Search Results (12)

Olive stones (OS) are a by-product of great interest from olive oil mills and the table olive industry due to their high content of phenolic compounds. In this work, the extraction of phenolic compounds from OS via microwave-assisted extraction (MAE) with aqueous acetone was assayed. A central composite design of experiments was used to determine the optimal extraction conditions, with the independent variables being temperature, process time, and aqueous acetone (v/v). The dependent variables were the total content of phenolic compounds (TPC) measured by the Folin–Ciocalteu method and the main phenolic compounds identified and quantified by UPLC. Under optimal conditions (75 °C, 20 min, and 60% acetone), 3.32 mg TPC was extracted from 100 g of dry matter (DM) OS. The most suitable extraction conditions were different for each polyphenol. Therefore, 292.11 μg vanillin/g DM; 10.94 μg oleuropein/g DM; and 10.11 protocatechuic acid μg/g DM were obtained under conditions of 60 °C, 15 min, and 100% acetone; 43.8 °C, 10.45 min, and 61.3% acetone; and 64.8 °C, 16.58 min, and 97.8% acetone, respectively. Finally, MAE was compared with the traditional Soxhlet method under the same conditions. As a result, MAE was proven to be an enhanced and more feasible method for polyphenol extraction from OS. Full article

This study investigates the effectiveness of electrocoagulation (EC) with locally sourced iron electrodes for treating olive mill wastewater (OMW) prior to adsorption with olive stone (OS). Using Response Surface Methodology (RSM), 60 experiments were conducted to evaluate various operational parameters, including current density (CD), reaction time (T), distance between electrodes (D), and the number of electrodes (N). The optimal conditions identified were a reaction time of 53.49 min, a current density of 15.1104 mA/cm², 1 cm electrode spacing, and six electrodes. Under these conditions, the removal efficiencies achieved were 54.46% for total phenols (TPh), 73.25% for total Kjeldahl nitrogen (TKN), 92% for turbidity, 58.91% for soluble chemical oxygen demand (COD_soluble), and 58.55% for total COD (COD_total), with an energy consumption of 14.3146 kWh/m³ and a projected cost of USD 3.92/m³. Following the EC process, the treated OMW underwent further adsorption using OS, enhancing pollutant removal. The combined EC and adsorption (ECA) method demonstrated superior performance, achieving TPh removal at 62.63%, TKN removal at 77.52%, and turbidity reduction at 83.73%. Additionally, COD_total removal increased to 72.88% with COD_soluble removal at 70.04%. This integrated approach significantly improves pollutant removal, presenting a promising solution for effective OMW treatment. Full article

Recycling olive waste, a major by-product of the olive oil industry, presents significant environmental and economic benefits. This study explores the potential of olive waste (OW) by-products, specifically their individual components such as olive stones (OS), olive oily pomace (OS) and olive oil-free pomace (OF), as sustainable alternatives to wood in eco-friendly composite materials, alongside other residues such as miscanthus, spent mushroom substrate and recycled textile waste. Composite panels were produced with densities ranging from 685 to 907 kg/m³ through thermocompression. The manuscript details the production methodology and assesses the panel’s thermal performance, water absorption, and mechanical strength. The aim is to assess the viability of these alternative materials in producing composites that could serve as environmentally friendly substitutes for traditional wood-based products. Oil-free pomace is a promising and effective alternative to wood, suitable for dry environments. Composite panels composed of miscanthus or spent mushroom substrate and oil-free pomace met the EN 312 standards for general-purpose products in dry conditions, highlighting their potential for use in sustainable applications. Full article

Olive mill waste (olive pomace, OP, and olive stone, OS) was used in this work to produce adsorbents for the removal of five phenolic acids typically found in olive mill wastewater. OP and OS were subjected to different treatments (combined or not) that were chemically modified (NaOH) or physically modified by two different methods, incipient wetness impregnation (IWI) and hydrothermal deposition (HD), and even biochar production obtaining a total of 16 materials. The materials were characterized by different analytical techniques such as N₂ absorption, scanning electron microscopy, infrared spectroscopy, and pH zero-potential charge. The mixture of five phenolic acids was used to evaluate in batch conditions the adsorption capacity of the prepared materials. OS chemically modified with IWI (OSM-IWI) and OS biochar with HD (BOS-HD) presented better adsorption capacity at 157.1 and 163.6 mg/g of phenolic acids, respectively, from a total of 200 mg/g. For some materials, the surface area cannot be correlated with adsorption capacity, unlike pHzpc, where high values fit better adsorption rates. The infrared spectroscopy profile indicates the presence of O-H and N-H functional groups and, the last one, red-shifted in the IWI preparation compared to the HD one. In addition to this, the prepared material from olive mill waste can be suitably used for the mixture of phenolic compounds. Full article

In the context of climate change and the circular economy, biochar agricultural and environmental applications have attracted a good deal of attention. Biochar has unique characteristics like surface area, porosity, water-holding capacity, pH, surface charge, and nutrients. This study reviews the biochar production from olive pomace (OP) and olive stone (OS) byproducts, its chemical and physical characterization, and its environmental application. The current review highlights the conditions for biochar production, the effects of pyrolysis temperature, and feedstock type on the physicochemical properties of biochar. High pyrolysis temperature (>500 °C) promotes a high specific surface area, high porosity (especially for OS biochars), and pH as well as the content of ash and fixed carbon, but generates low cation exchange capacity (CEC) and electrical conductivity (EC) and high values of O/C and H/C ratio. OP biochar also presents a high C amount, and ash content, i.e., rich in nutrients and high alkalizing capacity. OP biochar serves as an important source of plant nutrients, especially potassium. After adding both types of biochar, aggregate stability and the amount of water held in soil increase, and bulk density and bioavailability of trace elements decrease. Thus, biochar from olive mill wastes can be a potential plant nutrient reservoir, a good amendment to improve soil properties and long-term carbon sequestration. Results presented in this review can be used to build designer biochars from olive mill wastes to help solve environmental issues (water purification and pollutant remediation) and are suitable for improving soil physical chemistry characteristics and crop growth. Full article

Graphene-based materials have been widely studied in the field of supercapacitors. However, their electrochemical properties and applications are still restricted by the susceptibility of graphene-based materials to curling and agglomeration during production. This study introduces a facile method for synthesizing reduced graphene oxide (rGO) nanosheets and activated carbon based on olive stones (OS) with polyaniline (PAni) surface decoration for the development of supercapacitors. Several advanced techniques were used to examine the structural properties of the samples. The obtained PAni@OS−rGO (1:1) electrode exhibits a high electrochemical capacity of 582.6 F·g⁻¹ at a current density of 0.1 A·g⁻¹, and an energy density of 26.82 Wh·kg⁻¹; thus, it demonstrates potential for efficacious energy storage. In addition, this electrode material exhibits remarkable cycling stability, retaining over 90.07% capacitance loss after 3000 cycles, indicating a promising long cycle life. Overall, this research highlights the potential of biomass-derived OS in the presence of PAni and rGO to advance the development of high-performance supercapacitors. Full article

One drawback of biomass hydrothermal treatment (HTC) is the need of a water supply, which is especially important in the case of lignocellulosic biomass. This study has investigated the synergy resulting from co-HTC of two residual biomass materials that significantly differ in their physico-chemical compositions: (a) olive stone, OS, a hard and high-quality biomass, with low N content, whose potential to give a high heating value briquette by HTC has been proven, and (b) fresh grass pruning, GP, as it is gathered from gardens, with a high water content, moderate N fraction, and low calorific value. The work specifically focuses on the water saving that can be attained when the liquid product produced by one of them (grass, with 80% of moisture) can supply part of the water needed by the other (olive stone) when both are subjected to HTC simultaneously. It was found that, when instead of water, an additional amount of fresh GP is added (in particular 40 out of 110 g of water was provided by 54 g of GP), and a more basic processing water is obtained (pH of co-HTC increased by 40%, in relation of single OS processes). This in turn did not have a remarkable effect on OS final SY at any of the two temperatures studied (200 and 220 °C), not on the C densification. Other features such as N content of resulting OS hydrochars showed a rise in the case of hybrid processes, from 0.2% to 3.3%. Other features that were affected on OS HTC products because of the presence of the GP in co-HTC were the HC surface structure, hydrophobicity, and the presence of surface functionalities and their thermal stability towards pyrolysis; processing water also showed changes on mineral content when both biomasses there blended. Proving that a biomass like OS can be hydrothermally treated by a hybrid process involving less water, without being detrimental in terms of final SY and energy densification, can open a field of research aimed to make HTC processes more efficient in terms of hydric balance. Full article

Olive stones (OS) are a by-product generated in the olive oil production process. This residue is obtained in industries after the oil extraction process, and it is recognized as an interesting feedstock for the production of bioenergy and value-added products. Nevertheless, currently, it is only used as a low-cost solid biofuel for combustion. An alternative valorization approach has been developed based on an acid-catalyzed process for the solubilization of hemicelluloses [¹] and the production of furfural [²]. This process yields a solid cellulose and lignin-rich material, which can be further upgraded. In this work, an organosolv process for the delignification of the material and improvement of the enzymatic digestibility was applied and optimized. The organosolv stage was carried out with an ethanol:water ratio (50:50, w/w) in a Parr reactor, varying the temperature (140–190 °C) and the addition of the catalyst (0–100 mM H₂SO₄). The liquid fraction obtained was analyzed to evaluate the presence of value-added products, such as phenolic compounds with antioxidant activity. The total phenolic content was determined by the Folin–Ciocalteu method, obtaining a phenol concentration between 5 and 13 g GAE/L, corresponding to a phenol yield of 8 g GAE/100 g of processed material, which ranks in the range of those obtained from other plant sources, in other olive by-products such as exhausted olive pomace, up to 9 g GAE/100 g of extract have been reported [³]. The phenolic profile was obtained by capillary electrophoresis analysis, allowing the identification, among others, of vanillin and syringaldehyde as naturally occurring flavor components exhibiting antioxidant and antimicrobial properties. Therefore, with the present study, we were able to determine that the liquor obtained after the organosolv pretreatment of olive stones can also be valued as a bio-source of non-synthetic preservatives and additives for the food industry. Full article

Olive trees constitute one of the largest agroindustries in the Mediterranean area, and their cultivation generates a diverse pool of biomass by-products such as olive tree pruning (OTP), olive leaves (OL), olive stone (OS), and extracted olive pomace (EOP). These lignocellulosic materials have varying compositions and potential utilization strategies within a biorefinery context. The aim of this work was to carry out an integral analysis of the aqueous extractives fraction of these biomasses. Several analytical methods were applied in order to fully characterize this fraction to varying extents: a mass closure of >80% was reached for EOP, >76% for OTP, >65% for OS, and >52% for OL. Among the compounds detected, xylooligosaccharides, mannitol, 3,4-dihydroxyphenylglycol, and hydroxytyrosol were noted as potential enhancers of the valorization of said by-products. The extraction of these compounds is expected to be more favorable for OTP, OL, and EOP, given their high extractives content, and is compatible with other utilization strategies such as the bioconversion of the lignocellulosic fraction into biofuels and bioproducts. Full article

This work addresses for the first time the study of olive stone (OS) biomass pretreatment by reactive extrusion technology using NaOH as the chemical agent. It is considered as a first step in the biological conversion process of the carbohydrates contained in the material into bio-based products. OS is a sub-product of the olive oil extraction process that could be used in a context of a multi-feedstock and multi-product biorefinery encompassing all residues generated around the olive oil production sector. OS biomass is pretreated in a twin-screw extruder at varying temperatures—100, 125 and 150 °C and NaOH/biomass ratios of 5% and 15% (dry weight basis), in order to estimate the effectiveness of the process to favour the release of sugars by enzymatic hydrolysis. The results show that alkaline extrusion is effective in increasing the sugar release from OS biomass compared to the raw material, being necessary to apply conditions of 15% NaOH/biomass ratio and 125 °C to attain the best carbohydrate conversion rates of 55.5% for cellulose and 57.7% for xylan in relation to the maximum theoretical achievable. Under these optimal conditions, 31.57 g of total sugars are obtained from 100 g of raw OS. Full article

Activated carbon monoliths (ACMs), with 25 cells/cm², were prepared from the direct extrusion of Alcell, Kraft lignin and olives stones particles that were impregnated with phosphoric acid, followed by activation at 700 °C. These ACMs were used as catalysts for methanol dehydration reaction under air atmosphere. ACM that was prepared from olive stone and at impregnation ratio of 2, OS2, showed the highest catalytic activity, with a methanol conversion of 75%, a selectivity to dimethyl ether (DME) higher than 90%, and a great stability under the operating conditions studied. The results suggest that the monolithic conformation, with a density channel of 25 cells/cm² avoid the blockage of active sites by coke deposition to a large extent. Methanol conversion for OS2 was reduced to 29% in the presence of 8%v water, at 350 °C, although the selectivity to DME remained higher than 86%. A kinetic model of methanol dehydration in the presence of air was developed, while taking into account the competitive adsorption of water. A Langmuir-Hinshelwood mechanism, whose rate-limiting step was the surface reaction between two adsorbed methanol molecules, represented the experimental data under the conditions studied very well. An activation energy value of 92 kJ/mol for methanol dehydration reaction and adsorption enthalpies for methanol and water of −12 and −35 kJ/mol, respectively, were obtained. Full article

Commercial stoned table olives named “alcaparras” from Trás-os-Montes (Portugal) were chemically characterized. During three consecutive years (2004–2006) 30 samples (10 per year) were examined for their nutritional value (moisture, crude protein, total fat, ash, carbohydrates, and energy), with a detailed report of the fatty acids and tocopherols composition. Water was the major constituent (72.5 ± 5.5%), followed by fat (14.6 ± 5.1%). The average amount of protein and ash were 1.1% and 3.4%, respectively, reporting unusual ash values for table olives, related to the technological process. One hundred grams of fresh stoned table olives presented an average energetic value of 156 kcal, lower than most table olives. The lipids are rich in oleic acid (average of 77.7 ± 2.0%), followed by palmitic acid and linoleic acid. Samples showed an average of total tocopherols of 1.2 mg/100 g of fresh weight, being α-tocopherol the most abundant. Table olives are important sources of MUFA, as olive oil, recognized as a preventive factor in diseases in which free radicals are implicated, complemented by the amounts of vitamin E, with both antioxidant and vitamin action. Full article