USC Chemical Engineering Student Research Annual 2010 Calorific Values and Proximate Analysis of Sargassum spp. and Ulva spp. Carlo S. Alburo, Radzwell H. Conje, Maria Gracelda B. Pino, Engr. Patrick U. Tan* Department of Chemical Engineering, University of San Carlos, 6000 Cebu City, Philippines *Corresponding Author Abstract The potential of seaweeds, Sargassum spp. and Ulva spp., as biomass for energy production was investigated based on their calorific values. Further, calorific values were correlated with the proximate analysis, which covers moisture, ash, volatile matter and fixed carbon contents of the seaweeds, using multiple linear regression. The calorific value was measured using bomb calorimetry while the proximate analysis was conducted using gravimetric method. The seaweed samples were taken from three different spots in Mactan Island, namely, Cordova, Buaya, and Maribago. It was found that the calorific values of Sargassum spp. range from 8.50 MJ/kg to 12.94 MJ/kg while Ulva spp. have a mean calorific value of 13.48 MJ/kg on dry basis. This shows that the seaweeds have comparable calorific values with those of the conventional biomass fuels like bagasse, rice husks and corn cobs. Correlation between calorific values and proximate analysis for Sargassum spp.and Ulva spp. was finally established in this study as: CV ( MJ kg ) =13.3832−0.1546 M +0.0164 VM −0.0802 ASH with R 2 = 0.80. Keywords: Calorific Values, Proximate Analysis, Seaweeds, Correlations Page 1 of 23
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USC Chemical Engineering Student Research Annual 2010
Calorific Values and Proximate Analysis of
Sargassum spp. and Ulva spp.
Carlo S. Alburo, Radzwell H. Conje, Maria Gracelda B. Pino,
Engr. Patrick U. Tan*Department of Chemical Engineering, University of San Carlos, 6000 Cebu City, Philippines
*Corresponding Author
Abstract
The potential of seaweeds, Sargassum spp. and Ulva spp., as biomass for energy production was investigated based on their calorific values. Further, calorific values were correlated with the proximate analysis, which covers moisture, ash, volatile matter and fixed carbon contents of the seaweeds, using multiple linear regression. The calorific value was measured using bomb calorimetry while the proximate analysis was conducted using gravimetric method. The seaweed samples were taken from three different spots in Mactan Island, namely, Cordova, Buaya, and Maribago. It was found that the calorific values of Sargassum spp. range from 8.50 MJ/kg to 12.94 MJ/kg while Ulva spp. have a mean calorific value of 13.48 MJ/kg on dry basis. This shows that the seaweeds have comparable calorific values with those of the conventional biomass fuels like bagasse, rice husks and corn cobs. Correlation between calorific values and proximate analysis for Sargassum spp.and Ulva spp. was finally established in this study as:
Very few studies have been done to establish the calorific values of seaweeds, much less those of
endemic seaweeds in the Philippines. Lamare and Wing [12] reported the calorific values of 28 species in
New Zealand. Their report showed that for the macroalgae species, the calorific value varies from species
to species depending on the type of storage products that range from high-energy polysaccharide starch to
mannitol and glycerol. The constituents that contribute to the calorific value of the seaweeds are
carbohydrates, proteins and fats, which are all found to differ from species to species. It was reported that
Chlorophyta (green algae), Rhodophyta (red algae) and Phaeophyta (brown algae) have different calorific
values with Chlorophyta having the highest mean calorific content and the Rhodophyta having the lowest
as shown in Table 1. In a similar study, Littler and Murray [13] reported that Chlorophyta had the highest
average ash-free calorific content followed by Rhodophyta and lastly Phaeophyta.
1.3 The Calorific Value Determination
The calorific value can be determined using proximate analysis or adiabatic calorimetry [14].
However, obtaining data from bomb calorimetry is usually tedious and expensive. For that reason several
correlations are devised to predict the higher heating value from the proximate analysis data. Parikh et al.
[15] used 450 different types of biomass and presented the correlation:
HHV = 0.3536FC + 0.1559VM – 0.0078ASH [ 1]
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where HHV is the higher heating value in MJ/kg, FC is the fixed carbon content, VM is the volatile
matter content and ASH is the ash content of the sample content in weight % on dry basis.
Demirbas [16] calculated the calorific values (higher heating values, HHV) of 16 biomass samples
experimentally from both ultimate and proximate analyses. The HHV (MJ kg−1) of the biomass samples
as a function of fixed carbon was calculated from the following equation:
HHV (MJ/kg) = 0.196(FC) + 14.119 (R2= 0.9997) [2]
Sheng et al. [17] gave new correlation between the HHV and dry ash content of biomass (in weight
percent) as follows:
HHV (MJ/kg) = 19.914–0.2324 ASH [3]
Lamare and Wing [12] correlated ash and calorific values of seaweeds with an R2 of 0.859 as follows:
HHV (MJ/kg) = 19.59 – 0.2106 ASH [4]
The major advantage of these correlations is that they allow the determination of HHV of fuels simply
from their proximate analysis and thereby provide a useful tool for modelling of combustion processes.
These can also be used in examining old/new data for probable errors when experimental results lie much
outside the predicted results of HHV [15].
This study sought to explore the possibility of using locally available seaweeds as biomass fuel by
comparing their heating values against those of the conventional biomass outlined in Table 1. The study
also sought to establish relation between heating values and moisture contents of sun-dried seaweeds and
finally correlations between heating values and the proximate analysis were established for Ulva and
Sargassum species.
Page 5 of 16
2. Materials and Methods
2.1 Sampling
Algal samples were taken from different areas around Mactan Island. The places chosen were
dependent primarily on the abundance of seaweeds in one particular place. Ortiz and Trono [18] reported
that 72 species of Sargassum are found in the Philippines. Table 2 gives the standing crop of Sargassum
beds in Central Visayas.
Table 2. Standing crop of dominant Sargassum spp. in Central Visayas [18]
Site Standing Crop(kg wet weight per m2 )
Dominant Sargassum species
Tongo, Mactan Is. 2.5 S. siliquosum
Cordova, Mactan Is. 3.4 S. binderiMaribago, Mactan Is. 2.7 S. polycystum , S. oligocystumCaubyan Is. 4.9 S. polycystumDanajon Reef 6.7 S. polycystumBilangbilangan Is. 2.6 S. polycystum, S. oligocystumOlango Is. 1.28 S. polycystum, S. oligocystum
and S. siliquosum
In this study, Sargassum polycystum seaweeds were taken from the shores of Barangay Buagsong,
Cordova while Ulva lactuca was taken from Barangay Buaya. Both Sargassum oligocystum and Ulva
reticulata were taken from the shores of Maribago. The seaweeds were collected during low tides. One
liter of seawater samples was also taken during the collection of the species to determine its DO, pH,
temperature and salinity.
The seaweeds were collected by thallus (vegetative body of algae). Three thalli were collected for
Sargassum polycystum, Sargassum oligocystum and Ulva lactuca. The thalli would serve as the samples
of each species. There were three samples for each kind of species. And since Ulva reticulata thrive in
continuous mats, this species was obtained by composite sampling. The collection of seaweeds was done
by hand. Specimens adhering to the seaweeds were removed using knife and the collected species were
wrapped in a newspaper and placed in an ice bucket.
Water samples were analyzed within 24 hours after they were collected. pH was determined using the
pH meter and the salinity was measured using the hand refractometer. The temperature of the seawater
and its dissolved oxygen were measured using the thermometer and DO meter, respectively.
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The seaweed samples were brought to the University of San Carlos Marine Biology Department for
identification. The identification of the species was based on their external morphology, color and shape.
Pictures of the macroalgae aided the determination of species.
2.2 Preparation of Specimens for Analyses
The seaweed samples were cleaned with water and the epiphytes (any plant that grows upon or is
attached to the seaweeds) were removed. Excess water from the samples was then removed by gently
pressing the algae against tissue paper.
All the collected seaweed samples were sun-dried. To determine relationship between calorific value
and moisture content during sun-drying of seaweeds, one whole thallus of each species, Sargassum
polycystum and Ulva reticulata, was sampled for moisture content and calorific values analyses at
different intervals of time for three days. A total of seven samples were taken from the whole thallus of
each species during the sun-drying period and each sample had three replicates. Also, fresh samples were
oven-dried overnight to be moisture free (assumed 0% moisture) and their corresponding calorific values
were determined.
After all the seaweeds were sun-dried, they were stored and cut into small pieces for the proximate
analyses and calorific value determination. The whole experiment was conducted in two trials, one
month apart.
2.3 Proximate Analysis
Proximate analysis is an indirect method of measuring the calorific value of a sample. It converts the
component weights of proteins, fats and carbohydrates in the sample to their equivalent heating values.
Proximate analysis requires the values of the ash content, moisture content, volatile combustible matter
content, and the fixed carbon in order to determine the heating value of the sample. The Proximate
analysis method used in this study was based on AOAC[19].
2.4 Calorific Value Determination
In adiabatic calorimetry, direct combustion of the samples is done in a temperature-controlled bomb.
This jacket is maintained at the temperature of the bomb throughout the combustion process to eliminate
Page 7 of 16
the heat-leakage. The calorific value of the sample obtained from calorimetry is said to be more accurate
than that obtained from proximate analysis [14].
The calorific value was determined using Parr 1108 Oxygen Bomb Calorimeter based on ISO
1928:1995 [20]. Oxygen was supplied at a gauge pressure of 23 atm.
2.5 Correlations
Multiple linear regression analysis was employed to establish the correlations relating the calorific
values of seaweeds with their corresponding proximate analysis data. The methods of least squares
minimizing the error squared, was used to evaluate the adjustable parameters for each correlation
expression [21]. Calculations were aided using the 4-unknown calculator software [22]. Correlation
equations established were compared with those in the literature.
3. Results and Discussion
3.1. Calorific Values of Different Seaweed Species from Different Places (Maribago, Cordova and
Buaya)
A preliminary run was done to investigate available seaweed species in Maribago, Cordova and
Buaya. Table 3 shows the seawater conditions when the seaweed samples were obtained.
Table 3. Seawater conditions of sampling locations
Parameter Maribago Buaya Cordova
T (oC) 30.8 30 30
DO (g/ml) 7.17 3.14 3.12
Salinity (%) 29 26 36
pH 7.99 8.31 8.34
In Maribago, the most abundant species were S. oligocystum and U. reticulata. In Cordova, the most
abundant specie was S. polycystum. Figure 1 shows the calorific values of different seaweed species
harvested.
Page 8 of 16
S. Polyc
ystum
S. Olig
ocystu
m
S. Cras
sifoliu
m
S. Crys
taefoliu
m
U. Reti
culat
a
Ulva la
ctuca
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
Maribago
Cordova
Buaya
Species
Cal
orif
ic V
alu
es (
MJ/
kg)
Figure 1. Calorific Values of Different Seaweed Species from Maribago, Cordova and Buaya
From the Figure 1, it can be seen that the calorific values of Sargassum spp. range from 8.50 MJ/kg to
12.94 MJ/kg while Ulva spp. have a mean calorific value of 13.48 MJ/kg on dry basis which is in
agreement with values reported by Lamare and Wing [12].
The results also show that the local species of Ulva and Sargassum collected in Mactan have
comparable calorific values with those of the conventional biomass fuels like bagasse, rice husks and corn
cobs as cited in Table 2.
3.2 . Calorific value as a function of moisture content during sun drying
The most serious disadvantage of biomass fuel is that they often have high moisture content which
readily inhibits combustion [23]. In general, aquatic biomass contains 80 to 90% water [24]. The best way
to recover the lost energy because of high moisture content is through drying of biomass. In the study,
samples of Sargassum polycystum and Ulva reticulata were sun-dried to minimize the moisture content. It
was observed that when the moisture content was still higher than 40%, the calorific value of the seaweed
samples could not be determined by bomb calorimetry since no temperature change is observed during
ignition.
Figures 2 and 3 below show the relation between moisture content of the seaweed and its calorific
value for Sargassum polycystum and Ulva reticulata samples, respectively.
Page 9 of 16
0 5 10 15 20 25 30 35 406.0
7.0
8.0
9.0
10.0
11.0
trial 1
Moisture Content (kg/kg)
Cal
orif
ic V
alu
e (M
J/k
g)
In both figures, it can be clearly seen that at moisture content below 40%, the calorific values have
negative linear correlations with moisture content consistently in the two experimental trials done.
However, Figure 2 shows that the two experimental trials produced different correlations despite
involving the same species. This may be attributed to the morphology of Sargassum species. On the other
hand, Figure 3 shows that the two trials produced almost identical correlations. Compared to Sargassum
species, Ulva species are more homogenous in form and structure hence may promote uniform drying. It
is also seen that at moisture content 15% (or below), the calorific value of seaweeds is at par with those of
the conventional biomass fuels. Since the two trials produced two different correlations, only correlation
of Figure 3, using linear regression, is thus developed as:
CV ( MJkg )=11.20 — 0.098 M [5]
3.3 Correlation between the calorific values of seaweeds and proximate analysis data
After two to three days of sun-drying, the moisture content of the seaweeds lowered to 10 to 15% by
weight. Essentially all seaweed samples have negligible fixed carbon content (~0%) and have high
volatile matter (40-75%) and ash content (15-45%) on dry basis as shown in Table 4 and 5. The
combustibles of a solid fuel are the volatile matter and the fixed carbon. Since the fixed carbon content is
negligible, the volatile matter is the only contributor to the energy of seaweeds.
Page 10 of 16
Figure 3. Calorific Value of Ulva reticulata versus
moisture content
Figure 2. Calorific Value of Sargassum polycystum
versus moisture content
0 5 10 15 20 25 30 35 407.0
8.0
9.0
10.0
11.0
12.0
13.0
14.0
trial 1Linear (trial 1)trial 2
Moisture Content (kg/kg)
Cal
orif
ic V
alu
e (M
J/k
g)
Table 4. Proximate analysis and Calorific values of seaweeds for the 1st trial