover et al., 2011). Since it either
consumes CO
2
captured emissions from industrial sources or absorbs
greenhouse gases from the atmosphere, fuels and products made from
algae have lesser carbon footprints than its fossil-based equivalents
(Jonsson et al., 2020). Maximizing the utilization of this renewable
super-crop, whether farmed in raceway ponds, bioreactors, aquaculture
systems, or collected from wild stocks, is crucial for creating a bio-
economy. Advancements in algal biotechnology can prompt the devel-
opment of new algae-based products and environmental protection,
which can result in the development of novel strains and techniques
(Onyianta et al., 2020). This can facilitate the creation of new careers
and markets.
Nutrient algae have been utilized for millennia as food and feed.
Most of the world’s macroalgae (seaweed) consumption occurs in Asia.
Fig. 2. Four-step process to decarbonize the industrial emissions.
V.G. Sharmila et al.

Bioresource Technology 364 (2022) 128103
5
In the global carbon cycle, algae play a crucial role (Behera et al., 2022).
One of the largest carbon sinks on the planet is the ocean because of
phytoplankton, a form of microalgae. Algae’s potential to eliminate
toxins has been exploited in rehabilitating contaminated sites (Sharmila
et al., 2021). In contrast, its efciency in sequestering carbon was used
to create carbon capture systems that are less intricate and require less
maintenance than some other carbon capture techniques (Prabhu et al.,
2019). In the net-zero carbon economy, there seems to be an upsurge in
energy generating techniques during the past 10 years (Sebeia, et al.,
2019). Algal biofuels outperform rst- and second-generation biofuels in
terms of per-acre yield and environmental effects.
4. Algal cultivation techniques and its economic evaluation
The concept of “algal culture,” which refers to the genuine potential
of cultivating algae, needs to gain acceptance in the world as a viable
substitute for burning fossil fuels, which meant to be a “black gold” of
recent centuries (Ren et al., 2021). The macroalgae can be grown in
offshore and onshore environments using various techniques. Kelp
growth, raft culture, and oating cultivation are all included in offshore
cultivation which was given in Fig. 3. Rope or net cultivation is thought
to be a common cultivation technique since it requires less money for
installation and upkeep. When growing macroalgae, lagoons are
employed since the nutrients come from the seawater. The other tech-
niques for growing macroalgae include xed-off bottom, long lines, and
farming on rocks. Another cultivation technique is transplantation, in
which species of saplings are permitted to grow indoors before being
cultured in tanks and then rope-transplanted into the sea (Mishra et al.,
2019). Cultivation techniques must be improved to increase biomass
production and lower the cost of growing algae. Algal cultivation cost
analysis is essential for determining the nal product costs, which will
also help with future research strategies. By acquiring bioactive mate-
rials, integrated cultivation techniques are employed to render algae
cultivation commercially viable.
Closed photobioreactors (CPRs) and open raceway ponds (OPRs) are
the most common of the systems used to cultivate microalgae (Fig. 3).
Affordable initial investment costs, ongoing operational expenses, and
little energy are all needed for the ORPs to integrate the cultures. Pho-
tobioreactors (PBRs), on the other hand, are efcacious since they can be
functioned in a restricted condition and may be tailored to meet specic
needs (Mohsenpour et al., 2021). Because PBRs are enclosed systems
that take up less room, cultures can use light effectively. The methods
utilized to cultivate microalgae largely inuence whether the operation
is protable. According to researchers, OPRs have become more
nancially protable than PBRs since it provides better energy stability
(Jorquera et al., 2010). For a 100 ha area, it was calculated that the
production costs of biomass in OPRs, horizontal PBRs, and at plate
PBRs were 4.95, 4.16, and 5.96
€ /kg, respectively. The cost per gallon
for 100,000 kg of biomass is $2.95 in PBRs and $3.80 in OPRs, corre-
spondingly (Mathiot et al., 2019). OPRs provide biomass output at a
lower cost than PBRs. For PBRs, the cost of producing 10 M.G./yr of
biomass was predicted to be 32.57 $/gallon, compared to 12.74
$/gallon for OPRs (Maia et al., 2020). Additionally, it was estimated that
the selling price of microalgal lipids was 8.52 dollars per gallon for OPRs
and 18.10 dollars per gallon for PBRs (Madadi et al., 2021). Recent
research, however, reveals that PBRs, as opposed to OPRs, achieved a
higher level of lipid productivity. When grown in PBRs, Nannochloropsis
sp. showed a lipid content of 35 % (Lee et al., 2018). According to
studies, cultivating microalgae in PBRs instead of OPRs decreases the
probability of net cash income (NCI) for manufacturing lipids by 26 %.
Future economic viability will be possible due to the creation of pro-
ductive pathways and the development of diverse processing technolo-
gies. Microalgae cultivation in a photobioreactor is a desirable choice
due to the simplicity of harvesting, high biomass productivity, reduced
medium water evaporation, ease of control over the culture conditions,
and low danger of contamination. When compared to a photobioreactor,
however, microalgae cultivation in an open pond system is thought to be
less expensive. Open raceway pond and turf scrubber are two separate
open pond cultivation technologies that were subjected to techno eco-
nomic study by Hoffman et al (2017). A turf scrubber system required
USD 704.4/tonne in total costs for biomass production, compared to
USD 53.8/tonne for an open raceway pond. It was calculated that pro-
ducing biomass in a photobioreactor would cost USD 3.903.4/kg of dry
biomass. The cost of producing biomass has decreased signicantly due
to engineering and scientic developments, and it may now only be US
$0.57/kg dry biomass.
5. Various approaches/techniques for algal biorenery
Algal biomass is converted into different types of biofuels via
biochemical conversion, thermochemical conversion, chemical reac-
tion, and direct combustion methods. The biochemical conversion
method includes anaerobic digestion, alcoholic fermentation and
Interesterication. Anaerobic digestion is the conversion of organic
wastes into biogas, which consists of primarily methane and carbon
dioxide, with traces of other gases such as hydrogen sulphide. It involves
the breakdown of organic matter to produce a gas with an energy con-
tent of about 20–40 % of the lower heating value of the feedstock.
Fig. 3. Various methods of algal cultivation.
V.G. Sharmila et al.