Impregnation of olive mill wastewater on dry biomasses: Impact on chemical properties and combustion performances

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Energy xxx (2014) 1e11

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Energy

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Impregnation of olive mill wastewater on dry biomasses: Impact onchemical properties and combustion performances

Nesrine Kraiem a, b, c, Mejdi Jeguirim a, *, Lionel Limousy a, Marzouk Lajili b, Sophie Dorge c,Laure Michelin a, Rachid Said b

a Institut de Sciences des Mat�eriaux de Mulhouse, 15 rue Jean Starcky, 68057 Mulhouse, Franceb UR Etude des Milieux Ionis�es et R�eactifs, IPEIM, Avenue Ibn El Jazzar, Monastir 5019, Tunisiac Laboratoire Gestion des Risques, Environnement 3 bis, rue Alfred Werner, 68093 Mulhouse, France

a r t i c l e i n f o

Article history:Received 22 April 2014Received in revised form4 October 2014Accepted 12 October 2014Available online xxx

Keywords:Olive mill wastewaterImpregnationCharacterizationEnergy recoveryCombustion testsGaseous and particulate emissions

* Corresponding author. Tel.: þ33 3 89608661.E-mail address: [email protected] (M. Jeguirim

http://dx.doi.org/10.1016/j.energy.2014.10.0350360-5442/© 2014 Elsevier Ltd. All rights reserved.

Please cite this article in press as: Kraiem N,combustion performances, Energy (2014), h

a b s t r a c t

Mediterranean countries generate large amounts of olive oil byproducts mainly OMWW (olive millwastewater) and EOSW (exhausted olive solid waste). Although solid residues have various valorizationstrategies, there is no economically viable solution for the OMWW disposal. This study aims to recoverthe OMWWorganic contents through solid biofuels production. Hence sawdust and EOSW were used forthe OMWW impregnation. The potential of the obtained samples, namely: IS (impregnated sawdust) andIEOSW (impregnated exhausted olive solid waste) were evaluated. Therefore, the physicochemicalcharacterizations and thermogravimetric analyses of the samples were first performed. Secondly, thesamples densification into pellets and their combustion in a domestic combustor were carried out.Combustion efficiencies, gaseous and PM (particulate matter) emissions as well as ash contents wereevaluated.

The analysis finding shows that addition of OMWW leads to an increase of energy content through theheating values increase. An increase of the impregnated samples reactivity was observed and assigned tothe potassium catalytic effect. Combustion performances show that the OMWW addition has not anegative effect on their firing quality. Moreover, a beneficial effect on the pollutant emissions is observedwith IEOSW pellets. The developed strategy constitutes a promising issue for the OMWW disposal andrecovery.

© 2014 Elsevier Ltd. All rights reserved.

1. Introduction

In a context of sustainable development, the reduction of energycosts and the use of renewable energies potential based on pro-cesses that maximize energy efficiency and protect the environ-ment are key challenges for industrial companies. With thedepletion of fossil fuel resources, countries must move towardsrenewable energies for the development of their economy. In thisframework, agro-industrial companies are prompted to reduceand/or to valorize the generated wastes from their activities. In thisway, olive oil extraction industries, representing a significant eco-nomic and social activity in the Mediterranean countries, engen-dered two by-products: a solid residue and an aqueous effluent

).

et al., Impregnation of olive mttp://dx.doi.org/10.1016/j.ene

namely, OMSW (olive mill solid waste) and OMWW (olive millwastewater), respectively [1].

The treatment of OMWW represents a serious ecologicalproblem due to its high degree of organic pollution with a COD/BOD ratio (chemical oxygen demand/biological oxygen demand)evaluated to be between 2.5 and 5, its pH slightly acid [2] and itshigh content of recalcitrant compounds such as lignin and tannin[3]. Furthermore, OMWW contains phenolic compounds andlong-chain fatty acid responsible for the phytotoxic and anti-bacterial effect. Tunisia like the Mediterranean countries pro-duces large quantities of olive by-products estimated at 2009 bythe Tunisian national agency for waste management, namelyANGED (Agence Nationale de Gestion des D�echets) to be annu-ally: 600,000e1,200,000 tons of OMWW, 435,000e800,000 tonsof OMSW and 120,000e170,000 tons of sludge [4]. Hence, Tunisianeeds to identify an environmentally and economically viablesolution for the generated waste disposal. Several OMWWdisposal scenarios and methods have been studied in the litera-ture based generally on biological or chemical-physical

ill wastewater on dry biomasses: Impact on chemical properties andrgy.2014.10.035

N. Kraiem et al. / Energy xxx (2014) 1e112

treatments, membrane filtration and evaporation. Few attemptshave been tested to recover the OMWW energetic potential, butthere is no economically issue for OMWW due to high moisturecontent [1,5]. The common disposal ways were soil spreading andevaporation ponds. Although, the latter technique is the mostpopular, the residual oil layer floating in the pond surface pre-vents water evaporation.

The treatment of the solid residue (OMSW) has been wellinvestigated in literature [1,6]. It has been traditionally used asanimal feed but nowadays it undergoes a second oil extraction bychemical processes in seed-oil factories in order to extract its re-sidual oil, which leads to generation of EOMSW (exhausted olivemill solid waste). The thermal conversion is the main recoveryprocess for EOMSW because of its interesting energy content withlow heating value around 18 MJ kg�1 [7]. Separate treatments ofOMWW and EOMSW have been studied by several authors [5e9],but nowadays fully combined treatment is required. Such strategycould develop a green and low cost energy in order to serve millsand seed-oil factories through small sized plants [2]. Addition ofOMWW to suitable proportions of EOMSW following by biomasscombustion is a promising solutionwhich can avoid the factories topay disposal costs [2]. Recently, Chouchene and Jeguirim estab-lished a combined method for the treatment of OMWW [10e12].This method consisted on the impregnation of the OMWW on lowcost adsorbents such as sawdust or OMSW. The impregnatedsamples were therefore thermally oxidized in laboratory furnace.The authors showed that the addition of OMWW to both adsor-bents had not negative effect on gaseous emissions [11,12]. How-ever, the CO (carbon monoxide) and VOC (volatile organiccompounds) emissions from all the tested samples were higher dueto the absence of secondary air injection in their laboratory reactor[11]. Although the obtained promising results, the validation of theOMWW treatment strategy required the investigation of theimpregnated samples behavior during combustion tests in a do-mestic boiler.

In recent times, several researchers have examined the com-bustion of agro-industrial and agriculture residues in domesticboilers [13e17]. These biofuels were firstly densified and pelletizedin order to obtain adapted fuels for the different boilers. Also,pelletization increases the biomass energy density and decreasesthe moisture content leading to an increase of combustion effi-ciency as well as a reduction of smoke during combustion [18].Several researchers have produced pellets by blending the agro-industrial residues with wood residues. This step allows obtain-ing an agropellets with good quality that could be used directly inwood domestic boilers. In fact, the combustion performances aswell as the gaseous emissions obtained during combustion testscould reach the European standards.

This investigation aims to validate the strategy of the OMWWtreatment through its impregnation on different biomasses andthe direct combustion of the impregnated samples for small-scaleheat generation. Hence, the impregnation of OMWW was per-formed on sawdust and EOMSW for 5/1 mass fraction ratio.EOMSW is preferred to OMSW due its availability in seed-oilfactories as well as its higher adsorption efficiency since the re-sidual oil was removed. In order to reach this research purpose,firstly, characterization of the impregnated samples was per-formed using various analytical techniques as well through ther-mogravimetric analysis. Secondly, pellets from the differentsamples were produced and characterized according to the Frenchand European standards. Finally, combustion tests for thedifferent pellets were performed in a residential pellets boiler tocompare their combustion efficiencies as well as gas and particleemissions.

Please cite this article in press as: Kraiem N, et al., Impregnation of olive mcombustion performances, Energy (2014), http://dx.doi.org/10.1016/j.ene

2. Materials and methods

2.1. Samples preparation

OMWW and EOMSW used in this study were collected fromolive mill (three-phase centrifugal olive mill) at the seed oil factoryZouila located in Mahdia, Tunisia. Sawdust was provided fromsawmill located in Sayada, Tunisia. During impregnation tests,20 kg of EOMSWor sawdust with 10% of moisture (inwet basis, wb)were slowly added to 100 kg of OMWWwith 89% of moisture (wb)in a specific barrel. The impregnated samples weremixed regularly.In this specific investigation, in order to reduce the initial watercontent in the mixture which was initially 76% (wb) and thereforeto accelerate the drying process, the barrel was heated, from theunderside, using hot ashes provided by a combustor in the seed oilfactory. The upper face of the barrel was exposed to ambient air.Currently, solar drying of the impregnated samples is examined.

At the end of drying, different samples were taken from 10places for each mixture at time intervals of 2 h. Therefore, a ho-mogeneous IEOSW (impregnated exhaust olive solid waste) and IS(impregnated sawdust) were obtained with less than 15% ofmoisture. This level 15% was chosen in order to avoid the fermen-tation of the different preparations. Samples of ISW and EOMSWare analyzed in the following in their raw state. During the analysis,all samples are placed in an isothermal container to maintain theirproperties and moisture content.

2.2. Samples characterization

2.2.1. Proximate, ultimate analyses and energetic contentsThe optimization of an operating plant design for biomass

combustion involves the knowledge of the fuel composition as wellas its related energy properties. Hence, elemental compositions ofthe different prepared samples were performed by CHONS-NA2100 protein CE instrument analyzer (Carbon, Hydrogen, Oxygen,Nitrogen, Sulfur).

Proximate analysis was obtained using different techniques.Therefore, thewater content (M) is measured byweighting samplesbefore and after drying at 105 �C (about 1 g, wb) in an oven untilobtaining a constant mass according to the EN 14774-1 standard.The percentage of moisture content is calculated from the averageof three measures per sample. Bulk density is carried out accordingthe EN 15103 standard. The ash content is evaluated according totwo norms in order to evaluate differences between them. Ashvalue is obtained after sample combustion (about 1 g, wb) in amuffle furnace during 3 h at two temperatures 550 �C and 815 �Caccording to EN 14775 and DIN 51719 standards respectively. TheVM (volatile matter) content was obtained using the TG procedureanalysis. This method consists of heating the samples under ni-trogen flow at a heating rate of 10 �Cmin�1 from 20 �C to 110 �C andmaintaining at this temperature during 10 min to remove themoisture. Temperature is then increased at 20 �C min�1 to 900 �Cand kept for 10 min to obtain the weight loss corresponding to thevolatile matter content. The fixed carbon content is obtained bydifference.

The energy contents of the different samples were obtainedusing a calorimetric bomb IKA-C200 by determining the HHV (highheating values). HHV were obtained after combustion of a sample(about 0.6 g, wb) under a pure oxygen atmosphere at 35 bars ac-cording to EN 14961-1 specification. The LHV (low heating values)were calculated using the relationship between HHV and LHV givenby:

LHV ¼ HHV� hgð9H þMÞ=100 (1)

ill wastewater on dry biomasses: Impact on chemical properties andrgy.2014.10.035

N. Kraiem et al. / Energy xxx (2014) 1e11 3

where: H and M are the hydrogen percentage and the moisturepercentage (mass basis) of the received tested fuel respectively.Here, hg is the latent heat of steam in the same units as HHV andLHV. The energy density is obtained from the multiplication of thelow heating value by the bulk density.

2.2.2. Thermogravimetric analysisTGA (thermogravimetric analyses) were carried out using a MET-

TLER TOLEDO thermobalance (Mettler-Toledo SAS, Viroflay, France).Experiments were performed for a mass sample about 10 mg underinert and oxidative atmosphereswith a gasflow rate of 12 NL h�1 at aheating rate of 5 �C min�1 from room temperature to 900 �C.

2.3. Pellets production

The densification of the different impregnated sample, sawdustand EOSW (exhausted olive solid waste) was carried out using apelletizer KAHL 15/75 type (Amandus Kahl GmbH & Co, Reinbek,Germany) containing a die diameter of 6 mm and a length of30 mm. The specifications of the used pelletizer are: Die diameter(mm): 175, Diameter/length of roller (mm): 130/29, Number ofrollers: 2, Control motor (kW/min�1): 3, Roller speed (m/s):0.5e0.8. The capacity of the pelletizer depend on its properties(frequency, temperature, ...) and sample characteristics (composi-tion, moisture content...) and controlled manually. Generally, it isabout 2e3 kg/h.

Diameters and lengths of pellets produced are measured with anumeric caliper. Unit density is calculated from pellets mass andvolume. The pellet energy density is obtained from the multipli-cation of the low heating value by the unit density.

2.4. Experimental test setup

2.4.1. Combustion equipmentA commercially residential pellets boiler (Pellematic PES12 e

PVB 2000) supplied by €Okofen (Barberaz, France) was used toperform combustion tests. This boiler was already tested in previ-ous investigations [13,14]. A schematic diagram of the experimentalsetup is shown in Fig. 1. This boiler has a nominal power output of12 kWandwas equippedwith recycling combustion to improve thecombustion efficiency. The boiler is placed on a balance supplied bySartorius to determine the fuel consumption. Combustion gaseswere extracted with a fan maintained constant during combustiontest to have a constant draught. Heat of combustion is collected

Fig. 1. Schema of the experimental combustion setup.

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from flue gases through hot water heat exchanger (32 kW). Theheat exchanger and flue gas temperatures were recorded as well asthe hydraulic circuit water flow.

2.4.2. Measurement of gaseous and particles emissionsDuring combustion tests, a portable analyzer (TESTO 350XL/

TESTO454) measures the concentrations of the following gases (ona dry basis): CO2, CO, O2, VOC (volatile organic compounds), NO(nitrogen oxide), NO2 (nitrogen dioxide). Gaseous measurementswere realized according to the NF EN 304 standard.

In this present investigation, particles generated during theexperimental tests were collected into 12 size fractions from 29 nmto 10 mm using an ELPI (electrical low pressure impactor) analyzer.This apparatus was described in details in previous investigations[19e21]. The obtained results are presented in number and massconcentrations as function of size distribution.

2.4.3. Performance measurementsThe performance measurements are evaluated through the

determination of the combustion and boiler efficiencies. Thecombustion efficiency is calculated using the indirect method rec-ommended by the NF EN 12809 standard. This method required thedetermination of thermal (qa kJ kg�1), and unburned gaseous(qb kJ kg�1) and unburned carbon (in the ash) (qr kJ/kg) heat losses).In the following, the used formulas for calculation are presented.

qa ¼100� �Tg � Ta

����

Cpmd � ðC � CrÞ0:536*ðCOþ COrÞ

�

þ�CpmH2O � 1:244� ð9H þMÞ

100

�� (2)

qb ¼ 12644� CO� ðC � CrÞ0:536� ðCOþ CO2Þ � 100

(3)

qr ¼ 33500� Cr100

(4)

where:

Tg and Ta are the temperatures of the exhaust gases and primaryair, respectively (K).Cpmd and CpmH2O are the dry flue gases and water vapor specificheats (kJ K�1 m�3).CO and CO2 are concentration in the dry flue gases (% of volume).Cr is the unburned carbon content passing through ash (% ofmass).C is the carbon content in the pellet (% of mass).H is the hydrogen content in the pellet (% of mass).M is the moisture content in the pellet fuel (% of mass).

The combustion efficiency (q %) is determined:

q ¼ 100��qa þ qb þ qr

LHV

�� 100 (5)

The BE % (boiler efficiency) was calculated using the directmethod according to the NF EN 303-5 standard from the heat po-wer gain of water in the exchanger (PN kW) and the heat powercontent in the fuel (PC kW) ratio as described by Eqs. (6)e(8).

PN ¼ Qw$CPw$ðTout � TinÞ (6)

PC ¼ Qcomb$LHV (7)

ill wastewater on dry biomasses: Impact on chemical properties andrgy.2014.10.035

Table 2Proximate analysis and energy contents of raw samples.

Sample characteristic Sawdust IS EOMSW IEOSW

Moisturewb (%) 9.8 ± 0.5 9.6 ± 0.1 10 ± 0.4 15 ± 0.5Bulk densitywb (kg m�3) 103 ± 3 183 ± 2 529a ± 10 551a ± 13LHVwb (MJ kg�1) 16.4 ± 0.1 18.0 ± 0.4 16.9 ± 0.3 17.5 ± 0.7Fixed Carbon (%) 14.5 ± 0.1 17.6 ± 0.1 25.5 ± 0.2 17.5 ± 0.9Volatile matter (%) 75.2 ± 1.0 68.5 ± 0.3 61.5 ± 0.2 60.5 ± 0.1Ashdb (%) 0.6b ± 0.1 4b ± 0.1 3b ± 0.1 7b ± 0.2

0.5c ± 0.1 4c ± 0.1 3c ± 0.1 5c ± 0.1

a Bulk density.

N. Kraiem et al. / Energy xxx (2014) 1e114

BE ¼ PNPC

� 100 (8)

where:

Qw is the mass flow of water in the heat exchanger (kg s�1).CPw is calorific capacity of liquid water (kJ K�1 kg�1).Tin and Tout are the inlet and outlet temperatures of water in theexchanger (K) respectively.Qcomb is the pellets mass flow (kg s�1).

b Ash at 550 �C.c Ash at 815 �C.

2.4.4. Ash characterizationBottom ashes obtained during the combustion tests were

characterized by XRF (X ray fluorescence) using a Magix fromPHILIPS spectrophotometer apparatus. These residual ashes werepreviously shredded. Disks were manufactured under a mass oftwo tons during 2 min.

3. Results and discussion

3.1. Raw samples characteristics

Elemental compositions as well as the “H/C” and “O/C” ratios ofthe different samples are listed in Table 1. The analysis findingshows that elemental compositions of the different samples are inthe typical composition of biomass reported in literature[7,14,20,21]. The low standard deviations for the different samplesconfirm their homogeneity. Comparison of the different samplesshows that the addition of OMWW leads to an increase to carbonand hydrogen contents. Such behavior is attributed to the highpolyphenol contents in OMWW. The nitrogen content increasesalso by 1% wt with the addition of OMWW.

Table 2 shows the proximate analysis and energy contents ofraw samples. The main characteristics are within the typical rangeof agro-industrial residues [1,7]. Addition of OMWW leads to anincrease of energy content through the LHV values. Such behavior ispredictable since the impregnated samples have the highest carbonand hydrogen contents. In contrast, the OMWW addition leads toan increase of ash contents. This result is attributed to the highmineral contents in OMWW which has mainly from 9 to 13% ashcontent [10,11]. For impregnated samples (IEOSW, IS) ash contentsvalue determined at 815 �C are lower than those determined at550 �C. This result may be attributed to the evaporation of someminerals presented in OMWW. Obernberger concluded that the ashcontent of biomass fuels should be determined at 550 �C [22].Furthermore, Table 2 shows that the fixed carbon of samples are inthe same range as other biomasses like grapemarc (25%), olive husk(19%) and pine sawdust (17%) [13e15]. Adding OMWW has nosignificant trend on volatile matter and fixed carbon contents.

3.2. Thermal degradation

Figs. 2 and 3 show the residual mass percentage (X, TG) and itstime derivative (dX/dt, DTG) evolution obtained during pyrolysis

Table 1Ultimate analysis of raw samples (dry basis).

Sample % C % H % N % O H:C ratio O:C ratio

Sawdust 51.3 ± 0.2 6.4 ± 0.3 0.2 ± 0.1 41.5 ± 0.5 0.124 0.809IS 57.0 ± 1.1 7.3 ± 0.1 1.1 ± 0.1 31.1 ± 1.0 0.128 0.546EOMSW 51.3 ± 0.9 6.5 ± 0.2 0.9 ± 0.6 37.9 ± 1.6 0.127 0.739IEOSW 54.4 ± 0.8 6.8 ± 0.1 1.9 ± 0.1 30.8 ± 0.9 0.125 0.566

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and oxidation of the different tested samples, respectively. Inliterature, the thermal degradations of biomass under inert andoxidative atmosphere were discussed in details [12,24e26]. Py-rolysis curves have the typical biomass degradation shapes withthree regions corresponding to the following steps: 1) biomassdrying, 2) devolatilization step (named active pyrolysis) and 3)char formation (named passive pyrolysis). During the devolatili-zation step, the degradation profiles show different behaviors.Hence, EOSW and IEOSW samples have two DTG peaks correlativeto the degradation of hemicellulose and cellulose with closerdegradation rate. Such behavior is predictable since olive solidwaste contains a similar percentage of hemicellulose (21.5%) andcellulose (24.3%). In contrast, IS and sawdust samples have a singleDTG peak corresponding to cellulose decomposition since thislatter is the main wood component (40%). From the DTG curves, itis important to note that the degradation of impregnated samples(IS, IEOSW) occurred earlier. Such behavior can be assigned to thepotassium brought by OMWW. In fact, previous investigationsshowed that adding potassium catalyzes the thermal decompo-sition of biomass [27]. TG and DTG curves for the tested samplesunder oxidative atmosphere follow also the usual profiles of thebiomass oxidation with three steps: 1) drying biomass, 2) devo-latilization step and 3) oxidation of carbonaceous residues. Thethermal decomposition of impregnated samples under oxidativecondition started earlier as under inert conditions. Such behavioris also attributed to the potassium initially present in OMWWandimpregnated on the different biomasses (see minerals composi-tion in Table 7).

The thermogravimetric characteristics of the different samplesnamely: temperature range degradation, mass loss X, peak tem-perature Tpeak, peak rate R and reactivity RM under inert andoxidative atmospheres are shown in Tables 3 and 4 Reactivityvalues are in the same range as those of some other biomasses. ElMay et al. found 0.37% s�1 �C�1 and 0.55% s�1 �C�1 for date stonesunder inert and oxidative atmospheres, respectively [25]. Muniret al. have found 0.45e0.49 % s�1 �C�1 (N2) and 0.94e1.14 % s�1 �C�1

(Air) for different types of sugarcane bagasse [24]. Comparison ofthe different samples shows that the addition of OMWW leads tothe decrease of the peak temperature of the thermal degradationunder inert and oxidative atmospheres. Moreover, a pronouncedincrease of the reactivity is observed during the addition of OMWWto sawdust. Such behavior is attributed to the catalytic effect ofpotassium.

3.3. Pellets properties

Densification of samples by pelletizing increases energy densityof the different tested fuels and therefore optimizes transportationcosts and storage capacity. Table 5 summarizes the conditions usedfor pellets preparation. Different tests were performed to optimizethe granulation process, namely frequency of pelletizer, the die

ill wastewater on dry biomasses: Impact on chemical properties andrgy.2014.10.035

Fig. 2. TG and DTG curves of the different samples under inert atmosphere.

Fig. 3. TG and DTG curves of the different samples under oxidative atmosphere.

Table 4Thermogravimetric characteristics under oxidative atmosphere.

N. Kraiem et al. / Energy xxx (2014) 1e11 5

temperature and moisture contents. The selected parameters areshown in Table 5.

The characteristics of the prepared pellets are shown in Table 6.The obtained results are compared with the different quality re-quirements for pellets fuel such as EN 14961-6 (European standardfor solid biomassmade from sets andmixtures), AQHP (agro qualityhigh performance) (French requirement of Agro Quality HightPerformance) and AQI (French requirement of Industrial AgroQuality) [15,28]. Table 6 shows that IEOSW pellets could meet theFrench AQHP and AQI standards. However, a particular attentionshould be paid to the higher ash content, which may lead to slagand deposit formation in the furnace during a long operation time.The IS pellets have suitable characteristics. However, the low bulkdensity prevents them to reach the different French and Europeanstandards.

In addition, the minerals composition of the different pre-pared pellets was performed using inductively coupled plasmaatomic emission spectroscopy (ICP-AES). The mineral composi-tions of the four pellets are shown in Table 7. Table 7 shows thatthe addition of OMWW to dry biomasses leads to a higher in-crease of the K content as well as a significant increase to Na, Feand Ca contents.

Table 3Thermogravimetric characteristics under inert atmosphere.

Sawdust IS EOMSW IEOSW

T (�C) 130e531 120e570 137e570 128e518Tpeak (�C) 332 288 212e275 206e274e312R (% s�1) 0.097 0.074 0.041e0.05 0.044e0.051e0.02RM*103 (% s�1 �C�1) 0.29 0.26 0.39 0.46Char (%) at 900 �C 14.9 21.9 28.9 25.0

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3.4. Combustion tests

3.4.1. Thermal performanceThe main results of combustion tests of the different pellets are

summarized in Table 8. All the tested pellets have good boiler andcombustion efficiencies comparing to values found in literature.The comparison between the pellets produced from raw biomasswith those produced from impregnated biomasses shows that theaddition of olive mill wastewater has not a negative effect on thecombustion quality. The different pellets have close flow rates andexcess air. The air excess of impregnated biomasses is slightly lowerthan reference samples, which can be attributed to their higher ashcontent (especially for K and Fe, see Table 3), which induces ahigher reactivity of the pellets and then a lower oxygen concen-tration in the exhaust gas. However, the values of air excess (l) arefound in the same order of magnitude as those found in similarconditions of this study, which were estimated between 1.6 and 2.3[29] and 1.4e3.9 (NF EN 303-5). The boiler efficiencies for the tested

Sawdust IS EOMSW IEOSW

Devolatilizationstep

T (�C) 134e325 118e341 134e314 112e331Tpeak 1 (�C) 284 241 219e269 208e260R (% s�1) 0.16 0.17 0.054e0.035 0.042e0.042

Combustionstep

T (�C) 325e440 341e500 314e438 331e458Tpeak (�C) 415 409 375 380R (%.s�1) 0.13 0.11 0.076 0.079RM*103

(% s�1 �C�1)0.52 0.97 0.58 0.57

Ash (%)at 900 �C

0.8 4.3 3.2 5.6

ill wastewater on dry biomasses: Impact on chemical properties andrgy.2014.10.035

Table 5Operating pelletization conditions.

Sample

Pelletizer performance Sawdust IS EOMSW IEOSWFrequency of pelletizer 50 Hz 50 Hz 50 Hz 52 HzTemperature 70 �C 60 �C 70 �C 60 �CMoisture of raw material 16% 15% 16% 13%Moisture of final pellets 13% 9% 12% 7%

Table 7Pellets mineral contents.

Ultimate analysis (g/kg, wb) Samples

Sawdust IS EOMSW IEOSW

Na 0.009 4.761 3.201 7.627K 1.224 22.431 15.127 32.125P 0.056 0.819 0.541 0.985Mn 0.042 0.078 0.007 0.025Fe 0.043 3.553 0.173 4.287Mg 0.098 0.743 0.485 0.922Si 0.039 0.644 0.366 0.909Ca 1.215 3.602 4.665 6.193Al 0.030 0.384 0.199 0.571

N. Kraiem et al. / Energy xxx (2014) 1e116

pellets are lower than that estimated by the manufacturer (92.5%)as the boiler is designed principally for labeled wood pellets DINþ.In fact, boiler parameters are preset by the manufacturer and it wasnot possible to modify them in order to adjust and adapt the boilerto suit other fuels thanwood pellets. Combustion efficiencies of thedifferent pellets are higher than the minimum value specified bythe European Standard EN 303-5 (76%).

3.4.2. Gaseous emissions analysisFig. 4 shows the evolution of gaseous emissions versus time

during the combustion tests of the different pellets, namely O2(oxygen), CO2 (carbon dioxide), CO (carbon monoxide), NOx (ni-trogen oxides) and VOC (volatile organic compounds). The con-centrations of O2 and CO2 are expressed in %vol while CO, NOx andVOC concentrations are expressed in ppmv. The comparison of thedifferent pellets shows that sawdust (Fig. 4a) pellets have the morestable emissions. Such a behavior is predictable since the usedboiler was adapted only for wood pellets. The impregnation ofOMWW on sawdust leads to the occurrence of CO and VOC emis-sion fluctuations. Such behavior may be attributed to the accu-mulation of ash in the combustion plate, which may obstruct thearrival of primary air-flow and therefore instantaneous higheremissions of CO and VOC were occurred. These CO and VOCemissions could not be completely oxidized by the secondary air-flow. The fluctuation of gaseous emissions is more pronouncedduring the EOSW and IEOSW combustion tests. Such behavior ismay be attributed also to a higher ash content.

Since the emissions curves show a fluctuating evolution, themean values of the different emitted gas are calculated and pre-sented in Table 9. Moreover, emissions are corrected at 10% and 13%of oxygen in order to compare the results obtained with thedifferent pellets with results coming from the literature as shown inTable 9.

Table 9 shows different behavior concerning the impact ofOMWW impregnation on the gaseous emissions. Hence, the addi-tion of OMWW to sawdust leads to an increase of CO, VOC and NOxemissions. In contrast, the gaseous emissions are lower for IEOSWpellets comparing to EOSW pellets. Such behavior was alreadyobserved by Chouchene et al., during oxidation tests of OMWW/OSW blends performed in a laboratory reactor [11]. Such behaviormay be attributed to the well-known catalytic effect of potassium.

Table 6Pellets characteristics.

Samples

Sawdust IS EOMSW

Moisturewb (%) 13 9 12Diameter (mm) 6.0 ± 0.1 6.0 ± 0.2 6.0 ± 0.1Length (mm) 20e27 11e21 17e20runit (kg m�3) 1150 ± 57 1065 ± 74 1233 ± 62rapp (kg m�3) 601 ± 12 550 ± 5 626 ± 6LHVwb (MJ Kg�1) 16.4 ± 0.3 18.5 ± 0.4 16.3 ± 0.2Ash, 550db (%) 0.6 ± 0.1 4 ± 0.2 3 ± 0.1Ash, 815db (%) 0.5 ± 0.1 4 ± 0.1 3 ± 0.1

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This behavior may be depended on the dry biomass since it was notobserved in the case of sawdust.

Fig. 5 shows a comparison of boiler power, combustion effi-ciency and gaseous emissions of the different tested pellets withEuropean requirement and other biomass pellets examined in theliterature. Several investigations have examined recently thecombustion of various biomass pellets in low and medium boilerspower [13e17,30]. The obtained values in Table 7 and Fig. 6 showthat the combustion efficiency meets European standard (�76%)and are in the same range as other biomasses and agropellets asBrassica and poplar [31], Miscanthus and Swithgrass [32]. The ob-tained CO emissions were 459, 722 and 743 mg Nm�3 at 13% O2 forIEOSW, EOSW and IS pellets, respectively. These values meet Eu-ropean standard (�3000 mg Nm�3 at 13% of O2). The valuescalculated at 10% O2 are lower or closer than those obtained inliterature for various pellets. In fact, Gonz�alez et al. found COemissions of 1822 ppm at 13% of O2 (eq. 3340 mg Nm�3 at 10% O2)for tomato pomace and 1680 ppm at 13% of O2 for cardoon (eq.3080 mg Nm�3 at 10% O2) burned in a mural boiler of a 12 kW ofnominal power [29]. Limousy et al. found 353 ppm (606 mg Nm�3

at 10% of O2) for pellets corresponding to a blend from spent coffeegrounds and pine sawdust and 1785 ppm (3069 mg Nm�3 at 10% ofO2) for spent coffee grounds pellets burned in a domestic boiler(12 kW of nominal power) [14]. Garcia-Maraver et al. found550 ppm at 10% of O2 (eq. 733 mg Nm�3 at 10% O2) for Portuguesepine and 1900 ppm at 10% of O2 (eq. 2533 mg Nm�3 at 10% O2) forolive pruning burned in a domestic top feed pellet-fired boiler of22 kW of nominal power with a thermal load of 10 kW [17]. Díaz-Ramírez et al. found 285 mg Nm�3 at 10% of O2 for Brassica,202 mg Nm�3 at 10% of O2 for blend Poplar 50%-Brassica 50%,186 mg Nm�3 at 10% of O2 for Poplar and 117 mg Nm�3 at 10% of O2for DINplus [31]. Verma et al. found 4221 mg Nm�3 at 10% O2 forpeat pellets [15]. VOC emissions were 491, 777 and 1207 mg Nm�3

at 10% of O2 for IEOSW, EOSW and IS pellets, respectively. The ob-tained value for IEOSW is in the same range of wood DINplus(324 mg Nm�3 at 10% of O2) and spent coffee grounds pellets(539 ppm be 530 mg Nm�3 at 10% of O2) [14]. In addition, NOx

Standards

IEOSW EN 14961-6 AQHP AQI

7 �12 �11 �156.0 ± 0.1 e 6e8 6e1613e21 e 3.15e40 3.15e401245 ± 50 e e e

690 ± 14 �600 �650 �65019.8 ± 0.2 �14.1 �15.8 �14.97 ± 0.4 6 e e

5 ± 0.1 �5 �5 �7

ill wastewater on dry biomasses: Impact on chemical properties andrgy.2014.10.035

Table 8Comparison between different pellets combustion parameters.

Echantillon q (kg h�1) DTe (�C) Pu (kW) Pf (kW) hboiler (%) l [O2] (%) Tamb (�C) Tf (�C) hcombustion (%)

IEOSW 2.00 19.2 9.3 11 84.9 2.07 10.9 29.8 110 91.5EOMSW 2.70 21.1 10.3 12.3 83.7 2.40 12.3 23.1 124 88.4IS 2.3 19.5 9.7 11.8 81.8 2.35 12.1 24.6 113 88.2Sawdust 2.1 16.6 8.5 10.2 83.4 2.61 13.0 23.0 120 91.0

qcomb is the fuel mass flow (kg h�1), DTeau is the gradient of temperature of water in the heat recovery circuit (K), l is the air factor, [O2] is the mean oxygen proportion in fumes(%) and Tf is the flue temperature (�C).

N. Kraiem et al. / Energy xxx (2014) 1e11 7

emissions for IEOSW, IS and EOSW were 223, 255 and384 mg Nm�3 at 10% of O2, respectively. They are close to poplar(266mg Nm�3 at 10% O2) and Brazil nut shells (247mg Nm�3 at 10%O2) [16,23], higher than DINplus (176 mg Nm�3 at 10% O2) [31] andsunflower husk (179mg Nm�3 at 10% O2) [32]. Garcia-Maraver et al.found 105 mg Nm�3 at 10% of O2 for Portuguese pine and340 ppm at 10% of O2 (512 mg Nm�3 at 10% of O2) for olive pruning[17]. Limousy et al. found 201 ppm (377 mg Nm�3 at 10% of O2) forthe blend from spent coffee grounds and pine sawdust pellets and206 ppm (407 mg Nm�3 at 10% of O2) for spent coffee groundspellets [14]. Díaz-Ramírez et al. found 672mg Nm�3 at 10% of O2 forBrassica and 418 mg Nm�3 at 10% of O2 for blend Poplar 50%-Brassica 50% [31].Hence, one may conclude that OMWW impreg-nation does not generate an excess of pollutants comparing to otherbiomasses.

3.4.3. Particle matter analysisDuring the experimental combustion tests performed with the

different pellets, particles were collected in an ELPI (electrical lowpressure impactor), in order to observe the impact of the biomasscomposition and the combustion quality upon particle concentra-tions and distributions. As it was expected, sawdust presents thelowest particle emissions (143 mg Nm�3 at 10% O2) due to itselemental composition (0.6% wt of ash, Table 2) and also to the factthat pellet boilers are especially developed for this kind of fuel.

(a)

(c)

Fig. 4. Gaseous emissions during combustion tests of the dif

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Results obtained with the IS pellets indicate that the impregnationof sawdust with olive mill wastewater leads to a great increase ofthe particle concentration in the exhaust gas. As it is presented inTable 11, the impregnation step induces an important increase ofthe PM (particulate matter) concentration for IS (659 mg Nm�3)which could be explained by the high content of K and Ca incomparison with the pure sawdust (2.24 and 0.36 %wt in compar-isonwith 0.12 and 0.12 %wt onwet basis respectively). This result isdifferent than the one obtained with the EOMSW sample, wherePM concentration reaches the highest value (1038mg Nm�3), whileit corresponds to an intermediate value for IEOSW pellets(558 mg Nm�3). While the impregnation of olive mill wastewaterinduces an increase of K and Ca contents, respectively 3.2 and 0.62%wt for IEOSW pellets, and 1.5 and 0.46 %wt for the EOMSW (onwet basis), the PM concentration evolves at the opposite in com-parison to the others. It seems that the presence of K and Ca at thesurface of the EOMSW sample has a catalytic effect. Nevertheless,the results obtained with the non impregnated samples (sawdustand EOMSW) are in good agreement with those found in theliterature with the same input power (see Table 10), while Elmayet al. obtained particle concentrations close to 100 mg Nm�3 fordate stones (with a ash content of 0.8 %wt on dry basis) and of400 mg Nm�3 for rachis pellets (with a ash content of 5.6 %wt) [13].Limousy et al. studied the energetic potential of pure spent coffeegrounds or blended with pine sawdust (50/50 %wt) [14]. They

(d)

(b)

ferent pellets: (a) Sawdust, (b) IS, (c) EOSW, (d) IEOSW.

ill wastewater on dry biomasses: Impact on chemical properties andrgy.2014.10.035

Table 9Emissions values of CO2, O2 and CO, NOx and VOC reported at (a) 10% and (b) 13%of O2.

Sample CO2

(%)O2

(%)CO(mg Nm�3)

NOx

(mg Nm�3)VOC(mg Nm�3)

IEOSW 9 11 (a) 631 (a) 223 (a) 491(b) 459 (b) 162 (b) 357

EOMSW 8 12 (a) 993 (a) 384 (a) 777(b) 722 (b) 279 (b) 565

IS 8 12 (a) 1022 (a) 255 (a) 1207(b) 743 (b) 185 (b) 878

Sawdust 6 15 (a) 346 (a) 116 (a) 914(b) 252 (b) 84 (b) 665

Wood DINplus [14] 6 12 (a) 263 (a) 84 (a) 324(b) 191 (b) 61 (b) 236

spent coffeegrounds-pinesawdust [14]

9 8 (a) 606 (a) 377 (a) 205(b) 441 (b) 274 (b) 149

Spent coffeegrounds [14]

5 4 (a) 3069 (a) 407 (a) 530(b) 2232 (b) 296 (b)385

Peat [15] 19 1 (a) 2363 (a) 53 e

(b) 1718 (b) 39Brazil nut shells [16] e 11 (a) 290 (a) 247 e

(b) 211 (b) 179Sunflower husk [16] e 13 (a) 315 (a) 179 e

(b) 229 (b) 130Portuguese pine [17] e 18 (a) 733 (a) 105 e

(b) 533 (b) 76Olive pruning [17] e 18 (a) 2533 (a) 512 e

(b) 1842 (b) 372Tomato pomace [29] 7 10 (a) 3340 e e

(b) 2247Cardoon [29] 7 10 (a) 3080 e e

(b) 2240Industrial

wood wastes [30]e e (a) 797 (a) 660 e

(b) 580 (b) 480Peach stones [30] e e (a) 839 (a) 302 e

(b) 610 (b) 220Poplar [31] e 10 (a) 186 (a) 266 e

(b) 135 (b) 193Brassica [31] e 11 (a) 285 (a) 672 e

(b) 207 (b) 489

Fig. 6. Concentration (mg Nm�3) of the PM emissions according to their size distri-bution obtained from the combustion of different pellets in a domestic low powerpellet boiler (12 kW).

N. Kraiem et al. / Energy xxx (2014) 1e118

found that the particle concentration increases with the ash con-tent from 426 mg Nm�3 for the blend (with an ash content of 1.15 %wt) to 1472 mg Nm�3 for pure spent coffee grounds pellets (with aash content of 2 %wt). Garcia-Maraver et al. measured a particleconcentration close to 100 mg Nm�3 (10% O2) in the exhaust gas

Fig. 5. Evolution of gaseous emissions resulting fro

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during the combustion of pine pellets (ash content of 0.9 %wt onwet basis) at an input power of 14 kW, which corresponds also tothe results we obtained [17]. They also observed a PM emissioncorresponding to about 500 mg Nm�3 for olive pruning (ash con-tent of 5.5 %wt on wet basis), which corresponds to EOMSWemissions.

m Sawdust, IS, EOSW and IEOSW combustion.

ill wastewater on dry biomasses: Impact on chemical properties andrgy.2014.10.035

Table 10Comparison of PM emissions obtained with different pellet fired boilers fromvarious biomass fuels.

Pellets PM mg Nm�3

(at 10% O2)Boilerpower (kW)

Reference

Sawdust 143 12 This workIS 659 12 This workEOMSW 1038 12 This workIEOSW 558 12 This workPine 120 10 [17]

674 11 [33]220 16 [33]

Date rachis 200e410 12 [13]Date stone 95e123 12 [13]Spent coffee

ground (SCG)1472 12 [14]

SCG/Pine (50/50) 426 12 [14]Sun flower husk 655 40 [15]Olive pruning 500 10 [17]

Fig. 7. Size distribution of the PM emissions (%) obtained from the combustion ofdifferent pellets in a domestic low power pellet boiler (12 kW).

N. Kraiem et al. / Energy xxx (2014) 1e11 9

Fig. 6 presents the mass repartition of PM observed with thedifferent tested biomass according to the particle size distribution.As we can observe, the repartition of sawdust pellets mass particlesis quite homogeneous for diameters from 0.12 to 3.09 mm, and fordiameter from 0.32 to 3.09 for IS, EOMSW and IEOSW pellets. Aninteresting observation is that the difference of particles massdistribution observed from sawdust and IS is correlated with anincrease of the number of particles (116 � 106 Particles Nm�3 forsawdust and 187 � 106 Particles Nm�3 for IS), while the opposite isobserved with EOMSW and IEOSW (149 � 106 Particles Nm�3 forEOMSW and 249 � 106 Particles Nm�3 for IEOSW). Then, wedecided to represent the size distribution of particles in order tounderstand this behavior (Fig. 6).

The size distributions obtained with EOMSWand sawdust are ingood agreement with those presented in previous works for similarbiomasses [13,15,17]. As we can see in Fig. 7, ultrafine particles(0.04 mm of mean diameter) are present by a majority for theimpregnated pellets (68% for IEOSW and 35% for IS), while theircontribution remains low for the non-impregnated ones (0.4% forEOMSW and 11% for sawdust). It means that the increase of K andCa contents in biomass may have various effects on particle emis-sions: (1) an increase of the number of particles emitted during thecombustion process, which could be explained by a catalytic effectand the fractionation of big particles into smaller ones (2) a betteroxidation of the remaining fixed carbon contained in large parti-cles, which could be quickly oxidized in the presence of CO2 andH2O in the flue gas [34,35]. Then, if combustion is performed withpine pellets (sawdust), the increase of particle number as well asflying ash concentration (mass) after impregnation with olive millis associated to very low carbon content in pine pellet ashes, whileimpregnation leads to larger particles which distribution is quitesimilar to the IEOSW (Fig. 7) distribution and also to the increase ofultrafine particles (Fig. 7). When combustion is carried out withEOMSW pellets, the bulk density increases a lot (see Table 2) incomparison with pine pellets. Then, high pollutant and particleemissions may be associated to the difficulty for oxygen to diffuseinside the pellets. This observation was also done by Limousy et al.[14] for the combustion of spent coffee ground. Finally, the pres-ence of higher K and Ca levels in IEOSW induces an increase of thecarbon oxidation rate associated to a better catalytic effect. Thesecompounds are mainly present in the composition of ultrafineflying ash because their densities are low and also because they areeasily volatilized at low temperature during the combustion pro-cess as shown by Torvela et al. [36]. They observed that ultrafineparticles (<50 nm) are mainly composed by K, O, S, Cl and Zn during

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the combustion of wood logs using a biomass grate combustionunit with a nominal power output of 40 kW.

3.4.4. Ash characterizationResults of the boiler dust analyses of the traditional chemical

data for 17 oxides (normalized to 100%) are given in Table 11 andFig. 8. The major 6 oxides present in biomass ash of HAR (herba-ceous and agricultural residue) are respectively in descendingorder of magnitude K2O > SiO2 > CaO > P2O5 > MgO > Al2O3 [37].This order can change depending on the variety of biomass. Othercompounds as TiO2, SrO, CuO, Cr2O3, ZrO2, ZnO, Rb2O and otheroxides like Mn are minorities. Ash biomass from the food pro-cessing industry is generally high on K2O, CaO and P2O5. Othermajor components other than these can be introduced as Fe2O3,which characterize contaminated biomass. Indeed, the presence ofiron oxides between the major compounds in ash may be attrib-uted to the introduction of Fe during operations that accompanyfood products (harvesting, processing, etc.) and their biomass(storage, transport, drying, etc.) [17]. Moreover, the presence ofSrO, ZrO2 and Rb2O may be also attributed to the biomass storageand transport. In fact, these compounds are usually present innatural clays [38] and therefore left in the ash residues duringcombustion. Major compounds values for impregnated samples ofIS and IEOMSW are close to those of reference samples except forCaO which is higher for sawdust and EOMSW because this com-pound characterizes wood and woody biomass. K2O of IS andIEOMSW is higher than that of woody biomass (5e15 wt %) andthe same order as agricultural biomass (20e30 wt %) as shownin Table 10.

ill wastewater on dry biomasses: Impact on chemical properties andrgy.2014.10.035

Fig. 8. Elemental composition of boiler dust from pellets used in this study.

Table 11Ash analysis (%wt).

Element Sawdust IS EOMSW IEOMSW Pine sawdust [37] Portuguese pine [17] Grape marc [37] Olive husks [37]

C 9.587 6.304 0.680 5.159 e e e e

K2O 15.802 26.837 28.003 27.293 14.38 11.50 36.84 4.30SiO2 6.376 6.983 18.125 18.656 9.71 20.90 9.53 32.70CaO 47.800 13.879 29.586 17.655 48.88 26.20 28.52 14.50Fe2O3 5.513 13.625 1.896 9.219 2.10 21.60 1.77 6.30SO3 1.383 4.705 4.335 4.708 2.22 0.30 6.29 0.60P2O5 3.168 3.588 4.990 3.880 6.08 4.20 8.80 2.50Na2O 1.167 6.118 4.273 4.266 0.35 2.50 0.67 26.20MgO 4.585 2.735 3.748 2.925 13.80 4.30 4.77 4.20Cl 0.745 12.069 2.255 3.689 e 0.04 e e

Al2O3 1.614 1.453 1.566 2.020 2.34 6.20 2.63 8.40TiO2 0.196 0.152 0.168 0.231 0.14 e 0.18 0.30SrO 0.115 0.061 0.243 0.135 e e e e

CuO 0.019 0.119 0.111 0.070 e e e e

Cr2O3 0.170 1.139 0.120 0.044 e e e e

ZrO2 0.010 0.040 e e e e

ZnO 0.033 0.034 0.016 0.049 e 1.00 e e

Rb2O 0.043 0.017 0.010 0.012 e e e e

MnO2 1.613 0.486 e e e e

Br 0.018 0.013 e e e e

BaO 0.232 e e e e

Other oxides 0.001 0.000 0.000 0.001 e e e e

Sum 100 100 100 100 100 100 100 100

N. Kraiem et al. / Energy xxx (2014) 1e1110

4. Conclusion

This investigation aims to recover the organic contents of olivemill wastewater through the production of solid biofuels. Hencetwo dry biomasses (sawdust and exhausted olive mill solid waste)were used for the impregnation of the olive mill wastewater. The IS(impregnated sawdust) and IEOSW (impregnated exhausted olivesolid waste) were characterized and evaluated for biofuels pro-duction. The samples characterization shows that the addition ofolive mill wastewater leads to an increase of energy contentthrough the low heating values. Nevertheless, it leads to an increaseof ash contents. Thermal degradation analysis shows a pronouncedincrease of the reactivity during the addition of olive mill waste-water which can be assigned to the catalytic potassium effect. Thecomparison between the pellets produced from raw biomasseswith those produced from impregnated biomasses during com-bustion tests shows that the addition of olive mill wastewater hasnot a negative effect on the combustion quality. In particular, thegaseous emissions are lower for impregnated exhausted olive solidwaste pellets comparing to exhausted olive solid waste pellets.However, an increase in particles emissions is observed which isattributed to the high content of K and Ca in OMWW. The main

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results confirmed that the combined process of the treatment ofolive mill wastewater presented in this work may be a promisingissue for the valorization of its organic content. Hence, it will bepossible to use this wet biomass as feedstock for biofuel productionand thereby divide by 2 the consumption of solid biofuels such asOSW. This operation could generate as an example a benefit forZouila company of 650.000 euros/year. Moreover, the use ofOMWW for biofuels production will reduce their bad environ-mental impact and the different constraints for managing them inponds.

Acknowledgments

This work has been partially carried-out in the frame of theCNRS-DGRS 2013 GREENPOL (EDC 25950) and the authors grate-fully acknowledge CNRS-DGRS support. Authors would like tothank Zouila Company (Mahdia, Tunisia) for its technical support.Nesrine Kraiem thanks Institut Français de Tunisie (Grantn�808475L), Agence Universitaire Francophone (Bourse mobilit�e2013/2014) and Association Françaises des Femmes Diplom�ees desUniversit�es (Bourse Ren�ee G�erard 2014) for their financial support.

References

[1] Vitolo S, Petarca L, Bresci B. Treatment of olive oil industry wastes. BioresourTechnol 1999;67:129e37.

[2] Caputo AC, Scacchia F, Pelagagge PM. Disposal of by-products in olive oil in-dustry: waste-to-energy solutions. Appl Therm Eng 2003;23:197e214.

[3] Ero�glu E, Ero�glu _I, Gündüz U, Yücel M. Comparison of physicochemical char-acteristics and photofermentative hydrogen production potential of waste-waters produced from different olive oil mills in Western-Anatolia, Turkey.Biomass Bioenergy 2009;33:706e11.

[4] ANGED. Strategic options for the promotion of value of organic waste VDOTunisia. 2009.

[5] Miranda MT, Cabanillas A, Rojas S, Montero I, Ruiz A. Combined combustion ofvarious phases of olive wastes in a conventional combustor. Fuel 2007;86:367e72.

[6] Masghouni M, Hassairi M. Energy applications of olive-oil industry by-products: d I. The exhaust foot cake. Biomass Bioenergy 2000;18:257e62.

[7] Chouchene A, Jeguirim M, Khiari B, Trouv�e G, Zagrouba F. Study on theemission mechanism during devolatilization/char oxidation and directoxidation of olive solid waste in a fixed bed reactor. J Anal Appl Pyrol 2010;87:168e74.

[8] Droussi Z, D'orazio V, Provenzano MR, Hafidi M, Ouatmane A. Study of thebiodegradation and transformation of olive-mill residues during composting

ill wastewater on dry biomasses: Impact on chemical properties andrgy.2014.10.035

N. Kraiem et al. / Energy xxx (2014) 1e11 11

using FTIR spectroscopy and differential scanning calorimetry. J Hazard Mater2009;164:1281e5.

[9] Encinar JM, Gonz�alez JF, Martínez G, Rom�an S. Catalytic pyrolysis of exhaustedolive oil waste. J Anal Appl Pyrol 2009;85:197e203.

[10] Chouchene A, Jeguirim M, Trouv�e G, Favre-Reguillon A, Le Buzit G. Combinedprocess for the treatment of olive oil mill wastewater: absorption on sawdustand combustion of the impregnated sawdust. Bioresour Technol 2010;101:6962e71.

[11] Chouchene A, Jeguirim M, Favre-Reguillon A, Trouv�e G, Le Buzit G, Khiari B,et al. Energetic valorisation of olive mill wastewater impregnated on low costabsorbent: sawdust versus olive solid waste. Energy 2012;39:74e81.

[12] Jeguirim M, Chouch�ene A, R�eguillon AF, Trouv�e G, Le Buzit G. A new valor-isation strategy of olive mill wastewater: impregnation on sawdust andcombustion. Resour Conserv Recycl 2012;59:4e8.

[13] Elmay Y, Trouv�e G, Jeguirim M, Said R. Energy recovery of date palm residuesin a domestic pellet boiler. Fuel Process Technol 2013;112:12e8.

[14] Limousy L, Jeguirim M, Dutourni�e P, Kraiem N, Lajili M, Said R. Gaseousproducts and particulate matter emissions of biomass residential boiler firedwith spent coffee grounds pellets. Fuel 2013;107:323e9.

[15] Verma VK, Bram S, Delattin F, Laha P, Vandendael I, Hubin A, et al. Agro-pelletsfor domestic heating boilers: standard laboratory and real life performance.Appl Energy 2012;90:17e23.

[16] Cardozo E, Erlich C, Alejo L, Fransson TH. Combustion of agricultural residues:an experimental study for small-scale applications. Fuel 2014;115:778e87.

[17] Garcia-Maraver A, Zamorano M, Fernandes U, Rabaçal M, Costa M. Relation-ship between fuel quality and gaseous and particulate matter emissions in adomestic pellet-fired boiler. Fuel 2014;119:141e52.

[18] Lehtikangas P. Quality properties of pelletised sawdust, logging residues andbark. Biomass Bioenergy 2001;20:351e60.

[19] Jeguirim M, Dorge S, Trouv�e G. Thermogravimetric analysis and emissioncharacteristics of two energy crops in air atmosphere: Arundo donax andMiscanthus giganthus. Bioresour Technol 2010;101:788e93.

[20] Dorge S, Jeguirim M, Trouv�e G. Thermal degradation of Miscanthus pellets:kinetics and aerosols characterization. Waste Biomass Valorization 2011;2:149e55.

[21] El May Y. Measurement of gaseous and particulate pollutants during com-bustion of date Palm wastes for Energy recovery. Aerosol Air Qual Res2012;12:814e25.

[22] Obernberger I, Thek G. Physical characterisation and chemical composition ofdensified biomass fuels with regard to their combustion behaviour. BiomassBioenergy 2004;27:653e69.

[23] Ait Baddi G, Hafidi M, Gilard V, Revel J-C. Characterization of humic acidsproduced during composting of olive mill wastes: elemental and spectro-scopic analyses (FTIR and 13 C-NMR). Agronomie 2003;23:661e6.

Please cite this article in press as: Kraiem N, et al., Impregnation of olive mcombustion performances, Energy (2014), http://dx.doi.org/10.1016/j.ene

[24] Munir S, Daood SS, Nimmo W, Cunliffe AM, Gibbs BM. Thermal analysis anddevolatilization kinetics of cotton stalk, sugar cane bagasse and shea mealunder nitrogen and air atmospheres. Bioresour Technol 2009;100:1413e8.

[25] El may Y, Jeguirim M, Dorge S, Trouv�e G, Said R. Study on the thermalbehavior of different date palm residues: characterization and devolatilizationkinetics under inert and oxidative atmospheres. Energy 2012;44:702e9.

[26] Jeguirim M, Trouv�e G. Pyrolysis characteristics and kinetics of Arundo donaxusing thermogravimetric analysis. Bioresour Technol 2009;100:4026e31.

[27] Jensen Anker, Dam-Johansen Kim, Wojtowicz Marek A, Serio Michael A. TG-FTIR study of the Influence of potassium Chloride on Wheat Straw pyrolysis.Energy Fuels 1998;12:929e38.

[28] AFNOR. Norme europ�eenne, Norme française NF EN 14961-1/;: Bio-combustibles solides, Classes et sp�ecifications des combustibles, Partie 1/:Exigences g�en�erales. 2010.

[29] Gonz�alez JF, Gonz�alez-Garcı

a CM, Ramiro A, Gonz�alez J, Sabio E, Ga~n�an J, et al.Combustion optimisation of biomass residue pellets for domestic heating witha mural boiler. Biomass Bioenergy 2004;27:145e54.

[30] Rabaçal M, Fernandes U, Costa M. Combustion and emission characteristics ofa domestic boiler fired with pellets of pine, industrial wood wastes and peachstones. Renew Energy 2013;51:220e6.

[31] Díaz-Ramírez M, Sebasti�an F, Royo J, Rezeau A. Influencing factors on NOXemission level during grate conversion of three pelletized energy crops. ApplEnergy 2014;115:360e73.

[32] Association d'Initiatives Locales pour l'Energie et l'Environnement. Lesr�esultats des tests de combustion en laboratoire et sites pilotes, Colloque finaldu projet Life Green Pellets 23 septembre e Rennes n.d.

[33] Fernandes U, Costa M. Particle emissions from a domestic pellets-fired boiler.Fuel Process Technol 2012;103:51e6.

[34] Zhang Y, Gong X, Zhang B, Liu W, Xu M. Potassium catalytic hydrogen pro-duction in sorption enhanced gasification of biomass with steam. Int JHydrogen Energy 2014;39:4234e43.

[35] Mitsuoka K, Hayashi S, Amano H, Kayahara K, Sasaoaka E, Uddin MA. Gasifi-cation of woody biomass char with CO2: the catalytic effects of K and Caspecies on char gasification reactivity. Fuel Process Technol 2011;92:26e31.

[36] Torvela T, Tissari J, Sippula O, Kaivosoja T, Leskinen J, Vir�en A, et al. Effect ofwood combustion conditions on the morphology of freshly emitted fineparticles. Atmos Environ 2014;87:65e76.

[37] Vassilev SV, Baxter D, Andersen LK, Vassileva CG. An overview of the chemicalcomposition of biomass. Fuel 2010;89:913e33.

[38] Williams LB, Metge DW, Eberl DD, Harvey RW, Turner AG, Prapaipong P,Poret-Peterson AT. What makes a natural clay antibacterial. Environ SciTechnol 2011;45:3768e73.

ill wastewater on dry biomasses: Impact on chemical properties andrgy.2014.10.035