Research Journal of Recent Sciences ________________________________________________ ISSN 2277-2502
Vol. 1 (ISC-2011), 270-274 (2012)
Res.J.Recent Sci.

Lignin recovery, Biochar Production and Decolourisation of
Coir pith Black Liquor
Rojith G. and Bright Singh I.S.
School of Environmental Studies, Cochin University of Science and Technology, Kerala, INDIA

Available online at: www.isca.in
(Received 16th September 2011, revised 11th January 2012, accepted 25th January 2012)

Abstract
Coir pith black liquor obtained as a dark brown filtrate from oxidative delignification needs to be decolourised before releasing
to open environment. From this liquor industrially valuable lignin was recovered using acid precipitation method. ‘Biochar’
was produced by slow pyrolysis of coir pith at 500oC and 600oC. Water holding capacity and pH of the biochar were estimated.
CHNS analysis was carried out to identify the nutrient profile. Structural characterization was done using FTIR and SEM
Studies. Biochar produced at 600oC was found to be more suitable for decolourisation of the coir pith black liquor. FTIR
analysis indicated peak changes while SEM analysis indicated surface area and porosity changes. Biochar decolourisation
experiments were carried out on crude coir pith black liquor and also on lignin recovered coir pith black liquor.
Key words: Coir pith, black liquor, lignin recovery, biochar

Introduction
Coir pith, an agro industrial residual, is resistant to natural
degradation; polyphenol leaching makes it unfit for the
normal landfill practices either. It also pollutes the nearby
receiving water body by changing the physio-chemical
properties. Sustainable management of coir pith can be
achieved by converting it into useful products through
suitable techniques. Several investigations are advancing
aiming at utilization of coir pith for various applications such
as adsorption1, biomanure production2, in horticulture3,
lignocellulolytic enzyme production4, bio energy generation5
etc. These applications altogether can utilize only a small
percentage of the total annual production of coir pith and the
rest remains still as waste material leading to environmental
deterioration. This scenario emphasises the need for
advancement of research for further product development.
Physical and chemical structural binding of coir pith is the
primary hindrance that has to be addressed during the initial
phase of product development process. Pretreatment is the
widely used method to loosen the lignocellulosic binding6
and oxidative delignification has been accepted as an
effective pretreatment step7. Lignin and hemicelluloses shall
be solubilised due to this treatment. Solubility of lignin and
its derivatives by oxidative delignification generates highly
coloured filtrate rich in phenolic compounds8 termed as
‘Black Liquor’ which has to be treated before discharging
into open environment9. Black liquor also contains
industrially valuable products such as lignin, hemicelluloses,
poly phenols, etc which can be recovered 10. Acid
precipitation is an accepted method for lignin recovery11.
Lignin recovered can be further processed for the
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development of various products such as activated carbon,
vanillin, benzene, dispersant, emulsifying agents, etc 12. In
the present study black liquor generated due to oxidative
delignification is termed as coir pith black liquor (CBL).
Adsorptive property of coir pith has been explored by
various researchers for effluent treatment and to generate
activated carbon13. However, ‘biochar’ production from coir
pith is a relatively new area of investigation. Biochar is the
porous carbonaceous solid produced by thermo chemical
conversion of organic materials in an oxygen depleted
atmosphere which has the physiochemical properties suitable
for safe and long-term storage of carbon in the environment
and, potentially useful for improvement of soil quality.
Biochar has the potential to adsorb toxic and colouring
compounds from aqueous solutions. Usage of biochar as a
precursor for activated carbon also was previously reported 14.
Biochar production technologies include pyrolysis15 or
gasification16. Fourier Transformation Infra Red (FTIR)
Spectroscopy and Scanning Electron Microscope (SEM) are
common tools used for structural characterisation of the
biochar produced.
This paper reports the conversion of coir pith into biochar by
slow pyrolysis and its characterisation and application for
decolourisation of coir pith black liquor. The work includes
oxidative delignification of coir pith and attempts lignin
recovery from the coir pith black liquor and its consequent
decolourisation.

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Research Journal of Recent Sciences _____________________________________________________________ ISSN 2277-2502
Vol. 1 (ISC-2011), 270-274 (2012)
Res.J.Recent Sci.

Material and Methods
Table-1
pH Comparison: Before and after lignin recovery

Substrate and Oxidative Delignification: Coir pith
collected from a coir processing unit at Alleppey (Dt), Kerala
was washed, air dried and utilised for biochar production.
Oxidative delignification was performed by 2 % hydrogen
peroxide treatment on coir pith at pH 11.5 with substrate to
solution ratio 3g: 100ml. Coir pith black liquor obtained after
the oxidative delignification of coir pith was stored in an
amber coloured bottle and used for lignin recovery and
subsequent decolourisation.
Lignin recovery and decolourisation: Aliquots of 0.1, 0.2,
0.3 and 0.4ml H2SO4 were added respectively to each tube
containing 20 ml Coir pith Black Liquor (CBL) and pH
measured. The solution was centrifuged at 4000 rpm for 15
minutes. Lignin obtained as residue was dried at 60 oC and
stored for further analysis. Supernatant obtained by
centrifugation was maintained at 4oC for 24hrs and then
centrifuged again at 4000rpm for 15 minutes. The
supernatant thus obtained was subjected to spectroscopic
analysis within a scan wavelength of 400 to 800nm. pH of
the supernatant was also recorded.
Biochar production and characterization: Biochar was
produced by slow pyrolysis of coir pith in a muffle furnace at
500oC and 600oC for 30 minute. Water holding capacity of
the biochar was measured by transferring 1g of substrate into
a conical flask containing 100ml distilled water. The solution
after agitation for 30 minutes was filtered and the difference
in the initial and final volume gave the water holding
capacity of the substrate. pH of the biochar produced was
measured. Nutrient profile was assessed by CHNS analysis.
Morphological analysis was carried out by scanning electron
microscopy (SEM). Functional group analysis was done by
recording FTIR absorbance spectra at wave numbers from
400 to 4000cm-1 with scan resolution of 4cm-1. FTIR and
SEM images of raw coir pith were also taken for comparison.
Decolourisation by Biochar: Decolourisation was carried
out with respect to coir pith black liquor (CBL) and also with
lignin recovered coir pith black liquor (LCBL). A quantity of
1g biochar was added respectively to each conical flask
containing 100ml CBL and 100ml of LCBL. It was kept in a
rotary shaker at 75rpm for 24 hours. The solution was
filtered and absorbance measured using a spectrophotometer
within a scanned wavelength of 400 to 800nm.

Results and Discussion
Lignin Recovery and Decolourisation: Addition of
concentrated H2SO4 caused lignin precipitation which was
recovered as residue after centrifugation. Reduction of pH
below 3 is the reason for precipitation of lignin from black
liquor. Further pH variation of the filtrate after lignin
recovery was observed as shown in the Table-1.

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Volume
of
H2SO4 added
(ml)
0.1
0.2
0.3
0.4

pH of solution after
addition of H2SO4
3.21
2.2
2.04
1.65

pH of solution
after
lignin
recovery
3.05
2.05
1.80
1.70

Lignin recovery changed the colour of black liquor from dark
brown to pale yellow which indicated the removal of lignin
from solution.
Spectrophotometric reading indicated that
decolourisation was achieved to a greater extent by lignin
recovery. Reduction in colour led to the inference of the
removal of chromophores. Treatment with 0.4ml of H2SO4 /
20 ml of CBL favoured maximum decolourisation by way of
lignin recovery.
Biochar Production: Slow pyrolysis proved to be a feasible
method in product conversion process. Optimum conditions
for biochar production were found to be 600 oC and 30
minutes of pyrolysis. Water holding capacity of biochar
produced at 500oC was found to be 7 times greater than its
weight while it was found to be 9 times greater than its
weight in case of biochar produced at 600 oC. Accordingly 1
g of biochar can hold 9 ml water. It has to be pointed out that
raw coir pith holds water only 4.5 times greater than its
weight suggesting doubling the water holding capacity of
biochar. This property of the biochar could be effectively
utilised to improve water retention capacity of soil. pH of the
biochar along with the data on CHNS analysis are given in
the Table-2.
Table-2
Comparison of pyrolysis profile of biochar
S.
No
.

Pyrolysis
Temperatur
e in deg C

Water
Holding
Capacity

pH

C
%

H
%

N
%

S%

1
2

500
600

7
9

6.5
7.4

62.24
63.14

4.82
3.62

0.27
0.64

0.13
0.21

The nutrient profile of the biochar produced at 600oC was
found to have increased. However, decrease in H value was
observed for the biochar produced at 600 oC. Increase in the
C value indicated more carbon sequestration potential of the
produced biochar. This suggests the conversion of
lignocellulosic components to carbon during the process.
Biochar FTIR analysis: FTIR Images indicates peak
changes and helps identification of functional groups.
Observed prominent peaks and its associated functional
groups are given in Table-3.

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Research Journal of Recent Sciences _____________________________________________________________ ISSN 2277-2502
Vol. 1 (ISC-2011), 270-274 (2012)
Res.J.Recent Sci.
Table-3
FTIR Peak Assignment for coir pith biochar
Peaks
Functional Group
3420
0-H
2920
Aliphatic C-H Stretch
1610
C=C; C=N (Aromatic Structures)
1501
C-H, Lignin
1450
C-H, Lignin
1373
C-H, Lignin
1247
C-O
1110
C-O
1040
C-O
586-891 C=C-H (Aromatic -H)
Comparison of FTIR images as shown in Figure-1 indicates
significant changes in peak heights of associated functional
groups. Change in polysaccharide characteristic peaks

Figure-1
Comparison of FTIR spectrum of raw
coir pith, biochar produced at 500oC and 600oC

Figure-2
FTIR spectral analysis of biochar
produced at 500oC pyrolysis

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around 3430 and 1040 indicates dehydration and
depolymerisation
of
cellulose
and
hemicellulosic
components9. Change in aromatic peak around 1610 may be
due to transformation of lignin related products. FTIR
Spectrum of biochar produced at 500 oC and 600oC are given
in figure-2 and figure-3 respectively.
Biochar SEM Analysis: SEM images indicate structural
changes between raw coir pith and biochar. Surface area
increase was observed in biochar which was comparatively
higher in the case of the one produced at 600oC.
Fragmentation of structure favoured increased adsorptive
properties for biochar with increased porosity due to slow
pyrolysis. SEM Images of raw coir pith, biochar produced at
500oC and biochar produced at 600o C are shown in figure-4,
5 and 6 respectively.

Figure-1
SEM image of raw coir pith

Figure-2
SEM Image of Biochar produced at 500oC pyrolysis

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Research Journal of Recent Sciences _____________________________________________________________ ISSN 2277-2502
Vol. 1 (ISC-2011), 270-274 (2012)
Res.J.Recent Sci.

Figure-3
FTIR spectral analysis of biochar produced
at 600oC pyrolysis
Biochar Decolourisation: Decolourisation of CBL was
observed after 24 hr treatment with biochar. Increase in
surface area and porosity helps to adsorb more colouring
reagents of CBL to biochar. However, the decolourisation
doesn’t happen to that extent as occurred by lignin recovery
process. In the case of LCBL treatment with biochar,
increase in absorbance was observed. This slight increase in
colour may be due to the colour imparting reactions of
biochar with LCBL. Lignin transformed residues present in
the biochar might have induced colour to LCBL. In case of
CBL treatment the colour induced by biochar might have
been lesser than the adsorption of more coloured compounds
initially present in the CBL, and hence the decolourisation.

Figure-3
SEM Image of biochar produced at 600o C

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Conclusion
Lignin recovery and biochar production upholds the
sustainable concepts of waste management and product
development of coir pith. Lignin recovery and subsequent
decolourisation of the coir pith black liquor helps to
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Vol. 1 (ISC-2011), 270-274 (2012)
Res.J.Recent Sci.

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