Production, Characterization and Observation of Higher Carbon in Sargassum wightii Biochar From Indian Coastal Waters

Full text

Journal of Coastal Research
SI
86
193–197
Coconut Creek, Florida
2019
____________________
DOI: 10.2112/SI86-029.1 received 6 April 2019; accepted in
revision 14 May 2019.
*Corresponding author: zachariapu@yahoo.com
©Coastal Education and Research Foundation, Inc. 2019
Production, Characterization and Observation of Higher Carbon
in Sargassum wightii Biochar From Indian Coastal Waters
Sudhakaran Ajith†, Girindran Rojith†, Pariyappanal Ulahannan Zacharia†*, Ramachandran Nikki†,
Valiyakath Hussain Sajna†, Vazhamattom Benjamin Liya†, and George Grinson†
ABSTRACT
Ajith, S.; Rojith, G.; Zacharia, P.U.; Nikki, R.; Sajna, V.H.; Liya, V.B., and Grinson, G., 2019. Production,
characterization and observation of higher carbon in Sargassum wightii biochar from Indian coastal waters. In:
Jithendran, K.P.; Saraswathy, R.; Balasubramanian, C.P.; Kumaraguru Vasagam, K.P.; Jayasankar, V.; Raghavan, R.;
Alavandi, S.V., and Vijayan, K.K. (eds.), BRAQCON 2019: World Brackishwater Aquaculture Conference. Journal
of Coastal Research, Special Issue No. 86, pp. 193–197. Coconut Creek (Florida), ISSN 0749-0208.
Seaweed farming gains significance as a climate resilient strategy owing to significant carbon sequestration potential
and research advances to valorize products from seaweed resources. Conversion of seaweeds to biochar enhances
further carbon sequestration. In this study Sargassum wightii, belonging to brown algae has been converted into
biochar under different conditions of pyrolysis for possible application in aquaculture sector. The prepared biochar
was subjected to elemental (CHNS) analysis to assess the nutrient profile. Further, comparative analysis has been
done on raw seaweed and biochar based on the structural characterization using SEM, XRD and FTIR spectra.
Functional group changes were evidenced from FTIR and XRD spectra, whereas surface modifications were
elucidated by SEM analysis. The optimum temperature for biochar pyrolysis of S. wightii to yield higher carbon
content has been identified. A significant observation is that seaweeds in Indian coastal waters are capable of higher
carbon sequestration than in other waters.
ADDITIONAL INDEX WORDS: Seaweed, pyrolysis, nutrient profile, structural characterization.
INTRODUCTION
Seaweeds are macroscopic algae, ecologically and
economically highly significant renewable resources that are
being increasingly explored in the context of climate change
(FAO, 2014; Rebours et al., 2014). Seaweeds have great role in
combating the climate change for ocean acidification (Mongin et
al., 2016), carbon sequestration (Chung et al., 2013; Duarte et
al., 2013; Duarte et al., 2017) and climate resilient product
development (Sahoo, Elangbam, and Devi, 2012). Around 50%
of the total world carbon is fixed by marine primary producers,
which also accounts for 71% of all carbon storage (Chung et al.,
2011) of which seaweed also plays significant role. India with
along coastline of 7,516 km, have good scope for seaweed
farming that are yet to be optimally explored by the coastal
states. Seaweed farming has been identified as a prospective
climate resilient strategy for India (Zacharia, Kaladharan, and
Rojith, 2015) and research is advancing to valorize seaweed
based climate resilient products. The beneficial implications of
seaweed on climate change have been reported by several other
studies also (Miura, Ito, and Suenaga, 2018). Globally, around
900 species of green seaweed, 4,000 red seaweed and 1,500
brown seaweeds have been identified which consists of wild as
well as farmed. The 28.5 million tonnes of seaweed and other
algae are harvested mainly in Japan, Republic of Korea and
China which contributes to 80% of total seaweed production in
the world (FAO, 2016). Seaweed has great potential in carbon
sequestration and development of seaweed based products such
as biochar helps in stabilizing the carbon content. Studies show
that the total standing biomass of seaweeds along the Indian
coasts is around 2.6 lakh tonnes which has a greater carbon
sequestering efficiency at a rate of 9,052 tonnes/day with very
less emission of 365 tonnes/day.
Estimates on carbon sequestering capacity of seaweeds
suggest that they are capable of sequestering dissolved CO2 at a
rate of 80.5 mg/g wet weight per day with emission rate of 10
mg/g wet weight/day of which brown and green seaweeds are
capable of utilizing the same within the cells for photosynthesis
(Kaladharan, Veena, and Vivekanandan, 2009). Biochar is a
black, low density, carbon rich organic compound produced by
the process of pyrolysis under oxygen limited or anaerobic
conditions (Beesley et al., 2011). Conversion of biomass to
biochar is an effective method for long term carbon fixation
(Grierson, Strezov, and Shah, 2011). Seaweed biomass can be
used as a feedstock for the production of nutrient rich biochar
that has many applications in remediation of waste water and
soil amelioration (Bird et al., 2012). Compared to ligno-
cellulosic feedstock for the production of biochar, seaweed often
yields high proportions of biochar with a high exchangeable
nutrient content and Cation Exchange Capacity (CEC) (Bird et
al., 2011).
Bio-products derived from algae find many applications in
aquaculture and waste water treatment (Bulgariu and Bulgariu,
2012; Roberts et al., 2014). The structural properties of biomass
†ICAR-Central Marine Fisheries
Research Institute, Kochi, Kerala, India
www.JCRonline.org
www.cerf-jcr.org

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Journal of Coastal Research, Special Issue No. 86, 2019
are significant in the application point of view and accordingly
studies to elucidate the structure are also of importance.
The analytical tools such as X-Ray diffraction, Scanning
Electron Microscopy (SEM) and Fourier Transform Infrared
(FTIR) Spectroscopy have been reported to be valuable in
assessing the structural changes induced due to pyrolysis.
Production and characteristics of biochar has been reported,
from selected species of seaweed such as Saccharina, Undaria
and Sargassum (brown seaweeds), and Gracilaria,
Kappaphycus and Eucheuma (red seaweeds) (Roberts et al.,
2015). The composition of seaweed biochar may change based
on environment or location properties and a comparison of the
Indian seaweed biochar with other geographical locations has
been included in this study.
METHODS
Pyrolysis technique was applied for the production of biochar
from the seaweed sample. Analytical instruments such as CHNS
analyzer, (Fourier Transform Infrared Spectroscopy (FTIR), X-
Ray Diffraction (XRD) and Scanning Electron Microscope
(SEM) were used for structural characterization studies.
Sample Collection and Preparation
The material used in the present study, S. wightii, a species of
brown seaweed, was collected from southeast coast of India near
Mandapam, Tamil Nadu. The freshly collected sample was
soaked in fresh water for 12 hours and then washed thoroughly
with running water several times to demineralize and was
checked clearly for the removal of any debris like CaCO3
attached to it. Further it was air dried at room temperature for
two days and the sample was then stored in air tight polythene
bags for further use.
Pyrolysis
Pyrolysis was carried out in a muffle furnace to find out
optimum conditions for biochar production. 10 g of the sample
accurately weighed in a silica crucible was pyrolysed in oxygen
limited conditions at different temperatures and time interval.
The pyrolysis was carried out under different temperatures of
300oC, 350oC, 400oC, 450oC and 500oC for time interval of 30
and 60 minutes for each temperature set. Samples after pyrolysis
were cooled in desiccators and were used for further analysis.
Analysis
For the structural elucidation and characterization studies, the
samples were further analyzed at Sophisticated Test and
Instrumentations Centre (STIC), Cochin University of Science
and Technology, Cochin.
Elemental Analysis (CHNS)
The elemental analysis for Carbon, Hydrogen, Nitrogen and
Sulphur (CHNS) of the raw seaweed and the biochar produced
at different pyrolysis conditions were determined using the
Elementar Vario-EL-III analyzer. Based on the percentage of
carbon conversion, the samples were selected for further
structural analysis along with raw seaweed.
X-Ray Diffraction
Raw seaweed and seaweed biochar were used for analysis of
crystallinity change using Rigaku X-Ray diffractometer. The
radiation used was of Cuα radiation at a wavelength of 1.5418
Ao. The samples were scanned at a scan rate of 1o per minute
with scan angle (2θ) from 7o to 40o and the sampling rate was
0.02o (2θ). The crystallinity index was calculated using the
equation (Segal et al. 1959);
CrI= [(I002 – Iam)/I002] x100 (1)
Where CrI indicates the relative degree of crystallinity,
I002 is the maximum intensity (in arbitrary units) of the 002
lattice diffraction,
Iam is the intensity of diffraction in the same units at 2θ = 18o.
Fourier-Transform Infrared (FTIR) Spectroscopy
Comparison of structural changes of seaweed before and after
pyrolysis was performed by Thermo Nicolet, Avatar 370 Fourier
Transformation Infrared spectrometer (FTIR). FTIR spectrum of
the raw seaweed and seaweed biochar were taken with a
resolution of 4 cm-1 and 32 scans per sample. The absorbance
spectra were recorded at wave numbers from 500-4000 cm-1.
Scanning Electron Microscope (SEM) Analysis
Pyrolysis induced surface modifications were assessed by
Scanning Electron Microscope, JEOL Model JSM-6390LV.
SEM images were obtained for raw seaweed and biochar at
resolution of 10 and 50 μm.
RESULTS
Production of biochar from seaweed S. wightii was
successfully attained along with elucidation of carbon content
and structural changes. The structural characterization includes
nutrient profile, crystallinity, morphology and functional group
changes.
Biochar Production
Optimum pyrolysis condition for the production of biochar
with maximum carbon content from S. wightii seaweed was
found to be at 300oC for 60 minutes. The biochar produced by
the pyrolysis at 350oC and 400oC for 1 hour was seen visibly
ash. Thus the biochar produced by pyrolysis at 300oC for one
hour with highest carbon content was chosen for further analysis
and study.
The nutrient profile of raw seaweed and biochar produced
under different pyrolysis conditions are shown in Table 1. The
results indicate that carbon content of the biochar produced at
300oC by pyrolysis for one hour has increased and when
compared to raw seaweed, the carbon content has doubled.
Among the biochar produced at varying temperatures, the
biochar produced at 300oC for 60 minutes was found to have
increase in Hydrogen and Sulphur content. Increase in
temperature resulted in slight ash at 400oC to full ash at 450oC.
Figure 1 show the biochar produced at different pyrolysis
conditions. The C/N ratio of biochar produced under different
conditions of pyrolysis ranged from 23.30 to 37.27. The pH of
biochar produced in optimum conditions was found alkaline
with a pH value of 9.9.
As the pyrolysis temperature increases, the amount of stable
carbon content was also found to increase till optimum

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Journal of Coastal Research, Special Issue No. 86, 2019
Table 1. Comparison of nutrient profile of raw seaweed and seaweed biochar.
Type of sample
Pyrolysis
conditions
C%
H%
N%
S%
C/N ratio
H/C ratio
Raw seaweed
34.38
5.34
1.44
0.81
23.88
0.155
Biochar 1
300oC for 30 min
46.28
4.18
1.84
1.37
25.15
0.090
Biochar 2
350oC for 30 min
52.66
4.76
1.88
1.85
28.01
0.090
Biochar 3
400oC for 30 min
42.54
3.47
1.24
1.92
34.31
0.081
Biochar 4
300oC for 1 hour
68.21
6.18
1.83
2.05
37.27
0.090
Biochar 5
350oC for 1 hour
47.33
2.74
2.04
1.24
23.20
0.058
Figure 1. Biochar produced at various temperatures, a) 300oC for 1 hour,
b) 350oC for 1 hour, c) 400oC for I hour.
Figure 2. XRD spectrum of raw seaweed and seaweed biochar, a) Raw
seaweed, b) Biochars.
temperature (300oC pyrolysed for one hour) beyond which
increased ash content of the sample was observed.
The nutrient profile analysis points out towards the
distinctiveness of seaweeds collected from Indian coastal waters
as with higher carbon content for the resultant biochar. In the
present study, the percentage of carbon in seaweed biochar was
found to vary from 34.38 to 68.21. The highest C/N ratio of
37.27 was found for our biochar from Indian seaweed sample as
against the reported values of 29 for samples from Indonesia
(Roberts et al., 2015) was found to be alkaline with a pH 9.9.
XRD Analysis
The crystallinity index value of raw seaweed was found to be
231. It is observed that there has been a two-fold reduction in
the crystallinity index after pyrolysis with CrI value for biochar
reduced to 97.97. Figure 2 shows the XRD graphs of raw
seaweed and biochar.
Figure 3. SEM image of Seaweed biochar and raw seaweed at 50 μm, a)
Biochar at 50 μm, b) Raw seaweed at 50 μm,c) Biochar at 10 μm, d)
Raw seaweed at 10 μm.
Biochar SEM Analysis
Surface area increase was observed in biochar compared to
raw seaweed. Fragmentation of surface structure and increase in
porosity was also noticed. SEM images of raw seaweed and
biochar produced at 300oC for 60 minutes are shown in Figure 3.
Figure 3 illustrates that there has been considerable increase
in the surface projections which indicate increase in surface area
of biochar. SEM image of biochar at 10 μm shows an increase in
the micro pores present on the surface. It also shows the
formation of honey comb structure on the surface of biochar.
Biochar FTIR Analysis
The major peaks found in the FTIR analysis of raw seaweed
along with associated functional groups assigned are shown in
Table 2. Comparison of FTIR peaks of raw seaweed and
seaweed biochar has been made and is shown in Figure 4. The
FTIR spectra of seaweed biochar shows major peaks at 3410
cm-1, 2933 cm-1, 1610 cm-1,1420 cm-1,1320 cm-1, 1120 cm-1, 779
cm-1, 617 cm-1 and 517 cm-1. From the graph of FTIR spectra
(Figure 4), it is clear that some of the peaks have been lost
which can be attributed to the process of pyrolysis. Peaks at
2850 cm-1, 1510 cm-1, 1070 cm-1 and 1030 cm-1 have
disappeared, which represents C-H of alkyl groups, proteins,
guluronic acid and mannuronic acid respectively. The peak at

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Journal of Coastal Research, Special Issue No. 86, 2019
3420 cm-1 has shifted towards right and shows stretching
indicating a partial loss in O-H and dehydration of cellulose and
hemicelluloses. The peak corresponding to S=O group at 1220
cm-1 is also missing.
Table 2. Observed peaks in FTIR spectra and their functional groups.
Sl No
Peak values
(cm-1)
Functional group
1
3420
O-H stretching present in water and saccharide
2
2920
C-H stretching vibration from glucose
3
2850
C-H of CH3, CH2, CH
4
1640
=CO of algal polysaccharides
5
1510
N-H of 1o amines
6
1420
NH of primary amine
7
1320
Mannuronic acid
8
1220
S=O Fucoidan
9
1070
Guluronic acid
10
1030
Mannuronic acid
11
607
Carbohydrates
Figure 4. Comparison of FTIR spectra of raw seaweed and Seaweed
biochar.
DISCUSSION
Pyrolysis in muffle furnace is seen to be the suitable method
of converting the substrate seaweed into biochar on a lab scale.
The increase in the Hydrogen and Sulphur content of the biochar
could be attributed to the dehydration and depolymerisation of
cellulosic and hemicellulosic components along with associated
chemical transformations. The increase in percentage of carbon
content indicates enhanced carbon sequestration potential.
However further increase above certain temperature led to
decrease in carbon content due to increase in ash content of the
char. For soil amelioration activities, biochar having C/N ratio
between 25 and 35 is usually used, with an optimum range of
30-35.
Seaweed biochar could be mixed with soil to obtain the
optimum range of carbon and nitrogen. If the C/N ratio is too
low (indicating excess nitrogen), putrefaction or ammonia
formation can occur, resulting in reduced microbial activity. On
the contrary, if C/N value is too high then decomposition slows
and available nitrogen is not easily made available to the plants.
The alkaline property of the biochar can be explored during soil
amelioration activities where it can be added to acidic soils for
the process of neutralization.
The geolocations of seaweeds have influences on the final
product quality and is reflected in this study also. Seaweed
collected from Indian coast possesses unique properties as
against the reported properties of samples collected from foreign
coastal waters. The carbon content of seaweed samples was
found to be higher. It was reported by Roberts et al. (2015), that
the biochar produced from Sargassum varied in nutrient profile
with change in location from where the sample was collected.
The biochar produced from seaweed collected from China
yielded 28.9% carbon whereas sample collected from Indonesia
yielded 29.1% carbon. The pH of the samples does not vary
greatly with the location of the sample collected. The pH
reported by Roberts et al. (2015), for biochar produced from
Sargassum sp. ranged from 10.1 to 10.8 for different locations.
The present study clearly indicates the enhanced carbon
sequestration ability of seaweeds along the Indian coast and the
property could be well explored towards climate resilience,
further favoring large scale seaweed farming as well as product
valorization.
XRD analysis helps to identify the cellulose crystallinity
index change occurred due to the pyrolysis of seaweed. The
XRD values of maximum intensity and intensity of diffraction
around 18o could be substituted in the Crystallinity index
equation so as to obtain a quantitative value.
Changes in surface structure induced by pyrolysis are
elucidated by SEM images. The property could favour the
adsorptive applications of biochar in aquaculture water
treatment. The increase in surface projections and porosity
increases the area of adsorption, the property which can be
utilized for applications such as removal of pollutants,
remediation of aquaculture water and soil amelioration. This
increase in surface area is due to the escape of volatiles from the
surface due to increased temperature forming a more disordered
surface (Haykiri-Acma, Yaman, and Kucukbayrak, 2013). The
changes in surface area may also be due to the changes in the
cell wall structure which are also indicated by the FTIR
spectrum. FTIR spectra help identification of functional groups
which also indicate shifts and disappearance of several peaks.
The assignment of functional groups to the observed FTIR peaks
has been done with inputs from the works done by Matsuhiro
(1996); Pereira, Gheda, and Ribeiro-Claro (2013); Rodrigues et
al., (2015); Wang et al., (2017). Guluronic and Mannuronic
acids are the hetero-polysaccharides that form alginates, which
are the constituents of cell wall in brown algae.
CONCLUSION
Pyrolysis is the effective method to convert seaweed into
biochar. Optimum pyrolysis temperature helps conversion of
carbon in raw seaweed to an increased amount of stable carbon
in the biochar. XRD and FTIR spectra indicate change in
crystallinity and structure. SEM images indicated changes in
surface structure and increase in the porosity that occurred
during the pyrolysis process. It can be concluded from the
structural analysis that the property of adsorption can be
enhanced during the process of pyrolysis, which will find much
application in different sectors like aquaculture, soil
amelioration and bioremediation. It is indicative that seaweed in

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Journal of Coastal Research, Special Issue No. 86, 2019
Indian coastal water exhibits more carbon sequestration ability
in comparison to coastal waters of other nations. This enthuses
and warrants further research investigation in the field of
seaweeds.
ACKNOWLEDGMENT
The authors acknowledge the financial support provided by
the Indian Council of Agricultural Research (ICAR) funded
research scheme National Innovations in Climate Resilient
Agriculture (NICRA).
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