Qualitative and quantitative evolution of polyphenolic compounds during composting of an olive-mill waste-wheat straw mixture.

Olive-mill wastes represent a significant environmental problem in Mediterranean areas due to their important production during a short period of time. Their high polyphenol, lipid and organic acid concentrations turn them into phytotoxic wastes. This work examined the evolution of polyphenolic compounds during the composting of an olive-mill waste-wheat straw mixture by using quantitative (Folin-Ciocalteu) and qualitative (High Pressure Liquid Chromatography, HPLC) analyses. The polyphenol content decreased strongly by 93% while the significant correlations obtained between polyphenol content and different humification indices and lignin losses suggested that polyphenols contribute to the synthesis of humic substances. In addition, the significant correlation found between germination index, polyphenols and humification indices must be related to the progressive substrate detoxification as humification process progressed, leading to a non-phytotoxic and partially humified end-product. Nine polyphenolic compounds were identified by HPLC, most of which had disappeared by the end of composting, when only traces of hydroxytyrosol, caffeic and syringic acids and oleuropein were detected.

Optimisation of biodegradation conditions for the treatment of olive mill wastewater.

The aim of the present paper was to optimise the conditions of aerobic treatment of olive mill wastewater. To do so, the waste was treated following the experimental optimal design methodology studying the set of factors susceptible to influence the treatment (pH, C/N ratio, aeration and temperature). The results of a first series of experiments showed a strong correlation between the reduction in the levels of polyphenols and three of the parameters studied, i.e. the C/N ratio, aeration and temperature. Optimised conditions led to a 94% drop in polyphenols. Then, for a finer study of the conditions, just two parameters were varied, the pH and the C/N ratio. The results showed that the conditions of pH modification (addition of lime or sodium hydroxide) and the C/N ratio (urea or ammonium nitrate) allowed the microbiological activity to be very significantly improved. This led to polyphenol reductions of 51% and 76%.

Treatment of olive mill waste-water by aerobic biodegradation: an analytical study using gel permeation chromatography, ultraviolet-visible and Fourier transform infrared spectroscopy.

Liquid waste from olive oil mills was digested following inoculation with soil microorganisms and fractionated through various grades of gel. The fractionation showed the range of sizes of the molecules in the waste. In addition, the disappearance of the low molecular weight fraction, which is retained by the gel, and the increase of the high molecular weight fraction, which is excluded by the gel, during the last stages of the microbial treatment, indicates polymerisation of the low-molecular-weight subunits. Characterization of the fractions by UV-visible and FTIR spectroscopy confirmed the increase in their degree of polymerisation during the treatment. This is paralleled by a reduction in the amount of aliphatic components and a concomitant increase in aromatic structures.

Eliminating toxic compounds by composting olive mill wastewater-straw mixtures.

The present work studies the changes occurring in organic matter, phenols and biotoxicity on composting olive mill wastewater with barley straw. The total organic matter decreased, a drop of 25% was reached after the stabilization phase and 52% at the end of the maturation phase. Degradation of the phenols reached 54% and 95%, respectively, after these periods. The toxicity of the water extract, evaluated by the Photobacterium phosphoreum fluorescence, decreased to disappear after only 2 months of composting. This trend was confirmed by the tight correlation between the physico-chemical and toxicity parameters, indicating that the degradation of organic matter leads to a strong reduction of the C/N ratio and of toxicity. The results obtained indicate a normal process of humification occurring during the composting of the formerly highly toxic olive mill wastewater-straw mixture and resulting in a product, which has good agricultural properties as organic fertilizer.