Olive Tree Pruning Research Articles

Biomass gasification coupled to an EFGT-ORC combined system to maximize the electrical energy generation: A case applied to the olive oil industry

This research presents the modelling and simulation of an innovative small-scale power system composed of a downdraft gasifier, an externally fired gas turbine (EFGT) and an Organic Rankine Cycle (ORC) as a bottoming unit for increasing the electrical energy generation. Olive tree pruning (217 kg/h) was the biomass used, producing more than 200 kWe and an electrical efficiency of 20.7%. The producer gas achieved suitable mole composition (H2: 14.8%, CO: 19.5%, CH4: 2.2%, CO2: 9.3%, H2O: 12.0% and N2: 41.5%), lower calorific value (4.53 MJ/kg) and gasification efficiency (89%). The hot producer gas was burnt directly at atmospheric pressure in an EFGT, producing 150 kWe and exhaust gases at 290 °C. Five ORC working fluids were studied to maximize the electricity generation: isopentane, benzene, cyclohexane, R113, R245fa. Isopentane was the most suitable fluid, reaching 57.1 kWe and 20.45% of ORC thermal efficiency. On the other hand, despite R113 gave minor electricity production (49.1 kWe), this allowed to generate thermal power for CHP applications.

Possibilities of Energy Generation from Olive Tree Residues, by-products and Waste in Crete, Greece

The objective of the current work is the investigation of the current utilization of olive tree residues, by-products and waste for energy generation in Crete and their future prospects. The quantity of olive tree biomass in Crete has been estimated and its potential for energy generation has been calculated. Possibilities for using it for heat production, power generation, biogas production, pellet manufacturing and fermentable sugar production have been investigated. Experiences in other olive oil producing countries have been recorded together with the technologies used or experimented with so far. The energy potential of olive tree biomass in Crete has been estimated at 24.05 % of the TPES supply in the island. The only highly utilized olive tree by-product for heat generation by combustion in Crete is the olive kernel wood. Olive tree pruning have the highest energy content but they are underutilized in Crete. Their successful utilization in other countries for pellet manufacturing and power generation indicates that their exploitation should be promoted in Crete. The results of this study indicate that olive tree cultivation in Crete, apart from producing a high nutritional edible product, generates residues, by-products and waste which if properly utilized could contribute in the reduction of fossil fuels used and the carbon footprint due to energy use in the island.

Hygrothermal properties of clayey plasters with olive fibers

This research deals with how to use agricultural waste materials in constructions considering that the development of innovative materials has to respond to both environmental and energy issues. The leaves and the small branches derived from the pruning of olive trees were incorporated, after drying, into a clay-sand mixture to obtain a bio-based plaster. Earthen samples, containing different percentages of olive fibers, were prepared and tested to investigate their hygrothermal behaviour. Thermal conductivity and the effects of several parameters on thermal performance were analyzed. The evaluation of the hygric behaviour was based on the measurement of the water vapour diffusion resistance factor and of the isothermal sorption curves. Results showed that the addition of olive fibers in the earth matrix enhances the insulating and hygric performances. The ability of the material to exchange moisture was studied by calculating the ideal Moisture Buffering Value (MBVideal). Results showed that the effects of moisture adsorption/desorption improved with the increase of the fibers content.

Kinetic analysis of pyrolysis and combustion of the olive tree pruning by chemical fractionation

This paper presents a kinetic analysis of thermal decomposition of olive tree pruning from its basic compounds in pyrolysis and combustion reactions. Experiments were performed by TGA under inert and oxidant conditions and results indicated that the decomposition of the olive tree pruning was related to the material composition. Pseudo-mechanistic models were proposed estimating the yield of pyrolysis on its basic compounds (hemicelluloses, cellulose and lignin). Validity and reliability of the proposed kinetic models were verified by the good fitting between the simulated and experimental curves (with values of R2 higher than 0.99 in most cases). Moreover, during the fractionation process, an acid fraction was obtained with great fuel properties, a high calorific value and a low residue after its combustion.

Lignin characterization from two different pretreatments in bioethanol production processes from olive tree pruning

Biomass generated from pruning of olive trees is an abundant lignocellulosic residue that has been proposed for bioethanol production by means of a process including pretreatment, enzymatic hydrolysis, and fermentation. The pretreatment is critical step in the process, which allows the fractionation of the biomass. Lignin is the main byproduct of the process, and then its valorization is a key factor for the economical viability of the bioethanol production from olive tree pruning. In this work, two types of pretreatments have been compared steam explosion and organosolv in terms of the produced lignin suitability for further applications in the so-called new biorefinery concept. Starting from this fact, special emphasis was given to determine the physico-chemical properties of lignins produced by the two processes in order to determine their suitability for the development of added value products (e.g. materials, building blocks, additives). Overall, the lignin obtained from organosolv pretreatment had better properties for its further valorization as it presents more suitable qualities for higher-added value applications like fine phenolic chemicals production.

Assessing cellulose nanofiber production from olive tree pruning residue

Pruning operation in olive trees generates a large amount of biomass that is normally burned causing severe environmental concern. Therefore, the transformation of this agricultural residue into value-added products is imperative but still remains as a technological challenge.In this study, olive tree pruning (OTP) residue is evaluated for the first time to produce cellulose nanofibers (CNF). The OTP bleached pulp was treated by TEMPO-mediated oxidation and subsequent defibrillation in a microfluidizer. The resulting CNF was characterized and compared to CNF obtained from a commercial bleached eucalyptus kraft pulp using the same chemi-mechanical procedure.CNF from OTP showed higher carboxylate content but lower fibrillation yield and optical transmittance as compared to eucalyptus CNF. Finally, the visco-elastic gel obtained from OTP was stronger than that produced from eucalyptus. Therefore, the properties of CNF from OTP made this nanomaterial suitable for several applications.CNF from OTP showed higher carboxylate content as compared to eucalyptus CNF (1038 vs. 778μmol/g) but lower fibrillation yield (48% vs. 96%) and optical transmittance. Finally, the visco-elastic gel obtained from OTP was stronger than that produced from eucalyptus. Therefore, the properties of CNF from OTP made this nanomaterial suitable for several applications.

Use of clay and olive pruning waste for building materials with high hygrothermal performances

Several clayey materials incorporating different percentages of leaves and small branches derived from the pruning of olive trees were prepared and tested in Thermophysical Laboratory of Polytechnic University of Bari. Hygrothermal properties were measured according to technical standards. In order to consider the potential of earthen materials to improve indoor comfort, the software WUFI®Plus was used to simulate the hygrothermal behavior of a Test Building, placed in a Mediterranean climate. The analysis was carried out considering the internal surface of the walls of the building covered by two different plasters i.e. gypsum plaster and clayey plaster with 6% of olive waste. Results demonstrated that when considering an unconditioned scenario (without HVAC system) the clayey plaster lead up to a greater improvement of the hygric performances, unlike traditional coverings as gypsum plaster. However, in presence of HVAC system any significant variations occurs in terms of energy saving.

Thermal destruction of organic waste hydrophobicity for agricultural soils application

Use of organic amendments is a good strategy for combating the growing problem of soil degradation due to deterioration of organic matter content, particularly severe in semi-arid European Mediterranean regions, while at the same time providing an opportunity for recycling organic wastes. Olive mill pomace (OMP), the main by-product of the olive oil industry, is being used increasingly in olive grove soils for this purpose. Although the positive effects of OMP amendments have been widely studied, they also have some negative effects on soil. One of the most critical is that they increase water repellency (WR) due to the presence of poorly evolved, strongly aliphatic compounds. This detrimental effect has received very little attention, although it may impair plant water availability and infiltration rates, increase erosion and lower long-term soil quality. This study proposed, for the first time, thermal treatment as an effective way of reducing WR in organic amendments (i.e. mixtures of OMP, olive tree pruning, chicken manure and spent coffee grounds) prior to their application to soil. Thermal treatment at 275 °C proved effective in removing WR, while lower temperatures (175 or 225 °C) can even increase it. Changes by thermal treatment in the characteristics of the organic amendments studied with FTIR and UV–Vis spectroscopy and thermogravimetric analysis showed that it strongly reduced the aliphatic compounds mainly responsible for their hydrophobicity, concentrated aromatic compounds and increased thermostability. Heating also reduced phytotoxicity, making all of the organic amendments usable in the field (germination index over 100%). Therefore, heating at 275 °C could be an acceptable option for removing WR from organic amendments, enhancing their quality with more stable evolved characteristics.

Wastes from the olive oil production in sustainable bioremediation systems to prevent pesticides water contamination

Installation of biobed biopurification systems at farm level, traditionally composed of soil, peat and straw, to reduce point source contamination is difficult in some countries where peat is not environmentally or economically feasible. This study evaluates the use of local organic wastes from olive oil production such as wet olive cake and its vermicompost as substitutes of peat and olive tree pruning as substitute of straw to perform robust biobeds capable of removing mixtures of pesticides at high concentrations. Adsorption capacity of the novel biomixtures was comparable to or higher than traditional one. The biomixture with soil and olive tree pruning showed the highest pesticides adsorption, except for imidacloprid. The biomixture with soil, vermicompost and olive tree pruning showed dissipation efficiency of dimethoate, imidacloprid and oxyfluorfen (>73%) higher than traditional biobed. Meanwhile, the biomixture with soil and vermicompost was the alternative biomixture with the highest dissipation of diuron (54%) and tebuconazole (35%) but it was lower than traditional biomixture (59 and 47% for diuron and tebuconazole, respectively). The low dissipation of these compounds (<60%) is probably due to competitive and/or inhibitory phenomena between the pesticides in the mixture. Labile organic compounds from biomixture components such as water-soluble carbon constitute a more available carbon source for microorganisms that may counteracted the negative impact of high pesticide load on biomixture microbial populations, but they may have limited the pesticides dissipation. Novel biomixtures composed of olive oil mill waste may be a sustainable and less expensive alternative to traditional biomixture.

Torrefaction of olive tree pruning: Effect of operating conditions on solid product properties

In this work, the effect of experimental conditions of torrefaction on properties of olive tree pruning was investigated. This study has demonstrated that fuel properties of olive tree pruning were improved by torrefaction. For example, torrefaction at 300°C during 60min provided to raw biomass an increase on the ratio of fixed carbon to volatiles (from 0.23 to 0.39) and it improved its fuel quality. Elemental analysis revealed that the composition of olive tree pruning moved from lignocellulosic biomass to coal (for example, from O/C and H/C ratios of 1.02 and 0.17 for raw biomass to 0.90 and 0.15 for torrefied sample at 300°C during 10min). Also, as a result of torrefaction, a more homogeneous solid with higher heating value was obtained. However, bulk density of solid did not change significantly after torrefaction process. In addition, SEM analysis indicated that the olive tree pruning surface structure was broken and destroyed by torrefaction process. Also, the thermogravimetric analysis of native and torrefied samples in nitrogen atmosphere showed a strong degradation of hemicellulose and, also, in severe torrefaction conditions, a modification on the thermal stability of cellulose. Finally, an investigation on the pyrolysis kinetics of native and torrefied samples was presented. Lower energy activation values of main lignocellulosic pseudo-components were obtained for torrefied samples.

Lignin depolymerization for phenolic monomers production by sustainable processes

Biomass wastes (almond shell and olive tree pruning) were used in this work as raw materials for the extraction of high purity lignin by different delignification methods. A pretreatment stage was carried out to remove the major hemicelluloses content in the solid feedstocks. Afterward, two sulfur-free pulping processes (soda and organosolv) were applied to extract the largest fraction of lignin. The extracted lignin contained in the liquors was isolated using selective precipitation methods to design a tailor-made technique for obtaining high-purity lignin (in all cases more 90% of purity was reached). Soda process allowed the extraction of more lignin (around 40%–47%) than organosolv process (lower than 20%) regardless of the lignocellulosic source employed.Once the different lignin samples were isolated and characterized, they were depolymerized for the obtaining of small phenolic compounds. Three main streams were produced after the reaction: phenolic enriched oil, residual lignin and coke. After the purification of these fractions, their quantifications and characterization were conducted.The most abundant product of the reaction was residual lignin generated by the undesirable repolymerization of the initial lignin with yields around 30%–45%. The yield of the stream enriched in phenolic oil was higher than 20%. Coke, the lowest added-value product, presented a yield lower than 12% in all the cases. Lignin from organosolv presented higher phenolic oil yields, mainly due to their lower molecular size. This parameter was, thus, considered a key factor to obtain higher yields.

Design and Optimization of Sulfuric Acid Pretreatment of Extracted Olive Tree Biomass Using Response Surface Methodology

Olive tree biomass (OTB) represents an interesting feedstock for bioethanol production. In this study, olive tree pruning was water extracted and pretreated by dilute sulfuric acid to achieve high sugar recoveries from cellulosic and hemicellulosic fractions. Temperature (160 to 200 °C), acid concentration (0 to 8 g acid/100 g extracted raw material), and solids loading (15% to 35% w/v) were selected as operation variables and modified according to a Box-Behnken experimental design. The optimal conditions for the acid pretreatment were 160 °C, 4.9 g sulfuric acid/100 g biomass, and 35% solids loading (w/v), according to multiple criteria that considered the maximization of both the hemicellulosic sugars concentration in prehydrolysate and the overall sugar yield. These optimized conditions yielded a sugar concentration of 79.8 g/L, corresponding to an overall yield of 39.8 g total sugars/100 g extracted OTB. The fermentability of hemicellulosic sugars prehydrolysates from the acid pretreatment was evaluated by Escherichia coli after a detoxification stage by overliming. The prehydrolysates with lower concentrations of toxic compounds were fermented and achieved ethanol yields higher than 80% of the theoretical ethanol yield.

Long Term Amendment with Fresh and Composted Solid Olive Mill Waste on Olive Grove Affects Carbon Sequestration by Prunings, Fruits, and Soil.

The soil amendment with organic wastes represents a way to increase the soil fertility and the organic carbon (C) stored in the agro-ecosystems. Among the organic waste materials produced by agricultural and industrial activities, olive mill wastes derived from the olive oil extraction process may represent a suitable soil amendment. The aim of the study was to evaluate the effect of fresh (SOMW) or composted mixture of SOMW and shredded olive tree prunings (C-SOMW+P) on the vegetative and productive activities of olive trees, on the C stored in the tree non-permanent structures (prunings and fruits) and in the soil. The plots treated with SOMW or C-SOMW+P showed higher vegetative and productive activities than the untreated plots, and this was attributed to the higher total N and availability of P and K supplied by the amendments. Consequently, treatments increased the C sequestered in the tree non-permanent structures than in the control trees. However, no significant different effect between SOMW and C-SOMW+P treatments was found for the C stored in prunings and fruits, whereas it was evident a stronger influence of C-SOMW+P than SOMW on soil C sequestration. Indeed, about 50% the C supplied by the treatment with C-SOMW+P was sequestered in the olive grove system, with more than 90% of the sequestered C stored into the soil. The low amount of C sequestered in the soil following the addition of SOMW was attributed to its richness of moisture and easily degradable compounds that triggered the mineralization processes controlled by the soil microbial community. Although the 8 years of amendment produced a higher fruit yields than the control, no difference occurred between the characteristics and the oil content of the olive fruits. Only the total phenol content for the oil obtained from the SOMW-treated plots was significantly higher. The other considered fruit characteristics did not show significant differences.

Characterization and determination of the S/G ratio via Py-GC/MS of agricultural and industrial residues

To explore the potential values of lignin from agricultural residues (apple tree pruning, olive tree pruning and almond shell) and industrial residues (kraft black liquor) were used as raw materials for lignin extraction by different fractionation processes (kraft, organosolv, acetosolv and acetosolv and formosolv processes). The isolated lignins were characterized by Py-GC/MS, FTIR and GPC. The fractionation process influenced greatly the average molecular weight (Mw) that was measured by GPC. The harsh conditions during the acetosolv and acetosolv-formosolv processes promoted the repolymerization phenomena giving high Mw lignins. The EKL presented lower Mw due to higher retention times. All lignins exhibit higher relative abundances of S-type of phenols except for the almond shell lignin where G-type of phenols were the most abundant ones. The S/G ratios for hardwood type of lignin were analogous which ranged from 2.30 to 2.71, whereas almond shells lignin revealed an S/G ratio of 0.94. Kraft liquid fraction showed the highest lignin content (6.39%) and consequently the highest S/G ratio (2.71).

Endophytic Fungi as Pretreatment to Enhance Enzymatic Hydrolysis of Olive Tree Pruning.

Olive tree pruning, as one of the most abundant lignocellulosic residues in Mediterranean countries, has been evaluated as a source of sugars for fuel and chemicals production. A mild acid pretreatment has been combined with a fungal pretreatment using either two endophytes (Ulocladium sp. and Hormonema sp.) or a saprophyte (Trametes sp. I-62). The use of endophytes is based on the important role that some of them play during the initial stages of wood decomposition. Without acid treatment, fungal pretreatment with Ulocladium sp. provided a nonsignificant enhancement of 4.6% in glucose digestibility, compared to control. When a mild acid hydrolysis was carried out after fungal pretreatments, significant increases in glucose digestibility from 4.9% to 12.0% (compared to control without fungi) were observed for all fungal pretreatments, with maximum values yielded by Hormonema sp. However, despite the observed digestibility boost, the total sugar yields (taking into account solid yield) were not significantly increased by the pretreatments. Nevertheless, based on these preliminary improvements in digestibility, this work proves the potential of endophytic fungi to boost the production of sugar from olive tree pruning, which would add an extra value to the bioeconomy of olive crops.

Gasification of Olive Tree Pruning in Fluidized Bed: Experiments in a Laboratory-Scale Plant and Scale-up to Industrial Operation

Olive tree pruning was gasified with air in a laboratory fluidized bed (FB) reactor at 800, 850, and 900 °C and equivalence ratios (ERs) ranging from 0.12 to 0.35. A few additional tests were performed varying the fuel particle size, biomass feed rate, and oxygen enrichment in the air. The composition of the product gas was determined by measuring the light gas, water vapor, tar, and some inorganic contaminants. The solids produced were characterized by sampling from the cyclone and bed, providing approximate information about the char elutriation rate and residence time. The lower heating value of the gas, LHV (excluding benzene and tars), varied between 4.5 and 7.8 MJ/(Nm3) using air, whereas it increased to 9.3 MJ/(Nm3) using enriched air with 40% O2.. Carbon conversion increased with temperature (so did gasification efficiency), reaching 97% at 900 °C, indicating almost complete fuel conversion. Analysis of the results with the assistance of a previously developed FB gasification model indicated that ...

Kinetic modelling of torrefaction of olive tree pruning

The objective of this study is the proposal of a pyrolysis kinetic model that describes the thermal decomposition of olive tree pruning in different torrefaction conditions via thermogravimetrical measurements in nitrogen atmosphere. First, the determination of activation energies was performed by isoconversional methods of Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose and Friedman. Three stages were distinguished in which the activation energy keeps approximately constant and were related to the thermal degradation of the different constituents of the material (cellulose, hemicellulose and lignin). Then, Coast-Redfern method was applied to determine the kinetic function. The kinetic function that seems to determine the mechanism of thermal degradation of main components of olive tree pruning was nth order reaction. Finally, a detailed pseudo-mechanistic model (using least squares fitting in a parallel reaction scheme) was analyzed. This model was appropriate to predict the pyrolysis behavior of the olive tree pruning in all torrefaction conditions studied.

Study of the catalytic effect of nickel in the thermal decomposition of olive tree pruning via thermogravimetric analysis

The generation of problematic Ni-loaded waste from several applications alongside the high cost of the metal catalysts has caused the research effort to develop low cost Ni-catalysts. Therefore, the aim of this work is the study of the catalytic effect of nickel ions onto the thermal decomposition of the olive tree pruning (OTP) in nitrogen and oxygen-based atmospheres via thermogravimetric analysis. Experiments were carried out for the raw and Ni-OTP at three heating rates (5, 10 and 20 °C/min) and in three different reaction atmospheres (N2, 90% N2-10% O2 and 80% N2-20% O2). Results showed a slight displacement of the curves rightward in the first half of the curve for the Ni-OTP. Besides, the residual mass fraction was lower for Ni-OTP than for the raw one, changing the values from 24.59 to 15.94 for N2 atmosphere, from 10.45 to 4.11 for atmosphere with 10% of O2 and from 4.26 to 3.03 for atmosphere with 20% of O2. This behavior could be due to the inhibitory and catalyst effect that would be produced by the presence of nickel in the solid during the different stages of the thermal degradation. Besides, the environmental implication of presence of nickel during the thermal processes was analyzed and no negative environmental effect was observed.

The impact of biochars prepared from agricultural residues on phosphorus release and availability in two fertile soils

Biochars have a high variability in chemical composition, which is influenced by pyrolysis conditions and type of biomass. Essential macronutrient P retained in biochar could be released and made available to plants, enhancing plant growth. This study was conducted in order to evaluate whether biochar, produced from agricultural residues, could release P in water, as well as study its potential effect on plant growth and P uptake. Biochar samples were prepared from rice husks, grape pomace and olive tree prunings by pyrolysis at 300 °C and 500 °C. These samples were used for P batch successive leaching experiments in order to determine P release in water. Subsequently, rice husk and grape pomace biochars, produced by pyrolysis at 300 °C, were applied to two temperate soils with highly different pH. A three-month cultivation period of ryegrass (Lolium perenne L.) was studied in threefold replication, while three harvests were accomplished. Treatments comprised control soils (without amendment) and soils amended only with biochar. Results of P leaching tests showed a continuous release of P from all biochars as compared to raw biomass samples, for which the highest P concentrations were detected during the first extraction. Grape pomace and rice husk biochars pyrolyzed at 500 °C showed higher levels of water-extractable P, as compared to their corresponding raw biomass. Biochars, at 500 °C, leached more P in all four extractions, compared to biochars at 300 °C, apart from olive tree prunings biochars, where both pyrolysis temperatures presented a similar trend. Concerning plant yield of ryegrass, rice husk and grape pomace biochars showed positive statistically significant effects on plant yield only in slightly acidic soil in second and third harvests. In terms of P uptake of ryegrass, grape pomace biochars depicted positive significant differences (P < 0.05) in third harvest, in slightly acidic soil, while in first and second harvests positive significant differences were observed in alkaline soil. These results suggest that biochars derived from agricultural residues may act as a source of P in agronomic applications and improve plant growth, although soil conditions may play a significant role.

Seasonal variations in antioxidant compounds of Olea europaea leaves collected from different Italian cultivars

The objectives of this research were to study the best conditions for phenol extraction from olive tree leaves and to evaluate the content of phenolics and the antioxidant activity by in vitro assays in olive leaves harvested in different periods from four different Italian cultivars. The results showed that leaves/solvent ratio and temperature showed a significant and positive correlation with phenol extraction yield. In all harvesting periods the phenol content of Dolce Agogia samples was higher ( P ≤ 0.05) with respect to Moraiolo, Leccino and Frantoio samples. The results of analysis by high-performance liquid chromatography coupled with diode array detector (HPLC-DAD) showed that Dolce Agogia had the highest concentrations of hydroxytyrosol and oleuropein. Moreover the highest contents of bioactives have been found in olive leaves harvested in December and March. In these months, corresponding to olive harvest and pruning of olive trees, leaves represent a waste product and this interesting result could be useful in the production of nutraceuticals.