28046767 calorific values and proximate analysis of

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Calorific Values and Proximate Analysis of

Sargassum spp.and Ulva spp.

Carlo S. Alburo, Radzwell H. Conje, Maria racelda !. Pino,

"n#r. Patric$ %. &an'

Department of Chemical Engineering, University of San Carlos, 6000 Cebu City, Philippines

*Corresponding uthor!

Abstract

The potential of seaweeds, Sargassum spp" and Ulva spp., as biomass for energy production wasinvestigated 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, uaya, and Maribago. It was found that the calorific values of

Sargassum spp"range from !"#$.%& k'(kg to &%#"".") k'(kg while Ulva spp"have a mean calorific value

of &*"++."&k'(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 was finally established in this study as

with -% ).!).

#ey$ords! Calorific %alues, Pro&imate nalysis, Sea$eeds, 'ultiple (inear Correlations

(. )ntroduction

)")" Sea$eeds as iofuels

The /hilippines has an abundant supply of biomass resources which include agricultural crops 0rice

hulls, coconut husk and meat, cocoa, cassava and bagasse1, saw mill 0forest logs1 and furniture residues0sawn timber1. ut these biomass resources readily compete with food production and agricultural land

2&3. To address these constraints, a potentially viable alternative is to use a4uatic biomass, such as algae,

as the feedstock for second5generation biofuel and bioenergy production.

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67C Chemical 8ngineering 7tudent -esearch 9nnual %)&)


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6sing macroalgae 0or seaweeds1 as biofuel has the advantage of higher growth rates compared to

terrestrial crops and and avoids competing with the agricultural land. Moreover, seaweeds can mitigate

greenhouse gases emission since C:%from flue gas can be utili;ed as carbon source in algae growth.

9side from that, wastewater can be used to provide nutrients for seaweed growth 2%3.

/ast attempts in utili;ing seaweed as source of fuel started in +)elp /rogram of 6nited 7tates used the brown

seaweed 'acrocystis pyrifera as energy crop. ?owever the program was discontinued when it was

thought that the crisis was over 2*3. ut with the serious problems posed by global warming and the rapid

depletion of oil reserves today, the use of a4uatic biomass energy is now being reconsidered as a means of

C:%mitigation. /rocesses that are now considered for energy generation from a4uatic biomass include

direct combustion, anaerobic digestion, fermentation to alcohol, thermal li4uefaction, thermal

gasification, and pyrolysis 2"3. In =ermany, studies are ongoing for the closed cycle 7olar :xygen Fuel

Turbine 07:FT1 in which dried seaweeds 0specifically Ulva spp"1 are combusted in a fluidi;ed bed boiler

in -ankine cycle and the combusted products are returned to the cultivation ponds as algae nutrients

source 2$3. 9ccording toruton et al"2@3,in France, annual green tides generate about @),))) tons of wet

Ulva spp, 0or !,))) tons dry weight1 which have been considered to be utili;ed for local energy

production.

7eaweed species suitable for biomass energy should display high productivity in terms of standing

crop and biomass yield. The species should be easily cultivated and harvested. 9lso, chemical

composition of seaweeds should be accounted since it determines the fuel 4uality and dictates the process

of energy production 2"3. 7eaweeds that are considered as potential energy crops include 'acrocystis

pyrifera, (aminaria, Sargassum andUlva2@,",*3. These seaweeds are said to have high productivity and

biomass yield.

9mong the five species mentioned above, Sargassum and Ulvaspecies are chosen in this study

because of their local abundance and little economic value" Sargassumis a dominant genus in tropical and

subtropical waters in terms of standing crop, percent cover and height.

Ulvaspecies are common in the intertidal ;ones of the /hilippines, but, at certain times, could over5

proliferate, producing blooms or Agreen tide< in some protected bays. Common Ulva species that

proliferate in Cebu province are Ulva lactuca, Ulva fasciata and Ulva reticulata2+3. In Mactan Island

0Cebu1, central /hilippines, at least two species constitute the Ulvapopulation, either as free5living or

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attached form. Ulva lactucamainly consists of free5living population while the species referred to as

Ulva reticulataconsists mainly of attached population 2+3 " Ulva species are fre4uently found in nutrient5

rich saline waters, attached to the bottom of the waters 2!3.

)"+ he Calorific %alues

=ood knowledge of the heating or calorific value of a fuel and its ash compositions is needed for

control of ash5related conditions such as slagging, fouling, or erosion, management of environmental

emissions, heat rate calculations, and modifying operating parameters 2#,&)3. The calorific value of a

material is the amount of heat released by a material during combustion. It is affected by the ash and

moisture contents of the biomass. The net calorific value or lower heating value is defined as the heat to

be removed from the reaction products to obtain a final temperature e4ual to the initial temperature of the

reactants, assuming that the reaction products remain in gaseous phase, i.e. that the heat of condensation

of water is not available. :n the other hand, the reference state of the water for the gross calorific value

0higher heating value1 is li4uid state.

The ash 0inorganic1 content of a fuel lowers down the calorific value and may cause maBor problems at

high temperature combustion 0melting of ash and clogging of reactors1 2#,&)3. eber and Dygarlicke 2&)3

reported that ash5related problems, including slagging, agglomeration, corrosion, and erosion, can cause

fre4uent unscheduled shutdowns, decreasing the availability and reliability of the energy source.

The calorific value decreases with increasing moisture content. The presence of moisture in fuel lowers

its effective heating value since a portion of the heat of combustion is utili;ed in evaporating the

contained moisture, hence decreasing the calorific value. It is highly desirable, therefore, that the moisture

content be kept as low as possible 2#3.

The fixed carbon also affects the heating value of the fuel in such a way that the higher the fixed

carbon, the higher the thermal value of fuel. In general, an increase in the ash content corresponds to a

decrease in the fixed carbon content and hence a decrease in heating value 2&&3. Table & shows the

heating values of commonly used biomass fuels.

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&able (. &yical c-aracteristics of different biomass fuels used commercially for ener#y #eneration

&ye Calorific Value M/0$#1 2 moisture 2 as-

Fruit 7tems2&3 $ @* 5

:il5palm husks2*3 +5! $$ $

:il5palm fibers2*3

+5! $$ &)agasse2&3 +.+5! ")5@) &.+5*.!

Fibers2&3 && ") 5Phaeophyta2%3 #5&& 5 %$5"$

Chlorophyta2%3 !5&* 5 %"5")

-ice husks2&3 &" #

Mai;e Cobs2&3 &*5&$ &)5%) %Coffee husks2&3 &@ &) ).@

Cocoa husks2&3 &*5&@ +5# +5&"

=roundnut shells2*3 &@.+ *5&) "5&"

ood2&3 !."5&+ &)5@) ).%$5&.+

Coconut shell2&3 &! ! "

heat straw and husk2*3 &+5 +5&$ !5#

7witch grass2*3 &!5%) !5&$ @

Charcoal 2&3 %$5*% &5&) ).$5@

Eery few studies have been done to establish the calorific values of seaweeds, much less those of

endemic seaweeds in the /hilippines. 9t the international level, amare and ing 2&%3 reported the

calorific values of %! species in Gew Dealand. 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

high5energy 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 0green algae1, -hodophyta 0red algae1 and

/haeophyta 0brown algae1 have different calorific values with Chlorophyta having the highest mean

calorific content and the -hodophyta having the lowest as shown in Table &. In a similar study, ittler

and Murray 2&*3 reported that Chlorophyta had the highest average ash5free calorific content followed by

-hodophyta and lastly /haeophyta.

)"- he Calorific %alue Determination

The calorific value can be determined using proximate analysis or adiabatic calorimetry 2&"3.?owever, 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. /arikh et al"

2&$3 used "$) different types of biomass and presented the correlation

??E ).*$*@FC H ).&$$#EM ).))+!97? 284uation &3

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where ??E is the higher heating value in M'(kg, FC is the fixed carbon content, EM is the volatile

matter content and 97? is the ash content of the sample content in weight J on dry basis.

Kemirbas 2&@3 calculated the calorific values 0higher heating values, ??E1 of &@ biomass samples

experimentally from both ultimate and proximate analyses. The ??E 0M' kgL&1 of the biomass samples

as a function of fixed carbon was calculated from the following e4uation

??E 0M'(kg1 ).@0FC1 H &".& 0-%).###+1 284uation %3

7heng et al" 2&+3 gave new correlation between the ??E and dry ash content of biomass 0in weight

percent1 as follows

??E 0M'(kg1 .#&").%*%" 97? 284uation *3

amare and ing 0%))&1

The maBor advantage of these correlations is that they allow the determination of ??E 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 ??E 2&$3.

This study sought to explore the possibility of using locally available seaweeds as biomass fuel by

pitting its heating values against those of the conventional biomass outlined in table &. The study also

sought to establish relation between heating values and moisture contents of the seaweeds while being

sun5dried and finally correlations between heating values and the proximate analyses were established for

Ulva and Sargassumspecies.

+. Materials and Met-ods

+") Sampling

9lgal samples were taken from different areas around Mactan Island. The places chosen were

dependent primarily on the abundance of seaweeds in one particular place. :rti; and Trono 2&!3 reported

that +% species of Sargassumare found in the /hilippines. Table % gives the standing crop of Sargassum

beds in Central Eisayas.

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&able +. Standin# cro of dominantSargassum spp.in Central Visayas 5(67

7ite 7tanding Crop0kg wet weight per m% 1

Kominant Sargassumspecies

Tongo, Mactan Is. %.$ S" sili.uosum

Cordova, Mactan Is. *." S" binderi

Maribago, Mactan Is. %.+ S" polycystum, S" oligocystum

Caubyan Is. ".# S" polycystum

KanaBon -eef @.+ S" polycystum

ilangbilangan Is. %.@ S" polycystum, S" oligocystum

:lango Is. &.%! S" polycystum, S" oligocystumandS" sili.uosum

In this study, Sargassum polycystumseaweeds were taken from the shores of arangay uagsong,

Cordova while Ulva lactucawas taken from arangay uaya. oth Sargassum oligocystum and Ulvareticulatawere taken from the shores of Maribago. The seaweeds were collected during low tides. :ne

liter of seawater samples was also taken during the collection of the species to determine its K:, p?,

temperature and salinity.

The seaweeds were collected by thallus. Three thalli were collected for Sargassum polycystum,

Sargassum oligocystum andUlva lactuca. The thalli would serve as the samples of each species. There

were three samples for each kind of species. 9nd since Ulva reticulata thrive in continuous mats, this

species was obtained by composite sampling. The collection of seaweeds was done by hand. 7pecimens

adhering to the seaweeds were removed using knife and the collected species were wrapped in anewspaper and placed in an ice bucket.

ater samples were analy;ed within %" hours after they were collected. p? was determined using the

p? meter and the salinity was measured using the hand refractometer. The temperature of the seawater

and its dissolved oxygen were measured using the K: meter.

The seaweed samples were brought to the Marine iology Kepartment for identification. The

identification of the species was based on their external morphology, color and shape. /ictures of the

macroalgae aided the determination of species.

+"+ Preparation of Specimens for nalyses

The seaweed samples were cleaned with water and the epiphytes were removed. 8xcess water from

the samples was then removed by gently pressing the algae against tissue paper.

9ll the collected seaweed samples were sun dried. To determine relationship between calorific value

and moisture content during sun5drying of seaweeds, one whole thallus of each species, Sargassum

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polycystum and Ulva reticulata, was sampled for moisture content and calorific values analyses at

different intervals of time for three days. 9 total of seven samples were taken from the whole thallus of

each species during the sun5drying period and each sample had three replicates.

9fter all the seaweeds were sun5dried, 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.

+"- Pro&imate nalysis

/roximate 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 e4uivalent heating values.

/roximate analysis re4uires 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 /roximate

analysis method used in this study was based on 97TM K*&+% 07tandard /ractice for /roximate 9nalysis

of Coal and Coke1 but the temperatures were adBusted since proximate analysis of biomass is limited to

@))C only 2.

+"/ Calorific %alue Determination

In adiabatic calorimetry, direct combustion of the samples is done in a temperature5controlled bomb.

This Backet is maintained at the temperature of the bomb throughout the combustion process to eliminate

the heat5leakage. The calorific value of the sample obtained from calorimetry is said to be more accurate

than that obtained from proximate analysis 2&"3.

The calorific value was determined using /arr &&)! :xygen omb Calorimeter based on I7:

%!#$ 0Ketermination of gross calorific value by the bomb calorimetric method, and calculation of

net calorific value1.

*. Results and 9iscussion

-")" Calorific %alues of Different Sea$eed Species from Different Places 'aribago, Cordova and

uaya1

9 preliminary run was done to investigate available seaweed species in Maribago, Cordova and

uaya. Table * shows the seawater conditions when the seaweed samples were obtained.

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&able *. Seawater conditions of samlin# locations

Parameter 'aribago uaya Cordova

T 0oC1 *).! *) *)

K: 0g(ml1 +.&+ *.&" *.&%

7alinity 0J1 %# %@ *@p? +.## !.*& !.*"

In Maribago, the most abundant species were S" polycystumand U" reticulata" In Cordova, the most

abundant specie was S" oligocystum" Figure & shows the calorific values of different seaweed species

harvested.

;i#ure (. Calorific Values of 9ifferent Seaweed Secies from Mariba#o, Cordo


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samples could not be determined by bomb calorimetry since no temperature change is observed during

ignition.

Figures % and * below show the relation between moisture content of the seaweed and its calorific

value for Sargassum polycystumand Ulva reticulatasamples, respectively.

In both figures, it can be clearly seen that at moisture content below ")J, the calorific values have

negative linear correlations with moisture content consistently in the two experimental trials done.

?owever, Figure % shows that the two experimental trials produced different correlations despite

involving the same species. :n the other hand, figure * shows that the two trials produced almost

identical correlations. It is also seen that at moisture content &$J 0or below1, the calorific value of

seaweeds is at par with those of the conventional biomass fuels. 7ince the two trials produced two

different correlations, only correlation of Figure * is thus developed as

284uation "3

-"- Correlation bet$een the calorific values of sea$eeds and pro&imate analysis data

9fter two to three days of sun5drying, the moisture content of the seaweeds lowered to &) to &$J by

weight. 8ssentially all seaweed samples have negligible fixed carbon content 0N)J1 and have high

volatile matter 0")5+$J1 and ash content 0&$5"$J1 on dry basis. The combustibles of a solid fuel are the

volatile matter and the fixed carbon. 7ince the fixed carbon content is negligible, the volatile matter is the

only contributor to the energy of seaweeds.

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;i#ure *. Calorific Value of Ulva reticulata


10/13

9sh content is the remaining incombustible minerals of a fuel. Conse4uently, the calorific value

decreases with increasing ash content. In general, fuels should have ash content less than $J 2#3. ut

seaweeds in this study have been found to have high ash content which would then restrict the direct

combustion of seaweeds as biofuels.

Figure ", $ and @ are plots of calorific values against moisture contents, volatile matter contents, and

ash contents, respectively, covering all the sampled species of Ulva and Sargassum. It can be seen in

Figure " that the moisture content has a poor correlation with the calorific value, while volatile matter

content and ash content each have good correlations with the calorific value 0-% ).+*# and -% ).+%*,

respectively1.

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;i#ure 4. Calorific


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y multiple linear regression analysis, moisture, volatile matter and ash contents were correlated with

the calorific value. Constraints in the use of this correlation include &) to %)J moisture content, ") t)

+$J volatile matter and &$ to "$J ash content.

284uation $3

To measure how well the correlation fits the data, coefficient of determination 0-%1 was computed.

The -% computed was ).!). This means that !)J of the variation of the calorific values of the seaweed

samples has been explained by the linear regression e4uation established here.

3. Conclusion and Recommendation

7eaweeds have high potential to be used as solid biofuel since it has comparable calorific values to the

conventional biomass like bagasse, rice husks and corn cobs. ?owever, seaweeds had to be dried from

about !+J to &$J moisture content in order to obtain calorific values close to those of the conventional

biomass 0#))) &%))) k'(kg1. In the case of Ulva reticulata species, there was a highly negative

correlation between moisture content and calorific values. :n the bigger picture, 84uation $ can be used

to predict calorific values of Ulvaand Sargassumspecies.

In the case of sun5drying of Sargassumspecies, more experiments should be conducted to establish aconsistent correlation between moisture contents and calorific values. To improve -%, more species of

Sargassum should be included.

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2%3 -asmussen, M. and et" al. %))+. /rimary iomass /roduction from Marine 9lgae. 6niversity of

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power generation driven by methane produced from seaweed. 2orld cademy" $ &&*&5&&$&.

2"3 Chywoneth, K. 0%))%1. -eview of biomethane from marine biomass.3uel. &)&)%$5&)*)

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;i#ure 8. Calorific


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28046767 calorific values and proximate analysis of

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