International Biodeterioration & Biodegradation 54 (2004) 39–44www.elsevier.com/locate/ibiod

Chemical and spectroscopic analyses of organic matter transformationsduring composting of olive mill wastes

Ghita Ait Baddia, Jos)e Antonio Alburquerqueb, Jos)e Gonz)alvezb,Juan Cegarrab, Mohamed Ha.dia ;∗

aD�epartement de Biologie, Unit�e Sol et Environment, Facult�e des Sciencies Semlalia, Universit�e Cadi Ayyad, BP, Marrakech 2390, MoroccobDepartment of Soil and Water Conservation and Organic Waste Management, Centro de Edafolog�'a y Biolog�'a Aplicada del Segura,

CSIC, P.O. Box 4195, Murcia 30080, Spain

Received 6 June 2003; received in revised form 29 October 2003; accepted 11 December 2003

Abstract

A piled mixture of olive-mill wastes and wheat straw was composted for 1 year and several of its characteristics (total organic carbonand nitrogen, organic matter, lignin, cellulose, hemicellulose, total fats, water-soluble phenols and the germination index of cress, Lepidiumsativum L.) were monitored. In addition, the compost was characterized by Fourier transform infrared spectroscopy (FTIR). The resultsshowed the e:ciency of composting in reducing olive-mill toxicity. The C/N ratio and organic matter degradation were 160.50 and560:50 g kg−1, respectively, after 12 months of composting. Lignin, hemicellulose and cellulose amounts were reduced during the process,their depletion rates reaching .nal values of 44%, 76% and 58%, respectively. In addition, the fat and water-soluble phenol contentsdecreased by 97% and 66%, respectively. The germination index reached 99% at the end of the process. This demonstrated the absenceof phytotoxicity in the mature compost. The FTIR spectra showed that there was an enrichment in the aromatic groups and a degradationof the aliphatic groups.? 2003 Elsevier Ltd. All rights reserved.

Keywords: Organic carbon; Fiber; Phenols; Germination index; Infrared spectroscopy

1. Introduction

Among the various types of environmental pollutionaBecting the Mediterranean basin, there is that caused byolive-mill wastes. These wastes are often illegally disposedof in the environment. In Morocco, olive oil is extracted inindustrial or semi-industrial olive mills (200 factories), butmost of it is still obtained in traditional mills (16 000 units orMaasras) (Dpv/Maee, 1997). The extraction process carriedout in modern factories either uses a semi-continuous sys-tem or a discrete system based on pressure. In the traditionalmills, the extraction is performed only by the latter system.These extraction procedures produce great amounts of olivemarc (solid waste) and olive-mill wastewaters (OMWW,liquid waste). The marc includes mainly skin, pulp and pith,whereas OMWW were composed of 50% of liquid from

∗ Corresponding author. Tel.: +212-4443-4649x544; fax: +212-4443-7412.

E-mail address: ha.di@ucam.ac.ma (M. Ha.di).

fruits and 50% of water added during the extraction (Zenjariet al., 1999).After extracting its remaining oil, the marc is tradition-

ally used for combustion in ovens and baths. However, theOMWW is poured directly into the sewage system, kept inevaporation lagoons or simply spread on the land, all toofrequently resulting in an important environmental pollution(Ait baddi and Ha.di, 2001).Composting is one of the technologies aimed at utilizing

olive-mill wastes and producing a fertilizer product fromsuch wastes. This process permits the return to croplands ofthe nutrients taken up by olive tree cultivation. Moreover,composting avoids some of the drawbacks (phytotoxicity,microbiota inhibition) often observed when these wastes aredirectly applied to the soil. In Morocco, where agriculturehas a signi.cant role, organic fertilizer production by com-posting of the olive-mill wastes can be the best and cheap-est solution for farmers. To obtain a high-quality fertilizer,particular attention must be paid to the progress of the com-posting process. The compost properties depend on the de-gree of transformation reached during the bioremediation.

0964-8305/$ - see front matter ? 2003 Elsevier Ltd. All rights reserved.doi:10.1016/j.ibiod.2003.12.004

40 G. Ait Baddi et al. / International Biodeterioration & Biodegradation 54 (2004) 39–44

Obviously, the transformation process is not completelyachieved in the composting plant, but it continues in the soilafter applying the compost, thereby increasing long-termfertility. In spite of the scarcity of mills interested in utiliza-tion of the wastes, especially marc, various authors (Tomatiet al., 1995; Cegarra et al., 1996, 2000; Madejon et al.,1998; Filippi et al., 2002) have recently shown the suitabil-ity of composting for disposal of these olive-mill wastes andby-products.In this work, a pile made by mixing olive marc, OMWW

and wheat straw was composted for 1 year. In order to de-termine compost stability and maturity, changes in severalparameters (organic carbon, total fats, water-soluble phe-nols, etc.) were monitored. Also, Fourier transform infrared(FTIR) spectroscopy was used to follow the increasing ma-turity of olive-mill wastes during composting.

2. Materials and methods

A pile made by mixing 280 kg olive marc, 20 kg wheatstraw and 85 l OMWW was composted for 1 year. The pilewas turned every 15 days to aerate and homogenize themixture. The microbial activity was measured by monitoringthe temperature of the pile. All analyses were performedafter taking samples at the beginning of composting andafter 1, 3, 6 and 12 months. The main characteristics of rawmaterials are shown in Table 1.

2.1. Analytical methods

Total organic carbon (TOC) was determined in 0:5 g(dry weight) portions of each sample, using Anne’s method(Aubert, 1978) and total nitrogen (TKN) was determined in0:5 g samples by the Kjeldahl method. Organic matter loss(OM-loss) was calculated from the initial (X1) and .nal (X2)ash contents according to the equation (Paredes et al., 1996)

OM-loss (g kg−1)

= (100− 100[(X1(100− X2)]=[X2(100− X1)])x 10:

Lignin and cellulose concentrations were determined in1-g portions of each sample (fresh weight) according tothe American National Standards Institute and AmericanSociety for Testing and Materials (1977a, b) and thehemicellulose concentration by subtracting the celluloseconcentration from the deligni.ed sample (holocellulose)obtained by the method of Browning (1967). The losses of

Table 1Main characteristics of raw materials

Raw material Moisture (g kg−1 f.w.) pH Ash (g kg−1) TOC (g kg−1 d.w.) TKN (g kg−1 d.w.) C/N ratio

Marc 340:4± 0:2 5:9± 0:26 50:8± 0:3 520:2± 1:4 6:7± 0:3 77.9OMWW 830:0± 0:7 4:9± 0:20 60:4± 2:8 10:0± 0:7 0:7± 0:2 14.3Wheat straw 90:5± 0:3 6:8± 0:17 200:2± 0:3 460:4± 2:8 7:4± 2:3 62.7

f.w., fresh weight; d.w., dry weight.

lignin, cellulose and hemicellulose (g kg−1 initial value)were frequently used (Nuntagij et al., 1989; Cegarra et al.,2000).Total lipid content was determined by extraction with di-

ethyl ether and later weighing. Water-soluble phenolic sub-stances were measured by a modi.ed version of the Folinmethod (Maestro et al., 1991). To determine the germinationindex (GI), eight Lepidium sativum L. (cress) germinationwas followed each petri dish (10 for each stage) for 72 h,according to the method of Zucconi et al. (1981). GI wascomputed as the product of the percentage of viable seeds bythe percentage of root length divided by 100. As in all testsnoted above, these analyses were performed in duplicate.

2.2. Fourier transform infra-red spectroscopy (FTIR)

The infrared spectra of each composting step wererecorded between 4000 and 400 cm−1 wavenumbers byusing a Perkin-Elmer 1600 FTIR. Pellets were prepared bymixing 2 mg ground sample with 300 mg KBr, later com-pressing the mixture under vacuum for 10 min. In order tolimit moisture interference, both composting samples andKBr were dried at 105◦C for 72 h before making pellets.

3. Results and discussion

3.1. Composting process

Table 2 shows a substantial decrease in both the organicmatter (total OM-loss 560:5 g kg−1) and C/N ratio (.nalvalue 16.5) during the process. As reported by Hsu and Lo(1999) for composting of separated pig manure, there wasalso a clear increase in ash and nitrogen content.OM losses were higher during the .rst 3 months of com-

posting, owing to the greater activity of microorganisms thatused a large quantity of easily available compounds. Later,the degradation of organic matter was restricted by the highlignin content of the composting substrate. Changes in thecontent of the main components of organic matter (lignin,cellulose and hemicellulose) during composting are shownin Table 3. The lignin was less degraded than cellulose andhemicellulose, this component being considered as the frac-tion most recalcitrant in relation to biodegradation (Lynch,1993). Hemicellulose was the most highly degraded com-ponent, degradation reaching nearly 76% by the end ofcomposting. According to Eiland et al. (2001), xylans and

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Table 2Changes in some parameters during composting of the olive-mill wastes–straw mixture (dry weight basis)

Time (months) Ash (g kg−1)∗ TOC (g kg−1)∗ TKN (g kg−1)∗ C/N ratio OM losses (g kg−1)∗

0 40:3± 17:2 460:4± 4:2 6:7± 0:3 69.3 01 50:3± 12:2 490:4± 2:5 7:4± 0:3 66.7 200:6± 0:43 70:4± 5:1 440:4± 3 8:7± 0:3 51.1 440:4± 0:36 80:2± 2:1 440:4± 3 10:4± 2:5 32.7 490:6± 212 90:3± 0:9 340:2± 3:5 20:1± 0:5 16.5 560:5± 1

TOC, total organic carbon; TKN, total Kjeldahl nitrogen; OM, organic matter; ∗, ± SD.

Table 3Lignin, cellulose and hemicellulose content and losses (±SD) during composting of olive-mill wastes/wheat straw mixture

Time (months) Contents (g kg−1, dry weight basis) Calculated losses (% initial value)a

Lignin Cellulose Hemicellulose Lignin Cellulose Hemicellulose

0 330:6± 20:9 244:5± 0:8 424:6± 4:7 0 0 01 340:8± 1:7 249:7± 6:9 417:4± 16:5 16:6± 4:8 18± 2 21± 43 360:3± 4:5 263:1± 5:2 401:0± 3:9 37:7± 4:4 38± 1:4 45:7± 16 390:1± 2:5 233:0± 2:7 244:8± 4:8 39:2± 3:4 50:3± 0:7 70± 0:3

12 400:9± 0:6 223:2± 1:3 221:7± 0:7 43:8± 3:6 58± 0:1 76± 0:3

aLosses expressed in relation to initial value (0 months) for each compound (lignin, hemicellulose and cellulose).

other constituents of the hemicellulose are more easily de-graded than cellulose and lignin. Thus, the capacity to de-grade hemicellulose is more widespread amongst microor-ganisms. Sanchez-Mondero et al. (1999) have reported thatthe degradation of cellulose and hemicellulose release car-bohydrate oligomers, which can be used as an energy sourceby microorganisms. In our experiment, all these degradationprocesses were more intense during the initial 3 months, themost active phase of the composting process.During composting, humi.cation reactions are related to

the above degradation processes, as humic substrates areproduced by the condensation and polymerization of aro-matic units such as phenolic compounds with cellular de-bris such as sugars and amino-acids (Tomati et al., 1995;Sanchez-Mondero et al., 1999).Compost stability and degree of maturity are strictly

related to the concentration of polyphenols and lipids(Saviozzi et al., 1987; Dinel et al., 1996). Also, Kirchmannand Widen (1994) reported that a high content of thesecompounds is related to compost immaturity. Golod (1968)con.rmed that lipids aBect the physical properties of thesubstrates and Solbraa (1979) found that phenolic com-pounds, especially tannins, reduce plant growth. Addition-ally, Pare et al. (1997) reported that the short-chain aliphaticacids and polyphenolic compounds released during aero-bic and anaerobic decomposition, reduce seed germination,root development and harvest yield. In our experiment, thedecrease of the lipid and water-soluble phenol content after12 months of composting were, respectively, 97% and 66%(Fig. 1). Filippi et al. (2002) related similar decreases withthe reduction of toxicity during the initial phase of the com-posting process. Polyphenol decrease was con.rmed by our

0

1

2

3

4

5

6

7

8

0 5 10 15

Time (months)

Pol

yphe

nols

and

lipi

d co

nten

ts (

%)

Polyphenolslipid content

Fig. 1. Changes in lipid and water-soluble phenol contents during thecomposting of olive-mill waste–straw mixture.

quantitative and qualitative studies of these compounds (Aitbaddi et al., 2003a). The phenol and lipid decreases coin-cided with a clear increase in the germination index (Fig. 2),the value of this parameter being higher than 50% after the.rst 3 months and reaching 99% by the end of composting.

3.2. Infrared spectra

In Fig. 3, a great resemblance between the .ve IR spec-tra can be observed, and only peak intensity diBers. A broadband centred on 3400 cm−1 is due to the hydrogen vibrations

42 G. Ait Baddi et al. / International Biodeterioration & Biodegradation 54 (2004) 39–44

Composting time (months)

Ger

min

atio

n In

dex

(%)

0 121086420

10

20

30

40

50

60

70

80

90

100

Fig. 2. Changes in the germination index (GI) during the composting ofthe olive-mill waste–straw mixture.

4000 3500 3000 2500 2000 1500 1000 500

Wave number (cm-1)

12

6

3

1

0

3426

.6

-292

5.8

-173

4.5

-165

4.1

-150

8.3 -1

384.

0

-124

6.8

-105

2.6

-582

.2

Fig. 3. FTIR spectra of composted olive-mill wastes at various stages ofmaturation.

of alcoholic OH, phenol or carboxyl groups (COOH), butalso to N–H vibrations of amides. The signal at 2925 cm−1

is due to C–H stretching vibrations of fatty acids, waxes andvarious aliphatic components. The band 1740 is more typi-cal of esters, whereas band at 1720 cm−1 is more typical ofthe CKO stretch of aliphatic carboxyl groups. Absorption

at 1620–1660 cm−1 is characteristic of aromatic CKC vi-brations, in addition to quinines, conjugated carboxyls andketones. The peak at 1540 cm−1 is characteristic of amide IIstructures, con.rming the richness of this compost in nitro-gen (Ouatmane et al., 2000). Aromatic skeletal vibration ofthe lignocellulosic materials absorbs at 1510–1520. Signalsaround 1460–1420 cm−1 are generated by –CH–, –CH2–and CH3 radicals and 1460 cm−1 by alkyl bending (scis-soring) and also lignins. Carbonates are known for absorp-tion around 1420 cm−1 (Kodoma, 1985). The sharp peak at1384 cm−1 may correspond to some of mineral constituents(ammonium bicarbonate formed by ammonia and CO2 re-leased during composting). Absorption 1200–1280 cm−1 isoften attributed to CH stretch and OH deformation of car-boxyl groups, but also to C–O stretching of ethers from aro-matic cycles and N–H of amide II. Another broad band cen-tred around 1040 cm−1 is attributed to Si–O–Si silicates, toaromatic ethers and polysaccharides (CH stretch) and to thegroup Si–O–C.The infrared spectra of the composted olive-mill

waste/wheat straw mixture exhibited the same band pat-tern, indicating that no noticeable qualitative changes haveoccurred during the composting process. Changes duringcomposting aBected only band intensities, indicating thatthe increase of composting time does not involve signi.cantchanges in the compost composition. In our experiment, theintensity of some peaks was changed with the compostingprogress. In particular, the peak at 2925 cm−1 decreasedas could correspond to a preferential biodegradation ofaliphatic structures. Further, the peak at 1740 cm−1 alsodecreased. This unexpected decrease in carboxyl groups,which is not a typical behaviour of composting material,can be explained by ester breakdown resulting in the re-lease of alkyl material and the persistence of free carboxylgroups. This is typical in some composting material, e.g.sewage sludge. These results agree with those of Bennyet al. (1996) and Ouatmane et al. (2000).In addition to the above observations, the peak at

1540 cm−1 decreased during the process, explaining thedegradation of peptide structures. In contrast, the peaks at1650 and 1511 cm−1 increased, showing the enrichmentin aromatic CKC as compared with aliphatic carbon. Thisenrichment in aromatic structures was con.rmed in our ear-lier studies about humic and fulvic acids characterization(Ait baddi et al., 2003b, c). On the other hand, the increaseat 1420 and 1044 cm−1 indicated greater ash content, whichagrees with the chemical analysis. With increasing dura-tion of composting, infrared spectra become close to thoseobtained for mature composts reported by others authors(Inbar et al., 1989; Benny et al., 1996; Ouatmane et al.,2000).The compost obtained (Tables 2 and 3) was rich in stabi-

lized organic matter, as determined by its chemical compo-sition, most of it being composed of lignin. This fraction isrecognized as being both poorly biodegradable and an im-portant precursor of soil humic substances. Also, it should

G. Ait Baddi et al. / International Biodeterioration & Biodegradation 54 (2004) 39–44 43

be stated that the compost exhibited a clear absence of phy-totoxicity, as shown by the .nal value of the germinationindex (Fig. 2), and could be either used as suitable soilamendment or organic fertilizer.

4. Conclusion

During composting of the olive-mill waste/wheat strawmixture, a substantial decrease in both the organic matter andC/N ratio and an increase in the nitrogen content were ob-served. The OM-losses were higher during the .rst 3 monthsof composting. The lignin was less degraded than celluloseand hemicellulose, the latter being the most degraded com-ponent at the end of the process. Important decreases inphenol and lipid were also observed and were accompaniedby a clear increase of the germination index. Degradationof both aliphatic and peptide structures and an enrichmentof aromatic structures, as compared to aliphatic carbon, wasalso recorded, suggesting increasing humi.cation with thecomposting progress. The compost obtained, with a substan-tial richness of stabilized organic matter and an absence oftoxicity, may be considered as a suitable soil amendment ororganic fertilizer.

Acknowledgements

This research has been supported by AECI (AgenciaEspanola de Cooperaci)on Internacional), JER 6013 associ)eeQa l’Agence Universitaire Francophone, and PRAD 02/10(Projet de Recherche Agronomique et D)eveloppementfranco-marocain).

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