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Short communication Influence of microbial inoculation and co-composting material on the evolution of humic-like substances during composting of horticultural wastes M del Carmen Vargas-Garcı ´a * , F. Francisca Sua ´rez-Estrella, M Jose ´ Lo ´pez, Joaquı ´n Moreno Unidad de Microbiologı ´a, Departamento de Biologı ´a Aplicada, Universidad de Almerı ´a, 04120 Almerı ´a, Spain Received 25 May 2005; received in revised form 19 January 2006; accepted 20 January 2006 Abstract Four different raw materials (olive-oil mill, pruning waste, rice straw and almond shell waste) used as additives were mixed with pepper plant wastes for composting purposes. Three bacterial strains isolated from prior composting processes and identified as Bacillus shackletonni, Streptomyces thermovulgaris and Ureibacillus thermosphaericus were added to every windrow and their effect on humic-like substances evolution was studied. In all the cases, an increase in the humification indices (humic to fulvic acids ratio, humification ratio and humification index) was obtained. On the other hand, inoculation significantly affected the humification indices, and differences due to both raw materials and microbial inoculants could be observed. When inoculated in almond shell and rice straw heaps respectively, B. shackletonni and U. thermosphaericus induced higher humification levels than those obtained for other raw material/inoculant combinations. Thus, the improvement of composting processes by means of inoculation seems to depend on properties of raw materials and microorganisms applied. # 2006 Elsevier Ltd. All rights reserved. Keywords: Compost; Agricultural wastes; Microbial inoculants; Humification indices 1. Introduction The agriculture practiced in the southeast of Spain (intensive under plastic agriculture) prevailing in the last years have favored the progressive impoverishment of soil and the accumulation of huge amounts of different kind of wastes, mainly of vegetal nature. Among the different proposals to lessen the negative effect derived from both aspects, compost- ing seems to be one of the most interesting, since its influence is twofold. First, the biotransformation of wastes by means of this process allows the elimination of potentially dangerous residues [1–3] and second, compost, the final product obtained, improves soil quality when it is added as an organic amendment [4,5]. Benefits of compost addition affect physical properties, such as bulk density or total porosity, chemical characteristics as cation exchange capacity, atmosphere or soil pH [6] and biotic factors, mainly microbial growth [7]. Nevertheless, these positive effects take place only when the compost applied shows an adequate state of maturity. In this sense, the addition of products with an incomplete stabilization of their organic matter fraction causes damage to plant roots, inhibition of seed germination, suppression of plant growth and nutrient starvation [8,9]. The lack of a clear definition of maturity makes difficult to evaluate when compost has reached this stability level. Many different parameters are involved in this process and some of them can be related to the changes that take place in this phase. For a long time, the C/N ratio has been used as an index of compost maturity [10,11], but there is not a correlation between its value and the biochemical constitution of the product [12], so it is not representative of the product composition. Other parameters have been proposed by different authors to monitor the composting process, among which the potential to degrade cellulose [13], the cation exchange capacity [14] or oxygen and CO 2 respirometry [15] can be mentioned. Nature and amount of humic substances are of interest as well, since they allow establishing the compost maturity [16,17] on the basis of the determination of the agronomical value of the final product [5]. Thus, several authors suggest the different alkali extractable fractions of the organic matter, such as total extractable carbon www.elsevier.com/locate/procbio Process Biochemistry 41 (2006) 1438–1443 * Corresponding author. Tel.: +34 950 015891; fax: +34 950 015476. E-mail address: [email protected] (M. del Carmen Vargas-Garcı ´a). 1359-5113/$ – see front matter # 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.procbio.2006.01.011

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Page 1: Influence of microbial inoculation and co-composting material on the evolution of humic-like substances during composting of horticultural wastes

Short communication

Influence of microbial inoculation and co-composting material

on the evolution of humic-like substances during composting

of horticultural wastes

M del Carmen Vargas-Garcıa *, F. Francisca Suarez-Estrella,M Jose Lopez, Joaquın Moreno

Unidad de Microbiologıa, Departamento de Biologıa Aplicada, Universidad de Almerıa, 04120 Almerıa, Spain

Received 25 May 2005; received in revised form 19 January 2006; accepted 20 January 2006

Abstract

Four different raw materials (olive-oil mill, pruning waste, rice straw and almond shell waste) used as additives were mixed with pepper plant

wastes for composting purposes. Three bacterial strains isolated from prior composting processes and identified as Bacillus shackletonni,

Streptomyces thermovulgaris and Ureibacillus thermosphaericus were added to every windrow and their effect on humic-like substances evolution

was studied. In all the cases, an increase in the humification indices (humic to fulvic acids ratio, humification ratio and humification index) was

obtained. On the other hand, inoculation significantly affected the humification indices, and differences due to both raw materials and microbial

inoculants could be observed. When inoculated in almond shell and rice straw heaps respectively, B. shackletonni and U. thermosphaericus induced

higher humification levels than those obtained for other raw material/inoculant combinations. Thus, the improvement of composting processes by

means of inoculation seems to depend on properties of raw materials and microorganisms applied.

# 2006 Elsevier Ltd. All rights reserved.

Keywords: Compost; Agricultural wastes; Microbial inoculants; Humification indices

www.elsevier.com/locate/procbio

Process Biochemistry 41 (2006) 1438–1443

1. Introduction

The agriculture practiced in the southeast of Spain (intensive

under plastic agriculture) prevailing in the last years have

favored the progressive impoverishment of soil and the

accumulation of huge amounts of different kind of wastes,

mainly of vegetal nature. Among the different proposals to

lessen the negative effect derived from both aspects, compost-

ing seems to be one of the most interesting, since its influence is

twofold. First, the biotransformation of wastes by means of this

process allows the elimination of potentially dangerous

residues [1–3] and second, compost, the final product obtained,

improves soil quality when it is added as an organic amendment

[4,5]. Benefits of compost addition affect physical properties,

such as bulk density or total porosity, chemical characteristics

as cation exchange capacity, atmosphere or soil pH [6] and

biotic factors, mainly microbial growth [7]. Nevertheless, these

positive effects take place only when the compost applied

* Corresponding author. Tel.: +34 950 015891; fax: +34 950 015476.

E-mail address: [email protected] (M. del Carmen Vargas-Garcıa).

1359-5113/$ – see front matter # 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.procbio.2006.01.011

shows an adequate state of maturity. In this sense, the addition

of products with an incomplete stabilization of their organic

matter fraction causes damage to plant roots, inhibition of seed

germination, suppression of plant growth and nutrient

starvation [8,9].

The lack of a clear definition of maturity makes difficult to

evaluate when compost has reached this stability level. Many

different parameters are involved in this process and some of

them can be related to the changes that take place in this phase.

For a long time, the C/N ratio has been used as an index of

compost maturity [10,11], but there is not a correlation between

its value and the biochemical constitution of the product [12],

so it is not representative of the product composition. Other

parameters have been proposed by different authors to monitor

the composting process, among which the potential to degrade

cellulose [13], the cation exchange capacity [14] or oxygen and

CO2 respirometry [15] can be mentioned. Nature and amount of

humic substances are of interest as well, since they allow

establishing the compost maturity [16,17] on the basis of the

determination of the agronomical value of the final product [5].

Thus, several authors suggest the different alkali extractable

fractions of the organic matter, such as total extractable carbon

Page 2: Influence of microbial inoculation and co-composting material on the evolution of humic-like substances during composting of horticultural wastes

M. del Carmen Vargas-Garcıa et al. / Process Biochemistry 41 (2006) 1438–1443 1439

Table 1

Enzymatic activities related to lignocellulose biodegradation observed in

microbial strains used as inoculants

Enzymatic

activity

Strain

B.

shackletonni

U.

thermosphaericus

S.

thermovulgaris

Xylanase � � +

Poly-phenoloxydase � � �Extracellular oxidase + + +

Laccase + + �Tyrosinase � + �Peroxidase + + +

and humic and fulvic acids, as well as the ratio between them,

as the best indicators of compost maturity [18–20]. Therefore,

humification of the organic matter is a key process in

composting and any factor showing influence on it must be

taken into account.

Microbial activity plays a leading role on transformations

occurring during humification processes [21]. Thus, inocula-

tion with proper microorganisms may activate the biodegrada-

tion of organic matter [22,23] or improve the final

characteristics of the compost [7,24]. When the substrates

composted are of agricultural origin, lignocellulosic sub-

stances constitute an important fraction of the total organic

matter, what potentially makes lignocellulolytic microorgan-

isms the most adequate to conduct the humification process

[25]. Some of the compounds released from lignocellulose

degradation as a consequence of microbial activity, such as

polyphenols, sugar and aminocompounds, seems to promote

the humus formation [26].

According to what has been stated above, this study

proposes the analysis of compost inoculated with lignocellu-

lolytic microorganisms, as well as the establishment of

differences in the evolution of humic-like substances caused

by these microbial strains during composting of green

wastes.

2. Materials and methods

2.1. Compost heaps

Sun-dried and chopped (20–30 mm pieces) pepper plant wastes (PPW) were

mixed with four raw materials (olive-oil mill waste: OMW, pruning waste: PrW,

rice straw: RS and almond shell: AS) subjected to similar treatment and

arranged in trapezoidal heaps (1 m � 1.5 m base; 1 m high) with weights

varying from 400 to 500 kg depending on heap composition. The four raw

materials and pepper plant wastes were mixed in the proportion (v/v) producing

a C/N ratio over 25:

� H

eap OMW: 75% PPW, 16% OMW and 9% AS;

� H

eap PrW: 75% PPW, 10% PrW and 15% AS;

� H

eap RS: 75% PPW, 10% RS and 15% AS;

� H

eap AS: 75% PPW and 25% AS.

The heaps were subjected to forced aeration (1100–1200 cm3 s�1 at intervals of

4 h) conducted through three PVC tubes (5 cm diameter) and turning fortnight,

as bio-oxidative phase lasted (45 days). Moisture content and pH were mon-

itored and adjusted to 50% (w/w) and 6.5, respectively throughout the process.

After the bio-oxidative phase, the heaps were maintained in maturation for an

additional period of four and a half months, which prolonged the whole process

for 180 days.

2.2. Microbial inocula

Three microbial strains isolated from composting heaps at different stages

and selected on the basis of their capacity to show enzymatic activities related to

lignocellulose degradation (Table 1) were assayed in relation to their influence

on both the evolution of the composting process and the final characteristics of

the product obtained. Enzymatic activities were determined as described by He

et al. [27] for xylanase activity, and following indications of Rayner and Boddy

[28] for the other activities. Identification of microorganisms was performed by

molecular methods based on the analysis of the sequence obtained from the

direct amplification of the 16s rDNA gene. The sequences used for identifica-

tion and the similarity values were X90640, Z68094, AJ250318 and 99.8%,

99.0%, 95.3%, respectively for Ureibacillus thermosphaericus, Streptomyces

thermovulgaris and Bacillus shackletonni. Inocula were scaled-up as follows:

microorganisms were sequentially cultured in conical 2 L flasks with 750 mL of

medium and 20 L autoclavable propylene recipients with 7.5 L of medium. The

organisms were cultured statically in nutrient broth for 4 days at 40 8C. Each

composting heap was inoculated with sufficient volume of microbial suspension

to reach a proportion of 106 to 107 colony-forming units g�1 (CFU g�1) of

waste. A total of 32 different windrows were set up, 24 of them were inoculated

(four substrates, three inocula and two repeats) and the remaining 8 were used as

uninoculated control heaps (two repeats also).

2.3. Analysis

Samples were extracted at different stages of the composting process (0, 14,

28, 45 and 180 days) and investigated in relation to inoculum persistence (plate

count on nutrient agar incubated at 40 8C for 2 days) and humic-like substances

concentration. Days for sampling were chosen coinciding with turning days to

secure that material was representative of the whole heap and not just super-

ficial. Total organic carbon (TOC) and nitrogen (TN) were determined accord-

ing to modified methods of Mebius [29] and Bremmer and Mulvaney [30],

respectively, while the modified method of Kononova [31] was used for total

humic extracts (THE), humic (HA) and fulvic acids (FA). Humification indices,

humification ratio (HR = THE/oxidizable carbon � 100), humification index

(HI = HA/oxidizable carbon � 100) and CHA/FA (HA/FA ratio), were calculated

according to Iglesias Jimenez and Perez Garcıa [19].

Five replicates were used in all analysis, and data obtained were subjected to

statistical analysis using Statgraphics plus 4.0 software. One way analysis of

variance (ANOVA) was performed to compare the heap mean values for the

different levels of sampling time, substrates and inoculation pattern, and to test

whether there were any significant differences among the means at the 95%

confidence level. In order to determine which means were significantly

(P < 0.05) different from which others, multiple comparison tests (Fishers’s

least significant difference) were used.

3. Results and discussion

Counting data obtained for the different microbial strains

used as inoculants are shown in Table 2. A decrease in the

number of CFUs could be observed in all the cases, being the

beginning of the bio-oxidative phase the time at which this

descend was higher. At the end of this active stage of the

process and along the curing phase, the quantitative presence of

these microorganisms became stabilized or even an increase in

the population density of some of them could be detected. The

establishment of comparisons is rather difficult since available

data in relation to the persistence of inoculants as the process

progress are scarce. Most of the studies regarding to inoculation

in composting processes describe modifications on the process

Page 3: Influence of microbial inoculation and co-composting material on the evolution of humic-like substances during composting of horticultural wastes

M. del Carmen Vargas-Garcıa et al. / Process Biochemistry 41 (2006) 1438–14431440

Table 2

Evolution of microbial inoculants in the composting heaps

Time (day) OMW heap PrW heap RS heap AS heap

B. shackletonni

0 6.76 � 0.14 6.85 � 0.29 6.90 � 0.16 6.76 � 0.20

15 5.81 � 0.40 5.95 � 0.22 5.81 � 0.14 5.50 � 0.19

30 6.57 � 0.19 5.31 � 0.16 5.30 � 0.15 5.81 � 0.21

45 6.22 � 0.28 5.37 � 0.14 5.37 � 0.23 5.46 � 0.28

180 6.14 � 0.30 5.82 � 0.23 5.46 � 0.23 5.96 � 0.29

U. thermosphaericus

0 7.01 � 0.07 6.72 � 0.25 6.92 � 0.08 7.01 � 0.11

15 6.26 � 0.36 6.40 � 0.45 6.56 � 0.17 5.98 � 0.37

30 6.12 � 0.11 5.72 � 0.28 5.58 � 0.18 6.05 � 0.23

45 6.03 � 0.28 6.02 � 0.22 5.36 � 0.23 6.02 � 0.21

180 6.06 � 0.20 5.58 � 0.13 6.35 � 0.19 6.02 � 0.09

S. thermovulgaris

0 6.61 � 0.11 6.84 � 0.05 6.86 � 0.14 6.72 � 0.22

15 5.68 � 0.23 5.18 � 0.17 5.09 � 0.15 5.03 � 0.09

30 5.46 � 023 5.07 � 0.12 5.02 � 0.08 5.09 � 0.18

45 5.28 � 0.19 5.18 � 0.16 5.20 � 0.19 5.20 � 0.15

180 5.31 � 0.20 5.37 � 0.22 5.39 � 0.26 5.27 � 0.20

Results are expressed as log10 CFU g�1. OMW: olive-oil mill waste; PrW:

pruning waste; RS: rice straw; AS: almond-shell waste.

evolution and/or in the final product characteristics [32–34],

variations on microbial diversity along the composting process

[22,35,36] or changes in the rhizosphere microbiota when the

compost is applied to soil as amendment [37]. In this study,

microbial population of inoculants, mainly B. shackletonni and

U. thermosphaericus, were just slightly lower than the counts

for general thermophilic microbiota and, even at some stages,

Fig. 1. Temperature evolution during composting of heaps made of different raw m

almond-shell waste. (&) Heaps inoculated with Bacillus shackletonni; (^) heap

Streptomyces thermovulgaris; (*) control heaps. Turning days are signed by arrow

they were very similar (data not shown), what potentially

enables them to compete with the native microbiota and play

and important role on the biotransformations that take place

during composting.

In relation to thermal values (Fig. 1), differences could be

observed both on account raw material and microbial inoculant.

Although temperatures above 50 8C were reached in all the

cases, higher values were detected for those heaps made of

OMW, while lower temperatures were measured in the RS

heaps. As it was expected, a thermal reactivation was promoted

every time turning treatments were applied, especially in the

heaps in which inoculants were present. Therefore, higher

temperatures were maintained in these heaps for a longer time

in almost all the cases.

Data related to humic indices are shown in Tables 3 and 4.

Regardless the nature of composted substrate, most of the heaps

showed an increase in the humic-to-fulvic acid ratio (CHA/FA),

humification ratio (HR) and humification index (HI), being

CHA/FA the index showing a more regular pattern of increase

(Table 3). Nevertheless, some differences could be observed

depending on raw material. Thus, in OMWand RS heaps higher

changes were detected at the beginning of the process, while

CHA/FA values for PrW and AS heaps showed a second increase

between the end of the bio-oxidative phase and the conclusion

of the composting process. This curing stage was also the most

important phase for the evolution of HR and HI, since more

significant variations on these indices could be observed at this

time. These results are consistent with those previously

reported in relation to transformations of organic matter to

humic-like substances [17,38]. In the active initial phase of

aterials. OMW: olive-oil mill waste; PrW: pruning waste; RS: rice straw; AS:

s inoculated with Ureibacillus thermosphaericus; (4) heaps inoculated with

s.

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M. del Carmen Vargas-Garcıa et al. / Process Biochemistry 41 (2006) 1438–1443 1441

Table 3

Evolution of humic indices (CHA/FA: HA/FA ratio; HR: humification ratio; HI: humification index) in the different heaps

Time (day) OMW PrW RS AS

CHA/FA HR HI CHA/FA HR HI CHA/FA HR HI CHA/FA HR HI

0 0.58 a 11.43 a 3.55 a 0.46 a 12.15 a,b 3.37 a 0.50 a 11.10 a,b 2.95 a 0.42 a 9.26 a 2.40 a

14 0.72 b 11.09 a 3.89 a 0.59 b 10.49 a 3.36 a 0.71 b 10.37 a 3.65 a 0.54 b 10.13 a,b 3.09 a b

28 0.72 b 11.54 a 3.93 a 0.71 c 11.47 a,b 3.90 a 0.74 b 9.53 a 3.39 a 0.66 c 10.41 a,b 3.66 b,c

45 0.74 b 12.20 a 3.93 a 0.71 c 11.11 a,b 3.81 a 0.76 b 11.11 a,b 3.59 a 0.66 c 10.72 a,b 3.50 b,c

180 0.78 b 13.44 a 4.73 b 0.93 d 13.25 b 4.99 b 0.81 b 12.97 b 4.47 b 0.80 d 11.49 b 4.20 c

180/0 1.34 1.18 1.33 2.02 1.09 1.48 1.62 1.17 1.52 1.90 1.24 1.75

Data are mean values for different inocula. Within a column, means with the same letter are not significantly different (P < 0.05). OMW: olive-oil mill waste; PrW:

pruning waste; RS: rice straw; AS: almond-shell waste.

composting, the most easily available organic matter (simple

carbohydrates and organic acids) is mineralized and humic-type

substances do not change significantly; however, later in the

maturation stage, the formation of these compounds becomes

more notable as a consequence of microbial degradation of

cellulose, hemicellulose and even lignin [39].

These differences in the evolution of humification indices, as

well as the variation on the initial values for these ratios,

promoted the appearance of significant differences between the

four raw materials used. In all the cases, values for the indices

were significantly lower for the AS heaps, while higher ratios

were detected in the OMW heaps, although differences were

significant just for HI index.

The lower specific values for CHA/FA, HR and HI obtained in

these assays when compared to those described by other authors

[18,19,40] may be due to the different nature of raw materials.

However, the increase factor for these ratios (quotient between

final – 180 days – and initial – 0 days – values in Table 3) was in

agreement in most cases with those considered optimal for

maturity (1.7 for CHA/FA and 1.34 for HI according to Iglesias

Jimenez and Perez Garcıa [19]). Thus, the values obtained for

this increase factor for CHA/FAwere 2.02 (PrW Heaps), 1.90 (AS

Heaps), 1.62 (RS Heaps) and 1.34 (OMW Heaps), while values

of 1.75 (AS Heaps), 1.51 (RS Heaps), 1.48 (PrW Heaps) and

1.33 (OMW Heaps) were observed for the HI ratio.

In relation to the effect of inoculation on humification

during composting processes, a general influence of this

factor was found (Table 4). Nevertheless, when specific trials

were observed, some differences could be noted, mainly for

CHA/FA. Thus, the addition of inoculants in PrW heaps did not

produce a significant increase on CHA/FA when compared to

Table 4

Humic indices (CHA/FA: HA/FA ratio; HR: humification ratio; HI: humification in

composting processes

Inoculant OMW PrW

CHA/FA HR HI CHA/FA HR

Control 0.58 a 9.68 a 2.93 a 0.70 b 8.80 a

B. shackletonni 0.71 b 12.55 b 4.23 b 0.66 a,b 12.83 b

U. thermosphaericus 0.75 b 12.85 b 4.29 b 0.76 b 12.94 b

S. thermovulgaris 0.79 b 12.70 b 4.58 b 0.59 a 12.21 b

Data are mean values for different times. Within a column, means with the same let

pruning waste; RS: rice straw; AS: almond-shell waste.

control heaps, while just the action of U. thermosphaericus

inoculum led to a value of this ratio significantly higher than

that obtained in uninoculated RS heaps. In all the other cases,

and regardless of raw materials and inocula, the presence

of external microorganisms improved humification indices

significantly.

The influence of each microorganism used as inoculant was

also dependent on raw material. Thus, no differences could be

established between B. shackletonni, U. thermosphaericus and

S. thermovulgaris when they were added to OMW and PrW

heaps, except in the values of CHA/FA of the latest. However, the

action of U. thermosphaericus on RS heaps was more efficient

than that observed for the other inoculants, and a similar effect

was obtained for Bacillus on AS heaps.

The use of inoculants to speed up the composting process or

to obtain better final compost has been a controversial subject

for a long time and, in fact, contradictory results have been

described by different authors [22–24,32,41–45,]. Neverthe-

less, such controversy should not be surprising if we consider

the complexity of the biological events that take place and the

many factors the process depends on. One of the most

influential factors is the raw material used for composting, since

qualitative and quantitative chemical composition and, there-

fore, microbiological activity, relies on it. Given the strong

variations between substrates in that matter [46], it is not

difficult to understand the different ability of microorganisms

used as inoculants to biotransform the organic matter on each

material, as it has been stated by other authors [47]. Thus, a

prior study may be necessary to know the suitability of every

microbial species or even strain for a specific substrate when a

composting process is to be improved.

dex) in the different heaps according to the microbial inoculum used in the

RS AS

HI CHA/FA HR HI CHA/FA HR HI

2.87 a 0.66 a 8.43 a 2.51 a 0.49 a 8.40 a 2.33 a

4.26 b 0.61 a 11.30 b 3.51 b 0.76 c 11.20 b 4.22 c

4.50 b 0.88 b 11.71 b 4.52 c 0.61 b 11.47 b 3.53 b,c

3.91 b 0.66 a 12.57 b 3.91 b,c 0.62 b 10.54 b 3.40 b

ter are not significantly different (P < 0.05). OMW: olive-oil mill waste; PrW:

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M. del Carmen Vargas-Garcıa et al. / Process Biochemistry 41 (2006) 1438–14431442

4. Conclusion

The results described here suggest that inoculation in

composting processes can be a useful tool to increase the

humification degree in the final product and, therefore, to

improve the agricultural quality of compost by achieving a

higher stabilization and maturity levels. In order to reach the

best results, particularly when lignocellulosic wastes are

involved, the microorganisms considered for inoculation must

be selected on the basis of their ability to speed up the

biodegradation of raw materials at initial stages and this early

decomposition will favor a faster and more efficient humifica-

tion. This is an important result since works concerning the

capacity of microbial inoculants to improve composting

process and compost are scarce and contradictory.

Acknowledgement

This research has been funded by the Spanish ‘‘Ministerio de

Ciencia y Tecnologıa’’ (CICYT project no. AGL2001-2815).

References

[1] Strom PF. Pesticides in yard waste composting. Compost Sci Utiliz 2000;

8:54–60.

[2] Suarez-Estrella F, Lopez MJ, Elorrieta MA, Vargas-Garcia MC, Moreno J.

Survival of phytopathogen viruses during semipilot-scale composting. In:

Insam H, Riddech N, Klammer S, editors. Microbiology of composting.

Berlin: Springer; 2002. p. 539–48.

[3] Vinneras B, Bjorklund A, Jonsson H. Thermal composting of faecal matter

as treatment and possible disinfection method-laboratory scale and pilot-

scale studies. Bioresour Technol 2003;88:47–54.

[4] Parr JF, Stewart BA, Hornick SB, Singh RP. Improving the sustainability

of dryland farming systems: a global perspective. In: Singh RP, Parr JF,

Stewart BA, editors. Advances in soil science, vol 13. Berlin: Springer;

1990. p. 1–8.

[5] Sanchez-Monedero MA, Cegarra J, Garcıa D, Roig A. Chemical and

structural evolution of humic acids during organic waste composting.

Biodegradation 2002;13:361–71.

[6] Marinari S, Masciandaro G, Ceccanti B, Grego S. Influence of organic and

mineral fertilizers on soil biological and physical properties. Bioresour

Technol 2000;72:9–17.

[7] Requena N, Azcon R, Baca MT. Chemical changes in humic substances

from compost due to incubation with ligno-celulolytic microorganisms

and effects on lettuce growth. Appl Microbiol Biotechnol 1996;45:

857–63.

[8] Marambe B, Ando T. Phenolic acids as potential seed germination-

inhibitors in animal-waste composts. Soil Sci Plant Nutr 1992;38:727–33.

[9] Zucconi F, Pera A, Forte M, De Bertoldi M. Evaluating toxicity of

immature compost. BioCycle 1981;22:54–7.

[10] Golueke CG. Principles of biological resource recovery. BioCycle

1981;22:36–40.

[11] Poincelot RP. A scientific examination of the principles and practice of

composting. Compost Sci 1974;15:24–31.

[12] Robin D. Interet de la caracterisation biochimique pour l’evaluation de la

proportion de matiere organique stable apres decomposition dans le sol et

la classification des produits organo-mineraux. Agronomie 1997;17:

157–71.

[13] Smith DC, Hughes JC. A simple test to determine cellulolytic activity as

indicator of compost maturity. Commun Soil Sci Plant Anal 2001;32:

1375–749.

[14] Saharinen MH, Vuorinen AH, Kostikka M. Effective cation exchange

capacity of manure-straw compost of varying stages determined by the

saturation–displacement method. Commun Soil Sci Plant Anal 1996;

27:2917–23.

[15] Iannotti DA, Grebus ME, Toth BL, Madden LV, Hoitink HAJ. Oxygen

respirometry to assess stability and maturity of composted municipal solid

waste. J Environ Qual 1994;23:1177–83.

[16] Lopez MJ, Elorrieta MA, Vargas-Garcıa MC, Suarez-Estrella F, Moreno J.

The effect of aeration on the biotransformation of lignocellulosic wastes

by white-rot fungi. Bioresour Technol 2002;81:123–9.

[17] Veeken A, Nierop K, Wilde Vde, Hamelers B. Characterisation of NaOH-

extracted humic acids during composting of a biowaste. Bioresour Tech-

nol 2000;72:33–41.

[18] Domeizel M, Khalil A, Prudent P. UV spectroscopy: a tool for monitoring

humification and for proposing an index of the maturity compost. Bior-

esour Technol 2004;94:177–84.

[19] Iglesias Jimenez E, Perez Garcıa V. Determination of maturity indices for

city refuse composts. Agric Ecosyst Environ 1992;38:331–43.

[20] Pietro M, Paola C. Thermal analysis for the evaluation of the organic

matter evolution during municipal solid waste aerobic composting pro-

cess. Thermochim Acta 2004;413:209–14.

[21] Beffa T, Blanc M, Marilley L, Fischer JL, Lyon PF, Aragno M. Taxonomic

and metabolic microbial diversity during composting. In: De Bertoldi M,

Sequi P, Lemmes B, Papi T, editors. The science of composting. Part I.

London: Chapman and Hall; 1996. p. 149–61.

[22] Elorrieta MA, Lopez MJ, Suarez-Estrella F, Vargas-Garcıa MC, Moreno J.

Composting of different horticultural wastes: effect of fungal inoculation.

In: Insam H, Riddech N, Klammer S, editors. Microbiology of compost-

ing. Berlin: Springer; 2002. p. 119–32.

[23] Wani SP, Shinde PA. Studies on biological decomposition of wheat-straw.

II. Screening of wheat-straw decomposing microorganisms under field

conditions. Mysore J Agric Sci 1978;12:388–91.

[24] Gaind S, Pandey AK, Lata. Biodegradation study of crop residues as

affected by exogenous inorganic nitrogen and fungal inoculants. J Basic

Microbiol 2005;4:301–11.

[25] Tuomela M, Vikman M, Hatakka A, Itavaara M. Biodegradation of lignin

in a compost environment: a review. Bioresour Technol 2000;72:169–83.

[26] Ji R, Chen Z, Corvini PFX, Kappler A, Brune A, Haider K, Schaffer A.

Synthesis of [13C]- and [14C]-labeled phenolic humus and lignin mono-

mers. Chemosphere 2005;60:1129–81.

[27] He L, Brickerstaff GF, Paterson A, Buswell JA. Purification and partial

characterization of two xylanases that differ in hydrolysis of soluble and

insoluble xylan fractions. Enzyme Microb Technol 1993;15:13–8.

[28] Rayner ADM, Boddy L. Fungal Decomposition of Wood. Its Biology and

Ecology New York: Wiley; 1998.

[29] Mebius LJ. A rapid method for determination of organic carbon in soil.

Anal Chim Acta 1960;22:120–4.

[30] Bremmer JM, Mulvaney CS. Nitrogen-total. In: Page AL, Miller RH,

Keeney DR, editors. Methods of soil analysis. Part 2. Chemical and

microbiological properties. 2nd ed., Madison: ASA, SSSA; 1982 . p.

595–624.

[31] Kononova M. Soil organic matter Oxford: Pergamon Press; 1966.

[32] Faure D, Deschamps AM. The effect of bacterial inoculation on the

initiation of composting of grape pulps. Bioresour Technol 1991;37:

235–8.

[33] Rajbanshi SS, Endo H, Sakamoto K, Inubushi K. Stabilisation of chemical

and biochemical characteristics of grass straw and leaf mix during in-

vessel composting with and without seeding material. Soil Sci Plant Nutr

1998;44:485–95.

[34] Shin HS, Hwang EJ, Park BS, Sakai T. The effects of seed inoculation on

the rate of garbage composting. Environ Technol 1999;20:293–300.

[35] Lei F, VanderGheynst JS. The effect of the microbial inoculation and pH

on microbial community structure changes during composting. Process

Biochem 2000;35:923–9.

[36] Ryckeboer J, Mergaert J, Coosemans J, Deprins K, Swings J. Micro-

biological aspects of biowaste during composting in a monitored compost

bin. J Appl Microbiol 2003;94:127–37.

[37] Badr EL-Din SMS, Attia M, Abo-Sedera SA. Field assesment of composts

produced by highly effective cellulolytic microorganisms. Biol Fertil Soils

2000;32:35–40.

Page 6: Influence of microbial inoculation and co-composting material on the evolution of humic-like substances during composting of horticultural wastes

M. del Carmen Vargas-Garcıa et al. / Process Biochemistry 41 (2006) 1438–1443 1443

[38] Wu L, Ma LQ, Martinez GA. Comparison of methods for evaluating

stability and maturity of biosolids compost. J Environ Qual 2000;29:

424–9.

[39] Lynch JM. Substrate availibility in the production of composts. In:

Hoitink AJ, Keener HM, editors. Science and engineering of composting:

design, environmental, microbiological and utilization aspects. Columbus:

The Ohio University Press; 1992. p. 24–35.

[40] Chefetz B, Hatcher PG, Hadar Y, Chen Y. Chemical and biological

characterization of organic matter during composting of municipal solid

waste. J Environ Qual 1996;25:776–85.

[41] Golueke CG, Card BJ, McGauhey PH. A critical evaluation of inoculums

in composting. Appl Microbiol 1954;2:45–53.

[42] Kosinkiewiez B. Humus-like substances produced by bacteria: ability of

Pseudomonas sp. to form humus-like polymers. In: Biodegradation et

Humification. Rapport du premier colloque international. Nancy: Edition

Pierron; 1974. p. 379–89.

[43] Magan N, Hand P, Kirkwood IA, Lynch JM. Establishment of microbial

inocula on decomposing wheat straw in soil of different water contents.

Soil Biol Biochem 1989;21:15–22.

[44] Nakasaki K, Akiyama T. Effects of seeding on thermophilic composting of

household organic waste. J Fermentat Technol 1988;66:37–42.

[45] Solbraa K. An analysis of compost starters used on spruce bark. BioCycle

1984;25:46–8.

[46] Unsal T, Sozudogru Ok S. Description of characteristics of humic substances

from different waste materials. Bioresour Technol 2001;78:239–42.

[47] Smith DC, Hughes JC. Changes in maturity indicators during the degra-

dation of organic wastes subjected to simple composting procedures. Biol

Fertil Soils 2004;39:280–6.