vermicomposting of winery wastes: a laboratory study

Journal of Environmental Science and Health Part B, 40:659–673, 2005Copyright C© Taylor & Francis Inc.ISSN: 0360-1234 (Print); 1532-4109 (Online)DOI: 10.1081/PFC-200061595

Vermicomposting of WineryWastes: A Laboratory Study

Rogelio Nogales, Celia Cifuentes, and Emilio BenıtezEstacion Experimental del Zaidın, CSIC, Granada, Spain

In Mediterranean countries, millions of tons of wastes from viticulture and winery in-dustries are produced every year. This study describes the ability of the earthwormEisenia andrei to compost different winery wastes (spent grape marc, vinasse biosolids,lees cakes, and vine shoots) into valuable agricultural products. The evolution of earth-worm biomass and enzyme activities was tracked for 16 weeks of vermicomposting, ona laboratory scale. Increases in earthworm biomass for all winery wastes proved lowerthan in manure. Changes in hydrolytic enzymes and overall microbial activities duringthe vermicomposting process indicated the biodegradation of the winery wastes. Ver-micomposting improved the agronomic value of the winery wastes by reducing the C:Nratio, conductivity and phytotoxicity, while increasing the humic materials, nutrientcontents, and pH in all cases. Thus, winery wastes show potential as raw substrates invermicomposting, although further research is needed to evaluate the feasibility of suchwastes in large-scale vermicomposting systems.

Key Words: Spent grape marc; Lees cake; Vinasse biosolids; Vine shoots; Vermicompost-ing, Eisenia andrei; Enzymes activities; Chemical and phytotoxic properties.

INTRODUCTION

Wine production is a major food industry in the world, especially in countrieswith a Mediterranean climate. In the year 2000, approximately 275 106 Hl ofwine were produced in the world, 60% of this volume in countries in the Mediter-ranean area. Viticulture and the winery industry generate huge amounts ofwastes and by-products, the disposal of which raises a serious environmentalissue in the main grape-growing regions.

The main waste of the viticulture activities is the vine shoot (VS), wastegenerated during the pruning of the grapevines (Fig. 1). The principal by-product of the winery industry is the grape marc (GM), a by-product com-prising grape stalks, seeds, and skins left over after the crushing, draining,

Received July 1, 2004.Address correspondence to Rogelio Nogales, Estacion Experimental del Zaidın, CSIC,c/Profesor Albareda, 1, 18008-Granada, Spain; E-mail: [email protected]

659

660 Nogales, Cifuentes, and Benıtez

Figure 1: Processing and by-products of the viticulture activity and winery industry.

and pressing stages of wine production. Grape marc is commonly processedto produce alcohol and tartaric acid, which results in a new lignocelluloseby-product called spent grape marc (SGM). This by-product may be used asfuel for heating or for power-generating plants, as soil mulches, as organicamendments prior to composting with other organic wastes, and as animalfeedstuff.[1−3] In addition, the wine making produces other by-products, suchas the wine lees, the material that accumulates in the bottom of grape-juice orwine-fermentation tanks. This by-product is used to make alcohol and tartrates,leading to a new solid by-product named lees, cake (LC). Finally, the distilla-tion of the alcohol from low-quality wine, from wine lees, and from grape marcproduces large quantities of a viscose, acidic wastewater known genericallyas vinasse. The high polluting load of this wastewater has forced its purifica-tion through chemical and biological treatments,[4] rendering a purified liquideffluent and a solid organic waste named vinasse sludge or biosolid vinasse(BV).

A considerable number of studies have been made on the use of epigeicearthworms in composting processes using various organic materials, suchas manure, municipal biosolids, and agroindustrial wastes.[5] In this process,called “vermicomposting,” the action of earthworms on organic wastes is phys-ical and biochemical. The physical process includes the aeration, mixing, andgrinding of substrates, while the biochemical process involves microbial de-composition of organic wastes in the intestine of earthworms and outside of theearthworms. During vermicomposting, nutrients are released and convertedfrom organic wastes, and there is evidence that pathogens do not survive thisprocess.[6] Vermicomposting also accelerates organic-matter stabilization[7] andgenerates end products (vermicomposts) that have a high content in microbial

Vermicomposting of Winery Wastes 661

matter, stabilized humic substances, and chelating as well as phytohormonalelements.[8]

In the monitoring of the vermicomposting process, some enzyme activi-ties have been postulated as bioindicators of this process.[9,10] Dehydrogenasesmake up a very important enzyme group for evaluating vermicomposting pro-cesses because biological oxidation of organic compounds is generally a dehydro-genation process. In addition, this enzyme activity has been used as an indicatorof the microorganism activity during composting and vermicomposting.[11,12] Ofspecial interest in monitoring organic-matter stabilization are β-glucosidase,urease, and phosphatase, hydrolytic enzymes involved in the C, N, and P cycles,respectively.[9]

The aim of the present study was to evaluate the role of the earthwormsin composting wastes from viticulture and winery industries. The suitability ofthe different wastes was assessed by monitoring the growth and reproductionof earthworms, as well as tracking four enzyme activities over the course ofa 16-week laboratory experiment. In addition, the chemical composition andphytotoxicity of initial substrates as well as end products were also determined.

MATERIAL AND METHODS

Earthworms, Substrates, and TreatmentsClitellated and non-clitellated earthworms of the species Eisenia andrei

were obtained from a culture bank at the Estacion Experimental del Zaidın(CSIC), Granada, Spain. The spent grape marc (SGM) was obtained from awinery-distillery industry (Movialsa, Campo de Criptana, Spain), and the leescake (LC) and the biosolid vinasses (BV) from a vinasse wastewater treatmentplant (Tomelloso, Spain). Finally, the vine shoots (VS) were provided by theGonzalez-Byass Company (Jerez, Cadiz, Spain).

Three treatments comprising the following viticulture and winery by-products were examined: (SGM): spent grape marc, (LC/VS): lees cake mixedwith vine shoot in a 2:1 ratio (wet-weight basis), and (BV/VS): biosolid vinassemixed with vine shoot in a 2:1 ratio (wet-weight basis). The fourth treatmentwas manure, used as control (M). Each treatment was replicated three times.

Experimental Layout and ProcedureA total of 200 gr (dry-weight basis) of each substrate was placed in 1 L plastic

containers made from 12-cm lengths of PVC pipe (12 cm internal diameter)with a fine nylon mesh held in place at the bottom. Ten grams, equivalent to20 earthworms (clitellated and non-clitellated), were added to this material.The moisture content of the substrates was maintained at 80–85% throughoutthe vermicomposting period, and the containers were kept in darkness at 25◦C.


Throughout a 16-week vermicomposting period, the number and weight of theearthworms were measured every two weeks. The sorganic substrate in thecontainer was emptied and the earthworms were manually counted, weighed,and examined for sexual development. All earthworms and organic substratewere then returned to the container. Every four weeks a sample of the organicsubstrate was taken and stored in a plastic vial at 4◦C until enzyme activitiescould be determined. The chemical composition and the phytotoxicity of theinitial substrates and end products were also determined.

Chemical and Phytotoxicity AnalysisThe pH was measured with a glass electrode using a 1:2.5 sample:water

ratio. Total organic C and total N were determined by the dichromate oxidationand Kjeldahl methods, respectively.[13] Total humic substances were extractedwith a 0.1 M Na4P2O7-0.1 M NaOH solution. The extract was acidified to pH 1.0with H2SO4, and centrifuged to obtain humic acids (HA).[14] The water-solublecarbon (WSC) was extracted at 60◦C for 1 h with distilled water (1:10, w:v) andthen determined with potassium dichromate and sulphuric acid digestion at160◦C for 30 min. A spectrophotometric method was used to evaluate the Cr+3

produced by the reduction of Cr+6 (590 nm).[15] Total P was measured by thenitrovanadomolybdate method, total K was measured by photometry,[16] afterdigestion of the samples with H2SO4 + H2O2. Total micronutrients (Fe, Mn,Cu, and Zn) were determined by atomic-absorption spectrometry (AAS) afterdigestion of the samples with HNO3:HClO4.[17] The phytotoxicity bioassay wasa slight modification of the method described by Zucconi et al.[18] Water extracts(1:5) from the initial substrates and end products were incubated (25◦C) in thedark for 24 h with cress seeds (Lepidium sativum L.). Responses were evaluatedas the germination index (GI) calculated according to Eq. (1), where G andL are the germination percentage and radicle growth of organic substrates,respectively, and Go and Lo are the germination percentage and radicle growthof the control (distilled water):

GI = (G/Go) × (L/Lo) × 100 (1)

Enzyme AssaysFor the determination of the dehydrogenase activity (DH-ase), 0.2 g of or-

ganic sample was incubated for 20 h at 25◦C with 0.5 ml of 0.4% 2-p-iodophenyl-3 p-nitrophenyl-5 tetrazolium chloride (INT) as a substrate. Iodonitrotetra-zolium formazan (INTF) produced in the reduction of INT was extracted with amixture of acetone: tetrachloroetene (1.5:1) and measured in a spectrophotome-ter at 490 nm.[19] For the determination of β-glucosidase and phosphatase activ-ity, two ml of 0.05 M 4-nitrophenyl-β-D-glucanopyranoside (PNG) and 0.115 M4-nitrophenyl phosphate (PNPP) were used as the substrate, respectively. After


0.2 g of organic sample was incubated at 37◦C for 2 h with 2 ml of maleate bufferat pH 6.5, the samples were kept at 2◦C for 15 min to stop the reaction, and thep-nitrophenol (PNP) produced in the enzymatic reactions was extracted anddetermined at 398 nm.[20] Finally, to determine urease activity, 2 ml of 0.1 MpH 7.0 phosphate buffer and 0.5 ml 6.4% urea were added to 0.2 g of organicsample, and then the mixture was incubated at 30◦C for 90 min and the volumewas increased to 10 ml with distilled water. The ammonium released was mea-sured using an ammonium-selective electrode (ORION Research Inc., Beverly,MA, mod. 95-12). A control without urea was used with each sample.[21]

Statistical AnalysisAll results are the means of three replicates. Data were subjected to an

analysis of variance (ANOVA) using Statgraphics Plus 5.1 statistical software(Statistical Graphics Corp., Princeton, NJ), and Duncan’s multiple range testwas used to separate the means.

RESULTS AND DISCUSSION

Total Biomass and Number of Earthworms Duringthe Vermicomposting ProcessNo mortality of earthworms was detected in any of the substrates during

the 16-week experimental period. In the manure, only substrate (M), the totalbiomass of the 20 initial earthworms increased, reaching a maximum weight of21.78 ± 0.63 g biomass at week 4 (Fig. 2). At week 4, all initial earthworms hada developed clitellum and some cocoons were observed in the substrate. Fromthis week on, there was a decline in earthworm biomass, especially significantfrom 6 to 12 weeks. However, the number of earthworms increased appreciably,newly hatched earthworms appearing from the sixth week, reaching a maxi-mum number (94 ± 2 earthworms) at the end of the experimental period (Fig. 3).The earthworms counted at the end of the experimental period had low weights(90 ± 1.7 mg earthworm−1) and, in any case, had a clitellum. The absence of theclitellum and the low weight of the earthworms recorded after 16 weeks implythat all the fresh substrate contained in treatment (M) had been consumed andthat more manure would be necessary in order to maintain earthworm growthand reproduction.

Maximum earthworm biomass was also recorded at week 4 in the spentgrape marc (17.62 ± 1.81 g) and in the mixture of vinasse biosolids withvine shoots (16.16 ± 0.06 g), whereas in the mixture of lees cake and vineshoots the maximum was registered at week 2 (12.27 ± 0.20 g) (Fig. 2). Asin the manure, the total earthworm biomass declined afterward and conse-quently the initial earthworms lost their clitellum, although the total number


Figure 2: Evolution of the earthworm biomass during the vermicomposting process. SGM:spent grape marc; LC/VS: lees cake mixed with vine shoots; VB/VS: vinasse biosolids mixedwith vine shoots; M: manure. LSD denotes the least significant difference (ANOVA, P < 0.05)between weeks and treatments.

of earthworms increased due to the hatching of new earthworms (Fig. 3). Inall winery by-products, higher numbers of earthworms were recorded at theend of the experimental period than at the beginning (41 ± 2.5 earthwormsin SGM, 37 ± 2.6 earthworms in LC/VS, and 44 ± 3.6 earthworms in VB/VS),

Figure 3: Evolution of the number of earthworms over the vermicomposting process. SGM:spent grape marc; LC/VS: lees cake mixed with vine shoots; VB/VS: vinasse biosolids mixedwith vine shoots; M: manure. LSD denotes the least significant difference (ANOVA, P < 0.05)between weeks and treatments.


although their weights were very low (161 ± 3.5 mg earthworm−1 in SGM, 167mg earthworm−1 in LC/VS, and 155 mg earthworm−1 in VB/VS).

The results of this laboratory study suggest that the different winery by-products assayed may be suitable substrates for vermicomposting because theypromoted the growth and reproductivity of earthworms. Comparatively, earth-worms in the spent grape marc (SGM) and in the mixture of vinasse biosolidsand vine shoots (VB/VS) reached a higher biomass than in the mixture of leescake and vine shoots (LC/VB), the increases of earthworm biomass in theselatter substrates being similar to or slightly less than that recorded in otherlaboratory studies using organic wastes from the olive-oil,[22] dairy, and pa-per industries,[23,24] or from urban biosolids.[9] Nevertheless, the best resultsin terms of weight and earthworm reproduction resulted with manure alone,known to be one of the best natural feeds for epigeic worms.

Evolution of Enzyme Activities During theVermicomposting ProcessIn the manure (M) and spent grape marc (SGM), initial DH-ase activity

increased significantly after four weeks and then decreased sharply, with astabilization period (between months 4 and 8), until the end of the vermicom-posting period (Fig. 4). This decrease, which would indicate a lower microbialgrowth and enzyme synthesis by microorganisms,[10,25] could be a consequenceof the disappearance of available organic substrates (WSC) due to the vermi-composting process. In fact, the WSC concentration (Table 1), an indicator of

Figure 4: Evolution of dehydrogenase activity over the vermicomposting process. SGM:spent grape marc; LC/VS: lees cake mixed with vine shoots; VB/VS: vinasse biosolids mixedwith vine shoots; M: manure. LSD denotes the least significant difference (ANOVA, P < 0.05)between weeks and treatments.


Table 1: Characteristics of the initial substrates (IS) and end products (EP).

SGM LC/VS VB/VS M

IS EP IS EP IS EP IS EP

TOC g kg−1 546* 418 470* 365 503* 345 466* 276TKN g kg−1 15.6 14 18.3 28* 25.2 26.8 14.6 20.6*C/N 35* 29 26* 13 20* 13 32* 13HA g kg−1 0.22 4.45* 0.13 8.1* 0.20 12.3* 5.32 13.81*WSC g kg−1 9.43* 1.48 5.11* 0.34 17.58* 0.61 9.85* 0.81Polyphenols g kg−1 2.9* 1.7 32* 7 18* 4 2 1.7P205g kg−1 2.23 4.97* 3.98 8.82* 5.86 13.4* 4.37 9.55*K2O g kg−1 20.8* 18.2 10.7* 5.2 9.2 8.8 8.2 7.1*Fe mg kg−1 623 2497* 1163 4396* 1091 6733* 1971 6221*Mn mg kg−1 8 53* 13 96* 20 149* 73 185*Cu mg kg−1 22 30* 53 73* 100 171* 31 56*Zn mg kg−1 22 62* 13 114 57 209* 33 142*EC dS m−1 3* 1.66 5.12* 0.79 4* 1.02 4.52* 1.82pH 4.82 7.24* 6.38 7.68* 6.53 7.44* 7.29 7.79Germination index % 61 93* 2 68* 63 81* 37 64*

TOC: total organic carbon, TKN: total Kjeldahl nitrogen; C/N: carbon/nitrogen ratio, HA: humicacids, EC: electrical conductivity.∗Indicates a least significant difference (ANOVA p< 0.05) between the initial substrate andthe end product.

the most easily metabolizable organic matter,[25] was significantly higher inthis substrate at the beginning than at the end of the vermicomposting period.

The mixture of lees cake with vine shoots (LC/VS) showed a low initial DH-ase activity (Fig. 4). During the first weeks of vermicomposting, DH-ase activityincreased significantly, reaching a maximum at four weeks. Transit throughthe digestive system of the earthworms breaks down the organic matter in thissubstrate, increasing the surface:volume ratio,[26] and thus also the number ofmicroorganisms in this treatment. These modifications, along with the 80–85%moisture maintained during the vermicomposting process, would account forthe increase in the easily available organic matter (WSC) in this mixture duringthis period. From four weeks onward, DH-ase activity decreased significantly,possibly as a consequence of the decline in WSC, reaching similar values tothose found in the control (M) treatment at the end of the vermicompostingprocess.

On the contrary, the mixture of vinasse biosolids and vine shoots displayedthe highest initial DH-ase activity (Fig. 4), presumably related to the high lev-els of easily available carbon contained in this mixture (Table 1). During thevermicomposting, the behavior of this enzyme activity was similar to that foundin treatments M and SGM. After an initial non-significant increase during thefirst four weeks, DH-ase activity decreased, reaching its lowest activity at theend of the 16-week vermicomposting period. This implies that most of the easilyavailable organic carbon contained in this substrate had been decomposed by


Figure 5: Evolution of β-glucosidase activity over the vermicomposting process. SGM: spentgrape marc; LC/VS: lees cake mixed with vine shoots; VB/VS: vinasse biosolids mixed withvine shoots; M: manure. LSD denotes the least significant difference (ANOVA, P < 0.05)between weeks and treatments.

the combined action of microorganisms and earthworms during the vermicom-posting process.

The activity of β-glucosidase, which hydrolyzes terminal non-reducing β-D-glucose residues, increased significantly during the first eight weeks in themanure (M) and in the mixture of vinasse biosolids and vine shoots (VB/VS)(Fig. 5). This fact was probably due to the release of glucosides during this pe-riod. Afterward, β-glucosidase activity fell until the end of the vermicompostingprocess, indicating the depletion of readily available organic substrates duringthe last periods of the vermicomposting. These patterns resemble those reportedby other authors for vermicomposting process of other organic wastes.[9,10]

In the mixture of lees cake with vine shoot (LC/VB), β-glucosidase activityalso increased during the first four weeks, and, after a decrease from fourto eight weeks, this activity stabilized until the end of the vermicompostingperiod (Fig. 5). By contrast, in the spent grape marc (GMS), where initiallyβ-glucosidase activity was higher due to the greatest amount of total organiccarbon recorded in this substrate (Table 1), this activity declined lineally overthe vermicomposting period, at the end reaching the lowest values in all thesubstrates assayed.

The activity of urease, which catalyzes the hydrolysis of urea in CO2 andNH4, was at first significantly lower in the mixture of lees cake and vineshoot (LC/VS) than in the other substrates (Fig. 6), perhaps because this mix-ture contained high amounts of toxic substances such as phenolic compounds(32 g kg−1), which inhibit this activity.[27] Partial degradation of these com-pounds boosted urease activity during the first four weeks, and afterward this


Figure 6: Evolution of urease activity over the vermicomposting process. SGM: spent grapemarc; LC/VS: lees cake mixed with vine shoots; VB/VS: vinasse biosolids mixed with vineshoots; M: manure. LSD denotes the least significant difference (ANOVA, P < 0.05)between weeks and treatments.

enzyme activity declined until the end of the vermicomposting period. Ure-ase activity was initially higher in the mixture of vinasse biosolids and vineshoots (VB/VS) than in the other substrates, due presumably to the higherlevels of organic-N substrates in this organic material or to its higher mi-crobial biomass (Table 1). In these substrates, urease activity decreased dur-ing the vermicomposting process until the end of the experimental period,implying that urea-type substrates contained in these materials were de-graded by the microorganims in the organic substrate and in the gut of theearthworms.

The high phosphatase activity initially recorded in the VB/VS treatment(between 2.5 and 3 times higher than in the other substrates assayed; Fig. 7)could be related, as reported in other biosolids,[9,29] to the high amount of or-ganic phosphate compounds present in the vinasse biosolids, which may actas inducers of the enzyme synthesis.[28] During the first four weeks, the phos-phatase activity decreased sharply in this treatment, afterward remaining sta-ble until the end of the experimental period. In the treatments (M) and (LC/VB)the phosphatase activity showed no significant changes during the overall ver-micomposting process. Phosphatase stability was also observed in the spentgrape marc, after a fall in this activity between four and eight weeks. Stabilityof phosphatase activity during the last period of the vermicomposting processimplies that the substrates contained sufficient available organic phosphorusto maintain this activity or to immobilize this enzyme in the microbial cells ofthe humus matrix.[29]


Figure 7: Evolution of phosphatase activity over the vermicomposting process. SGM: spentgrape marc; LC/VS: lees cake mixed with vine shoots; VB/VS: vinasse biosolids mixed withvine shoots; M: manure. LSD denotes the least significant difference (ANOVA, P < 0.05)between weeks and treatments.

Changes in Chemical Composition and Phytotoxicityof the SubstratesThe vermicomposting process significantly altered physical and chemical

properties of different assayed substrates (Table 1). The end products weremuch darker in color than at first and had been processed into a homogeneousmixture after 16 weeks of combined action of earthworms and microorganisms.A fraction of total organic carbon contained in the winery by-products was lostas CO2 (between 19 and 31%) by the end of the vermicomposting period. Thesereductions were similar to or greater than those recorded in other urban andagroindustial wastes,[10,24,30] although they were smaller than in the manuresubstrate. Microorganisms in the intestine of earthworms and gut enzymes, aswell as microorganisms present in the substrate, were involved in the decom-position of organic matter contained in the substrates.[31] Due to the reductionof total organic carbon and to the scant changes or increases in total Kjeldahlnitrogen by the end of the vermicomposting period, the C:N ratios of all endproducts were lower. According to Senesi,[32] a decline of C:N ratio to less than20 indicates an advanced degree of stabilization and maturity of organic mat-ter. This took place in all end products, except in the spent grape marc, wherethe vermicompost had a C:N ratio of 29.

Comparatively, the end products had significantly higher levels of humicacids than did the initial substrates in all the treatments assayed (Table 1).Increases of humic acids imply that the organic matter contained in the ini-tial substrates was partly humified during the vermicomposting period. Water-soluble carbon significantly diminished during vermicomposting and the end


product had low WSC levels. These reductions apparently resulted because theWSC contains the most easily metabolizable fraction of organic matter,[25,33]

and therefore constitutes the fraction most quickly degraded by the combinedaction of the microorganisms and earthworms.[9] In addition, a small portionof WSC probably disappeared as leachates drained by the irrigation of the sub-strates contained in the pots. On the other hand, the levels of polyphenols alsosignificantly fell at the end of the vermicomposting period. This implies thatthe vermicomposting, as in other aerobic processes,[34,35] effectively degradesthese toxic compounds.

Total phosphorus and total micronutrients increased by the end of thevermicomposting period, apparently because of mineralization of organicmatter.[30] By contrast, total potassium concentrations and conductivity werelower in the end products than in the initial substrates. These decreases may beattributed to the leaching of soluble salts by excess water that drained throughsubstrate contained in each pot. Benıtez et al.[36] have found that the leachatescollected during the vermicomposting process had high potassium concentra-tions and high conductivity. Finally, the vermicomposting was effective in rais-ing the acidic pH of the winery by-products, which at the end of the periodreached neutral values.

Finally, the mixture of lees cake and vine shoot (LC/VS) initially showed avery low germination index, indicating that this substrate had a high phytotoxi-city. The presence of phytotoxic compounds such as polyphenols in this substrateappears to be responsible for the strong inhibition of cress seed germination.The other substrates also initially had moderate phytotoxicity. After vermicom-posting, germination indexes increased significantly in all substrates, and theend products had values >60%, this being the level at which phytotoxicity isconsidered to disappear.[18] These increases, also observed in vermicompostingprocesses using other organic wastes,[10,22,23] rendered end products that canbe considered stable organic amendments useful for agriculture.

CONCLUSIONS

Our laboratory study demonstrated that vermicomposting is an alternativetechnology for the management of winery wastes (spent grape marc, vinassebiosolids, lees cakes, and vine shoots). Although results were best when earth-worms were fed with manure, Eisenia andrei also grew and reproduced fa-vorably in the winery wastes, especially in the spent grape marc and in themixture of vinasse biosolids and vine shoots. The combined action of microor-ganisms and earthworms enhanced biodegradation of the winery wastes, asreflected by the depletion of overall microbial and hydrolytic enzyme activities,especially during the final stages of the vermicomposting period. In comparisonwith the initial substrates, the resulting vermicomposts had lower C:N ratios,


conductivity, and phenolic-compound content. On the contrary, they had higherpH, humic acids, and nutrient contents (except potassium), and their phytotox-icity was significantly reduced. These changes improved the agricultural valueof the winery wastes, and the resulting vermicomposts may be used as organicamendments of soils, especially in those with low organic-matter content.

ACKNOWLEDGMENTS

This study was financed by the Comision Interministerial de Ciencia y Tec-nologıa (CICYT) through project REN2003-04693 and by Consejerıa de Edu-cacion y Ciencia of Junta de Andalucia through a coordinated action. E. Benıtezwishes to thank the Science and Technology Ministry “Programa Ramon y Ca-jal” for funding this research. We thank the Movialsa Company, the vinassewastewater plant, and the Gonzalez-Byass Company for providing the winerywastes used in this study. Finally, we would also like to thank David Nesbittfor assisting in the translation of the original manuscript into English.

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vermicomposting of winery wastes: a laboratory study

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