Hafedh Rigane

Polyphenolic compounds progress during olive mill wastewater sludge and poultry manure co-composting, and humic substances building (Southeastern Tunisia)

In Mediterranean areas, olive mill wastes pose a major environmental problem owing to their important production and their high polyphenolic compounds and organic acids concentrations. In this work, the evolution of polyphenolic compounds was studied during co-composting of olive mill wastewater sludge and poultry manure, based on qualitative (G-50 sephadex) and quantitative (Folin–Ciocalteu), as well as high pressure liquid chromatography analyses. Results showed a significant polyphenolic content decrease of 99% and a noticeable transformation of low to high molecular weight fraction during the compost maturation period. During this step, polyphenols disappearance suggested their assimilation by thermophilic bacteria as a carbon and energy source, and contributed to humic substances synthesis. Polyphenolic compounds, identified initially by high pressure liquid chromatography, disappeared by composting and only traces of caffeic, coumaric and ferulic acids were detected in the compost. In the soil, the produced compost application improved the chemical and physico–chemical soil properties, mainly fertilising elements such as calcium, magnesium, nitrogen, potassium and phosphorus. Consequently, a higher potato production was harvested in comparison with manure amendment.

Cocomposting of Olive Mill Wastewater with Manure and Agro-industrial Wastes

The use of olive mill wastewater (OMW) for composting was studied by the addition of this liquid waste to a mixture of olive husks, poultry manure and confectionery wastewater. The composting process was compared with that of another pile of similar composition, but without olive mill wastewater. In order to study the effects of both composts on plant yield and soil properties, a field experiment was carried out with potato. Three amendments were applied: manure and two composts with same rate 30 tonnes/ha. The olive mill wastewater addition produced compost with higher organic matter concentrations and higher electrical conductivity, and a stabilized and humified organic matter lower than the compost produced without olive mill wastewater. The olive mill wastewater compost application to soil did not injure plants, producing a similar plant yield to both compost without olive mill wastewater and manure. The olive mill wastewater compost application to soil also improved the chemical and physicochemical properties of the soil mainly fertilizing elements such as calcium, magnesium, nitrogen, potassium and phosphorus. With respect to potato yield, both composts showed higher plant production in comparison to manure, reaching a potato yield of 46 and 47 t/ha in amended soil with compost with and without OMW, respectively.

Valorization of Organic Wastes by Composting Process and Soil Amendment

Agricultural wastes disposal is becoming a serious environmental problem. Indeed, these residues may be highly polluting and phytotoxic. The removal of the produced solid and liquid residues is causing serious environmental problems. The direct application of organic wastes, such as olive husks or olive mill wastewaters, to soil has been considered as an inexpensive method of disposal in addition to the recovery of their mineral and organic components. Nevertheless, due to their ligno-cellulosic contents, olive husks are potentially environmentally harmful biomass. Fresh olive husks (not biologically stabilized) may have phytotoxicity due to their monogenic chemical composition (only lignin and cellulose), to phenols coming from olive oil processing, to its high Carbon/Nitrogen (C/N) ratio and to the presence of hormon inhibitors (De Bertoldi et al., 1986). According to several authors (De Jager et al., 2001; Palm et al., 2001), the improvement of soil fertility mainly under low input agricultural systems requires the input of stabilized or mature organic wastes. Many studies (Gallardo-Lara and Nogales, 1987; He et al., 1992; Ouedraogo et al., 2001; Stamatiadis et al., 1999) have shown that application of mature composts at reasonable rates improves plant growth, soil physical properties and increases available soil nutrient levels.

Evolution of Humic Fractions in Calcimagnesic Soils And Brown Isohumic Soils Amended With Compost and Manure

The composting process of organic wastes consists of the bioconversion of biologically unstable wastes to stabilized products for application to soils. This study was carried out on different soils (brown isohumic soils in Sfax region in southern Tunisia and calcimagnesic soils in Korba region in northern Tunisia). The mineralization process of organic matter is more important in isohumic soils, showing less tenors of fine fractions than in calcimagnesic soils. The study of different humic fractions in amended soils shows that humic acid tenors and the polymerization rates are linked to soil nature. Calcimagnesic soils ensure a more important humification than isohumic soils.