2. Chemosphere 345 (2023) 140515
2
Keywords:
Lignocellulosic biomass
Biochar
Circular bioeconomy
Waste management
Environmental remediation
intrinsic mechanisms. In addition to its environmentally friendly nature, biochar has several recyclable and
inexpensive benefits. Nourishing and detoxification of the environment can be undertaken using biochar by
different investigators on account of its excellent contaminant removal capacity. Studies have shown that biochar
can be improved by activation to remove toxic pollutants. In general, biochar is produced by closed-loop systems;
however, decentralized methods have been proven to be more efficient for increasing resource efficiency in view
of circular bio-economy and lignocellulosic waste management. In the last decade, several studies have been
conducted to reveal the unexplored potential and to understand the knowledge gaps in different biochar-based
applications. However, there is still a crucial need for research to acquire sufficient data regarding biochar
modification and management, the utilization of lignocellulosic biomass, and achieving a sustainable paradigm.
The present review has been articulated to provide a summary of information on different aspects of biochar,
such as production, characterization, modification for improvisation, issues, and remediation have been
addressed.
1. Introduction
Worldwide population expansion endangers natural sustainability,
and the concurrent utilization of fossil fuels accelerates anthropogenic
global warming that posing a grave danger to societal stability (Choz
havendhan et al., 2022; Ashine et al., 2023; Selvakumar et al., 2022).
The difficulties of mitigating such impacts have been driven by many
influenceable factors, accordingly, it should be looked for comparable,
affordable, and sustainable alternatives to petroleum-derived goods
(Jayakumar et al., 2023). According to latest researches, non-renewable
resource alternatives have emphasized on the recycling and recovering
of energy crops and lignocellulosic waste, which are low-maintenance
plants grown solely for transformation of energy (Amalina et al.,
2022; Kasirajan et al., 2022). Hence, the rise in agricultural production
brought about by the expanding population is anticipated to produce
100 million tons of crop residue yearly, according to linear economic
modeling. Keeping this in view, growing interest has been demonstrated
in producing valuable products from agricultural by-products, particu
larly lignocellulosic biomaterials, which has resulted in the production
of biomass-based carbon known as biochar (BC) (Chen and Pilla, 2022).
In this regard, a carbon-enriched biomaterial known as biochar is syn
thesized whenever biomass is burned using a technique, which is
commonly known as thermochemical conversion technology.
The thermochemical conversion technologies utilized for the trans
formation of biomass-dependent feedstocks into biochar encompass
different processing methods such as fast, slow, and flash pyrolysis,
hydrothermal carbonization, combustion, torrefaction, bio-gasification,
and direct thermal liquefaction. Historically, the most widely recognized
type of BC is charcoal, which derived from wood. Such type is pre
dominantly utilized as one of the traditional solid fuels (Amalina et al.,
2022). So far, various BC types have been practiced over several de
cades. In this line, the majority of agricultural by-products and woody
biomass which are come under lignocellulosic biomass classification
known to be mainly composed with lignin, hemicellulose, and cellulose.
Agricultural byproducts and waste are a rich source of lignocellulosic
materials, which are available in an array of configurations and have
different proportions of the three main components. An array of
different carbon structures from various biomasses are produced as a
result of the decomposition process, which is mediated by various
breakdown pathways (Vijayaraghavan, 2019).
The synthesized biochar via thermochemical conversion techniques
can be employed for different applications. The development of the bio-
circular economy can be significantly aided by the manufacture of bio
char from waste by-products disposed from industry, agricultural and
transportation sectors. The unique characteristics of biochar, such as its
surface area, functionality, porous structure, and adsorption capacity,
are responsible for its beneficial applications. Application of biochar
with higher stability and resilience due to its higher fixed carbon content
facilitates better carbon sequestration in the soil. Despite being suitable
for plant uptake and agricultural uses, biochar rich in nutrient elements
is more effectively used mostly for adsorption due to its higher surface
area and electrical conductivity. The feedstock composition and
temperature system used in thermochemical conversion technologies
are reported to have varied levels of impact on the features permitting
such applications (Bonga et al., 2020). Along with carbon sequestration
to lessen its impact on climate change, biochar having potential char
acteristic to ameliorate the fertility of soil. Further, the utilization of
selective functional materials associated with biochar property impro
visation can be also sustainable approach. This is concerned because the
pyrolysis method always seems to turn waste biomaterials into biochar,
reducing emissions of anthropogenic carbon dioxide (CO2). Besides that,
leveraging BC is found to be excellent contribution in reducing green
house gas emissions while it is amending in soil for nurseries towards
absorbing the atmospheric carbon to maintain sustainable soil quality.
Hence, it significantly reduces the need for synthetic fertilizers in agri
cultural production. Correspondingly, it improves the biological, phys
ical and chemical, and characteristics of the soil that can facilitate plant
growth and health. The use of BC effects primarily depends on the raw
materials/precursors used, the carbonization methods, the application
techniques, and the dosage (Moreno-Riascos and Ghneim-Herrera,
2020). With respect to applications, BC’s quality as well as the quan
tity are affected by several operational parameters.
The yield and technical (properties of the BC are influenced by the
substrate and operational factors, such as particle size, temperature of
the system, heating rate, residence time, and others. Some activities are
better suited to biochar than others because it is produced in varying
amounts and of varying quality from various classes of feedstocks
(Bonga et al., 2020). Likewise, a variety of factors, such as types of
feedstock, composition of biomass, temperature of the system, heating
rate of the system, and particle size, have an impact on the biochar that
is formed from biowaste. Instead of affecting the quality of biochar, the
aforementioned processing parameters have a direct impact on its
output. Determining the application of BC requires in-depth expertise in
studying its characteristics. Furthermore, a variety of analytical tools are
utilized to characterize the biochar produced, which can be influenced
by a wide range of circumstances and employed for environmental
remediation. Different analytical techniques, such as X-ray Diffraction
analysis, scanning electron microscopy, Fourier transform infrared ra
diation, and Brunauer– Emmett–Teller analysis, are used to examine
biochar produced from bio-waste. To identify the parameters associated
with the aforementioned analysis, proximate and ultimate analyses of
biochar were also performed. In this regard, the features of BC, such as
its surface area, morphological and crystalline nature, heating value,
pH, and thermal characteristics, were evaluated. In an oxidizing envi
ronment, the thermogravimetric response can be used to assess the py
rolytic response of BC. Scanning electron microscopy (SEM) analysis
revealed a diverse and rough texture structure that supported morpho
logical changes. XRD analysis confirmed the crystalline nature of BC.
The present comprehensive review provides an overview of BC pro
duction strategies and exploitation of lignocellulosic biomass sources,
and recent innovations in biochar utilization technologies have been
discussed. In addition, the review highlights the barriers, limiting fac
tors, characterization techniques, merits, demerits, challenges, appli
cations, environmental benifications, economic assessment, bio-circular
M. Jayakumar et al.
3. Chemosphere 345 (2023) 140515
3
economy, prospects, and challenges.
2. Synthesis of biochar from various lignocellulosic feedstock
and its sources
2.1. Biochar
Biochar can be produced from different biomass precursors, such as
stalks, shells, grasses, and husks, through appropriate conversion tech
niques, such as biochemical and thermochemical methods, that are
carried out in an inert atmosphere or with very little air present. Biochar
is a bioactive carbon containing high levels of aromatizing solids. It is
manufactured with the intention of being employed for a multitude of
uses, including as an adsorbent and fuel in the industrial and agricultural
sectors, because it has a very good specific surface area and high energy
content, and is enriched with minerals and carbon.
Over the past decade, various valorization methodologies for waste
biomass processing have been studied and developed. In this way, a
variety of innovative thermochemical technologies, such as pyrolysis,
torrefaction, hydrothermal combustion, hydrothermal liquefaction,
gasification, and biochemical processes, such as aerobic and anaerobic
digestion, and physicochemical methods, such as lipid extraction, have
been proven as possible biomass conversion methods. Because it is very
simple to valorize leftover biomass from an environmental and financial
standpoint, pyrolysis has gained significant interest among the research
community and policymakers as a significant thermochemical
conversion process. Carbon-rich BC can be manufactured at low-cost,
using waste solid residues that containing outstanding porous struc
ture using one of the traditional thermochemical conversion processes,
known as slow pyrolysis (Mukherjee et al., 2022).
Several limiting factors, namely, temperature, nature of feedstocks,
particle size, rate of heating, types of pyrolysis reactors, catalyst, purg
ing gas, pressure, heating time, and flow rate of the feedstock consid
erably affect the production and properties of the BC during the
thermochemical conversion technologies (Suriapparao and Tejasvi,
2022). Aforementioned factors do have a crucial effect on production
and yield of the BC. Numerous types of feedstocks can be employed for
the synthesis of BC including agricultural biomass, industrial biomass,
municipal solid waste, forestry biomass, and food processing bio-wastes.
Lignocellulosic feedstock sources and related processing parameters are
presented in Table 1.
2.2. Biochar composition
According to Wijitkosum and Jiwnok (2019) study, slow pyrolysis
can produce comparatively high-quality BC with stable carbon content
and a low ratio of H/C. Studies on BC analysis revealed that the BC
synthesized from corncob, and rhizomes and stems of cassava had the
highest levels of carbon and hydrogen, with values of 81.35% and
2.42%, respectively. On the other hand, the BC made from cassava
rhizomes and cassava stems had 64.25% carbon and 2.73% hydrogen
and 62.95% carbon and 2.2% hydrogen, respectively. In addition, the
Table 1
Lignocellulosic feedstock sources and its process parameters.
Lignocellulosic
feedstock and its sources
Proximate analysis (wt. %) Other
characterization
Chemical characterization (wt. %) Ultimate analysis (wt. %) Reference
AC MC VM FC HHV
(MJ/
kg)
BD
(kg/
m3
)
CE HC LG EV C H O N
Agricultural biomass
residue (AR): Pigeon
pea stalk (PPS)
2.00 7.59 76.71 13.70 NR 278 33.00 24.00 18.30 4.70 41.62 6.10 51.57 0.71 (Sahoo et al.,
2021)
ABR: Bamboo (B) 1.58 10.74 71.65 16.03 NR 317 47.29 21.19 24.53 5.11 46.98 6.21 46.65 0.16
Industrial waste (IW):
Leucaena leucocephala
bark
7.20 4.90 69.80 18.10 16.80 166 30.85 15.01 34.75 NR 45.78 10.67 32.08 1.77 (Anupam et al.,
2016)
ABR: Corn cob 2.30 12.77 91.16 6.54 16.00 NR NR NR NR NR 42.10 5.90 NR 0.50 (Biswas et al.,
2017)
ABR: Wheat straw 6.63 12.81 83.08 10.29 14.68 NR NR NR NR NR 38.34 5.47 NR 0.60
ABR: Rice straw 15.00 11.69 78.07 6.93 14.87 NR NR NR NR NR 36.07 5.20 NR 0.64
ABR: Rice husk 15.14 10.89 73.41 11.44 12.87 NR NR NR NR NR NR 6.34 NR 1.85
ABR: Cocoa pods husks 11.38 3.80 76.14 21.49 16.49 NR NR NR NR NR 43.55 5.18 38.51 NR (Ghysels et al.,
2020)
Anaerobic digestate
(AD): cocoa pod husks
17.28 9.09 80.91 17.19 16.07 NR NR NR NR NR 41.93 5.24 34.35 NR
AD: Cocoa Pod husks
and cow manure
13.43 11.43 77.07 21.19 14.34 NR NR NR NR NR 38.34 4.72 41.32 NR
ABR (Banana biomass
wastes (BBW)): Peels
9.28 11.56 88.02 2.70 16.15 NR 9.90 41.38 8.90 NR 35.65 6.19 45.94 1.94 (Kabenge et al.,
2018)
BBW: Leaves 9.05 6.67 83.35 7.60 17.57 NR 35.58 23.46 10.58 NR 38.57 6.44 43.49 2.45
BBW: Pseudo-stem 9.36 7.98 89.43 1.21 15.04 NR 38.48 25.36 5.77 NR 33.46 6.44 49.94 0.80
ABR (BBW): Banana
pseudo-stem
11.00 10.20 88.80 0.20 15.50 NR 44.00 17.50 37.30 9.70 37.93 4.46 55.37 1.87 (Abdullah et al.,
2014)
ABR (BBW): Banana
Fruit bunch stem
20.60 11.40 79.10 0.30 12.70 NR 39.80 27.80 18.00 6.00 35.58 4.62 57.16 2.19
ABR: Wheat stem 10.60 2.40 71.40 17.70 NR NR NR NR NR NR 47.40 6.70 45.50 0.20 (Wilson et al.,
2018)
ABR: Blackbutt 1.60 5.30 79.50 18.90 NR NR NR NR NR NR 48.90 6.60 44.20 0.00
ABR: Pineapple residue 6.24 2.15 72.12 19.50 17.73 NR 27.35 21.15 10.25 NR NR NR NR NR (Wang et al.,
2022)
ABR: Banana Pseudo-
stem
23.53 1.93 59.77 14.78 13.28 NR 17.17 8.11 35.00 NR NR NR NR NR
Forest biomass: Beech
wood
0.50 8.70 84.30 15.20 NR NR NR NR NR NR 49.10 5.70 44.50 0.15
ABW: Pea pod (PP) 3.50 7.00 78.00 18.00 NR NR 45.00 41.00 3.00 NR 39.32 4.75 53.30 2.40 (Stella Mary
et al., 2016)
ABW: Orange peel (OP) 5.50 13.00 51.00 39.00 NR NR 54.10 49.00 12.00 NR 40.43 4.83 52.90 1.56
ABW: Cauliflower (CL) 18.86 9.00 70.00 24.10 NR NR 40.00 50.00 8.00 NR 31.80 3.20 59.40 4.01
Corncob NR NR NR NR NR NR NR NR NR NR 41.66 6.84 50.76 0.74 (Wijitkosum
and Jiwnok,
2019)
Cassava rhizome NR NR NR NR NR NR NR NR NR NR 37.60 6.15 55.37 0.88
Cassava stem NR NR NR NR NR NR NR NR NR NR 41.55 6.04 51.14 1.27
M. Jayakumar et al.
4. Chemosphere 345 (2023) 140515
4
oxygen content of BC made from cassava stems was found to be highest
(33.44%), whereas that of BC prepared from corncobs was the lowest
(15.23%). The availability of carbon percentage was seen in corncobs
(39.69%), followed by rhizomes of cassava (26.65%) and stems of cas
sava (21.40%). However, the opposite trend was seen with respect to
hydrogen and oxygen. In particular, cassava stem BC had the greatest
total pore volume and surface area, measuring 0.1219 cm3
/g and
200.46 m2
/g, respectively. Corncob BC was known to be the second-best
choice with 56.35 m2
/g for surface area and 0.0405 cm3
/g for pore
volume, and BC obtained from cassava rhizome came in third with
18.38 m2
/g and 0.0284 cm3
/g. According to the average value of pore
diameter, the BC made from cassava rhizomes showed the largest value
at 61.69 Å. The BC made from corncobs and cassava stems had showed
28.72 Å and 24.35 Å, respectively. Based on the previous studies com
positions of BC are summarized in Table 2.
2.3. Biochar and its properties
The precursors of BC, methodologies of pyrolysis, processing pa
rameters are significantly influencing the properties of BC. The total
carbon content, ash content, total phosphorus, nitrogen, calcium, mag
nesium, potassium, sulfur, aluminum, sodium, and copper concentra
tions, the capacity on cation exchange potential of BC derived from
wood are observed to be higher than those of BCs made from manure.
The pyrolysis temperature can increase the pH, ash content, and surface
basicity, nevertheless the surface acidity found to be decreased while
increasing temperature. In general, the components of BC are moisture,
labile carbon, ash, fixed carbon, and other volatile chemicals. In contrast
to the carbon found in most organic materials, the carbon present in BC
is altered by heating to produce aromatic compounds that are remark
ably increasing resistant to biological degradation. Because of this, the
carbon-based compounds present in BC remain much stable for a very
long period to several decades. Hence, they are therefore believed to be
successful at long-term carbon sequestration. In concern with BC com
positions, the proximate analysis, major and minor elements, and other
properties of different BCs are presented in Table 3.
3. Biochar production technology
3.1. Pyrolysis
Pyrolysis is a thermo-chemical process that includes breaking down
big molecules of biomass under pressure and oxygen-free conditions at
the temperatures typically between 300 ◦
C and 1000 ◦
C (Costa et al.,
2022; Piersa et al., 2022; Zhu et al., 2022). Using such a technique,
biomass wastes are converted into high-value gas (non-condensable
syngas), liquid (bio-oil), and solid products (BC) (Zhu et al., 2022).
Biochar is known to be a carbonaceous solid material that can be
exploited as an adsorbent, catalyst, and fuel. The syngas contains low
molecular gases including CH4, CO2, H2, CO, and others that has proven
to use in gas engines after being processed. Yet another product, the
bio-oil, is the primary material produced in the thermal conversion of
biomass at higher temperatures with shorter residence time, i.e., fast
pyrolysis. It can be used to generate heat in boilers, is composed of
water, alcohol, phenolic compounds, aliphatic compounds, aromatic
hydrocarbons, and N2 based chemicals (including and amines, pyridine,
and pyrazine) (Kant Bhatia et al., 2021). Pyrolysis is classified into two
stages, namely, primary and secondary stages for breaking down re
actions that makes up thermal degradation of precursors molecule (Patel
et al., 2020). The biomass components are broken down and devolatil
ized into their fundamental components during the primary pyrolysis
process. Biomass dehydration, dehydrogenation, and decarboxylation
take place during this devolatilized process. The critical pyrolysis pro
cess begins in secondary stage, whereas the larger molecules are broken
down to produce the principal products, such as BC, bio-oil, and other
gases (Patel et al., 2020; Kant Bhatia et al., 2021). Furthermore, method
of pyrolysis is divided into three processing categories, that are slow,
flash, and fast processing which depend on the setting that can be
controlled during the procedure (Adekanye et al., 2022; Piersa et al.,
2022; Zhu et al., 2022). Comparatively, slow pyrolysis produces more
char, in general, it is operated between 300 ◦
C and 700 ◦
C with
0.1–1 ◦
C/s rate of heating for long retention time (Patel et al., 2020;
Costa et al., 2022). It encourages the process of making BC with a
favorable environment for secondary processes, although about just as
much pyrolysis-oil and gaseous products are also produced (Kant Bhatia
et al., 2021). Rapid pyrolysis is one of the common processing methods
that used to produce bio-oil products. In this case, high heating rates
(10–1000 ◦
C/s) are carried out at moderate temperatures (between
400 ◦
C and 800 ◦
C) over a small residence time (0.5–2s) (Patel et al.,
2020; Piersa et al., 2022). The flash pyrolysis method typically occurs at
high temperature (between 800 and 1000 ◦
C) with high heating rate
(greater than 1000 ◦
C/s) for a short time (less than 0.5s) (Piersa et al.,
2022). However, industrial use of flash pyrolysis is fairly restricted due
to the complex reactor’s architecture that enables it to operate at
elevated temperatures with an incredibly rapid rate of heating (Gabhane
et al., 2020). Fig. 3 depicts the different types and mechanism of the
pyrolysis for BC production.
Adekanye et al. (2022) claimed that the temperature had a signifi
cant affect on physiochemical properties of BC including its functional
groups, surface area and porosity. They found that the organic mole
cules’, such as aliphatic alkyl and esters groups disintegrate at higher
temperatures, result in an increased porosity and surface area by
removing of pore-blocking substances (Chi et al., 2021). Biochar pro
duced at low-temperature is found to be hydrophilic nature and mimics
the surface structure of graphene with fewer functional groups. Bio
char’s preparation at higher temperatures exhibit hydrophobic, reor
ganize functional groups, and may introduce novel groups like carboxyl,
lactone, phenol, pyridine, etc. that can act as electron donors and ac
ceptors. Biochar made at lower temperatures, however, is hydrophilic
(Chi et al., 2021; Kant Bhatia et al., 2021). Farobie et al. (2022) have
conducted a thorough investigation of the production of biochar and
bio-oil using Sargassum sp. through slow pyrolysis in batch reactors at
the temperatures between 400 and 600 ◦
C with retention period of
10–50 min. The acquired bio-oil product was primarily composed with
aliphatic hydrocarbons (12.08–16.65%), furan derivatives
(12.51–21.53%), carboxylic acids (25.07–35.01%), and N-aromatic
compounds (12.86–14.78%). The fact that the BC’ H/C and O/C atomic
ratios were found to be smaller than those of the substrate is proofed for
decarboxylation and dehydration activities during the pyrolysis (Farobie
et al., 2022). The kinds of biomass resources have an impact on the yield
and purity of biochar. Forestry plant pyrolysis yields 30% biochar
compared to lignin-derived biochar’s 45.69% yield, showing that lignin
content influences biochar yield (Chi et al., 2021; Kant Bhatia et al.,
2021).
3.2. Gasification
A thermochemical process known as gasification turns carbonaceous
material into gaseous fuel (CH4, CO2, H2, CO, etc.) and minute amounts
of hydrocarbons at high temperatures (more than 700 ◦
C) in O2-poor
environment (Gabhane et al., 2020; Ochnio et al., 2020). Gasification
nevertheless generates a lower yield of 5–10% char as a byproduct in
addition to gaseous products (Wang et al., 2021). Fig. 4 depicts the
process of gasification. There are two stages to the gasification process.
The drying process, which is the first, fully evaporates the biomass’s
moisture content without any energy recovery. The second stage in
volves the gasification agents’ oxidation and combustion processes.
Such gents generally produce CO, CO2, and H2O when they interact with
the combustible molecules during gasification (Yaashikaa et al., 2020).
The qualities of the reactant, related to the system agent, and substrate,
along with the gasification conditions have great influence on the
effectiveness and quality of BC. While comparing with syngas, the
M. Jayakumar et al.
5. Chemosphere
345
(2023)
140515
5
Table 2
The properties of BCs produced from different of biomass and their composition.
Biochar Reactor type Pyrolysis
temperature (◦
C)
Heating rate
(◦
C/min)
Residence
time
Biochar
size
BET, SA
(m2
/g)
PD
(nm)
pH Ultimate analysis (%) Yield
(%)
Reference
C H O N
Rubber wood saw dust (RWS) Moving bed reactor
(MBR)
550 (Slow
Pyrolysis (SP))
10.00 45 min NR 2.15 217.16 10.02 86.70 3.32 7.89 0.49 NR (Ali et al.,
2022)
Sewage sludge (SS) MBR 550 SP 10 45 min NR 18.42 162.39 8.41 24.27 0.87 5.13 2.97
RWS50:SS50 MBR 550 SP 10 45 min NR 10.29 189.78 8.69 55.14 2.10 6.11 1.73
RWS75:SS25 MBR 550 SP 10 45 min NR 6.22 203.47 9.04 71.15 2.73 6.65 1.10
Banana Pseudostem biochar (BB):
BB300
Muffle furnace with
tubular reactor (MF-TR)
200-600 SP 5.00 1:00 h NR 4.98 10.39 NR NR NR NR NR NR (Xu et al.,
2018)
BB400 MF-TR 200-600 SP 5.00 1:00 h NR 6.62 11.85 NR NR NR NR NR
BB500 MF-TR 200-600 SP 5.00 1:00 h NR 11.27 15.60 NR NR NR NR NR
BB600 MF-TR 200-600 SP 5.00 1:00 h NR 8.53 19.45 NR NR NR NR NR
Banana stem and leaf biochar (BSL-
BC)
MF 400 10.00 3:00 h 0.154
mm
15.73 17.04 9.98 58.19 3.38 19.78 1.38 NR (Liu et al.,
2022)
Rice husk biochar (RH-BC) Water via HTC 180 NR 20 min 2937 nm 5.02 20.20 NR 47.20 4.20 34.18 0.90 57.90 (Hossain et al.,
2020)
Animal manure (AM): BC from
Poultry litter
MF 450 10.00 1:00 h 1 mm 12.959 NR 9.99 22.11 NR NR NR 57 (Sarfaraz et al.,
2020a)
BC from Swine MF 450 10.00 1:00 h 1 mm 12.357 NR 10.24 38.27 NR NR NR NR
BC from Cattle manure MF 450 10.00 1:00 h 1 mm 7.041 NR 9.59 16.42 NR NR NR 58
Crop straws (CS): BC from Rice
straw
MF 450 10.00 1:00 h 1 mm 4.619 NR 10.41 43.95 NR NR NR NR
BC from Soybean straw MF 450 10.00 1:00 h 1 mm 3.610 NR 9.46 69.17 NR NR NR NR
CS: Corn straw biochar (CSB) MF 450 10.00 1:00 h 1 mm 4.235 NR 10.08 67.78 NR NR NR 26
Woody agricultural wastes
(WAW): Mulberry biochar (MB)
(MB 350)
MF 350–650 NR NR <75 μm 2.89–8.05 2–50 7.17 69.28 4.75 17.39 1.37 NR (Li et al.,
2022b)
MB 450 MF 350–650 NR NR <75 μm 2.89–8.05 2–50 10.02 76.83 3.77 10.44 1.19
MB 550 MF 350–650 NR NR <75 μm 2.89–8.05 2–50 10.16 72.40 2.70 14.99 1.51
MB 650 MF 350–650 NR NR <75 μm 2.89–8.05 2–50 9.87 73.25 2.12 14.26 1.08
WAW: Cinnamon biochar (CB) (CB
350)
MF 350–650 NR NR <75 μm 2.89–8.05 2–50 6.37 68.35 3.77 24.43 0.67
CB 450 MF 350–650 NR NR <75 μm 2.89–8.05 2–50 5.04 82.57 3.01 11.64 0.29
CB 550 MF 350–650 NR NR <75 μm 2.89–8.05 2–50 5.12 75.08 3.44 19.09 0.41
CB 650 MF 350–650 NR NR <75 μm 2.89–8.05 2–50 8.92 83.95 2.68 9.78 0.83
Medulla tetrapanacis biochar
(MTBC)
Vacuum furnace (VF) 700 NR 2:00 h 75 μm 198.51 NR NR 61.58 1.48 36.87 0.07 NR (Li et al.,
2022a)
Urea modified MTBC (UBC1-1) VF 700 NR 2:00 h 75 μm 707.56 NR NR 69.07 2.42 19.27 9.24 NR
UBC1-2 VF 700 NR 2:00 h 75 μm 1116.94 NR NR 68.94 2.56 16.96 11.54 NR
Pine saw dust biochar (PDBC):
P350
Stainless steel
cylindrical vessel
(SSCV)
350 8.30 1:00 h 1 mm 16.20 NR 5.00 75.60 4.73 18.26 0.25 34 (Askeland
et al., 2019)
PDBC: P500 SSCV 500 8.30 1:00 h 1 mm 278.00 NR 6.50 88.00 3.08 6.63 0.41 21
PDBC: P750 SSCV 750 8.30 1:00 h 1 mm 397.40 NR 8.50 93.80 1.07 2.65 0.56 20
Pea straw biochar (PSBC): S350 SSCV 350 8.30 1:00 h 1 mm 22.20 NR 8.85 61.30 3.89 18.50 1.08 29
PSBC: S500 SSCV 500 8.30 1:00 h 1 mm 46.70 NR 10.00 64.40 2.52 15.76 1.11 25
PSBC: S750 SSCV 750 8.30 1:00 h 1 mm 157.70 NR 10.42 63.90 0.66 10.54 0.95 23
M.
Jayakumar
et
al.
6. Chemosphere 345 (2023) 140515
6
performance of BC (quality and yield), had substantially impacted by the
equivalency ratio. It is known as the ratio between actual flow of air flow
and the flow of air necessary for stoichiometric burning of the biomass
(Ochnio et al., 2020).
The equivalency ratio of air supply relative to the air needed for the
stoichiometric burning of feedstock in combustion is determined by the
characteristic nature of the biomass used. Improving this equivalence
ratio generally raises the gasification temperature, which impacts the
performance of the BC by increasing the production of CO2 and H2 while
reducing the production of carbon dioxide, methane, and hydrocarbons
(Kant Bhatia et al., 2021). Yao et al. (2011) (Yao et al., 2011) report that
the output of char reduced from 0.22 to 0.14 kg/kg of the biomass
feedstock as the equivalency ratio rises from 0.1 to 0.6; however, the
carbon content present in the acquired BC minimally getting into reduce
Table 3
Proximate analysis elemental composition and other selective properties of BC.
Biochar Elements (mg/kg) Proximate analysis (%) BD (kg/
m3
)
PV
(cm3
/g)
Reference
Si Ca Fe K P Mg Cu MC AC VM FC
RWS 6731 241,156.7 1308 23,504 3120 7283.33 110 4.44 5.79 11.51 78.26 181.74 NR (Ali et al.,
2022)
SS 102,415.3 116,085.7 104,031.3 49,341.33 183,740 14,071.67 1120 4.95 65.61 14.40 15.04 567.32 NR
RWS50:
SS50
54,572.82 178,621.2 52,669.1 36,441 122,720 10,677.54 830 4.71 35.71 12.95 46.63 317.87 NR
RWS75:
SS25
7552.41 209,889.3 26,998.5 29,982.4 71,640 8980.76 560 4.55 20.49 12.54 62.42 273.86 NR
BB300 NR NR NR NR NR NR NR NR NR NR NR NR 0.00959 (Xu et al.,
2018)
BB400 NR NR NR NR NR NR NR NR NR NR NR NR 0.01458
BB500 NR NR NR NR NR NR NR NR NR NR NR NR 0.03932
BB600 NR NR NR NR NR NR NR NR NR NR NR NR 0.04389
BSL-BC NR 1260 NR 5910 10.00 5710 NR NR 17.27 NR NR NR 0.0680 (Liu et al.,
2022)
MB 350 NR NR NR NR 0.46 NR NR NR 7.10 NR NR NR NR (Li et al.,
2022b)
MB 450 NR NR NR NR 0.54 NR NR NR 7.67 NR NR NR NR
MB 550 NR NR NR NR 0.60 NR NR NR 8.26 NR NR NR NR
MB 650 NR NR NR NR 0.76 NR NR NR 9.13 NR NR NR NR
CB 350 NR NR NR NR 0.11 NR NR NR 2.66 NR NR NR NR
CB 450 NR NR NR NR 0.06 NR NR NR 2.37 NR NR NR NR
CB 550 NR NR NR NR 0.06 NR NR NR 1.88 NR NR NR NR
CB 650 NR NR NR NR 0.08 NR NR NR 2.62 NR NR NR NR
RH-BC 63,000 15,700 4000 32,600 1500 1000 200 3.00 9.40 52.50 35.00 180 0.025 (Hossain
et al., 2020)
PLB NR 238,900 28.80 56,000 33,300 27,900 7.70 NR 72.61 NR NR NR NR (Sarfaraz
et al.,
2020a)
SMB NR 70,200 282.80 36,700 48,800 58,400 20.70 NR 50.33 NR NR NR NR
CMB NR 13,600 855.40 26,600 9400 700 31.20 NR 77.32 NR NR NR NR
RSB NR 15,300 118.90 59,700 6000 500 17.60 NR 37.97 NR NR NR NR
SSB NR 26,500 41.50 6900 8300 1300 20.50 NR 14.39 NR NR NR NR
CSB NR 6100 33.10 22,300 4500 400 18.40 NR 10.32 NR NR NR NR
Fig. 1. Production strategies of biochar and its applications.
M. Jayakumar et al.
7. Chemosphere 345 (2023) 140515
7
from 88.17 to 71.16%. Studies elsewhere revealed that the limiting
factors, such as particle size, moisture content present in the biomass,
airflow rate, and compactness were found to be in good relation to
characteristics of BC produced in a top-lit updraft type gasifier. It was
found that raising the airflow velocity from 8 to 20 L/min can enhance
the BET surface area of the BC particle and as well as basic functional
groups (pH > 7.0). However, acidic functional groups have not seen
since the process is oxidative. While increasing the moisture content in
the feedstock from 10 to 14% resulted in a drop in pH, in general, 12 to
7.43which lead to an increase in carboxylic functional groups. In addi
tion, it was found that the basic functional groups of BC have been
declined from 0.115 to 0.073 mmol g− 1
of the feedstock compaction
force that rose from 0 to 3 kg, whereas the functional groups, such as
carboxylic acid observed to grow during 0–0.016 mmol g− 1
. To deter
mine the optimal oxygen carrier, also examine the impacts of the
preparation techniques, active ingredients, Fe and Ca loadings, and ratio
of steam to biochar (S/C).
The outcomes show that the oxygen carrier made using the co-
precipitation approach has a greater gasification efficiency (96.93%),
a stronger redox activity, and better dispersion. The production of
combustible syngas and biochar from waste biomass can both be
accomplished through gasification, which is a thermochemical tech
nique. The type of biomass used to make the biochar mostly determines
how much alkali and alkaline earth metals are present (Patra et al.,
2021).
3.3. Hydrothermal carbonization
A wet thermochemical process known as hydrothermal carboniza
tion uses a variety of feedstocks, such as municipal sludge, lingo cellu
losic biomass, cellulose, food wastes, animal manures, sludge from pulp
and paper industry, algae and agricultural residues, etc. to create BC.
Also, a liquid by-product which found to be in rich in organic and
inorganic substances (Jeyasubramanian et al., 2021). It is done at a high
temperature of 180–300 ◦
C and pressure while supercritical water is
present (above 1 MPa) (Babinszki et al., 2020). During the hydrothermal
carbonization process, a number of physiochemical processes connected
to hydrolysis, decarboxylation, and dehydration reactions take place.
Wet pyrolysis is another name for hydrothermal carbonization, which is
also known as that process’ solid byproduct known as hydrochar (Pra
sannamedha et al., 2021). Hydrochar is superior to raw biomass with
respect to energy density (Aragón-Briceño et al., 2021). Fig. 5 represents
hydrothermal carbonization process.
Hydrochar can be applied for soil enhancement, bioenergy produc
tion, carbon sequestration, and wastewater treatment (Aragón-Briceño
Fig. 2. Various biomass sources that can be used as precursors for
BC production.
Fig. 3. Mechanism and various types of pyrolysis practices.
M. Jayakumar et al.
8. Chemosphere 345 (2023) 140515
8
et al., 2021; Jeyasubramanian et al., 2021). When the feedstock includes
a high level of moisture, hydrothermal carbonization is favorable
because it doesn’t require a drying procedure (Babinszki et al., 2020).
The existence and/or greater amounts of intractable products, such as
furfural, phenols, 5-HMF and their derivatives, ammonia are closely
associated with the type of lignocellulosic materials and processing
factors (Aragón-Briceño et al., 2021).
3.4. Torrefaction
Torrefaction is newly emerging thermo-chemical process carried out
by heating biomass feedstock in an inert atmosphere at low range of
temperature (200–300 ◦
C) with relatively long residence period (15–60
min) at low heating rate as shown in Fig. 6 (Wang et al., 2020a; Lee
et al., 2021). In this case, the biomass precursors have been transformed
into solid (biochar), and liquid products (bio-oil). In addition, a fewer
amount of gaseous mixtures (CO2, CO, CH4, etc.) also produced (Jiang
et al., 2021). Torrefied biomass (biochar), which is cheaper and more
environmentally benign than raw biomass, has more consistent char
acteristics and a greater heating value. It has comparatively lower
moisture content, smaller ratio of O/C and H/C, and superior in hy
drophobicity characteristic (Jeyasubramanian et al., 2021; Komiyama,
2021).
Particle size, moisture content, energy density, heating rate, surface
area, and other properties of feedstock are changed during the torre
faction process (Lee et al., 2021). Torrefaction, a partial pyrolysis pro
cess that can take place in both wet and dry environments that occur
when a substance is partially heated (Yaashikaa et al., 2020). In dry
torrefaction, feedstocks can be roasted at temperatures between 200 ◦
C
and 300 ◦
C in either an oxidizing or dry non-oxidizing (inert) atmo
sphere. In contrast, biomass is purified using pure water or dilute acid at
temperature between 180 and 260 ◦
C. Additionally, the biomass can be
preprocessed to upgrade using steam (Chen et al., 2021).
Jiang et al. (2021) (Jiang et al., 2021) have examined on different
Fig. 4. Process of gasification.
Fig. 5. Hydrothermal carbonization practice.
M. Jayakumar et al.
9. Chemosphere 345 (2023) 140515
9
feedstocks types, roasting temperatures, and holding times affect the
ability of biochar to retain moisture under constant temperature and
humidity conditions. As a result, too high roasting temperature
(>275 ◦
C) had showed diminutive effect on the hygroscopicity of BC,
and the hygroscopicity of BC increases slightly with rising holding time
at the same roasting temperature, but the same It was shown to increase
with rising roasting temperature at holding time. Similar study by Lin
and Zheng (2021) proved that roasting temperature had a greater
impact on toasted biomass (bichar’s hygroscopicity) than roasting time.
With respect to a research by Gao et al. (2021), torrefaction pressure had
a considerable impact on the pyrolysis kinetics on biomass used. The BC,
typically synthesized by roasting, can be used for a variety of purposes,
including solid fuels, sorbents, soil conditioners, and energy storage
(Yaashikaa et al., 2020).
3.5. Mechanochemical technology
Mechanochemical Technology is a technology that produce nano-
biochar (nanosize) in low cost and an environmentally friendly
manner by utilizing great energy ball mill (Kumar et al., 2020). As the
mechanochemical process is solvent-free, sustainability indicators can
be improved. However, the significant differences in reaction outcome,
reaction selectivity, and reduction in reaction time make it a more
interesting technique (Shen et al., 2020). To improve the efficiency of
feedstock conversion into useful products the mechanical milling has
been widely used. According to Shen et al. (2020) (Shen et al., 2020), a
pre-treatment via size reduction using ball mill had a showed a notable
conversion of lignocelluloses feedstocks. When compared to untreated
samples, yields of BC can be increased up to 1.1–14.8 folds with aid of
ball milling pretreatment. Furthermore, ball milling also contributes to
increasing reagent contact with biomass through particle size reduction
and the formation of additional surface area by physical movement or
mixing. Consequently, ball mill can originally activate and enhance the
different surface functional groups of BC for wider functions (Kumar
et al., 2020). The quality of biochar created by ball processing are
profoundly depend on the rotational speed, treatment time, substrate
stacking and geometric parameters of the ball process. It is additionally
conceivable to get the nanoscale BC by expanding the processing time.
Conversely, the milling process is fraught with difficulties due to factors
such as feedstock nature, purity, biochar homogeneity, recovery, and so
on (Jeyasubramanian et al., 2021).
3.6. Functionalization/activation or engineered biochar
It is recommended that biochar be functionalized/engineered to
progress physiochemical properties such as particular surface range,
surface useful bunch, cation exchange ability, and pore structure in
arrange to realize the specified objective with high efficiency. To
progress biochar execution and planning natural application, biochar
can be engineered in physical, chemical, and organic ways as appeared
in Fig. 7 (Kazemi Shariat Panahi et al., 2020). Physical designing tech
niques such as processing adjustment, CO2/steam activation, magneti
zation, or microwave light are to the recent advancements to move
forward the desirable physicochemical properties of BC at a low cost and
with minimal environmental hazard.
Biochar can be actuated employing an assortment of chemicals in to
two approaches, as follows (1) Oxidation of BC using solid acids, and
other oxidizing operators, and (2) amalgamation of BC-based materials
with metal oxides, chitosan, amino acids, carbon nanotubes, and among
others. Biochar can also be modified biologically by colonizing micro
organisms in its porous structure to develop biofilm for improving its
ability (Delagah et al., 2020). Ibrahim et al. (2021) were investigate the
hydrothermal functionalization technique to improve surface function
alities of BC. The result appeared that the basic aqueous solution
effective functionalizes the surface of the BC particles and makes strides
its execution without altering the surface range at lower concentration
in shorter time. According to Stephanie et al. (2021) including useful
group to the enacted biochar improved salt evacuation capacity, giving
cation and anion selectivity. Different types of biomass conversion
technology, process conditions, advantages, disadvantages and chal
lenges are presented in Table 4.
4. Techniques for biochar characterization
To ascertain its capacity for removing pollutants or for other appli
cations, biochar is characterized. Predicting how biochar will affect the
environment is also made easier with the aid of structural and elemental
analysis. Besides, interact of metals with BC is determined by the func
tion of pH. In such a way the metal interaction differs with respect to pH
that may result in ion speciation of metal contaminants. In this regard,
BC can be demonstrated for its potential to act as a high efficacious bio-
adsorbent for removing the metal-based pollutants. In recent times,
different methods used to characterize the BC, such as elemental
Fig. 6. Torrefaction process for BC production.
M. Jayakumar et al.
10. Chemosphere 345 (2023) 140515
10
analysis, surface functional groups determination, and structural char
acterization. In addition, various contemporary characterization
methods, including, Nuclear Magnetic Resonance (NMR), X-ray
Diffraction (XRD), Brunauer Emmett Teller (BET), Scanning Electron
Microscopy (SEM), Thermogravimetric Analysis (TGA), Fourier Trans
form Infrared Spectroscopy (FTIR), proximate and ultimate analysis,
Fig. 7. Functionalization/activation or engineered biochar process.
Table 4
Process technology, process conditions, advantages, disadvantages and challenges.
Technology Temperature
(⁰C)
Residence
time (min)
Yield
(wt.
%)
Advantages Disadvantages Challenges Reference
Slow Pyrolysis 300–700 >60 24–55 Highly stable
High biochar yield
Accept a wide range of
particle size
Flexible thermochemical
conversion.
Advance cure of gases
required
High CO concentration
Possibility of requiring
additional energy
Economic feasibility and
Agricultural coproduction
(Adekanye et al.,
2022; Farobie
et al., 2022)
Fast Pyrolysis 400–800 0.5–2sec 15–20 High yield of bio-oil
High product recover
Efficient energy conversion
Scale up is economically
feasible
Little biochar yield
Acceptable particle
feedstock (1–2 mm) is
required.
Limited commercial
experience
Little stability of bio-
oil
Design and operation of
reactor
Biomass collection for
industrialization
(Mukherjee et al.,
2022; Zhu et al.,
2022)
Flash Pyrolysis 800–1000 <0.5sec 10–15 Production of fuel with higher
energy density
Bio-oil yield is high
Extremely High
heating rate
Low thermal stability
Presence of solid in oil
Increase viscosity over
time
Dissolution of biochar
alkali in bio-oil
Reactor design for high
hotness and heating rate
How to use in industrial
scale
(Akhil et al.,
2021)
Gasification 700–1000 12–24sec 14–25 Low emission of pollutants Do
not emit excess non-CO2
Greenhouse gases High
energy recovery Non-
hazardous by-product
Higher risk of
contamination Low
biochar yield Low
carbon storage
efficiency
Thermodynamics of
operation is not well
understand Distribution of
fuel and Temperature
across reactor
(Mohammadi and
Anukam, 2022;
Wang et al.,
2021)
Torrefaction 200–300 15–60 70–91 Negligible biological
activities Low O/C ratio
Homogeneous output Less
expensive and easier
Low volume density
enhancement No
commercial unit in
operation yet Higher
caloric values
Process heating method
Torgas treatment Process
heat source
(Viegas et al.,
2021; Piersa
et al., 2022)
Hydrothermal
carbonization
180–300 5–240 33–84 Uniform chemical and
structural properties High
amount of oxygenated
functional group Low energy
consumption Less ash and
acidic volatiles
Uneven practice size
spreading Porosity is
low Untrained pore
structure
Commercially unproven
technology Logistics
Economics
(Babinszki et al.,
2020; Garcia
et al., 2022)
Mechanochemical
Technology
– – – Reduce carbon portions Free
toxic chemicals/solvent
Noncomplex post treatment
Operate at room temperature
Consume high energy
Non homogenous
biochar
Reaction of biomass at
microscopic and molecular
level Optimization of
operational parameters
(Shen et al., 2020;
Kumar et al.,
2020)
Functionalization/
Activation or
engineered bio char
– – 20–45 High metal remediation
efficiency High biochar
surface functional group
Higher O content
Formation of less polar
biochar Affected by
modification
techniques
In depth mechanisms and
large scale
functionalization process
Lifetime of engineered
biochar
(Ibrahim et al.,
2021; Kazemi
Shariat Panahi
et al., 2020)
M. Jayakumar et al.
11. Chemosphere 345 (2023) 140515
11
Raman spectroscopic analysis, etc., have recently been reported for BC
characterization studies. The main goal of recent literature on BC
characterization aims to distinguish the BC from other organic matters.
However, among the aforementioned characterization methods SEM
morphological studies and FTIR studies for identifying functional groups
can be used to support the determination of further properties of BC.
4.1. Fourier transform infrared spectroscopy
The drawbacks of dispersive instruments were addressed by the
development of FTIR spectrometry. This technique is based on a vibra
tional approach, particularly, for analyzing the different functional
groups present on the surface of BC particles (Ault and Axson, 2017).
The biochar in the mixture and ancillary settings saw significant alter
ations with the temperature increase. Effective observation of these
progressions would require a non-destructive FTIR device (El-Azazy
et al., 2022). The higher temperature ranges of 650–800 ◦
C were shown
by the spectra to have a significant loss in aromatic groups. Yet another
technique, Diffuse Reflectance Infrared Fourier Transform Spectroscopy
is used after the pelletizing the sample using KBr. The sample makes
contact with an attenuated total reflectance crystal (ATR), hence, the
existence of functional groups can be detected in ATR-FTIR (El-Azazy
et al., 2022). Numerous researchers characterized the biochar produced
from biomass through FTIR. At the same time, ATR is often considered
due to its ease of operation and time efficiency compared with FTIR
analysis.
According to Sahoo et al. (2021), the FTIR analysis can be used to
investigate the influence of temperature on the functional groups of BC
during pyrolysis. They found that the temperature had great influence
on the functional groups of BC while the pyrolysis had been taken place
within the range of 300–750 ◦
C. Numerous peaks were vanished
throughout the pyrolysis of pigeon pea stalk and bamboo based BC, such
results were occurred due to the acceleration of dehydration from the
biomass used, which cleared that while pyrolysis temperature increases,
the polar functional groups are subjected to diminish. Adekanye et al.
(2022), investigated the characterization maize cob BC via FTIR. They
investigated on the functional groups of BCs which had been prepared at
300, 400, and 500 ◦
C. The results showed that the rise in temperature
exhibited the distending of the O–H group, which found in the range of
band, 3383-3402 cm− 1
. However, O–H group is the responsible for
enhancing the intensity of BC for condensation. On the other hands, the
prevalence of the functional group, C–H, in the BC is almost certainly
because of the presence of alkanes that induce the breakdown of
hemicellulose. Besides that, the presence of double bond hydrocarbons
(alkenes) in biochar accelerates the degradation of lignin as displayed by
the C–
–C bonds. The functional C–O group is a member of the carboxylic
(cellulose and hemicellulose) groups. Particularly, these groups accel
erate the reaction rates of decarboxylation by creating the glycosidic
bonds in the BC to be disrupted throughout heating process. Moreover,
as stated by Alfattani et al. (2022), the FTIR spectra showed different
peaks at wave numbers of 3428, 3465, 3442, and 3411 cm− 1
for the BC
obtained from thin-shelled walnut, paper shelled walnut, hard-shelled
walnut, and medium shelled walnut, which clearly showing the dis
tending vibrations of phenols –OH hydroxyl groups.
The other protuberant characteristic band peaks were found at 2849
and 3050 cm− 1
, as well as 2925 and 3075 cm− 1
, which indicated the
presence of CH group that may be generated by the existence of meth
ylene/methyl groups in thin-shelled walnut and medium-shelled walnut
biochar’s. A previous study showed that the stretching vibrations of the
aromatic C–
–C ring were due to lignin, which was represented by the
FTIR peak at 1587 cm− 1
. In addition, in some studies on BC, aromatic
skeleton vibrations were observed owing to the C–H bonds on the mo
lecular plane deformations. This might account for the medium band
intensity in the 1398–1401 cm− 1
region. The existence of phenolic OH
and aromatic CO stretching attributed to the prevalence of lignin,
hemicellulose, and cellulose was confirmed by the FTIR band peak of the
paper-shelled walnut biochar at 1265 cm− 1
. However, several studies
have shown that the medium band intensity in the range of 1401 to
1398 cm− 1
was assigned to vibrations corresponding to the aromatic
skeleton combined with C–H.
4.1.1. Scanning electron microscopy
The Scanning electron microscopy can be used to investigate the
surface structures in terms of the morphological behavior of the syn
thesized BC. The SEM analysis of BC indicated that temperatures and
different processes lead to a substantial deviation when compared with
the shape and size of the initial biomass particles. Moreover, in biochar
experiments, the significant improvement in the biochar pore charac
teristics may be enhanced by increasing the temperature of the system.
SEM images provide a comprehensive explanation of the mesoporous
and microporous distributions, as well as the nature of the pores present
in the BC particlescle. In addition, SEM analysis can predict the
morphology of the BC adsorbent before and after the adsorption pro
cedure for certain applications. Additionally, energy-dispersive X-ray
spectroscopy coupled with SEM can be employed to identify the
composition of the elements present in the biomass precursor-derived
BC. Several investigations have been reported on BC based on the uti
lization of SEM-EDX analysis to determine the elemental composition
and surface morphology of BC applied for the adsorption of organic and
inorganic contaminants. The main drawback of SEM-EDX is that it is
ineffective for determining organic pollutants.
4.2. Brunauer-Emmett-Teller analysis
One of the extensively studied techniques, the BET method, can be
used to determine the specific surface area of the particles. To date,
numerous reports have documented the use of BC for the investigation of
surface area. The specific surface area is an essential characteristic of
any adsorbent for the effective removal of pollutants from soil and
aquatic environments. The BET surface zone increased significantly after
pyrolysis compared to its crude biochar counterparts. Particularly in the
crude feedstocks, there were no material micropores, but pyrolysis
created new micropores in the char.
4.3. Nuclear magnetic resonance spectroscopy
NMR spectroscopy, another widely studied technique, can be used to
examine the structural makeup of BC molecules. In this technique, a
strong radio recurrence (RF) pulse is used to quantify the reverberation
frequencies of specific cores inside the atom, and NMR can also be
applied to determine the makeup of BC particles. A solid-state technique
can be used to represent the carbon functional groups available in BC.
Moreover, it can be used to determine the structure of char molecules
and the general quantity of aromatic ring formation. The compositions
of the aromatic and aliphatic hydrocarbons were also examined using
NMR spectroscopy. Recently, the degree of carbonization of BC and its
stability have been compared using NMR.
5. Utilization of biochar
5.1. Direct utilization of biochar
5.1.1. Adsorbent for water pollutants
In order to combat water pollution, a different biomass feedstocks
have been employed as precursors for pyrolysis to produce BC. Char
acterization analyses and adsorption experiments yielded positive re
sults, demonstrating the potential of BC as an bio-based adsorbents (Liu
et al., 2017; Hou et al., 2019). Researchers looked into using novel BC
prepared from nutshells of pecan as an bio-adsorbent to remove the
synthetic dye (reactive red 141) (Zazycki et al., 2018). The results
showed that the raw pecan nutshell removed only 23% of the dye from
the aqueous solution. According to these results, such a BC can be an
M. Jayakumar et al.
12. Chemosphere 345 (2023) 140515
12
alternative as bio-based adsorbent with respect to less expensive and
environmentally friendly treatment of textile effluents. According to a
study on the removal of U (VI) from groundwater using hydrothermal
carbonized BC, the material could be used as a reactive barrier medium
as well as an efficient bio-based adsorbent for U (VI) removal. Overall,
producing biochar using HTC is safe for the environment, carbon
neutral, and effective for adsorptive removal of U (VI) from the water
bodies (Kumar et al., 2011). The majority of interactions, such as ion
exchange, electrostatic attraction, physical adsorption, and chemical
bonding are known to be the common adsorption mechanisms (Tan
et al., 2015).
Depending on the characteristics of the BC, such as feedstock type,
pH, and pyrolytic temperature, biochar composites have been employed
to facilitate the heavy metals interaction and adoptive removal from
water and soil. Bentonite clay biochar composites for metal removal
were formed using biochar manufactured from sweet sorghum. High Zn
(II) adsorption capacity was demonstrated using bentonite and biochar,
while very low Cr (IV) adsorption affinity was found (Shukla et al.,
2021). Dong et al. (2011) have documented about the characteristics
and mechanisms of hexavalent chromium removal using the BC pro
duced from tailing of sugar beet processing. They found that the 123
mg/g of Cr (VI) was removed under the acidic environment.
5.1.2. Adsorbent for air pollutants
Pyrolysis appears to offer additional opportunities because intro
ducing BC to the soil causes the emission of greenhouse gases (sulfur
oxides, CO2, and nitrogen oxides) that are scrubbed from effluent flue
gas. It has been proven that CO2 precipitates on the surface of BC during
exothermic reactions. The literature suggests that the use of BC can be
appropriate when applied at low temperatures for selective catalytic
reduction (Yaashikaa et al., 2020). Accordingly, carbon emissions have
been reduced while burning fossil fuels. Numerous researchers have
tested the adsorption of SO2 using activated carbon. Chemical processes
are used to produce activated carbon in the majority of cases. Because
there are chemical compounds surrounding the surface of activated
carbon that can exchange pollutants with environmentally friendly ions,
chemical-based methods have been found to increase the adsorptive
removal of SO2 (Sumiyati et al., 2019).
5.2. Indirect utilization of biochar
5.2.1. Catalysts
High porosity and high specific surface area are known to be the key
limiting factors that significantly contribute to determine the ability of
BC to perform as a catalyst. Appropriate pore size and high surface area
work together to improve mass transfer and catalytic selectivity (Shukla
et al., 2021).
5.2.1.1. Catalysts for syngas cleaning. The use of biomass pyrolysis to
acquire syngas and bio-oil, BC catalysts are incorporated to improve
their quality. Toluene, phenol, naphthalene, and styrene are among the
polycyclic aromatic hydrocarbons found in the tar produced during the
production of syngas. These substances should be reduced during the
downstream processing (Shukla et al., 2021). So far, two reputable ways
are known as effective to reduce and get rid of the tar:
i) Tar is catalytically converted to H2 and CO through dry gasification
and steam. Tar can be catalytically transformed into CO and H2.
These CO and H2 are regarded as crucial syngas constituents. The
removal of tar is influenced by the char made from different biomass
precursors, such as char obtained from rice straw and corn straw
(Yaashikaa et al., 2020).
ii) Tar breaks down into free radicals followed by to form low-
molecular-weight compounds which lead to the formation of coke
on a catalyst supported by biochar. The most powerful catalyst for
transforming heavy hydrocarbons into lighter ones is activated
carbon.
5.2.1.2. Process catalyst for production of biodiesel. Due to the emer
gence of biodiesel, recent studies have proven that the BC has been
established as a promising catalyst. Investigation of a BC based solid acid
catalyst can be more effective for the biodiesel production (Dehkhoda
et al., 2010). In the presence of methanol as the reagent, the results
revealed that the BC based catalyst with the highest acid density and
surface area had showed the excellent catalytic activity for biodiesel
production using canola oil as feedstock. Additionally, though the cat
alysts having similar acid densities, catalyst having higher surface area
can significantly improve the activity of transesterification process
compared to the catalyst having lower surface area. Furans and phenols
are valuable chemicals that were produced with high selectivity utilizing
bio-based activated carbon catalysts. According to the findings,
bio-based activated carbon catalysts produced furans and phenols with
high catalytic activity and selectivity at a relatively low temperature
(350 ◦
C) (Li et al., 2020). It was investigated whether fatty acids could
be catalytically esterified using solid acid catalysts manufactured from
activated carbon and BC (Kastner et al., 2012).
According to these findings, activated carbon derived from wood can
be sulfonated with SO3 to produce solid acid catalysts. The reusability
potential of such catalysts is determined by hydrophobicity, particle
strength, surface area, and sulfonic acid-based functional groups. To
create solid acid catalysts. (2018) synthesized biochar using a sulfona
tion process. Using simultaneous esterification and transesterification to
produce biodiesel, the sulfonic acid group density and acid density of the
BC-based solid acid catalysts were predicted to have excellent acidic site
concentrations and reactive transesterification activities.
6. Emerging applications and beneficiaries of biochar
6.1. Wastewater treatment applications
Biochar generated from biomass has gained considerable popularity
lately, particularly for its effectiveness in removing heavy metals, toxic
substances, and contaminants from wastewaters and industrial effluents.
Due its unique and remarkable physiochemical characteristics, such as
high surface area, cation exchange capacity, aromatic character, carbon
content, and low H/C ratio, biochar can be a promising effective ma
terial with affordable low cost (Yaashikaa et al., 2020).
The investigation on copper nitrate modified biochar (Cu-BC) made
by Liu et al. (2017) showed that the Cu-BC held a significant potential
for removing doxycycline hydrochloride (DOX) from the water while
considering towards high efficiency and cost effective process applied to
realistic water. Such a Cu-BC has shown excellent sorption efficiency
that can remove 93.22% of doxycycline hydrochloride from its aqueous
solution. So far, many researchers conducted a meta-analysis to consider
the financial and ecological potential of BC and activated coal for
removing toxic contaminants. However, the analysis showed that BC
evacuates more effectively than activated coal (Yaashikaa et al., 2020;
Suhaimi et al., 2022).
It was proven that the biochar obtained from bamboo exhibited as
potential bio-adsorbent to remove methylene blue from the aqueous
solutions. Studies showed that the temperature of the pyrolysis process
had a significant impact on the adsorptive performance. The biochar
pyrolyzed at 500 ◦
C had the highest adsorptive performance that
showed that maximum adsorption capacity (86.6 mgg− 1
). In such way,
BC can be exploited as a great medium for the treatment of wastewater
because of its excellent adsorbing behavior of pollutants like heavy
metals, pesticides, and other organic pollutants as well (Qambrani et al.,
2017).
In study elsewhere, walnut shell-based biochar revealed that it had
similar properties to adsorbents used for commercial water purification,
M. Jayakumar et al.
13. Chemosphere 345 (2023) 140515
13
which was determined as surface area of 58 m2
/g and pH (Alfattani
et al., 2022). By chemically co-precipitating Fe3+
/Fe2+
on orange peel
powder followed by pyrolyzed at various temperatures (250, 400, and
700 ◦
C) resulted in different novel magnetic BCs (MOP250, MOP400,
and MOP700), in particular, MOP250 had showed a much higher ca
pacity for phosphate sorption than their non-magnetic counterparts.
These imply that magnetic biochar can be futuristic bio-based sorbent
that can simultaneously remove phosphate and organic contaminants
from wastewater (Chen et al., 2011). Yao et al. (2011) claimed that the
BC manufactured from anaerobically digested sugar beet tailings had the
highest capacity for removing the phosphate, with a removal rate of
73%. Additionally, sugar beet tailings that have been anaerobically
digested can be used as feedstock to create high-quality BC, which can
then be used as adsorbents to recover phosphate. Moreover, the removal
of Cu (II) and Zn (II) from aqueous solutions using BC produced via
pyrolysis of hardwood at 450 ◦
C (HW450) and corn straw at 600 ◦
C
(CS600) was characterized and investigated. The results showed that
biochar made from plant residue or agricultural waste can function as an
efficient surface sorbent, but their capacity to handle mixed waste
streams needs to be carefully assessed on a case-by-case basis (Chen
et al., 2011). The characteristics of BC manufactured from soybean
stover and peanut shells, as well as trichloroethylene (TCE) adsorption
in water, were examined by Ahmad et al. (2012). The outcome showed
that the properties of the BCs had a significant impact on TCE adsorp
tion. The high aromaticity and low polarity of BCs produced at 700 ◦
C
were attributed to their high adsorption capacity. Evaluation of the
effectiveness of TCE removal from water depended heavily on the py
rolysis temperature’s influence on the BC properties.
The adsorptive removal of atrazine from an aqueous solution and the
characteristics of BC made from agricultural waste were studied by Liu
et al. (2015). The analysis showed that the initial atrazine concentration
and temperature both increased the adsorption capacity. Due to the
effects of adsorption and hydrolysis, more atrazine compounds were
removed from basic solutions than from acidic solutions. With a capacity
of 0.0064 mg dissolved organic carbon per mg C, 200 mg C per liter of
BC can remove 90% of organic matters from the water within 20 min,
according to Ashish and Salvi (2019) experiments on the removal of
natural organic matter in water. Because of its physiochemical proper
ties, BC acts as a super sorbent capable of removing organic and inor
ganic contaminants from soil as well as water. Biochar and activated
carbon (AC) have similar activities, but they differ in terms of raw ma
terials or feedstock, production techniques, and targeted physi
ochemical properties (Nag et al., 2011; Jiang et al., 2012; Oleszczuk
et al., 2012).
In anaerobic digestion, BC is frequently used as a support or additive
media as well as a filter medium to remove pathogens, heavy metals, and
suspended matter. Additionally, the effectiveness of biochar as a
support-based catalyst for the degradation of dyes and resistant con
taminants was examined (Enaime et al., 2020). The banana leaf petiole
and the resulting BC would be a promising adsorbent for waste water
remediation because the presence of hydroxyl and carboxyl functional
groups in a material has been related to its ability to adsorb metals in
waste waters (Waweru et al., 2020). Biochar has been widely applied as
an additive/support media during anaerobic digestion and as filter
media for the removal of suspended matter, heavy metals and patho
gens. Biochar was also frequently tested for its efficiency as a
support-based catalyst for the degradation of different dyes and recal
citrant contaminants (Enaime et al., 2020). The presence of hydroxyl
and carboxyl functional groups in a material has been related to its
ability to adsorb metals in waste water and thus the banana leaf petiole
as well as its resulting BC would be a promising adsorbent for waste
water remediation (Waweru et al., 2020).
6.2. Control of greenhouse gas emissions applications
According to Mukherjee et al. (2022), BC has shown an excellent
performance for capturing the CO2 (2.8 mmol g− 1
) from the flue gas
stream while comparing to commercial activated carbon. Due to their
high soil stability, biochar at high temperatures has shown positive
response to reduce CO2 (Ahmad et al., 2012). Awasthi et al. (2020)
looked into the impact of bamboo BC on mitigating the emissions of
GHGs. According to the findings, increasing biochar decreased total
carbon and nitrogen losses by 542.8 to 148.9% and 53.5 to 12.6%,
respectively. A lifecycle analysis regarding the utilization of biochar
manufactured from yard waste, switch grass, and stover was executed.
They claimed that the price per tonne of CO2 for biochar made from
stover, switch grass, and yard waste, respectively, was about 30, 45, and
1.5 euros. Additionally, it was claimed that amendment of BC in the soil
had a substantial improvement in ability to absorb greenhouse gases
(Ashish and Salvi, 2019; Suhaimi et al., 2022).
In coastal saline soil, Lin et al. (2015) investigated how applying
biochar affected crop growth, GHGs emissions and carbon sequestration.
The study showed that the application of cornstalks increased emission
of N2O up to 17.5%, however, in case of cumulative GHG emissions,
CH4, CO2, and N2O were not notablyimpacted by BC. The corn stalk
treatment’s CO2-equivalent mitigation potential was lower (0.1 t CO2-eq
ha− 1
t− 1
C) than that of the biochar treatments, which ranged from 3.17
to 3.84 t CO2-eq ha− 1
t− 1
C.
6.3. Agricultural applications
According to numerous studies, incorporating biochar into soils can
boost the amount of organic matter there and increase the soil’s fertility
(Bhat et al., 2022; Garcia et al., 2022). Many research studies show that
adding biochar to soils will improve the desired porosity and structure,
soil texture, and enhance distribution of particle size and density
(Qambrani et al., 2017). Biochar will enable the provision of appropriate
space for microbes that can grow conveniently to assist the binding of
substantial micro and macro nutrients through surface area and
porosity. Various studies offered proof that adding BC can increase
growth rate of different crops. Besides, it can improve the quality of
water, decrease the leaching of valuable nutrients increase water
retention ability, and increase the use of fertilizers (Singh et al., 2022).
Applying BC to soils dramatically boosted growth rate and increased
plant nutrient uptake from the fertilizers (Chem et al., 2017). Biochar
can aid to assist for increasing soil fertility and fertilizer efficiency
through its reactivity of functional groups, and strong stability. In
addition to improving nutrient adsorption (e.g., NO3
−
, NH4
+
, and PO4
3−
),
which reduces unwanted leaching of nutrient. Furthermore, biochar can
later release the absorbed nutrients into the soil. Moreover, biochar may
speed up pesticide deterioration in soil and lessen pesticide uptake by
plants. One way that incorporating biochar into soil can improve
pesticide clearance rates is by stimulating the chemical hydrolysis pro
cess (Ding et al., 2017). Furthermore, combining biochar with composts,
crop wastes, and decomposed manures increases the effectiveness of
nutrient usage (Garcia et al., 2022).
Contrary to biochar created from other sources synthesized from
crop straws had higher levels of carbon, an alkaline nature, low CO2
emissions, a high CEC, the ability to sequester carbon, and was more
suited to boosting the fertility of the soil (Sarfaraz et al., 2020b). Novak
(2014) showed that it is possible to create biochar with particular
qualities that have the power to significantly affect the physicochemical
characteristics of the soil and even target particular soil attributes like
pH. According to Jin et al. (2016), biochar would be useful for stabi
lizing soil that has been polluted with isoproturon, imidacloprid, and
atrazine. However, the adsorptive removal capacity of the mixtures may
be higher or lower than expected without taking a cross-effect between
the soil and BC into account. Xiao et al. (2017) have observed that BC
has a notable ability to improve composting due to its positive interac
tion with the microbes. It is clear that introducing BC for the purpose of
composting can result in enhanced physicochemical characteristics of
the compost product due to increased microbial activity and promote
M. Jayakumar et al.
14. Chemosphere 345 (2023) 140515
14
organic matter decomposition, lower emissions of ammonia (NH3) and
greenhouse gases (GHGs), and improve quality of compost by boosting
nutrient content, promoting maturity, and lowering phytotoxicity.
6.4. Renewable energy applications
Carbon-based materials are adaptable platform materials that can be
employed in contemporary energy-storage applications. Traditional
carbon compounds made from coal and petrochemicals typically require
large amounts of energy or are synthesized under difficult conditions.
The development of efficient processes for producing high-performance,
environmentally friendly carbon products from renewable resources is
desired. Biochar, a bio-carbon made from biomass that has an easy-to-
tune porosity and abundant surface functional groups, may be a good
choice as a sustainable carbon source (Wu-Jun Liu et al., 2019). Biochar
was synthesized by pyrolyzing coco peat at two different temperatures
and its characteristics were examined. The fixed carbon content was
determined using proximate analysis and provided good results for the
required purpose. Because of its high fixed carbon content and other
physicochemical characteristics, biochar has the potential to replace
traditional fossil fuels, such as coal, according to the results obtained
after analyzing the raw sample and biochar (Guo et al., 2015).
6.5. Environmental pollution control applications
Recently, environmental pollution control and contaminant reme
diation have gained increasing interest owing to the utilization of bio
char derived from lignocellulosic biomass. Currently, innumerable
contaminants, such as antibiotics (AB), pesticides, heavy metals (HVs),
volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons
(PCAHs), polychlorinated biphenyls (PCBPs), and endocrine disruptors
(EDs) are released into the water, air, and soil environment owing to
rapid urbanization and industrialization. As a result, ecology and gen
eral public health may be seriously threatened by exposure to these
contaminants. Numerous environment-friendly remediation technolo
gies have been developed to remove these toxins from the natural
environment. In light of the idea of “green restoration,’ biochar has
gained considerable interest since it is proven to be a potential, multi
functional, porous carbon compound. The BC production strategies and
environmental remediation using BC derived from lignocellulosic
biomass and the types of feedstock utilized for BC are displayed in Figs. 1
and 2, respectively.
6.6. Other emerging applications
Biochar’s can be employed for functions other than agriculture, en
ergy storage and treating wastewaters due to their inherent and adapt
able qualities. Ink manufacture, building, civil engineering, paper
making, and the synthesis of composite materials have all employed
biochar as a substitute for carbon black. Some of these applications have
even reached limited commercial use (Garcia et al., 2022). Low-cost
carbon fillers to boost the conductivity and mechanical qualities of
epoxy composites. Comparative analysis is done on the electrical and
mechanical characteristics of composites containing multiwall carbon
nanotubes and biochar distributed in epoxy resin. The outcome revealed
that using higher but controllable amounts of biochar could produce
very good dielectric properties comparable to low carbon nanotube
loadings and mechanical properties at low heat-treated biochar levels
(Id et al., 2017). Biochar was synthesized by Bartoli et al. (2020) by
pyrolyzing agricultural waste to create carbon nano-spheres with a large
surface area (1500 m2
/g). Such BC can be used as an anode for a Li-ion
battery for impressive discharge capacity up to 1169 mA h/g.
The viability of the use of BC as a reliable replacement for conven
tional and cutting-edge materials in many different industries. For better
thermal and acoustic qualities, Bartoli et al. (2020) studied the use of BC
made from leftover biomass as a concrete filler. The results indicate that
adding biochar also significantly boosted concrete’s ability to absorb
sound at frequencies between 200 and 2000 Hz and that doing so
reduced the material’s heat conductivity by 2 wt percent. This suggests
that the concrete’s compressive strength will suffer as a result of the
biochar addition. Dixit et al. (2019) have found that BC can be a po
tential replacement to cement as a mineral ingredient in
ultra-high-performance concrete, improving hydration as a result of its
better nucleation and internal curing effects. In conclusion, biochar can
be thought of as a sustainable substitute to help increase the degree of
hydration while reducing the need for cement in UHPC. Table 5 lists
several treatment procedures: biochar, contaminants, process perfor
mance parameters, and removal of obstacles.
7. Environmental and economic assessments
7.1. Environmental assessment
In regard to wastewater depollution, biochar is a renewable resource
that has a lot of promise to alleviate a number of environmental prob
lems. The environmental and financial impacts of bioenergy production
and biochar application were studied by Nie et al. (2020). The findings
showed that onsite biochar application can offset up to 82,000 metric
tons of CO2-equivalent emissions from the reduction of fertilizer use;
ethanol is less competitive; more than 99% of bioenergy is derived from
pyrolysis-based bio-power; the net offset potential significantly de
creases when N2O emissions from crop-land are taken into account; and
biochar can contribute up to 42.4–51.02% of the total emission
sequestration.
7.2. Economic assessment
In accordance with this review of the literature by Garcia et al.
(2022), slow pyrolysis is the preferable method for making biochar,
while agricultural applications (for fertilization and soil conditioning)
are the most researched and commercially viable uses of the substance.
A key player in the expanding biochar market could come from the
Alentejo region of Portugal, given the abundance of feedstock and the
sizeable potential application areas for biochar in agriculture. For this
Portuguese location, the production potential and prospective advan
tages of biochar were also calculated, demonstrating that agricultural
application can successfully result in numerous environmental, eco
nomic, and social benefits.
Biochar can be applied in aqueous media that has been extensively
studied, and all of these studies have led to the same conclusion: BC can
be a new and workable bio-adsorbent. Due to its great adsorption ca
pacity, BC and its favorable environmental and economic effects (Tan
et al., 2015). Fru et al. (2018) looked into the socio-economic and
environmental feasibility of BC usage for cassava cultivation. In com
parison to the control (583267 fCFA) with a corncob biochar (353436
fCFA) and MRR of 12.33% with an MRR of 7.80%, the results showed
that farmers utilizing rice husk biochar experienced larger profits with
net benefits of 1.44 million fCFA and a marginal rate of return of
33.06%.
8. Biochar an excellent practice for strengthening the circular
economy
In a circular economy, raw materials, products, after-use collection,
and waste management are defined from top to bottom, along with
several loops at different stages. A robust and long-term economic plan
was created when loops were gradually built. Material, process, and
social improvements should be encouraged from a value chain
perspective that considers both financial and ecological considerations.
It should also foster novel approaches and transformative development
(Roy and Choudhury, 2022). A proper understanding of the bioeconomy
should be taken into account when deciding how to proceed with any
M. Jayakumar et al.
15. Chemosphere 345 (2023) 140515
15
research or business endeavors (Kawashima et al., 2019). This study
focuses on the circular bioeconomy concept and uses biochar to provide
a workable solution for its compelling management. During pyrolysis,
larger organic particles break down into smaller atoms that are released
as gas, condensable vapor (oil), and powerful combustion products
(Kawashima et al., 2019). This investigation is focused on the circular
bioeconomy concept and uses biochar to provide a workable solution for
its compelling management. In the process of pyrolysis, larger organic
particles break down into smaller atoms, which are released as gas,
condensable vapor (oil), and powerful combustion products (Yaashikaa
et al., 2020). To promote local businesses and employment, avoid the
negative impacts of long-distance transportation, and improve the effi
ciency of resources and synergies for various local actors in the transi
tion to a circular bio-economy, LCB feedstock must be used under
specific process conditions. Decentralized BC production is the most
efficient method for meeting the local demand for by-products with
specific characteristics.
9. Biochar development challenges and prospects
9.1. Challenges
There is now unprecedented potential for the growth of biochar
owing to the current demand for environmental protection, the corre
sponding legislation that supports it, and advancements in technology.
However, there are still obstacles to biochar production that must be
overcome. Although biochar made from waste biomass has been thor
oughly investigated, there are still several difficulties in its practical
manufacturing and use. The conversion practice available to make
biochar sustainable is also essential because the majority of currently
available or future technologies will demand a significant initial
expenditure (Kong et al., 2014; Wang et al., 2020b; Cui et al., 2022). The
underlying mechanisms, as well as any potential long-term conse
quences of repeatedly substituting labile carbon for recalcitrant carbon,
are still unknown (Montanarella and Lugato, 2013). The focus should be
on developing innovative, low-cost solutions that offer a comprehensive
approach to manage and exploit the co-products and by-products
produced. Wetland plant lignocellulosic biomass has a higher moisture
content than dry lignocellulosic biomass (agricultural leftovers), which
increases the transportation and pyrolysis costs. Therefore, additional
pre-drying before pyrolysis is required for the synthesis of wetland plant
BC in addition to standard pre-treatments, such as grinding and chop
ping, which increases the cost of the equipment and uses more energy.
9.2. Prospects
It is imperative that adsorbents can regenerate, be renewed, be
economically viable, and be easily disposed of and handled. A multitude
of benefits, including the ability to regenerate, wide surface area,
reutilization, and pore volume, make biochar made from waste biomass
a desirable choice for the remediation of numerous contaminants. Uti
lizing them will undoubtedly help to realize the waste-to-value concept.
Governments should encourage and provide incentives for the industrial
use of biochar at the policy level (Shyam et al., 2022). To comprehend
the sustainability of the designed biochar, it is necessary to perform a
techno-economic analysis. Prior to its widespread use, the possible
environmental and ecological consequences of engineered biochar must
be considered. It should be emphasized that while biochar engineering
may be able to mitigate some of the drawbacks of pure biochar if used
improperly, it may even exacerbate them (Kazemi Shariat Panahi et al.,
2020). The lifespan of manufactured biochar, as well as the methods
used for its recycling, is another piece of information that is lacking. To
avoid biomagnification of nanoparticles, engineered biochar needs to be
determined what will happen to it, particularly those that contain
nanoparticles (Kazemi Shariat Panahi et al., 2020). The type of feed
stock, pyrolysis conditions, and engineering techniques must all be
considered in future research when specifically examining biochar for
each environmental use. The creation of biochar uses renewable waste
biomass as a fuel, reducing the stress associated with waste management
and dependence on petroleum while also helping to sequester carbon
(Kumar et al., 2020). An extensive study on the merging pyrolysis and
carbonization of biomass for quality output is warranted to scale up
production (Kamali et al., 2022). The surface shape and function of char,
among other changes, might improve the uptake of specific
Table 5
Treatment practice, biochar, pollutants, process performance and removal conditions, pros, cons and challenges.
Treatment Biochar Pollutant(s) Process performance
and removal
conditions
Pros Cons Challenges References
Wastewater
treatment
Rice straw Cu2+
and
Zn2+
dominant controlling
mechanism on Ion
exchange adsorption
for Cu2+
& Zn2+
cations is the
Removal of heavy
metal
Carbon release from
biochar that increases
in the solution to be
treated, by heavy
metals and stability of
BC
Inadequate data on
optimization of BC-based
systems with respect to the
wastewater treatment
(Enaime et al.,
2020)
Control of
greenhouse
gas
emissions
Corn straw CO2, N2O
and CH4
Broadcasted into the
soil surface & then
mixed into 30 -cm soil
depth
Reduced CO2 emission
by 18–25%, CH4
emission by 124% &
132%, N2O by
71–110% and 39–47%
Biochar produced from
agricultural residues
has negative emission
potential
Biochar safety is a new
environmental concern.
(Yang et al.,
2020)
Agricultural
application
Rice husk
and Elm
sawdust
Al and Pb Total potassium and
carbon improved by
6.7-fold 72%,
respectively
Improve soil health,
fertility, and
productivity
BC have inconsistent
agronomic effects due
to their properties, soil
types, and crop species,
BC may effect yield of any
corp that has not yet been
discussed
(Wang et al.,
2014)
Renewable
energy
application
Corn cob
and Khat
stem
CO2, CH4 and
gases causes
global
warming
Torrefaction and
Pelletization
Replace the fossil fuel,
mitigate greenhouse
gas effect
High moisture content
and low fixed carbon,
energy-density
Still lack of technology and
biomass collection and
transportation is cost and
there is no sustainable
supply of biomass
(Jifara et al.,
2022)
Other
Emerging
application
Dry
Distillers
Grains
CO2
emissions
Used as the inert filler
to concrete in the
place of coarse
aggregate
Potential solutions
need to find for
simultaneous carbon
sequestration.
Bio-enhanced
concretes is found to be
low strength
There are great challenges in
expanding the use of BC for
cementitious applications,
the source and the
production method of
biochar
(Cuthbertson
et al., 2019)
M. Jayakumar et al.
16. Chemosphere 345 (2023) 140515
16
contaminants. Additional research is still required to develop a new
higher-performance and lesser-cost biochar modification technology,
expand the use of BC in wastewater treatment, particularly for munic
ipal and industrial wastewater, and further enhance the ability of the
material to bind heavy metals, nitrogen, phosphorus, and organic pol
lutants (Oliveira et al., 2017; Xiang et al., 2020). Therefore, it is advised
that future research should use the knowledge already learned from
laboratory scales and pilot scales for field uses in order to evaluate the
degree of trustworthiness of the outcomes obtained in laboratories. Such
research will be crucial to determining the degree of success in biochar
soil application operations by correlating biochar production circum
stances, the class of feedstock utilized, and their effects on soil and
biochar properties. Therefore, some challenges still need to be addressed
in the future, including careful assessment of the potential hazards and
negative effects of waste lignocellulosic biomass-derived biochar
(WLBB) on humans and the environment, as well as the development of
appropriate preparation procedures that can reduce dangerous com
pounds in WLBB.
10. Conclusions
Waste lignocellulosic biomass is a potential resource for producing
biochar that can be used in various emerging applications. This waste
valorization direction, with significant growth potential, provides new
possibilities, especially in environmental science and engineering
practices. In addition, based on the option of treating wastes that
contribute to maintaining a sustainable environment, the practical
application of biochar is also made possible by inexpensive feedstock
and a simple preparation procedure. Many techniques for producing
active biochar have been described, including gasification, hydrother
mal carbonization, mechanochemical technology, pyrolysis, and func
tionalization. In addition, the characterization techniques, merits,
demerits, challenges, utilization, applications, environmental assess
ment, economic assessment, circular economy, challenges, and pros
pects of biochar are explored. Biochar’s emerging applications, such as
wastewater treatment, energy production, agricultural practices, and
environmental remediation, are emphasized. Thus, this review con
cludes that waste lignocellulosic biomass can be effectively utilized as a
raw material for biochar production using different methods for various
potential applications in many sectors.
Funding
The present study was not received any financial grants.
Author contribution statement
Mani Jayakumar: Conceptualization, Visualization, Supervision,
Review and Editing. Abas Siraj Hamda, Lata Deso Abo, Bulcha Jifara
Daba and Magesh Rangaraju: Data collection and Writing- Original draft
preparation. S. Venkatesa Prabhu: Conceptualization, Visualization,
Supervision, Review and Editing. Abdisa Jabesa: Supervision, Review
and Editing. Selvakumar Periyasamy: Visualization, Review, Data
curation and Editing. Suresh Sagadevan: Formal analysis, Review and
Editing. Baskar Gurunathan: Conceptualization, Supervision, Review
and Editing.
Ethics approval and consent to participate
Not applicable.
Declaration of competing interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
Data availability
No data was used for the research described in the article.
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