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Journal of Engineering Science and Technology Vol. 14, No. 1 (2019) 012 - 026 © School of Engineering, Taylor’s University
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PHYSICO-CHEMICAL CHARACTERISATION OF CARBONISED ORCHARD RESIDUES AND POTENTIAL
FOR IN SITU RE-UTILISATION: A CASE STUDY AT PULAU TEKAK BESAR, TASIK KENYIR
MOHAMMAD HARIZ A. R.*, MUHAMAD RADZALI M., NOOR SARINAH M. N., NUR ALYANI S., HASLIANA K.
Agrobiodiversity and Environment Research Center, Malaysian Agricultural
Research and Development Institute, P.O. Box 12301, 50774 Kuala Lumpur, Malaysia
*Corresponding Author: [email protected]
Abstract
Waste generated from plant pruning and cutting can be one of the major issues in
the development of new orchard area. This was also the challenge when new
orchard is developed in Pulau Tekak Besar, Tasik Kenyir, Terengganu, Malaysia.
In order to manage the waste rapidly, method of pyrolysis was selected to recycle
and re-utilise the abundance of plant biomass waste. A study was carried out to
evaluate the suitability of the system for field practice. Initial inventory obtained
biomass quantity of 1206 kg (d.w) from 18 point locations covering an area of
0.2267 hectare. The biomass was subsequently chopped and carbonised using a
conventional vertical kiln pyrolysis system. The total amount of final carbonised
product was 381.9 kg (d.w) with recovery average of 31.7% (w w-1 d.w). Further
characterisations identified that product from 8 points fulfil one of the important
criteria of biochar which is to have carbon contents of more than 50% while the
remaining can be described as pyrogenic carbonaceous material (PCM). Cation
exchange capacity (CEC) showed value of the carbonised materials are mostly
between 10.0 to 20.0 cmol kg-1, which is within the range of the soil CEC in the
area (7.4 to 21.0 cmol kg-1). The pH was alkaline ranging from 7.9 to 10.0, which
can be good sources to stabilise acidic soil of newly introduced plants in the area.
Overall study indicated suitability of the carbonised materials for in-situ
reutilisation, particularly with appropriate integration in soils. Further researches
are required to study the application rate and effectiveness in improving plant
growth and nutrient uptake.
Keywords: Pyrolysis, Waste inventory, Biochar, Pyrogenic-carbonaceous-
material (PCM).
Physico-Chemical Characterisation of Carbonised Orchard Residues and . . . . 13
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1. Introduction
Pulau Tekak Besar in Tasik Kenyir, Terengganu, Malaysia was developed as part
of an eco-tourism project under the commercial name of Kenyir Tropical Park
(KTP). It is an integrated orchard farm planted with multiple rare fruit species
covering an area of approximately 5.3 hectares. The development concept was
similar to forest farming system in which selected rare fruit species were cultivated
within the existing forest system. Preservation of the natural forest is the main
reason for such concept to be implemented. It offers sustainability by increasing
plant species diversity while maintaining land development activities at very
minimal level. Apart of Pulau Tekak Besar, KTP also covers Pulau Sungai Tekak
with a combined area of approximately 10 hectares.
The diversity of plant species has made KTP an attractive eco-tourism
destination. Inventory and surveys conducted have identified 43 species of plants
from 17 families naturally originating from the area [1]. There were in total another
76 species of rare fruits introduced from the families of Anacardiaceae, Clusiaceae,
Phyllanthaceae, Malvaceae, Euphorbiaceae and Sapindaceae making the islands
rich in plant diversity. In view of this, a systematic management approach is
required for the purpose of effective preservation and conservation of the area.
Biomass residue management is one of the important components in orchard
management and maintenance. It involves planning and pursuing an acceptable
method for reutilisation, recycling and disposal. The management strategy has
similar hierarchical approach to agricultural waste management. The process flow
followed standard methods of waste generation, collection, treatment and
utilisation [2]. The advancement of technology today has included the use of
geographical information system (GIS) as part of an effective waste management
system approach [3]. This is to ensure proper allocation and reallocation of the
biomass waste. GIS integrates the use of spatial data with non-spatial data [4],
including quantitative and qualitative aspects of data analysis [5].
During the development phase, large amounts of residues consisting of plant
pruning, branches and decayed woody materials were generated from the area.
These residues were arranged in piles at specific locations and points within the
park to be disposed. Residues such as plant pruning and degraded wood waste
present a problem to the environment if improperly managed. It can be a major
source of pollution if contacts with water causing eutrophication, a phenomenon of
high biological and chemical oxygen demand [6]. Pulau Tekak Besar is basically a
man-made island surrounded by water body. Therefore, there is high probability of
phenomena such as eutrophication to occur. In other aspects, degraded woods also
may become a target of pest and disease. Insects such as termites and beetles attack
woods for shelter and foods [7]. Meanwhile, development of molds, decay and
stains may also occur which are caused by fungi, which grow suitably on mild
temperature and moisture [8].
In order to effectively manage the waste, a rapid and effective method of
pyrolysis was applied. It is a thermochemical process [9] in which organic materials
decompose at high temperature in absence or near absence of oxygen [10]. Under
this process, the biomass waste is pyrolised to form carbonised solid, liquid and
gaseous end products. Among other options such as composting and natural
degradation, pyrolysis was selected due to its effectiveness for short-term
processing time and ability to destroy diseases.
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Journal of Engineering Science and Technology February 2019, Vol. 14(1)
Current technology available for a low cost pyrolysis includes a vertical drum-
kiln production unit [11]. The process is a bottom-up approach with ignition of
biomass begins at the bottom of the drum. It is useful for small scale and portable
application [12]. In Malaysia, drum kiln technology is widely used in coconut
charring process. This conventional technique is popular for coconut charcoal
producer in Teluk Intan, Perak. The pyrolysation technique, however, might be
slightly different in terms of its process compared to other countries.
The solid carbonised end product from pyrolysis can be characterised based on
certain criteria. As described in European Biochar Certificate [13], it can be
classified as either biochar or pyrogenic carbonaceous material (PCM), subject to
characteristics such as total carbon content, which must be more than 50%.
Although not being classified as biochar, PCM has similar carbonised features,
which are also suitable for use as soil conditioner. It can improve soil structure and
increase recalcitrant organic C in soil [14].
The challenge in managing orchard waste requires the introduction of new low cost
and rapid technique for processing of biomass waste. Other factors that are important
include logistics and practicality. There is also a need to evaluate the quality and
quantity of the products of processed waste biomass for potential reutilisation.
Carbonisation through pyrolysis is suggested since it fulfils all these criteria.
This paper evaluates a case study on the inventory of waste generation and
carbonisation from 18 selected locations in Pulau Tekak Besar, Tasik Kenyir, and
Terengganu, Malaysia. Characterisation of raw materials and carbonised products
were conducted based on physical and chemical attributes. Also discussed is the
potential use for in-situ application.
2. Materials and Methods
2.1. Waste collection and locations
The island of Pulau Tekak Besar is located in the north of Tasik Kenyir,
Terengganu, Malaysia (50 10’ 07”U and 1020 44’ 16”T) [15]. During waste
inventory conducted from January to June 2014, there were 69 orchard residue
and waste locations within the island. Standard method to identify the specific
plant species of the orchard wastes include analysis of the leaf type as one of the
parameters for identification. Since there are difficulties due to degraded leaf and
other small plant parts, GPS point characterisations were carried out. These
residue points were located using GPS hand held device (Garmin Rino®
530HCx). Each of the residue point was eventually plotted into map using
software Arc-GIS ver 10. In order to manage the waste effectively, the residue
locations were divided into 6 different zones (Fig. 1). In this study, 18 locations
of waste covering an area of 0.2267 hectare located at zone 5 and 6 were selected
for assessment and characterisation.
2.2. Inventory of waste
Amount of waste generated was being assessed at each point location. The residues
were chopped into small pieces and the total weight was determined. Samples were
collected for physico-chemical and moisture analysis.
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2.3. Biochar production
The overall waste was pyrolised for approximately 5 to 6 hours. For ease of
practicality and low cost, production technique at Pulau Tekak Besar was carried
out using vertical drum-kiln method similar to previous work [16]. Upon
completion, the carbonised product was collected for characterisation.
2.4. Physico-chemical analysis
For moisture analysis, samples were analysed using MX-50 (AnD) moisture
analyser. One gram of sample was used for this analysis carried out in triplicate.
Samples of both raw material and carbonised product were ground followed by
analysis of pH, electrical conductivity (EC) and ash content. The pH and EC was
analysed with Eutech PC700 (Eutech Instruments) using 1:10 w:v ratio. Ash
content was determined according to AOAC [17]. Samples were also taken for
chemical characteristics on the elemental C, H, N and S using Vario El analyser
(Elementar). Additional analysis on elemental O was obtained as balance between
C,H,N,S and ash percentage. Cation exchange capacity (C.E.C) was conducted
using the barium acetate method [18]. Analysis of P and exchangeable cations (K,
Ca, Mg, and Na) were outsourced to Laboratory & Technical Service Centre,
MARDI Serdang. The exchangeable cations were determined by acid digestion
followed by the use of Inductively Coupled Plasma- Atomic Emission
Spectroscopy (ICP-AES, Perkin Elmer).
2.5. Statistical analysis
Statistical analysis was carried out to determine the significance between the
results. All analysis were carried out using one-way ANOVA and Tukey pairwise
test. The analysis was performed on MINITAB version 17.
3. Result and Discussion
3.1. Inventory of waste
Figure 1 showed the mapping of agro-forestry residues in Pulau Tekak Besar, Tasik
Kenyir. Out of 69 locations identified, 18 points with total area of 0.2267 hectare
were selected for inventory and case study. Selection of the area and locations were
based on the zoning area with higher density of waste composition points. In this
study, zone 5 and 6 are the area with the highest number of points. In zone 5, point
number 27, 29, 30, 32, 33, 34, 36, 37, 38 were selected while in zone 6, it was point
6, 7, 10, 13, 21, 22, 23, 25, 28.
Most of the waste biomass were left at the area during pruning and clearing
activities that were carried out for development phase of the park. The residues were
arranged in piles at specific locations. Since there were challenges in waste
characterisation, direct waste point characterisation was applied. Using this approach
the waste were divided into specific zones and identified by GPS points. The
uncertainties of the waste homogeneity at the specific waste GPS points were
estimated at ±15% based on expert judgement. The evaluation and sample collection,
however, were carried out with proper observation thus, only samples representing
the area were selected. The uncertainty is therefore, can be reduced in future if both
characterisation using GPS points and standard plant identification can be done.
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Journal of Engineering Science and Technology February 2019, Vol. 14(1)
Zoning of the waste area is important, particularly for the purpose of organising
the collection and re-utilisation of waste for specific purpose. Analysis using the
Arc-GIS evaluated zone 1, zone 2 and zone 3 with covered area of 0.64, 0.62 and
0.62 hectare, respectively. Zone 1 was the area where intensive development
activity occurred (Fig. 1). Zone 2 and zone 3 were the hilly area of the island.
Although there were structural developments in zone 4, the area was mostly plateau
and thus covered 1.2 hectare. The remaining of the zone 5 and zone 6 which were
mostly trees also constitute bigger zoning area at 1.2 and 1.0 hectare, respectively.
The division of the area into six zones, therefore, ensured that the waste
management activities were carried out more efficiently.
Fig. 1. GIS mapping of selected orchard residue
location at Zone 5 and 6, Pulau Tekak Besar.
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Journal of Engineering Science and Technology February 2019, Vol. 14(1)
Table 1 showed the characteristics of raw materials and carbonised product at
all selected location points under study. Mass of the initial raw material was found
to be 1206 kg (d.w) while the yield of the carbonised product was 381.9 kg (d.w).
The conversion rate of raw materials to product was calculated at average of 31.7%
(kg/kg d.w). The yield was in agreement with Brendova et al. [19] who used slow
pyrolysis process and reported biochar yield of 35 wt.%. Herath et al. [20] and
Sensoz et al. [21] also obtained similar yields.
While the average biochar yield was 31.7% (w/w d.w), carbonised product from
point 6, 7, and 23 recovered almost 45% (w/w d.w) from initial weight. The greater
yield may be due to variations in the temperature during production, particle size,
holding time and presence of foreign non-combustible substances (e.g., dirt). A
study conducted by Al-Wabel et al. [22] on the effects of different pyrolysis
temperature of conocarpus waste showed trend of yield reduction by approximately
20% when pyrolysis was conducted at two temperature difference of 200 oC and
400 oC. It was further elaborated, as highlighted earlier in the study by Yang et al.
[23], that decomposition of three main constituents of hemicellulose, cellulose and
lignin occurred at different temperatures, mostly within the scale of low pyrolysis
(<500 oC). Hemicellulose may decomposed at 220-315 oC, cellulose at 315-400 oC
and lignin from 200 700 oC. Slight difference in pyrolysis temperature below 400 oC may affect the rate at which these three constituents degrade. Other studies have
also shown the yield sharply reduced if the temperature varies between 300 oC to
400 oC. As identified in Rao and Sharma [24] and Lee et al. [25], these studies were
mostly observed on thermos-gravimetric study. Therefore, it can be explained in
this study that since self-charring field pyrolysis method was used, slightly lower
temperature differences of the pyrolysis may give higher overall yield. At the other
end, lower yield (lesser than 25%) as identified in Table 1 may be attributed to
higher pyrolysis temperature.
Table 1. Rate conversion and final composition (% w/w)
of carbonised products at selected agro residue location point.
Point
Location
Raw
materials
before
(kg f.w)
Raw
materials
before
(kg d.w)
Carbonised
produced
(kg f.w)
Carbonised
produced
(kg d.w)
Carbonised
/raw
materials
(%w/w f.w)
Carbonised
/raw
materials
(%w/w
d.w)
6 40 35.7 21.5 14.7 53.8 41.3 7 40 35.1 20 16.8 50.0 47.7
10 102 90.2 54 30.6 52.9 34.0
13 40 35.2 18 14.0 45.0 39.7 21 56 43.5 19 17.2 33.9 39.5
22 60 50.0 23 16.6 38.3 33.1
23 80 66.6 36 32.5 45.0 48.8 25 42 34.8 20 9.2 47.6 26.5
27 135 118.4 38 35.0 28.1 29.6
28 85 77.9 29 16.9 34.1 21.7 29 103 91.5 25 23.1 24.3 25.3
30 120 102.2 37 33.5 30.8 32.8 32 98 87.4 31 27.9 31.6 32.0
33 70 62.6 20 12.9 28.6 20.5
34 58 49.4 20 18.0 34.5 36.5 36 60 50.4 20 9.8 33.3 19.4
37 65 56.0 27 22.4 41.5 39.9
38 132 119.2 52 30.7 39.4 25.7
Total 1386 1206.0 510.5 381.9 36.8 31.7
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Self-charring or self-heating is a process where the system undergoes pyrolysis
without depending on external heating. It means that the temperature cannot be
controlled and the carbonisation relies on the existing raw material itself to provide
the heat. In other words, self-heating is an exothermic process where the released
heat from pyrolysis increased the temperature of the adjacent or existing biomass
[26]. This creates a chain of carbonisation through slow pyrolysis. Figure 2 shows
the vertical drum-kiln design used in this study. It was a bottom up slow
pyrolysation process where self-heating process pyrolyse or carbonise the biomass
beginning from the bottom part in the upward direction. It may take up to 6 hours
for a complete carbonisation process.
Fig. 2. Schematic diagram of vertical drum
kiln pyrolysis with bottom up carbonisation.
3.2. Physico-chemical characteristics
There were variable differences in the amount of ash in the carbonised products
(Table 2). Charred carbonised product have higher percentage of ash compared to
raw materials. High ash content is associated to alkaline properties, which makes
the carbonised product a good liming source for soil application [27]. This
relationship of higher ash content with alkaline pH properties can be seen from
Table 2. The changes on ash and pH occurred during carbonisation where
devolatilization process contributed to the reduction in dry weight of the materials.
Transitional metals, however, do not volatilize but collectively form ash and its
percentage in the end product may be influenced by carbonisation temperature and
residence time [28]. Detailed analysis of the results in Table 2 showed that biochar
from several locations have a higher ash content compared to others (p < 0.05). In
view of this, comparison on the difference of carbon percentage will further define
the characteristics of each material.
The pH of the carbonised products become alkaline with highest value
approaching 10.0 for location point 13 (Table 2). In accordance with United States
Salinity Laboratory Staff [29], the results showed significant differences when
Physico-Chemical Characterisation of Carbonised Orchard Residues and . . . . 19
Journal of Engineering Science and Technology February 2019, Vol. 14(1)
compared to other point sources (p < 0.05). Biochars were also classified based on
EC or salinity. The electrical conductivity of biochars (p < 0.05) from point 6, 10, 32,
37 and 38 are particularly low, while a few others are classified on the upper groups.
Lowest value obtained was 304.7 μS/cm while the highest is 8270 μS/cm. As earlier
evaluated by Nor Ayshah Alia et al. [15], for eventual application, alkaline properties
of the product may increase or correct soil pH of any introduced plants, at 4.0 to 4.8.
In addition to pH, values of EC from low to moderate are appropriate for soil
applications.
Table 2. Moisture content (%), ash (%), pH and electrical conductivity (EC) of
raw materials and carbonised products at selected agro residues location point.
Point
Location
Moisture
content %
Raw materials Carbonised products
Ash % pH EC (μS/cm)
Moisture
content
%
Ash % pH EC (μS/cm)
6 10.8 BCD 1.1 BC 5.2DE 180.7G 31.4CDE 4.1 DEF 8.5 CDE 360.0E
7 12.2 BCD 4.8 A 4.5HI 151.5G 16.2 FGH 4.9 CDE 9.9 A 1010.3DE
10 11.6 BCD 0.5C 4.5HI 410.3 CDE 43.3 ABC 4.6 DEF 8.6CD 304.7E
13 12.1 BCD 0.9 BC 4.5HI 383.7DE 22.4 EFG 3.4FGH 10.0A 982.7DE
21 22.4 A 2.0 BC 5.0EFG 1776.5B 9.6H 5.3 BCD 8.7C 4445.0 C
22 16.7 ABC 3.0 B 5.7 B 522.5 C 28.0 DEF 7.7 A 7.9EF 4145.0 C
23 16.7 ABC 1.9 BC 5.7 BC 437.0 CD 9.6H 6.1 BC 7.5F 5895.0B
25 17.1 AB 0.4C 4.8 EFGH 498.5 C 53.9A 5.5 BCD 8.0DEF 3495.0 C
27 12.3 BCD 1.0 BC 5.1DEF 524.5 C 7.8H 3.9 EFG 7.9EF 3710 C
28 8.3 D 1.0 BC 4.8 EFGH 136.0G 41.6ABC 3.6 EFG 9.0 BC 832.7DE
29 11.2 BCD 0.2C 4.2I 351.5DE 7.6H 4.3 DEF 8.6CD 1863.7D
30 14.8 BCD 1.0 BC 6.4 A 379.5DE 9.4H 6.0 BC 9.0 BC 1869.0D
32 10.8 BCD 2.1 BC 4.5HI 222.0FG 9.9GH 5.7 BCD 8.4 CDE 415.7E
33 10.6 BCD 0.7C 4.8FGH 113.3G 35.7CD 2.2H 9.0 BC 569.3DE
34 14.9 BCD 0.4C 4.6GH 320.3EF 9.8H 4.2DEF 8.0 DEF 8270.0 A
36 16.0 ABC 0.5C 5.3 CD 316.3EF 51.0 AB 6.3B 9.4 AB 1010.3DE
37 13.8 BCD 0.7C 4.7GH 328.7DEF 17.2 FGH 2.7GH 8.8 BC 348.3E
38 9.7 CD 1.4 BC 3.7J 8646.7 A 41.0 BC 3.2 FGH 8.8 BC 340.3E
Note: Statistical analysis using one-way ANOVA; Tukey pairwise analysis indicates that column that have the same letter are statistically similar
Elemental analysis in Table 3 shows percentage in carbon content when raw
materials were carbonised. The results obtained significance difference to each
other (p < 0.05). Average carbon content for raw materials varied between 41.1%
to 61.1%. However, carbon content of the carbonised product ranges between
24.5% to 83.4%. Tukey pairwise analysis showed carbonised material with more
than 50% C content belongs to the upper group while the rest falls in the lower
group. Pyrolisation of biomass have variable effects of increasing and decreasing
in the percentage of carbon content of final products. Study by Windeatt et al. [30]
on eight different agricultural residues showed increase in percentage of carbon
content in the end products when compared to the raw materials. Study by Ghani
et al. [31] also highlighted carbon content increases with the increasing of
pyrolisation temperature. Therefore, lower carbon content in the carbonized
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Journal of Engineering Science and Technology February 2019, Vol. 14(1)
products at several residue points in this study may have attributed to the conditions
during pyrolysis.
Table 3. Chemical characteristics of raw materials and
carbonised products at selected agro residues location point.
Point
Location
Raw Materials Carbonised products
C [%] H [%] N [%] S [%] O [%] as
difference C [%] H [%] N [%] S [%]
O [%] as
difference
6 61.1A 6.0 BCD 1.0G 0.2 B 30.7 28.3FG 3.5 CDE 0.3 BCD 0.4 A 63.4
7 52.7C 5.1 EFG 1.0G 0.2 B 35.8 24.5G 3.2 DE 0.3 BCD 0.1 B 67.0
10 58.4 AB 5.9 BCD 1.7 EFG 0.2 B 33.3 31.6 EFG 4.8 A 0.4B 0.2 AB 58.5
13 38.9E 5.5 DEF 4.2 B 0.2 B 50.3 83.4 A 2.8 E 0.6A 0.1 B 9.7
21 56.9 B 6.6 AB 1.7 FG 0.1 B 32.6 32.1 EFG 3.9 ABCD 0.4BC 0.1 B 58.2
22 59.0 AB 6.1 BCD 2.4 DEF 0.1 B 29.4 29.9FG 3.3 CDE 0.2 DE 0.1 B 58.7
23 44.9D 7.0 A 1.4G 0.1 B 44.8 34.7 EFG 4.1 BCDE 0.3 BCDE 0.1 AB 58.0
25 56.9 B 6.3 ABC 2.3 DEF 0.1 B 34.0 35.9 EFG 4.1 ABCD 0.3BCD 0.1 B 54.1
27 57.3 B 6.1 BCD 2.5 DE 0.1 B 33.0 37.9 EFG 4.0 ABC 0.2 CDE 0.1 B 53.7
28 44.1D 6.1 BCD 5.3 A 0.1 B 43.4 44.6CDE 4.1 ABCD 0.2 DE 0.0 B 47.5
29 58.3 AB 5.7 CDE 2.6CD 0.2 B 33.1 38.8DEF 4.0 ABCD 0.2 CDE 0.1 B 52.3
30 45.3D 6.0 BCD 5.4 A 0.1 B 42.2 51.9 BCD 4.1 ABCD 0.2 DE 0.0 B 37.7
32 44.4D 6.2 ABCD 4.8 AB 0.1 B 42.4 52.9 BC 3.9 ABCD 0.3 BCD 0.0 B 37.7
33 59.4 AB 6.4 ABC 2.8CD 0.2 B 30.6 54.8 BC 3.7 BCDE 0.2 DE 0.0 B 38.9
34 45.5D 6.5 AB 4.6 AB 3.6 A 39.3 59.0 B 3.5 CDE 0.2 DE 0.0 B 33.1
36 44.1D 6.1BCD 3.4C 1.1 B 44.8 63.1 B 4.6 AB 0.2 CDE 0.0 B 25.7
37 41.9DE 4.8 FG 2.9CD 0.0 B 49.7 63.9 B 3.8 ABCDE 0.3 BCD 0.0 B 29.3
38 42.2DE 4.7 G 3.0CD 0.0 B 48.8 61.6 B 3.3 CDE 0.1 E 0.0 B 31.7
Note: Statistical analysis using one-way ANOVA; Tukey pairwise analysis indicates that column that
have the same letter are statistically similar.
The in-situ kiln used in the study is a bottom up self-charring pyrolysis where
manual termination of combustion is required at the end of the pyrolysis process. It
is possible that the process occurred with less efficiency thus affecting the elemental
C content of the end products. By definitions of European Biochar Certificate [13],
sample of the end product from 8 points (13, 30, 32, 33, 34, 36, 37, 38) fulfil one of
the important criteria of biochar due to carbon percentage of more than 50%.
However, the remaining point samples (6, 7, 10, 21, 22, 23, 25, 27, 28, 29) were still
higher in carbon, with percentage between 24% to 50%, which are still significantly
higher if compared to samples obtained through burn-to-ash or complete combustion
method. These black charring samples, having similar physical attribute to biochar,
are defined as pyrogenic carbonaceous material (PCM).
Additional analysis on the ratio of O/C and H/C was carried out to observe the
trends using the Van Krevelen diagram. Figures 3 and 4 showed the results of the
ratio analysis based on the earlier characterisations of biochar obtained from 8
points and PCM on the remaining 10 points. As observed in study by Tag et al.
[32], the graph obtained in Fig. 3 on samples with biochar characteristics showed
similar trends on raw material to biochar. The normal trends were observed where
raw materials were at the right top while the biochars at the left bottom (Fig. 3).
The graph obtained in Fig. 4 for PCM however, was opposite to normal Van
Krevelen diagram for biochar. The figure shows that the raw materials were at the
left top while the PCM at the right top. One of the factor that contributed to this
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Journal of Engineering Science and Technology February 2019, Vol. 14(1)
trend was due to the lower C contents in the carbonised samples compared to the
raw materials (Table 3). Lower C contents resulted to higher O/C ratio for PCM
and thus, change the normal positions in the diagram. This observation may suggest
that pyrolysation of the 10 points PCM were not efficient where losses of carbon
occurred during the process. This affected the final C contents in the product. PCM
still however, contributes to positive effects if applied to soil. In-situ applications
of both carbonised biochar and PCM may increase soil carbon contents. It could
also reduce the decomposition of native organic C in soil [33].
Fig. 3. Van Krevelen diagram of raw material and
carbonised product from 8 points with biochar characteristics.
Fig. 4. Van Krevelen diagram of raw material and carbonised product
from 10 points with characteristics of pyrogenic carbonaceous material.
The trend of O/C and H/C of the raw materials can be observed from Figs. 3
and 4. It was identified that the value of O/C is between 0.50 to 1.29 while H/C is
between 0.09 to 0.15. The results are comparable to other biomass sources. Study
by Vassilev et al. [34] on wood and woody biomass groups obtained the values of
O/C between 0.65 to 0.79 and H/C between 0.11 to 0.17. The trends of the H/C
values are comparable however, the ranges of minimum and maximum for O/C
values are bigger in this study. Lower O/C can be contributed from higher carbon
percentages at 50% to 60% (Table 3). This characteristic was also observed in other
local biomass source. Rubber-wood saw dust for instance, which contains of 53.4%
22 Mohammad Hariz A. R. et al.
Journal of Engineering Science and Technology February 2019, Vol. 14(1)
carbon, has O/C value of 0.69 [35]. Variable differences in other characteristics
such as the percentage composition of cellulose and lignin can also contributed to
the O/C values. Couhert et al. [36] described bigger quantity of O in cellulose as
compared to lignin. This ultimately increases the ratio of O/C. A trend of higher
O/C value at above 1.0 can be observed from a local biomass of meranti-wood saw
dust, which has O/C value of 1.26 [37]. Therefore, a bigger range in the minimum
and maximum values obtained in this study is justifiable to represent the
characteristics of different types of local biomass sources.
From Table 4, C.E.C of the biochar mostly below 20 cmol/kg (p < 0.05).
Highest was measured at point 30 at 25.0 cmol/kg. Shenbagavalli and Mahimairaja
[38] reported ranges of C.E.C between 3.2 to 16.0 cmol/kg for 2 hours slow
pyrolysis of biomass waste using specially designed pyrolysis-stove. The C.E.C
value were quite similar to those obtained in this study although raw materials and
method of pyrolysis differs. In comparison, study on local biomass of coconut
shells and rice husk showed C.E.C value of 5.1 and 18.3 cmol/kg respectively [16].
Earlier study on the soil properties in Pulau Tekak Besar identified CEC value
within the range of 7.4 to 21.0 cmol/kg [15]. Therefore, the value obtained in this
study indicates that characteristics of CEC of the carbonised materials are almost
identical to the soil properties of Pulau Tekak Besar.
Table 4. CEC and chemical percentage of other macronutrients
of carbonised products at selected agro residues location point.
Point location CEC (cmol/kg) P [%] K [%] Ca [%] Mg [%] Na [%]
6 15.0 AB 0.01 BC 0.15 EFGH 0.27 G 0.18 CDE 0.05 BCD
7 20.0 A 0.03 BC 0.44 AB 0.47 B 0.17 DE 0.04 BCDE
10 15.0 AB 0.07 A 0.42 ABC 0.45 BC 0.17 DE 0.06 BCD 13 17.5 AB 0.01 C 0.25 CDEFGH 0.12 H 0.11G 0.05 BCDE
21 15.0 AB 0.02 BC 0.56 A 0.40 BCD 0.29 B 0.09 A
22 2.5 B 0.02 BC 0.26 CDEFG 0.27 G 0.22 C 0.06 ABC 23 11.7 AB 0.02 BC 0.32 BCDE 0.25 G 0.20 CD 0.07 AB
25 20.0 A 0.02 BC 0.34 BCD 0.25 G 0.16 EF 0.04 BCDE
27 17.5 AB 0.02 BC 0.27 CDEFG 0.40 BCD 0.12 FG 0.04 BCDE
28 15.0 AB 0.03 B 0.58 A 0.80 A 0.42 A 0.04 BCDE
29 23.3 A 0.03 BC 0.30 BCDEF 0.31EFG 0.15 EFG 0.07 AB
30 25.0 A 0.02 BC 0.29 BCDEF 0.32 DEFG 0.18 CDE 0.02 DE 32 10.0 AB 0.02 BC 0.08 H 0.40 BCDE 0.17 DE 0.03 CDE
33 11.7 AB 0.01 C 0.15 FGH 0.06 H 0.01H 0.02 DE
34 17.5 AB 0.02 BC 0.33 BCD 0.30 FG 0.16 EF 0.02 DE 36 18.3 AB 0.01 C 0.25 CDEFG 0.06 H 0.05 H 0.04 BCDE
37 11.7 AB 0.02 BC 0.19 DEFGH 0.14 H 0.11FG 0.03 CDE
38 13.3 AB 0.01 C 0.11GH 0.37 CDEF 0.18 CDE 0.01E
Note: Statistical analysis using one-way ANOVA; Tukey pairwise analysis indicates that column that
have the same letter are statistically similar.
Carbonised products, mainly biochar have minimal C.E.C when initially
produced but its value increased over time in soil due to surface oxidation [39].
Higher C.E.C value increases the capacity of the soil combinations to control the
leaching of positively charged ammonium ions after fertiliser or manure application
[40]. In view of this, it is possible that initial C.E.C value of 10-20 cmol/kg may
eventually increase over several period of time once applied to soil.
Results for available P and exchangeable K, Ca, Mg and Na obtained in this
study (Table 4) were relatively low although statistically significant (p < 0.05) in
comparison to different waste points. Values were initially obtained as ppm but
Physico-Chemical Characterisation of Carbonised Orchard Residues and . . . . 23
Journal of Engineering Science and Technology February 2019, Vol. 14(1)
converted to percentage for standardization. Since the biomass used in this study is
from orchard and forest pruning, it is possible that the amount of macronutrients to
be lower in value as compared to other waste agricultural products. Although
percentage of macro nutrients is low, it is still important to maintain nutrient
balance in an ecosystem.
Comparison between macronutrients in Table 4 showed that the carbonised
products are higher in percentage of K and Ca. In view of this, Oram et al. [41]
describes the added advantage of biochar of having more available form of K. This
may result to more availability and absorptivity of the nutrient in plant.
Nutrient conservation can be achieved through appropriate processing and re-
utilising of biomass. Silver et al. [42] suggested that forest trimmings or prunings
could increase nutrient uptake and reduce competition for nutrients. Therefore, it
must be emphasized that in-situ re-utilisation of pyrolysis products of biomass
harvests from pruning is one of the mechanism to achieve this aim. Pyrolisis,
through method of slash-and-char can be the best alternative to slash-and-burn [43].
It avoids destruction of forests and functioned as carbon and nutrient conservation
technique in comparison to conventional slash-and-burn [44].
The overall results suggest that carbonisation of biomass waste is suitable for
application in the area where new orchard is being developed. Although vertical
drum-kiln technique is already common especially in coconut industry in Malaysia,
its applicability and advantage to convert orchard waste into useful carbonised
products were thoroughly discussed in this paper. The carbonised products, which
consist of both biochar and PCM, has been the subject of interest due to its
additional benefits and suitability as organic amendment in soil. Further study is
required for determination its effectiveness on plant nutrient uptake particularly in
relation to microclimate and soil environment in Pulau Tekak Besar.
4. Conclusion
From the above discussions, carbonisation of orchard residue is a potential method
to retain higher carbon contents of biomass. This was observed through 8 sample
points of having more than 50% C while several other points still contain higher
percentage. Ratio of carbonised/raw materials, which is in average of 31.7% (w w-
1 d.w), is higher compared to conventional method of slash-and-burn, which
ultimately account for the amount of ash after burning. Other attributes of
carbonised products such as C.E.C value between 10.0 to 20.0 cmol kg-1 is
compatible to existing soil condition in the study area of Pulau Tekak Besar.
Salinity of the carbonised products between 304.7 μS/cm and 8270 μS/cm are
suitable for plants. It can be concluded that carbonised product of pyrolysis can be
useful for soil application and in-situ reutilisation. It is also an alternative method
for effective biomass or solid waste management in any orchard area. Study on the
effects of the carbonised products on specific plant growth can be carried out to
determine its effectiveness and efficacies.
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