**2. Composting process**

The composting in a controlled biooxidative process that involves a heterogenous organic substrate in the solid state that evolves through a thermophile stage and the temporary release of phytotoxins, leading to the production of carbon dioxide, water, mineral salts and stabilized organic matter containing humic like substances. By using this method, it is possible to transform olive residues mixed with poultry manure into organic fertilizers with no toxicity to improve soil fertility and plant production.

In this work, we presented examples of solid and liquid wastes chosen in composing essays.

#### **2.1 Solid wastes**

The raw materials (olive husks) characterized by high organic carbon, very low nitrogen and important ash contents, were co-composted with poultry manure containing high nitrogen and ash rates (Table 1, Hachicha et *al*., 2003). Two combinations of sifted or non sifted olive husks mixed with poultry manure at 8:2 ratio were selected (Hachicha et *al*., 2003). The sifting operation was performed using a densimetric method that allows its separation into 40% pulp and 60% stone fragments. The latter was used as a substitute for raw olive husks in the role of energy supplier. The sifting was retained to compare the qualities of composts (produced from materials with or without sifting) and to test the possibility of utilization of olive husks without sifting to reduce treatment price. In fact, two windrows were constructed one for each formula.

#### **2.1.1 Preparation of windrows**

Windrow 1, composed by a mixture of non sifted olive husks and poultry manure and windrow 2 composed by a mixture of sifted olive husks and poultry manure. These will produce respectively compost C1 and compost C2. The windrows had triangular shape with 3 m wide of the base and 2-3 m high. Each windrow was constituted of 10 tons of the mixture. Olive husks are characterized by a very high C/N ratio due to high carbon and low nitrogen contents. The olive husks are mainly composed of lignin and cellulose fibres with

husks are organic fertilizers that improved soil fertility (Fiestas Ros de Ursinos, 1986; Tomati and Galli, 1992). The olive husk composts bring essentially potaasium (K), in addition to Nitrogen (N), Phosphorus (P) and Magnesium (Mg) and obviously organic matter (OM). Soil amendment with compost enhances its microbial activity and improves its physical and chemical properties. Thus, farmer's interest for recycling organic wastes in agriculture as fertilizers or amendments is increasing. The composting studies were performed on olive husks mixed (80 %) with 20% poultry manure. The initial mixture was realized in order to reach a C/N ratio of 30. The obtained compost was characterized physically and chemically

The objectives of the present work were to assess the suitability of a waste compost to supply some essential plant nutrients such as N, P, K, iron (Fe), manganese (Mn), zinc (Zn) and copper (Cu); evaluate and compare the effects of manure and compost on soil chemical properties of studied soils in the same zone and to prove the effect of compost on crop

The composting in a controlled biooxidative process that involves a heterogenous organic substrate in the solid state that evolves through a thermophile stage and the temporary release of phytotoxins, leading to the production of carbon dioxide, water, mineral salts and stabilized organic matter containing humic like substances. By using this method, it is possible to transform olive residues mixed with poultry manure into organic fertilizers with

In this work, we presented examples of solid and liquid wastes chosen in composing essays.

The raw materials (olive husks) characterized by high organic carbon, very low nitrogen and important ash contents, were co-composted with poultry manure containing high nitrogen and ash rates (Table 1, Hachicha et *al*., 2003). Two combinations of sifted or non sifted olive husks mixed with poultry manure at 8:2 ratio were selected (Hachicha et *al*., 2003). The sifting operation was performed using a densimetric method that allows its separation into 40% pulp and 60% stone fragments. The latter was used as a substitute for raw olive husks in the role of energy supplier. The sifting was retained to compare the qualities of composts (produced from materials with or without sifting) and to test the possibility of utilization of olive husks without sifting to reduce treatment price. In fact, two windrows were

Windrow 1, composed by a mixture of non sifted olive husks and poultry manure and windrow 2 composed by a mixture of sifted olive husks and poultry manure. These will produce respectively compost C1 and compost C2. The windrows had triangular shape with 3 m wide of the base and 2-3 m high. Each windrow was constituted of 10 tons of the mixture. Olive husks are characterized by a very high C/N ratio due to high carbon and low nitrogen contents. The olive husks are mainly composed of lignin and cellulose fibres with

in order to define its fertilizing capacities and use safety.

no toxicity to improve soil fertility and plant production.

productivity.

**2.1 Solid wastes** 

constructed one for each formula.

**2.1.1 Preparation of windrows** 

**2. Composting process** 

other chemical elements at low concentrations (Vlyssides et *al*., 1996). The direct application of these solid wastes in soil causes problems because of their phytotoxicity (De Bertoldi and *al.*, 1983). The sifting operation uses a densymetric method that allows their separation into 40% pulp and 60% some fragments. The sifted olive husk compost gives more nitrogen and more synthesised and polymerised humic acids than unsifted olive husk compost (Hachicha, 2002; Hachicha and *al*., 2003). Poultry manure contain relatively high concentrations of total nitrogen (more than 2.5% of dry matter), of ash (more than 40% of dry matter) and relatively low C/N ratio (Table 1).

During the composting process several parameters were followed such as temperature, pH, electrical conductivity (EC) and ash ratio. Maturity was evaluated by the determination of the C/N ratio, cation exchange capacity (CEC) and humic acid concentrations (Mustin, 1987). Moreover, during the composting process, moisture was kept at 45-50% by adding water and aeration was assured by windrow turning. Temperatures were measured daily basis at different positions in the core of windrow using mercury thermometers and the average of all measurements was recorded. Samples for analysis were collected weekly at different points along the windrows.


Table 1. Properties of the initial solid wastes and mixtures (Hachicha et al., 2003).

#### **2.1.2 Soil amendment**

For amendment tests, we applied two types of composts: compost 1 and compost 2. The essays were realized in plots and in field.

Valorization of Organic Wastes by Composting Process and Soil Amendment 395

The data related to the effect of temperature on the composting process indicate that optimum decomposition takes place between 55 and 60°C (Morel et al*.,* 1984). For both windrows, high core temperatures (60-70°C) remained for three months in windrow 2 and for four months in windrow 1. The presence of more easily biodegradable compounds in the sifted olive husks (material 2) and an important fraction of cellulose and lignin in raw material 1, could explain the difference showed in the thermophilic phase length. The

The pH variation ranged from 6.5 to 8, which consists to aerobic composting (Gardena and Wang, 1981). Nevertheless, for both analysed windrows, pH slightly decreased over the first two weeks and gradually increased during the active phase for each substrats with a trend towards stabilization. The initial drop in pH has been reported by other authors (De Bertoldi and *al*., 1983; Hardy and Sivasithamparam, 1989; Sikora and Sowers, 1983) and is considered to be a consequence of the acid-forming bacteria activity which breaks down complex carbonaceous material to organic acid intermediates. However, the products formed are readily consumed and simultaneous protein degradation starts releasing basic compounds which increase the pH (Godden and Penninck, 1990). In both windrows, the pH showed a progressive increase (slightly more rapid for 1) with similar behaviour. For both produced

For both windrows, EC rose progressively. This increase, which took place especially during higher temperatures, may be attributed to the important mineralization that liberates ions. No significant difference was observed between the two windrows. After 150 composting days, E.C. for each final product was 1.5 ms cm-1 against 0.8 for the unsifted olive oil

We have chosen C/N ratio and cation exchange capacity (CEC) as indicators of maturation progress. However, a large number of parameters were tested by different authors (Morel and *al*., 1984; Stentiford and Pereira, 1985). The aerobic fermentation produces an important quantity of CO2 noted here by a decrease in organic carbon content. Nitrogen constitutes the second most important element after carbon in the composting process. Over the composting cycle, the Kjeldahl nitrogen concentration (Table 2) increased. For final products, nitrogen content was about 2.5% dry solid. Increases in total nitrogen have also been reported during the composting of sludge and animal manure (Bernal et *al*., 1996; Tikia et *al*., 1998). In addition, to the weight losses due to the strong degradation of carbon compounds, a small nitrogen increase during composting could be attributed to fixing bacteria (Jodice and Nappi, 1986) or to inorganic nitrogen immobilizing phenomenon (Tam and Tikia, 1999). Consequently, the decrease of the C/N ratio (Table 2) during composting was mainly caused by the loss of carbon concentrations and the accumulation of nitrogen. Stability was reached within three months for the unsifted husks and two months for the sifted material. In both cases, the C/N ratio remained around 13 after 150 days of

• **Temperature** 

• **pH evolution** 

characteristics of composts were shown in table 2.

composts, pH remained at alkaline levels.

• **Electric conductivity (EC)** 

processing solid residue. • **Maturity assessment** 

Cultures have been achieved in plots containing 15 Kg of soil situated in a zone characterized by arid climate. The prepared plots are distributed in sets of 9 units:


Every test set includes 9 plots, four of which have been condemned during the analysis cycle. The various plots controlled during the production cycle permitted to follow the beginning of the tuberization and the development of different plant tubers.

We applied compost and poultry manure (PM) in different percentages: 100% C.1 (Compost 1), 50% C.1 or C.2 + 50% PM (Compost 1 or Compost 2 mixed with manure in same quantities), 75% C.1 or C.2 + 25%PM (Compost 1 or Compost 2 mixed with manure at 75%/25%), 25% C.1 or C.2 + 75% PM (Compost 1 or Compost 2 mixed with manure at 25%/75%), 200% C.1 or C.2 (the quantity of applied compost is double compared to 100%) and 100% PM ( poultry manure).

In field experiment, the compost was applied soil harvested with tomato cultures (Rio Grande variety) realized in three experiment soils of the same zone. The region is characterized by calcimagnesic soils characterized by calcareous parent rock containing in most cases active lime. The compost retained for tests is the compost 1 which was applied on soil and where studies (Hachicha et *al*., 2003) showed its agronomic interest. In fact, these authors recorded the same potato yield with both composts, the agronomic field test showed that the sifted olive husk compost (compost 2) acted more positively on the tuber size of potato whereas the non sifted olive husk compost (compost 1) was more beneficial to the plant height and to the leaf weight. In addition, the compost 1 was prepared without sifting the starting materials. In order to improve the soil fertility and to valorise olive husks, tests of amendments by the composts have been exercised on some soil types in this region.

In order to evaluate the quality of soils amended with cow manure and those amended by the compost of olive husks, samples of soils have been appropriated for determination of textural classification, pH, electric conductivity, total lime, active lime, organic matter, organic carbon, total nitrogen, C/N ratio, major elements (Ca, Mg, P, K) and trace elements. Analyses were also realized on leaves of tomato to test the similarity between compost and manure and to testify their values referring to World fertilizer use manual (Halliday and Trenkel, 1992).

#### **2.1.3 Crop production**

The assessment of the agronomic quality of produced composts has been achieved through potato cultures (Spunta variety) in plots and tomato cultures in field experiment. The compost is applied on soils by spreading of 40 tons/ha (the same dose is applied for manure in this zone).

#### **2.1.4 Evolution of composting process**

The principal parameters controlling composting process are pH, Electric conductivity, temperature, cation exchange capacity (CEC), C/N ratio.

#### • **Temperature**

394 Material Recycling – Trends and Perspectives

Cultures have been achieved in plots containing 15 Kg of soil situated in a zone


Every test set includes 9 plots, four of which have been condemned during the analysis cycle. The various plots controlled during the production cycle permitted to follow the

We applied compost and poultry manure (PM) in different percentages: 100% C.1 (Compost 1), 50% C.1 or C.2 + 50% PM (Compost 1 or Compost 2 mixed with manure in same quantities), 75% C.1 or C.2 + 25%PM (Compost 1 or Compost 2 mixed with manure at 75%/25%), 25% C.1 or C.2 + 75% PM (Compost 1 or Compost 2 mixed with manure at 25%/75%), 200% C.1 or C.2 (the quantity of applied compost is double compared to 100%)

In field experiment, the compost was applied soil harvested with tomato cultures (Rio Grande variety) realized in three experiment soils of the same zone. The region is characterized by calcimagnesic soils characterized by calcareous parent rock containing in most cases active lime. The compost retained for tests is the compost 1 which was applied on soil and where studies (Hachicha et *al*., 2003) showed its agronomic interest. In fact, these authors recorded the same potato yield with both composts, the agronomic field test showed that the sifted olive husk compost (compost 2) acted more positively on the tuber size of potato whereas the non sifted olive husk compost (compost 1) was more beneficial to the plant height and to the leaf weight. In addition, the compost 1 was prepared without sifting the starting materials. In order to improve the soil fertility and to valorise olive husks, tests of amendments by the composts

In order to evaluate the quality of soils amended with cow manure and those amended by the compost of olive husks, samples of soils have been appropriated for determination of textural classification, pH, electric conductivity, total lime, active lime, organic matter, organic carbon, total nitrogen, C/N ratio, major elements (Ca, Mg, P, K) and trace elements. Analyses were also realized on leaves of tomato to test the similarity between compost and manure and to testify their values referring to World fertilizer use manual (Halliday and

The assessment of the agronomic quality of produced composts has been achieved through potato cultures (Spunta variety) in plots and tomato cultures in field experiment. The compost is applied on soils by spreading of 40 tons/ha (the same dose is applied for manure

The principal parameters controlling composting process are pH, Electric conductivity,

characterized by arid climate. The prepared plots are distributed in sets of 9 units:


beginning of the tuberization and the development of different plant tubers.

composts either 1 or 2.

and 100% PM ( poultry manure).

Trenkel, 1992).

in this zone).

**2.1.3 Crop production** 

**2.1.4 Evolution of composting process** 

temperature, cation exchange capacity (CEC), C/N ratio.

have been exercised on some soil types in this region.

The data related to the effect of temperature on the composting process indicate that optimum decomposition takes place between 55 and 60°C (Morel et al*.,* 1984). For both windrows, high core temperatures (60-70°C) remained for three months in windrow 2 and for four months in windrow 1. The presence of more easily biodegradable compounds in the sifted olive husks (material 2) and an important fraction of cellulose and lignin in raw material 1, could explain the difference showed in the thermophilic phase length. The characteristics of composts were shown in table 2.

#### • **pH evolution**

The pH variation ranged from 6.5 to 8, which consists to aerobic composting (Gardena and Wang, 1981). Nevertheless, for both analysed windrows, pH slightly decreased over the first two weeks and gradually increased during the active phase for each substrats with a trend towards stabilization. The initial drop in pH has been reported by other authors (De Bertoldi and *al*., 1983; Hardy and Sivasithamparam, 1989; Sikora and Sowers, 1983) and is considered to be a consequence of the acid-forming bacteria activity which breaks down complex carbonaceous material to organic acid intermediates. However, the products formed are readily consumed and simultaneous protein degradation starts releasing basic compounds which increase the pH (Godden and Penninck, 1990). In both windrows, the pH showed a progressive increase (slightly more rapid for 1) with similar behaviour. For both produced composts, pH remained at alkaline levels.

#### • **Electric conductivity (EC)**

For both windrows, EC rose progressively. This increase, which took place especially during higher temperatures, may be attributed to the important mineralization that liberates ions. No significant difference was observed between the two windrows. After 150 composting days, E.C. for each final product was 1.5 ms cm-1 against 0.8 for the unsifted olive oil processing solid residue.

#### • **Maturity assessment**

We have chosen C/N ratio and cation exchange capacity (CEC) as indicators of maturation progress. However, a large number of parameters were tested by different authors (Morel and *al*., 1984; Stentiford and Pereira, 1985). The aerobic fermentation produces an important quantity of CO2 noted here by a decrease in organic carbon content. Nitrogen constitutes the second most important element after carbon in the composting process. Over the composting cycle, the Kjeldahl nitrogen concentration (Table 2) increased. For final products, nitrogen content was about 2.5% dry solid. Increases in total nitrogen have also been reported during the composting of sludge and animal manure (Bernal et *al*., 1996; Tikia et *al*., 1998). In addition, to the weight losses due to the strong degradation of carbon compounds, a small nitrogen increase during composting could be attributed to fixing bacteria (Jodice and Nappi, 1986) or to inorganic nitrogen immobilizing phenomenon (Tam and Tikia, 1999). Consequently, the decrease of the C/N ratio (Table 2) during composting was mainly caused by the loss of carbon concentrations and the accumulation of nitrogen. Stability was reached within three months for the unsifted husks and two months for the sifted material. In both cases, the C/N ratio remained around 13 after 150 days of

Valorization of Organic Wastes by Composting Process and Soil Amendment 397

Clay tenor and organic matter were more important in soil 2 amended by compost, whereas active lime was recorded only in soil 3 (Table 3) (Rigane and Medhioub, 2010). This parameter is important in soil which causes quickly the immobility of the soluble precursors and by the transformation of unsoluble components (such as lignin) caused by an active biological activity, developed with aerated structure in constructed clods of clay-humus-

**Amended soil**

Soil 2 amended by compost

Soil 2 amended by manure

> Soil 2 amended with compost

Soil 2 amended with compost

Soil 3 amended with compost

Soil 3 amended by manure

> Soil 3 amended with compost

Soil 3 amended by compost

Soil 1 amended with compost

Clay (%) 11 15 10 18 12 14 Sand (%) 69 66 59 44 63 55 Silt (%) 20 19 31 38 25 31 pH 7.77 7.85 7.83 7.91 8.19 8.14 EC (mmhos/cm) 11.43 8.42 10.2 9.82 1.87 1.85 Total lime (%) 4.6 5.3 3.4 2.7 21.6 25.7 Active lime (%) - - - - 2.7 4.2 Organic carbon (%) 0.74 0.62 0.7 0.87 0.58 0.78 Organic matter (%) 1.2 1.07 1.2 1.5 1 1.34 C/N 12.33 10.68 11.66 11.6 11.6 11.6 Total Nitrogen (%) 0.06 0.058 0.06 0.075 0.05 0.067 Available P (ppm) 169 166 174 108 58 101 Available K (ppm) 225 180 294 235 140 150 Fe (%) 4.7 3.5 2.7 3 2.2 2.5 Zn (%) 0.97 0.82 0.65 0.56 0.4 0.4 Cu (%) 0.37 0.35 0.28 0.31 0.26 0.25 Mn (%) 1.2 1 0.98 0.85 0.72 0.65

Fig. 2. Soil productivity in different soils.

amended with compost

Soil 1 amended by compost

Table 3. Soil analyses (Rigane and Medhioub, 2010).

CaCO3 (Duchaufour, 1997).

Soil 1 amended by manure

Production (T/Ha)

Parameters Soil 1


composting. During the composting process, microbial activity permitted the increase of cation exchange capacity and humic acid contents (Bernal et *al.*, 1996; Tikia et *al*., 1998).

Table 2. Comparison of fertilizing values of composts 1 and 2.

An increase in CEC (cation exchange capacity) values was observed from the beginning of the composting process. Stabilization was reached five months later. In final products, the CEC recorded was about 140 meq/100g organic matter for compost 1 and 150 meq/100 g organic matter for compost 2, against about 176 meq /100g for manure. The mass of potato obtained in different plots were observed in figure 3 which showed a significant differences between the effects of composts 1 and 2. In fact, all plots amended with compost 1 showed potato masses less than 84 g, whereas in plots amended with compost 2, the potato masses exceed 260 g (Figure 1).

Fig. 1. Mass of potato obtained in different plots.

In field experiment, the productivity of cultivated soils amended with compost 1 which was chosen for economic reasons by removal of sifting operation is presented in Figure 2. The high productions were recorded in soils 2 and 3 amended with compost. This fact is explained by the positive roles of clay and active lime which permit to organic matter retention in soil, and also the role of compost which permits to produce more fertilizing elements related to starting materials.

Fig. 2. Soil productivity in different soils.

composting. During the composting process, microbial activity permitted the increase of cation exchange capacity and humic acid contents (Bernal et *al.*, 1996; Tikia et *al*., 1998).

Elements Compost 1 Compost 2 Manure pH 8.51 8.44 8 organic matter (% dry matter) 40.1 40.25 43.5 C/N 13.65 13.32 16.9 Nitrogen (%dry matter) 1.87 2.10 2.00 P (ppm) 4891 6830 4600 K (ppm) 10660 12190 10250 Ca (g/l) 21.43 22.57 16.4 Mg (ppm) 5472 7747 3800

An increase in CEC (cation exchange capacity) values was observed from the beginning of the composting process. Stabilization was reached five months later. In final products, the CEC recorded was about 140 meq/100g organic matter for compost 1 and 150 meq/100 g organic matter for compost 2, against about 176 meq /100g for manure. The mass of potato obtained in different plots were observed in figure 3 which showed a significant differences between the effects of composts 1 and 2. In fact, all plots amended with compost 1 showed potato masses less than 84 g, whereas in plots amended with compost 2, the potato masses

In field experiment, the productivity of cultivated soils amended with compost 1 which was chosen for economic reasons by removal of sifting operation is presented in Figure 2. The high productions were recorded in soils 2 and 3 amended with compost. This fact is explained by the positive roles of clay and active lime which permit to organic matter retention in soil, and also the role of compost which permits to produce more fertilizing

composition of amendment

Table 2. Comparison of fertilizing values of composts 1 and 2.

Fig. 1. Mass of potato obtained in different plots.

elements related to starting materials.

exceed 260 g (Figure 1).

600 Mass (g)

Clay tenor and organic matter were more important in soil 2 amended by compost, whereas active lime was recorded only in soil 3 (Table 3) (Rigane and Medhioub, 2010). This parameter is important in soil which causes quickly the immobility of the soluble precursors and by the transformation of unsoluble components (such as lignin) caused by an active biological activity, developed with aerated structure in constructed clods of clay-humus-CaCO3 (Duchaufour, 1997).


Table 3. Soil analyses (Rigane and Medhioub, 2010).

Valorization of Organic Wastes by Composting Process and Soil Amendment 399

biological treatments of the OMW as well as their direct application to agricultural soils as a

The Composting technology is a biological process used for treatment of organic wastes to obtain organic soil fertilisers (Mustin, 1987). Composting experiments with OMW showed that OMW needed lignin–cellulosic wastes as bulking agents and other materials as a nitrogen source for its suitable composting, so that the phytotoxicity could be eliminated and a final product with stabilised and humified organic matter obtained by several authors (Tomati et al. 1995; Vlyssides et al. 1996; Paredes et al. 2000; Paredes et al. 2005). The objective of thist work was to study the effects of OMW on the composting of organic wastes

To study the possibility of treatment of OMW by composting, two piles were prepared by mixing olive husks (OH) with poultry manure (PM) and both humidified with confectionery

The OH are characterized by the high values of dry matters, C/N ratio, calcium and magnesium contents. The PM is characterized by relatively high pH, mineral matter, phosphorus and potassium. As liquid effluent, the confectionery wastewaters showed the relatively high humidity, electric conductivity, organic matter, nitrogen and sugars. The OMW was acidic (pH 5.3) with conductivity (20 mSm-1) and important concentrations of N, P and K and organic matter (OMW is characterized by black color) and high content of phenolic compounds (8900 mg l-1). The OMW used in the present study were obtained from a OMW disposal site in the city of Agareb in Sfax region (Southern Tunisia), which derived

Pile 1: Olive husks (OH)(75%) + Poultry Manure (PM)(25%) + Confectionery wastewaters (CWW) + Olive Mill Wastewaters (OMW). The final result after composting constitutes compost C1. The volumes of CWW and OMW used were similar (2.8 m3 for each

Pile 2: Olive husks (OH)(75%) + Poultry Manure (PM) (25%) + Confectionery wastewaters (CWW). The final result after composting constitutes compost C2. The volume of CWW

The air blowing was stopped during the compost maturity period (6 months). In fact, OM degradation was greater in pile 1 in the mixture with OMW which may be explained by the longer thermophilic phase for this pile. The temperature increased quickly at the beginning

In both piles, the temperature was maintained between 60 and 70 °C for about 100 days, which will contribute to the transformation of highly polymerized substrate (lignin and cellulose) by thermophilic microorganisms and also to the hygienisation of the end-

of the process to thermophilic values, reaching the maximum level (68°C) (Figure 3).

wastewaters (CWW). Olive mill wastewater (OMW) was added to one pile (pile 1).

fertilizer have been widely tested.

**2.2.1 Composting operation**

from olive oil production plants.

wastewater).

used was 5.6 m3. • **Temperature** 

The piles presented the following compositions:

and the behaviour of the compost obtained on soil properties.

Compared to normal ranges in leaves (Halliday and Trenkel, 1992), the leaves in vegetables in all experiment soils grown under temperate conditions were considered as normal (Table 4) (Rigane and Medhioub, 2010). In fact, the application of composts in experimental soils showed no negative effect on tomato crop. Nevertheless, Basing on deficiency levels presented by Halliday and Trenkel (1992), the leaves vegetables in amended soils showed deficiency in N, P and K elements.


\* World Fertilizer Use Manual (1992)

Table 4. Leaf analysis (Rigane et Medhioub, 2010).

#### **2.2 Liquid wastes**

The amounts of liquid wastewaters such as olive mill wastewaters (OMW) which is produced in Mediterranean countries are important in the world. Olive oil production has normally been concentrated in the Mediterranean basin countries: Spain, Portugal, Italy, Greece, Turkey, Tunisia and Morocco. These seven countries alone account for 90% of world production. The high content of mineral salts and the presence of organic compounds, such as fatty acids and polyphenols in the OMW generate difficulties of their disposing and utilization of large amounts of this liquid. The disposal and treatment of this liquid waste are the main problems of the olive oil industry because of its high organic load and content of phytotoxic and antibacterial phenolic substances, which resist to biological degradation (Aktas et al. 2001). The beneficial effects are linked to its high nutrients concentration, especially K, and its potential for mobilizing soil ions, while, negative effects are associated with its high mineral salt content, acidity with low pH and the presence of phytotoxic compounds, mainly polyphenols (Paredes et al. 1999). Besides, other authors have observed negative effects on plants and soil properties when OMW is used directly as an organic fertiliser (Sierra et al. 2001; Casa et al. 2003; Cereti et al. 2004).

The treatment of OMW and their disposal are becoming a serious environmental problem. Different methods were used based on thermal concentration, physical and chemical and biological treatments of the OMW as well as their direct application to agricultural soils as a fertilizer have been widely tested.

The Composting technology is a biological process used for treatment of organic wastes to obtain organic soil fertilisers (Mustin, 1987). Composting experiments with OMW showed that OMW needed lignin–cellulosic wastes as bulking agents and other materials as a nitrogen source for its suitable composting, so that the phytotoxicity could be eliminated and a final product with stabilised and humified organic matter obtained by several authors (Tomati et al. 1995; Vlyssides et al. 1996; Paredes et al. 2000; Paredes et al. 2005). The objective of thist work was to study the effects of OMW on the composting of organic wastes and the behaviour of the compost obtained on soil properties.
