**2.2.1 Composting operation**

398 Material Recycling – Trends and Perspectives

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

N (%) 3.1 3.15 3.1 3.17 3.18 3.14 2.9- 4.9 % P (%) 0.19 0.15 0.12 0.13 0.2 0.17 0.4-0.7 % K (%) 1.2 1.3 1 1.2 1.2 1 2.7- 5.9 % Ca (%) 3.2 3 3 3 3.5 3.3 2.4-7.2 % Fe (ppm) 63 75 62 60 57 48 101-291 ppm Zn (ppm) 38 23 39 27 37 31 20-85 ppm Mn (ppm) 29 30 27 32 0.28 35 55-220 ppm Cu (ppm) 6.5 6.1 5.8 5 7.3 6.1 10-16 ppm

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

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

Soil 2 amended with manure

Soil 3 amended with compost

Soil 3 amended with manure

Normal Ranges in leaves\*

Soil 2 amended with compost

deficiency in N, P and K elements.

amended with compost

\* World Fertilizer Use Manual (1992)

**2.2 Liquid wastes** 

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

fertiliser (Sierra et al. 2001; Casa et al. 2003; Cereti et al. 2004).

Soil 1 amended with manure

Elements Soil 1

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

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 from olive oil production plants.

The piles presented the following compositions:

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 wastewater).

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 used was 5.6 m3.

#### • **Temperature**

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

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-

Valorization of Organic Wastes by Composting Process and Soil Amendment 401

Fig. 4. Organic matter evolution during composting process (Rigane and Medhioub, 2010).

Composting time (days)

by the high soluble salt content provided from OMW.

40

50

60

Organic matter (%)

70

80

90

OMW.

The difference between two composts can be attributed to the higher content of easily degradable organic compounds provided by OMW. OM decomposition bring about an increase in pH and EC in the piles, as recorded by Paredes et al. (2005), which was explained as a consequence of the degradation of acid-type compounds, such as carboxylic and phenolic groups, the mineralisation of compounds, such as proteins, amino acids and peptides, to ammonia and the relative increased concentration of ions, due to the loss of pile weight. This fact was observed in the higher pH and electrical conductivity of both composts in comparison to manure (Table 5). The EC in the compost prepared with OMW (C1) was more important than manure (M) and C2 without OMW which can be explained

0 20 40 60 80 100 120 140 160 180

**Pile 2** 

**Pile 1** 

This observation can explain the significant difference in the humification ratio (CHA/CFA) between composts and manure (Table 5). Respect to organic matter humification, a higher humification ratio was recorded in C2 without OMW. Therefore, a positive correlation was observed between CEC and CHA/CFA (Rigane et Medhioub, 2011). In fact, the CEC was more important in compost C2 prepared without OMW which it reached 255 meq/100g, while in compost C1 with OMW, it had 237 meq/100g. Both composts, particularly C1 with OMW, had high levels of macronutrients, especially K and Ca (Table 5), compared with those found in manure. Moreover, a higher EC was recorded in composts than manure and mainly in the OMW compost. This was probably linked to the soluble salts contained in

product (compost) due to pathogen, weed and seed reduction. When the temperature started to decrease, the piles were turned in order to improve both the homogeneity of the material and the fermentation process. The thermophilic phase (T > 40°C) lasted approximately 105 and 120 days for mixtures 2 and 1, respectively. The biooxidative phase of composting was considered finished when the temperature of the piles was stable and close to that of the atmosphere. This occurred after 180 and 160 days in piles 1 and 2, respectively.

Fig. 3. Temperature evolution during composting process of studied piles (Rigane and Medhioub, 2011).

#### • **Organic matter evolution**

The initial OM concentrations were approximately equal in both piles (Table 2). However, OM degradation was more important in the mixture without OMW (pile 2), which may be due to the longer thermophilic phase for this pile (Figure 4). According to Paredes et al. (2005), this fact can be explained by the higher content of easily degradable organic compounds provided by OMW.

product (compost) due to pathogen, weed and seed reduction. When the temperature started to decrease, the piles were turned in order to improve both the homogeneity of the material and the fermentation process. The thermophilic phase (T > 40°C) lasted approximately 105 and 120 days for mixtures 2 and 1, respectively. The biooxidative phase of composting was considered finished when the temperature of the piles was stable and close to that of the atmosphere. This occurred after 180 and 160 days in piles 1

Fig. 3. Temperature evolution during composting process of studied piles (Rigane and

The initial OM concentrations were approximately equal in both piles (Table 2). However, OM degradation was more important in the mixture without OMW (pile 2), which may be due to the longer thermophilic phase for this pile (Figure 4). According to Paredes et al. (2005), this fact can be explained by the higher content of easily degradable organic

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180

**Composting time (days)**

**Pile 2**

**Pile 1** 

and 2, respectively.

Medhioub, 2011).

10

20

30

40

Temperature (°C)

50

60

70

• **Organic matter evolution** 

compounds provided by OMW.

#### Fig. 4. Organic matter evolution during composting process (Rigane and Medhioub, 2010).

The difference between two composts can be attributed to the higher content of easily degradable organic compounds provided by OMW. OM decomposition bring about an increase in pH and EC in the piles, as recorded by Paredes et al. (2005), which was explained as a consequence of the degradation of acid-type compounds, such as carboxylic and phenolic groups, the mineralisation of compounds, such as proteins, amino acids and peptides, to ammonia and the relative increased concentration of ions, due to the loss of pile weight. This fact was observed in the higher pH and electrical conductivity of both composts in comparison to manure (Table 5). The EC in the compost prepared with OMW (C1) was more important than manure (M) and C2 without OMW which can be explained by the high soluble salt content provided from OMW.

This observation can explain the significant difference in the humification ratio (CHA/CFA) between composts and manure (Table 5). Respect to organic matter humification, a higher humification ratio was recorded in C2 without OMW. Therefore, a positive correlation was observed between CEC and CHA/CFA (Rigane et Medhioub, 2011). In fact, the CEC was more important in compost C2 prepared without OMW which it reached 255 meq/100g, while in compost C1 with OMW, it had 237 meq/100g. Both composts, particularly C1 with OMW, had high levels of macronutrients, especially K and Ca (Table 5), compared with those found in manure. Moreover, a higher EC was recorded in composts than manure and mainly in the OMW compost. This was probably linked to the soluble salts contained in OMW.

Valorization of Organic Wastes by Composting Process and Soil Amendment 403

soils (Bernal et al. 1993). However, these parameters were increased significantly by the organic amendment type, particularly with composts. The increases of Corg, Norg and plant-available nutrient contents and CEC values in soil amended with organic fertilisation were also observed by Cabrera et al. (1997), in study of effects of applications of OMW sludge compost. After cropping the compost C1 prepared with OMW showed a residual organic content more important than manure and compost C2. Besides, Mg and P contents

With the vast amounts of olive and poultry residues production in Mediterranean countries, their treatment and disposal are becoming a serious environmental problems. An attention has been paid to wastes and technologies are available nowadays for reducing their pollutant effects and for their transformations in a final product which can be used without any pollution risk. By using composting technologies, it is possible to transform these residues mixed with appropriate percentages into organic fertilizers (composts) with no

The composting of liquid or solid organic agro-industrial wastes offers an important advantages: valorization of wastes, reducing the decrease of farm manure used for soil

The composting is a controlled biological process which involves a heterogeneous organic

This technology could have an important repercussion in many countries of the world, since they suffer water restrictions and the increase of organic waste volumes. Thus, it requires new environmental and economically viable management options. In this work, we were interested in agricultural valorisation of composts obtained by mixtures of olive husks,

It can be deduced that composting is a suitable alternative for the recycling wastes. The obtained compost had a stabilised and humified organic matter and an important tenors of macronutrients which were recorded due to OM mineralization. The positive effects on soil fertility and productivity increased with the application of compost. However, the composting of organic wastes depends on raw materials. In fact, the composting of wastes containing OMW for example requires a longer time and this could be the major concern

Aktas, E.S., Imre, S. Ersoym, L. (2001). Characterization and lime treatment of olive mill

Bernal, M.P., Navarro, A.F., Roig, A, Cegarra, J. and Garcia, D. (1996). Carbon and nitrogen

Cabrera, F, López, R., Martín, P. & Murillo, J.M. (1997). Aprovechamiento agronómico de

transformation during composting of sweet sorghum bagasse. Biol. Fert. Soils, 22,

solid substrate may resolve the problem of wastes which can be liquid or solid.

were more important in soil amended with C1 with OMW.

phytotoxicity to improve soil fertility and plant production.

amendment and absence of negative effects on crop qualities.

regarding the use of compost in soil with sufficient maturity.

wastewater. *Water Research* Vol. 35, pp. 2336–2340.

composts de alpechín. *Frutic Prof*. Vol. 88, pp. 94– 105.

poultry manure, Olive mill wastewaters,...

**3. Conclusions** 

**4. References** 

141-148.


Table 5. Physical and chemical characteristics of manure and two types of composts.

#### • **Soil amendment essay**

In soils amended with two composts were recorded a higher fertilizing values than those amended with manure (Table 6). Tomati et al. (1996), in an experiment with potato grown on soil amended by compost or manure mixtures, obtained higher crop yields with OMW compost.


Table 6. Comparative effects of composts 1 (C1) and 2 (C2) on potato yield production.

The soil analysis showed that the addition of compost produced great changes in soil pH. This observation was also deduced by Gallardo-Lara and Nogales (1987) in a calcareous soil amended with solid waste compost.

In addition, the studied composts increased significantly the soil salinity, according to the EC values. In the most cases, the increases of Corg, Norg, P and K nutrient contents and the CEC values in soil due to organic amendment were also observed in soils with composts.

The levels of chlorides and sodium were for all time higher in the soils with composts and manure. The Corg, Norg, and available K concentrations and the CEC values of the amended soils decreased after cropping compared to value before cropping for each parameter. This fact is considered as a consequence of the OM mineralisation, plant uptake and fixation of phosphorus as calcium phosphates hardly available to plants in calcareous soils (Bernal et al. 1993). However, these parameters were increased significantly by the organic amendment type, particularly with composts. The increases of Corg, Norg and plant-available nutrient contents and CEC values in soil amended with organic fertilisation were also observed by Cabrera et al. (1997), in study of effects of applications of OMW sludge compost. After cropping the compost C1 prepared with OMW showed a residual organic content more important than manure and compost C2. Besides, Mg and P contents were more important in soil amended with C1 with OMW.
