Olive Oil Waste Treatment: A Comparative and Critical Presentation of Methods, Advantages & Disadvantages

Olive (Olea europaea L.) Seed as New Source of Cholesterol-Lowering Bioactive Peptides: Elucidation of Their Mechanism of Action in HepG2 Cells and Their Trans-Epithelial Transport in Differentiated Caco-2 Cells

The production of olive oil has important economic repercussions in Mediterranean countries but also a considerable impact on the environment. This production generates enormous quantities of waste and by-products, which can be exploited as new raw materials to obtain innovative ingredients and therefore make the olive production more sustainable. In a previous study, we decided to foster olive seeds by generating two protein hydrolysates using food-grade enzymes, alcalase (AH) and papain (PH). These hydrolysates have shown, both in vitro and at the cellular level, antioxidant and antidiabetic activities, being able to inhibit the activity of the DPP-IV enzyme and modulate the secretion of GLP-1. Given the multifunctional behavior of peptides, both hydrolysates displayed dual hypocholesterolemic activity, inhibiting the activity of HMGCoAR and impairing the PPI of PCSK9/LDLR, with an IC50 equal to 0.61 mg/mL and 0.31 mg/mL for AH and PH, respectively. Furthermore, both samples restored LDLR protein levels on the membrane of human hepatic HepG2 cells, increasing the uptake of LDL from the extracellular environment. Since intestinal bioavailability is a key component of bioactive peptides, the second objective of this work is to evaluate the capacity of AH and PH peptides to be transported by differentiated human intestinal Caco-2 cells. The peptides transported by intestinal cells have been analyzed using mass spectrometry analysis, identifying a mixture of stable peptides that may represent new ingredients with multifunctional qualities for the development of nutraceuticals and functional foods to delay the onset of metabolic syndrome, promoting the principles of environmental sustainability.

Treatment technologies for olive mill wastewater with impacts on plants

Olive mill wastewater (OMW), produced during olive oil production, contains high levels of salt contents, organic matter, suspended particles, and toxic chemicals (particularly phenols), which all result in increased biological and chemical oxygen demand. Olive Oil Mills' Wastes (OMW), which have dark brown color with unpleasant smell, consist mainly of water, high organic (mainly phenols and polyphenols) and low inorganic compounds (e.g. potassium and phosphorus), as well as grease. OMW components can negatively affect soil's physical, chemical, and biological properties, rendering it phytotoxic. However, OMW can positively affect plants' development when it's applied to the soil after pretreatment and treatment processes due to its high mineral contents and organic matter. There are various approaches for removing impurities and the treatment of OMW including chemical, biological, thermal, physiochemical, and biophysical processes. Physical techniques involve filtration, dilution, and centrifugation. Thermal methods include combustion and pyrolysis; biological techniques use anaerobic and aerobic techniques, whereas adsorption and electrocoagulation act as physiochemical methods, and coagulation and flocculation as biophysical methods. In contrast, combined biological treatment methods use co-digestion and composting. A comparison of the effects of both treated and untreated OMW samples on plant development and soil parameters can help us to understand the potential role of OMW in increasing soil fertility. This review discusses the impacts of untreated OMW and treated OMW in terms of soil characteristics, seed germination, and plant growth. This review summarizes all alternative approaches and technologies for pretreatment, treatment, and recovery of valuable byproducts and reuse of OMW across the world.

Methods for Intensifying Biogas Production from Waste: A Scientometric Review of Cavitation and Electrolysis Treatments

This article presents future trends in research using microbiological methods to intensify bioprocesses for biogas production. The pretreatment by combinations of physical and chemical methods, such as cavitation and electrolysis, is considered. The approach of the article involved reviewing the residual area on the intensification technologies of anaerobic digestion with current methods to improve the quality and quantity of biogas. The most valuable reported positive results of the pretreatment of biological raw materials in the cavitation process were reviewed and are presented here. A model of the effect of electrolysis on the species diversity of bacteria in anaerobic digestion was developed, and changes in the dominance of the ecological and trophic systems were revealed on the basis of previous studies. The stimulating effect on biogas yield, reduction in the stabilization period of the reactor, and inactivation of microorganisms at lower temperatures is associated with different pretreatment methods that intensify anaerobic digestion. More research is recommended to focus on the electrolysis treatment of different types of waste and their ratios with optimization of regime parameters, as well as in combination with other pretreatments to produce biomethane and biohydrogen in larger quantities and in better qualities.

Olive Mill Wastewater Remediation: From Conventional Approaches to Photocatalytic Processes by Easily Recoverable Materials

Olive oil production in Mediterranean countries represents a crucial market, especially for Spain, Italy, and Greece. However, although this sector plays a significant role in the European economy, it also leads to dramatic environmental consequences. Waste generated from olive oil production processes can be divided into solid waste and olive mill wastewaters (OMWW). These latter are characterized by high levels of organic compounds (i.e., polyphenols) that have been efficiently removed because of their hazardous environmental effects. Over the years, in this regard, several strategies have been primarily investigated, but all of them are characterized by advantages and weaknesses, which need to be overcome. Moreover, in recent years, each country has developed national legislation to regulate this type of waste, in line with the EU legislation. In this scenario, the present review provides an insight into the different methods used for treating olive mill wastewaters paying particular attention to the recent advances related to the development of more efficient photocatalytic approaches. In this regard, the most advanced photocatalysts should also be easily recoverable and considered valid alternatives to the currently used conventional systems. In this context, the optimization of innovative systems is today’s object of hard work by the research community due to the profound potential they can offer in real applications. This review provides an overview of OMWW treatment methods, highlighting advantages and disadvantages and discussing the still unresolved critical issues.

Biostimulant Potential of Humic Acids Extracted From an Amendment Obtained via Combination of Olive Mill Wastewaters (OMW) and a Pre-treated Organic Material Derived From Municipal Solid Waste (MSW)

Olive mill wastewaters (OMW) contain significant levels of phenolic compounds with antimicrobial/phytotoxic activity and high amounts of undecomposed organic matter that may exert negative effects on soil biology. Among OMW detoxification techniques, those focusing on oxidative degradation of phenolic compounds are relevant. The composting (bio-oxidation) process in particular, exploits exothermic oxidation reactions by microorganisms to transform the organic matrix of OMW into an amendment biologically stable and feasible to use in agriculture. This process consists of an active phase during which organic compounds are rapidly decomposed, and a curing phase characterized by a slow breakdown of the remaining materials with the formation of humic substances (HS) as by-products. In this study, bio-oxidation of OMW was performed using a pre-treated organic material derived from municipal solid waste (MSW). The obtained amendment (OMWF) was stable and in accordance with the legislative parameters of mixed organic amendments. HS were then extracted from OMWF and MSW (control amendment, Amd-C), and differences in structural properties of their humic acid (HA) fraction were highlighted via spectroscopy (Fourier Transform Infrared) and Dynamic Light Scattering. To assay a potential use of HA as biostimulants for crops, 12-day old Zea Mays L. plants were supplied with HA at 0.5 mg and 1 mg C L-1 for 2 days. HA from both amendments increased plant growth, but HA from OMWF was more effective at both dosages (plus 35-37%). Also, HA from OMWF enhanced both nitrogen assimilation and glycolysis by increasing the activity of nitrate reductase (∼1.8-1.9 fold), phosphoglucose isomerase (PGI) (∼1.8-2 fold) and pyruvate kinase (PK) (∼1.5-1.8 fold), while HA from Amd-C targeted glycolysis preferentially. HA from OMWF, however, significantly stimulated plant nutrition only at lower dosage, perhaps because certain undetermined compounds from detoxified OMW and incorporated in HA altered the root membrane permeability, thus preventing the increase of nutrient uptake. Conversely, HA from Amd-C increased nutrient accumulation in maize at both dosages. In conclusion, our results indicate that the amendment obtained via OMW composting using MSW had a reduced pollution load in terms of phenolic compounds, and HA extracted from OMWF could be used as valuable biostimulants during maize cultivation.

Degradation of olive mill wastewater by the induced extracellular ligninolytic enzymes of two wood-rot fungi

Olive mill wastewater (OMWW) is a major problem in olive oil - producing countries, due to its high organic load and concentration in phenols that are toxic for marine life, plants and soil microorganisms. In the present study, two mushroom species were tested in regard to their OMWW's oxidative capacity, Pleurotus citrinopileatus LGAM 28684 and Irpex lacteus LGAM 238. OMWW (25% v/v) degradation was investigated for several culture conditions, namely pH, agitation speed, nitrogen-based supplements and their concentration. The selected values were pH 6, agitation rate 150 rpm, 30 g L^-1 corn steep liquor as nitrogen source for P. citrinopileatus and 20 g L^-1 diammonium tartrate for I. lacteus. The two strains performed well in cultures supplemented with OMWW, generating very high titers of oxidative enzymes and achieving more than 90% color and phenols reduction within a 24 days cultivation period. In addition, the amount of glucans present in the fungal biomass was assessed. Hence, P. citrinopileatus and I. lacteus appear as potent degraders of OMWW with the ability to use the effluent as a substrate for the production of biotechnologically important enzymes and valuable fungal glucans.

Synthesis and in vitro antiproliferative evaluation of PEGylated triterpene acids

A set of PEGylated derivatives of oleanolic and maslinic acids has been semi-synthesised, attaching ethylene glycol, diethylene glycol, triethylene glycol or tetraethylene glycol to the C-28 carboxyl group of these natural triterpenes and some derivatives. Another set of PEGylated derivatives has been semi-synthesised by connecting the same four ethylene glycols to the hydroxyl groups of the A ring of these triterpenic acids, through a carbonate linker, by reaction with trichloromethyl chloroformate. The aqueous solubility of some of these PEGylated derivatives has been compared with that of maslinic acid. The cytotoxic effects of 28 triterpenic PEGylated derivatives in three cancer-cell lines (B16-F10, HT29, and Hep G2) have been assayed. The best results have been achieved with the HT29 cell line, and specifically with the oleanolic acid derivatives having ethylene glycol or tetraethylene glycol attached to the C-28 carboxyl group, which are approximately 27-fold more effective than their natural precursor. Eight PEGylated derivatives have been selected to compare the cytotoxicity results in the HT29 cancer-cell line with those of a non-tumour cell line of the same tissue (IEC-18), four of which were less cytotoxic in the non-tumour cell line. These compounds showed apoptotic effects on treated cells, with percentages of total apoptosis between 20% and 53%, relative to control, at 72h and IC₅₀ concentration, and between 29% to 62%, relative to control, for the same time and IC₈₀ concentration. We have also found that with the treatment of these compounds in HT29 cancer cells, cell-cycle arrest occurred in the G0/G1 phase. Finally, we have also studied changes in mitochondrial membrane potential during apoptosis of HT29 cancer cells, and the results suggest an activation of the extrinsic apoptotic pathway for these compounds.

Inhibitive action of stored olive mill wastewater (OMW) on the corrosion of copper in a NaCl solution

Stored OMWs are greatly enriched in phenolic compounds, mainly HT and tyrosol. But, after 4 years the concentrations of these compounds decrease. We find that OMW acts as a mixed-type corrosion inhibitor.

Characterization of olive mill wastewater fractions treatment by integrated membrane process

BACKGROUND

Up to now, the management of olive mill wastewaters, a three-phase mill by-product, remains an unsolved problem, in particular for those regions where huge quantities of vegetable water are produced. Olive mill wastewaters were therefore treated to evaluate the characteristics of permeate and retentate fractions produced by an integrated membrane system working at two different volume concentration factors.

RESULTS

The effect of two membrane-based filtration steps (microfiltration and nanofiltration) on the content of chemical oxygen demand, dry matter, sensory quality, phenolic compounds and antioxidant activity of permeate and retentate samples was evaluated. Furthermore, the effect of two different volume concentration factors (VCF), in the nanofiltration step, were investigated. At high VCF values, the total phenolic content in the retentate fraction was found to be 3.7-fold higher than the starting one, while the reduction of chemical oxygen demand in the permeate fraction was greater than 97% also at lower VCF values.

CONCLUSION

Each filtration step has provided useful information concerning the utility and appropriateness of the processes chosen, suggesting a sustainable hypothesis of 'normal industrial practice' that can be included in current processes of oil extraction, in order to purify water and recover phenolic compounds with high added value.

Enhanced reduction of phenol content and toxicity in olive mill wastewaters by a newly isolated strain of Coriolopsis gallica

The search for novel microorganisms able to degrade olive mill wastewaters (OMW) and withstand the toxic effects of the initially high phenolic concentrations is of great scientific and industrial interest. In this work, the possibility of reducing the phenolic content of OMW using new isolates of fungal strains (Coriolopsis gallica, Bjerkandera adusta, Trametes versicolor, Trichoderma citrinoviride, Phanerochaete chrysosporium, Gloeophyllum trabeum, Trametes trogii, and Fusarium solani) was investigated. In vitro, all fungal isolates tested caused an outstanding decolorization of OMW. However, C. gallica gave the highest decolorization and dephenolization rates at 30 % v/v OMW dilution in water. Fungal growth in OMW medium was affected by several parameters including phenolic compound concentration, nitrogen source, and inoculum size. The optimal OMW medium for the removal of phenolics and color was with the OMW concentration (in percent)/[(NH4)2SO4]/inoculum ratio of 30:6:3. Under these conditions, 90 and 85 % of the initial phenolic compounds and color were removed, respectively. High-pressure liquid chromatography analysis of extracts from treated and untreated OMW showed a clear and substantial reduction in phenolic compound concentrations. Phytotoxicity, assessed using radish (Raphanus sativus) seeds, indicated an increase in germination index of 23-92 % when a 30 % OMW concentration was treated with C. gallica in different dilutions (1/2, 1/4, and 1/8).

Valorization of solid waste products from olive oil industry as potential adsorbents for water pollution control--a review

The global olive oil production for 2010 is estimated to be 2,881,500 metric tons. The European Union countries produce 78.5% of the total olive oil, which stands for an average production of 2,136,000 tons. The worldwide consumption of olive oil increased of 78% between 1990 and 2010. The increase in olive oil production implies a proportional increase in olive mill wastes. As a consequence of such increasing trend, olive mills are facing severe environmental problems due to lack of feasible and/or cost-effective solutions to olive-mill waste management. Therefore, immediate attention is required to find a proper way of management to deal with olive mill waste materials in order to minimize environmental pollution and associated health risks. One of the interesting uses of solid wastes generated from olive mills is to convert them as inexpensive adsorbents for water pollution control. In this review paper, an extensive list of adsorbents (prepared by utilizing different types of olive mill solid waste materials) from vast literature has been compiled, and their adsorption capacities for various aquatic pollutants removal are presented. Different physicochemical methods that have been used to convert olive mill solid wastes into efficient adsorbents have also been discussed. Characterization of olive-based adsorbents and adsorption mechanisms of various aquatic pollutants on these developed olive-based adsorbents have also been discussed in detail. Conclusions have been drawn from the literature reviewed, and suggestions for future research are proposed.

Clay improvement with burned olive waste ash

Olive oil is concentrated in the Mediterranean basin countries. Since the olive oil industries are incriminated for a high quantity of pollution, it has become imperative to solve this problem by developing optimized systems for the treatment of olive oil wastes. This study proposes a solution to the problem. Burned olive waste ash is evaluated for using it as clay stabilizer. In a laboratory, bentonite clay is used to improve olive waste ash. Before the laboratory, the olive waste is burned at 550°C in the high temperature oven. The burned olive waste ash was added to bentonite clay with increasing 1% by weight from 1% to 10%. The study consisted of the following tests on samples treated with burned olive waste ash: Atterberg Limits, Standard Proctor Density, and Unconfined Compressive Strength Tests. The test results show promise for this material to be used as stabilizer and to solve many of the problems associated with its accumulation.

Selective cytotoxic activity of new lipophilic hydroxytyrosol alkyl ether derivatives

Recent data suggest that hydroxytyrosol, a phenolic compound of virgin olive oils, has anticancer activity. This communication reports the synthesis of decyl and hexadecyl hydroxytyrosyl ethers, as well as the cytotoxic activity of hydroxytyrosol and a series of seven hydroxytyrosol alkyl ether derivatives against A549 lung cancer cells and MRC5 non-malignant lung fibroblasts. Hydroxytyrosyl dodecyl ether (HTDE) showed the highest selective cytotoxicity, and possible mechanisms of action were investigated; results suggest that HTDE can moderately inhibit glycolysis, induce oxidative stress, and cause DNA damage in A549 cells. The combination of HTDE with the anticancer drug 5-fluorouracil induced a synergistic cytotoxicity in A549 cancer cells but not in non-malignant MRC5 cells. HTDE also displayed selective cytotoxicity against MCF7 breast cancer cells versus MCF10 normal breast epithelial cells in the 1-30 μM range. These results suggest that the cytotoxicity of HTDE is more potent and selective than that of parent compound hydroxytyrosol.

Rhizosphere dynamics during phytoremediation of olive mill wastewater

The potential of phytoremediation as a treatment option for olive mill wastewater (OMW) was tested on five perennial tree species. Cupressus sempervirens and Quercus ilex proved tolerant to six-month OMW treatment followed by six-month water irrigation, whereas Salix sp. and Laurus nobilis and, later, Pinus mugo suffered from phytotoxic effects. Test plants were compared to controls after treatment and irrigation, by monitoring biochemical and microbiological variations in the rhizosphere soil. OMW-treated soils were exposed to 50-fold higher phenols concentrations, which, irrespective of whether the respective plants were OMW-resistant or susceptible, were reduced by more than 90% by the end of the irrigation cycle, owing to significantly increased laccase, peroxidase and β-glucosidase activities, recovery/acquisition of bacterial culturability and transitory development of specialized fungal communities sharing the presence of Geotrichum candidum. Of all results, the identification of Penicillium chrysogenum and Penicillium aurantiogriseum as dominant rhizosphere fungi was distinctive of OMW-tolerant species.

Vermicomposting of olive oil mill wastewaters

The disposal of olive oil mill wastewaters (OMW) represents a substantial environmental problem in Italy. A vermicompost process could be an alternative and valid method for the management of OMW. In a laboratory experiment, the OMW were absorbed onto a ligno-cellulosic solid matrix and 30 adult earthworms of Eisenia fetida specie were added. The experiment was carried out for 13 weeks. The number of earthworms increased throughout the experimental period and after 2 weeks about 90% of the earthworms had become sexually mature. The decrease in total organic carbon (about 35%), C : N ratio (from 31.2 to 12.3) and biochemical parameters (hydrolytic enzymes averagely 40% and dehydrogenase 23%), and the increase in humification rate (pyrophosphate extractable carbon (PEC) from 17.6 to 33.3 mg g(-1), and PEC : water-soluble carbon from 1.76 to 2.97) indicated the mineralization and the stabilization of organic matter at the end of the vermicomposting process. At the end of the experiment, the extracellular beta-glucosidase, phosphatase, urease and protease activities, measured in the pyrophosphate extract of the vermicompost, were found to be always higher or equal to that measured at the beginning of the vermicomposting process, suggesting that the enzymes bound to humic matter resisted biological attack and environmental stress. Moreover, the results obtained from the phyto-test showed that the OMW lose their toxicity and stimulate plant germination and growth.

Synthesis of hydroxytyrosyl alkyl ethers from olive oil waste waters

The preparation of a new type of derivatives of the naturally occurring antioxidant hydroxytyrosol is reported. Hydroxytyrosyl alkyl ethers were obtained in high yield by a three-step procedure starting from hydroxytyrosol isolated from olive oil waste waters. Preliminary results obtained by the Rancimat method have shown that these derivatives retain the high protective capacity of free hydroxytyrosol.