Olive Solid Waste Research Articles

Environmental impacts analysis of Moroccan olive cake combustion in Stirling motor cogeneration system: Case study

Morocco is the world's 5th largest olive oil producer with 160,000 tons in 2020/2021 and the production of 1 L of olive oil generated approximately 5 kilos of waste olive cake, this type of waste is dangerous for the environment and especially for groundwater. To address this issue and take into account the thermal properties of olive waste, our project's goal is to produce power and heat by using solid olive waste in a Stirling cogeneration system. Therefore, the goal of this article is to examine by using CFD tools the environmental impacts of the Moroccan solid olive waste burning in a CHP (combined heat and power) unit. The idea is to integrate a smart renewable energy system based on olive cake and the Stirling motor to produce electricity in order to employ this electrical energy for water pumping in rural areas.The impact of the excessive air ratio on temperature profile and exhaust has been investigated and discussed. In addition, the pollutant species in air has been presented, and compared with guideline values given by some international organization for health and environment. Results show that the highest excess air ratio gives high temperatures with a homogeneous distribution around the Stirling motor hot heat exchanger, and minimum emissions of CO, CO2, NO, NO2 and NH3 that do not exceed the values set by WHO, OSHA, and NIOSH.

Enhancing mechanical and thermal properties of sustainable cement mortar through incorporation of olive solid waste aggregates

This research paper presents a comprehensive investigation into the characterization of cement mortar incorporating olive solid waste aggregates (OSW) as a partial replacement for natural sand. Different levels of OSW content (0%, 5%, 10%, and 15%) were used to create samples, enabling a comparison of their mechanical and thermal properties against the reference mortar. The primary objective of this study is to analyze the mechanical and thermal performance of lightweight cement mortar, with a secondary focus on establishing correlations between distinct testing methods, including compressive strength, sclerometer, and thermal tests. Mechanical properties were assessed through compressive strength testing. After a 28-day curing period, the mortar containing 5% OSW exhibited a compressive strength of 33 MPa. Notably, it demonstrated a 15.6% reduction in density compared to the reference mortar. An examination of the relationship between destructive compressive strength tests and non-destructive sclerometer tests (NDST) revealed a linear correlation, suggesting the effectiveness of the sclerometer test in estimating cement mortar compressive strength. Furthermore, we investigated the thermal characteristics of OSW-incorporated cement mortar. The mixture containing 5% OSW exhibited a thermal conductivity of 0.87 W/m·K, representing a 21% reduction compared to the reference mortar. These findings underscore the potential of OSW to enhance the thermal properties of the resulting cement mortar. Additionally, the observed correlation between compressive strength and thermal conductivity highlights a significant connection between these properties. This study primarily addresses the mechanical and thermal attributes of cement mortar incorporating OSW while also exploring correlations between testing methods. The resulting cement mortar meets the minimum strength requirements for structural applications as a construction material.

Chromium(VI) Toxicity and Active Tolerance Mechanisms of Wheat Plant Treated with Plant Growth-Promoting Actinobacteria and Olive Solid Waste.

The present study aimed to assess the potential of plant growth-promoting Actinobacteria and olive solid waste (OSW) in ameliorating some biochemical and molecular parameters of wheat (Triticum aestivum) plants under the toxicity of high chromium levels in the soil. With this aim, a pot experiment was conducted, where the wheat plants were treated with a consortium of four Actinobacterium sp. (Bf treatment) and/or OSW (4% w/w) under two levels of nonstress and chromium stress [400 mg Cr(VI) per kg of soil] to estimate the photosynthetic traits, antioxidant protection machine, and detoxification activity. Both Bf and OSW treatments improved the levels of chlorophyll a (+47-98%), carotenoid (+324-566%), stomatal conductance (+17-18%), chlorophyll fluorescence (+12-28%), and photorespiratory metabolism (including +44-72% in glycolate oxidase activity, +6-72% in hydroxypyruvate reductase activity, and +5-44% in a glycine to serine ratio) in leaves of stressed plants as compared to those in the stressed control, which resulted in higher photosynthesis capacity (+18-40%) in chromium-stressed plants. These results were associated with an enhancement in the content of antioxidant metabolites (+10-117%), of direct reactive oxygen species-detoxifying enzymes (+49-94%), and of enzymatic (+40-261%) and nonenzymatic (+17-175%) components of the ascorbate-glutathione cycle in Bf- and OSW-treated plants under stress. Moreover, increments in the content of phytochelatins (+38-74%) and metallothioneins (+29-41%), as markers of detoxification activity, were recorded in the plants treated with Bf and OSW under chromium toxicity. In conclusion, this study revealed that the application of beneficial Actinobacteria and OSW as biofertilization/supplementation could represent a worthwhile consequence in improving dry matter production and enhancing plant tolerance and adaptability to chromium toxicity.

Visible light-driven ZnO nanoparticles/carbon nanodots hybrid for broad-spectrum antimicrobial activity

A Hybrid composite of zinc oxide nanoparticles (ZnO-NPs) and carbon nanodots (CNDs) was synthesized by the sol–gel method. CNDs were obtained from olive solid wastes by pyrolysis and chemical oxidation methods. The combination of CNDs and ZnO materials led to the formation of a hybrid nanocomposite, where CNDs adsorbed on the surface of ZnO particles leading to an increase of its ζ- potential to be −28 mV; this refers to the hydroxyl and carboxyl groups attached on CNDs, which localized on the surface of ZnO after the hybridization, as well their sizes have been enlarged from 23.5 to 105 nm which is an indication of the successful hybridization of those moieties. Additionally, the CNDs enhance the visible-light photocatalytic activity of ZnO, showing a decrease in the energy band gap from 3.1 to 2.8 eV, where CNDs play as an intermediate energy level above the valence band of ZnO. Antimicrobial activity tests were also performed against Gram-positive and Gram-negative bacterial and fungal strains under dark and sunlight modes. The hybrid exhibits excellent antimicrobial activity within minimal inhibitory concentrations (7.8–62.5) µg/L, and the inhibition growth percentage was 99.9%, an inhibition zone ranged from (19 to 38) mm, and the kill time kinetic was one to two hours. The antimicrobial activity mechanism was also studied by the glutathione oxidation test showing that the broad-spectrum antimicrobial is directly related to its ROS-forming ability with a percent glutathione deficiency oxidation percentage of (88.2%) for dark mode and (95%) for sunlight mode. The findings of this study demonstrate the ability of synthesized hybrid nanocomposite as an antimicrobial active material for broad-spectrum microbial strains and other environmental solutions.

Interactive Effect of Arbuscular Mycorrhizal Fungi (AMF) and Olive Solid Waste on Wheat under Arsenite Toxicity.

Heavy metal such as arsenite (AsIII) is a threat worldwide. Thus, to mitigate AsIII toxicity on plants, we investigated the interactive effect of olive solid waste (OSW) and arbuscular mycorrhizal fungi (AMF) on wheat plants under AsIII stress. To this end, wheat seeds were grown in soils treated with OSW (4% w/w), AMF-inoculation, and/or AsIII treated soil (100 mg/kg soil). AMF colonization is reduced by AsIII but to a lesser extent under AsIII + OSW. AMF and OSW interactive effects also improved soil fertility and increased wheat plants' growth, particularly under AsIII stress. The interactions between OSW and AMF treatments reduced AsIII-induced H2O2 accumulation. Less H2O2 production consequently reduced AsIII-related oxidative damages i.e., lipid peroxidation (malondialdehyde, MDA) (58%), compared to As stress. This can be explained by the increase in wheat's antioxidant defense system. OSW and AMF increased total antioxidant content, phenol, flavonoids, and α-tocopherol by approximately 34%, 63%, 118%, 232%, and 93%, respectively, compared to As stress. The combined effect also significantly induced anthocyanins accumulation. The combination of OSW+AMF improved antioxidants enzymes activity, where superoxide dismutase (SOD, catalase (CAT), peroxidase (POX), glutathione reductase (GR), and glutathione peroxidase (GPX) were increased by 98%, 121%, 105%, 129%, and 110.29%, respectively, compared to AsIII stress. This can be explained by induced anthocyanin percussors phenylalanine, cinamic acid and naringenin, and biosynthesic enzymes (phenylalanine aminolayse (PAL) and chalcone synthase (CHS)). Overall, this study suggested the effectiveness of OSW and AMF as a promising approach to mitigate AsIII toxicity on wheat growth, physiology, and biochemistry.

Positive Interaction of Selenium Nanoparticles and Olive Solid Waste on Vanadium-Stressed Soybean Plant

The purpose of the current study was to determine the possible improvement in soybean plants’ tolerance against vanadium-induced stress in response to the application of olive solid waste (OSW) and selenium nanoparticles (Se-NPs), by assessing metabolites and plant defense systems. Drawing upon this aim, a pot experiment was performed where the soybean plants were grown with a fertilization treatment (including, control, OSW, Se-NPs, and Se-NPs + OSW) under vanadium stress (including non-stress and 350 mg sodium orthovanadate per kg of soil). Enhancement of hydrogen peroxide (H2O2) and malondialdehyde (MDA) accumulation in vanadium-stressed plants confirmed the oxidative damage in unfertilized plants. Results indicated the positive effects of the combined treatment (Se-NPs + OSW) in improving the plant stress tolerance by causing a balance in the produced ROS and detoxified ROS in the plant. It was mainly stimulated through the improvement of the photosynthetic parameters, anthocyanin metabolism pathway, phenylpropanoid pathway, non-enzymatic antioxidant metabolites (tocopherols, malondialdehyde, polyphenols, and flavonoids), antioxidant enzymes, and biochemical components involved in the ASC/GSH cycle (ascorbate, ascorbate peroxidase, dehydroascorbate reductase, monodehydroascorbate reductase, glutathione, glutathione reductase, and glutathione peroxidase), and antioxidant direct scavenging enzymes (peroxidase, catalase, and superoxide dismutase), which finally resulted in higher plant biomass. In conclusion, the simultaneous application of OSW and Se-NPs treatments provided a reliable protection for soybean plants in vanadium-contaminated soils through the activation of antioxidant and non-antioxidant defense mechanisms.

Olive Industry Solid Waste-Based Biosorbent: Synthesis and Application in Wastewater Purification.

In this work, we present a process for converting olive industry solid waste (OISW) into a value-added material with ionic receptors for use in the removal of toxic metal ions from wastewater. This 3D polymer is a promising adsorbent for large-scale application, since it is a low-cost material made from agricultural waste and showed exceptional performance. The synthesis of the network polymer involved the carboxymethylation of OISW and curing of the carboxymethylated OISW at an elevated temperature to promote the formation of ester linkages between OISW's components. FT-IR, atomic force microscopy, and thermal analysis were performed on the crosslinked product. The adsorption efficiency of the crosslinked carboxymethylated OISW toward Pb(II), Cu(II), and other toxic metal ions present in sewage was evaluated as a function of adsorbent dose, temperature, pH, time, and initial metal ion. The percentage removal of about 20 metal ions present in a sewage sample collected from a sewer plant located in the Palestinian Territories was determined. The adsorption efficiency did not drop even after six cycles of use. The kinetic study showed that the adsorption process follows the Langmuir isotherm model and the second-order adsorption rate. The experimental Qe values of 13.91 and 13.71 mg/g were obtained for Pb(II) and Cu(II) removal, respectively. The thermodynamic results confirm the spontaneous metal bonding to the receptor sites of the crosslinked carboxymethylated OISW.

Impact of olive solid waste on the mechanical performance of cement mortars

Impact of olive solid waste on the mechanical performance of cement mortars

Natural source compatibilizers for olive waste/recycled polypropylene matrix composites

AbstractA simple, environmentally friendly process was developed for surface hydrophobization of cellulose‐rich waste to improve their compatibility with recycled polypropylene (rPP), helping reduce costs while recycling environmentally problematic waste such as solid olive waste (also called olive pomace). In this study, an improvement of the interfacial bonding strength between the hydrophilic waste particles and the hydrophobic matrix was achieved by surface hydrophobization of the waste using a ring‐opening polymerization reaction of epoxidized soy‐bean oil (ESBO) with SnCl2 as a catalyst. The treatment on cellulose based filter paper led to a contact angle of 128°. The composite containing treated olive pomace has shown an increase in the elongation of 92% and an increase in the stress at yield of 15%, indicating improved compatibility.

Physicochemical Characterization and Antibacterial Properties of Carbon Dots from Two Mediterranean Olive Solid Waste Cultivars.

Carbon nanomaterials have shown great potential in several fields, including biosensing, bioimaging, drug delivery, energy, catalysis, diagnostics, and nanomedicine. Recently, a new class of carbon nanomaterials, carbon dots (CDs), have attracted much attention due to their easy and inexpensive synthesis from a wide range of precursors and fascinating physical, chemical, and biological properties. In this work we have developed CDs derived from olive solid wastes of two Mediterranean regions, Puglia (CDs_P) and Calabria (CDs_C) and evaluated them in terms of their physicochemical properties and antibacterial activity against Staphylococcus aureus (S. aureus) and Pseudomonas aeruginosa (P. aeruginosa). Results show the nanosystems have a quasi-spherical shape of 12–18 nm in size for CDs_P and 15–20 nm in size for CDs_C. UV–Vis characterization indicates a broad absorption band with two main peaks at about 270 nm and 300 nm, respectively, attributed to the π-π* and n-π* transitions of the CDs, respectively. Both samples show photoluminescence (PL) spectra excitation-dependent with a maximum at λem = 420 nm (λexc = 300 nm) for CDs_P and a red-shifted at λem = 445 nm (λexc = 300 nm) for CDs_C. Band gaps values of ≈ 1.48 eV for CDs_P and ≈ 1.53 eV for CDs_C are in agreement with semiconductor behaviour. ζ potential measures show very negative values for CDs_C compared to CDs_P (three times higher, −38 mV vs. −18 mV at pH = 7). The evaluation of the antibacterial properties highlights that both CDs have higher antibacterial activity towards Gram-positive than to Gram-negative bacteria. In addition, CDs_C exhibit bactericidal behaviour at concentrations of 360, 240, and 120 µg/mL, while lesser activity was found for CDs_P (bacterial cell reduction of only 30% at the highest concentration of 360 µg/mL). This finding was correlated to the higher surface charge of CDs_C compared to CDs_P. Further investigations are in progress to confirm this hypothesis and to gain insight on the antibacterial mechanism of both cultivars.

Electrosorption of phenolic compounds from olive mill wastewater: Mass transport consideration under a transient regime through an alginate-activated carbon fixed-bed electrode

Olive mill wastewater (OMWW) is an environmentally critical effluent, specifically due to its high content of phenolic compounds (PCs), which are hazardous due to their antimicrobial activities in water. However, their properties have good health effects at suitable doses. For the first time, the electrosorption of PCs from actual OMWW has been proposed for their possible recovery as value-added compounds, while decontaminating OMWW. A bio-sourced alginate-activated carbon (AC) fixed-bed electrode was prepared based on the reuse of olive pomace solid waste as powdered AC. At the optimal AC content (1% w/v), the internal ohmic drop voltage was lower (2.26 V) and the mass transport coefficient was higher (9.7 10−5 m s−1) along with the diffusivity (7.3 10−9 m2 s−1), which led to enhanced electrosorption rates. Afterward, an optimal electrode potential was obtained (−1.1 V vs. Ag/AgCl), while higher voltages led to faradaic reactions. Moreover, the adsorption capacity was lower (123 mg g−1) than that of electrosorption (170 mg g−1) and was even higher (307 mg g−1) with actual effluents. This was probably due to the influence of electromigration, which was confirmed by new models that could predict the electrosorption kinetics well considering mass transport and acid dissociation constants.

Bioethanol Production from Olive Solid Residues by Using Rhodotorula Minuta

Bioethanol is an attractive fuel with higher potential for energy security and environmental safety. Olive solid residues were used as a raw material for the production of bioethanol through the use of different preliminary treatments . Separate treatments with cellulose, hydrochloric acid (HCl 5%), sulfuric acid (H2SO4 2%), and liquid ammonia NH4OH (20%) were used to convert cellulose and hemicellulose into monosaccharaides. The production of ethanol was observed during the fermentation process using R. minuta under anaerobic conditions. After 3 days of fermentation, lowest concentrations of ethanol of 0.233, 0.249, 0.261, and 0.275 g/ l were produced from olive waste powder sample as a result of separate pretreatment with cellulase, hydrochloric acid (HCl 5%), sulfuric acid (H2SO4 2%), and liquid ammonia NH4OH (20%), respectively, whereas the untreated sample showed ethanol yield of 0.264 g/ l.. The highest ethanol concentrations for the same samples were 0.510, 0.564, 0.737, and 0.696 g/ l, respectively, whereas that for the untreated samples was 0.445 g/ l. The highest concentration of ethanol produced (0.737 g/ l) was achieved after 3 days of fermentation of olive solid waste pretreated with H2SO4 2% at 30 oC and pH 5. The average yield of ethanol resulted from these saccharification and fermentation processes following the pretreatment of olive solid waste was 0.59 g/10 g dry olive solid residues.

Optical properties and photoactivity of carbon nanodots synthesized from olive solid wastes at different carbonization temperatures.

Carbon nanodots (CNDs) have many fascinating properties, such as optical properties (UV-Visible absorption and fluorescence emission), which make them good candidates in many applications, such as photocatalysts for the degradation of several organic pollutants. This study aims to synthesize CNDs from olive solid wastes at different carbonization temperatures from 300 to 900 °C and study the effect on the optical properties of the CNDs, such UV-Vis, fluorescence, quantum yield, and energy bandgap, in addition to the influence on the photoactivity of the CNDs as photocatalysts for the degradation of methylene blue (MB). CNDs were prepared from olive solid wastes (OSWs) by pyrolysis at different temperatures (300–900 °C) for conversion to carbonized material, and then oxidized chemically in the presence of hydrogen peroxide (H2O2). It was found that an increase in the carbonization temperature of the OSWs leads to an increase in the product yield with a maximum value at 500 °C, and it then decreased dramatically. On the other hand, a decrease in fluorescence due to the diminishment of oxygen groups and the destruction of the surface of the CNDs was observed. The higher quantum yield (5.17%) and bandgap (2.77 eV) were achieved for CNDs prepared from OSWs that carbonized at 300 °C. The rate and degradation efficiency of MB were studied with the different synthesized CNDs, and it was found that an increase in the carbonization temperature leads to a decrease in the rate and degradation efficiency of MB, with the highest degradation rate of 0.0575 min−1 and degradation efficiency of 100% after 120 minutes of light irradiation being realized for the sample carbonized at 300 °C.

KINETICS AND ISOTHERM STUDY FOR ADSORPTION OF METHYL ORANGE DYE INTO LOW COST AGRICULTURAL BY-PRODUCT (OLIVE SOLID WASTES) AS ADSORBENT

The removal of dyes from wastewater is a matter of great interest in the field of waste water treatment. The effluents from many industries often contain one or more toxic dyes. methyl orange (MO) is one of the most common water-soluble dyes. Therefore, an increased interest has been focused on removing such dyes from wastewaters. In general, several methods are used for the removal of dyes from wastewater. Among the treatment methods, adsorption is comparatively superior. Agricultural wastes are renewable and available abundantly at no or low costs. Due to the abundant availability at no or low costs, little processing cost and ability to biodegrade Olive Solid Wastes (OSW) materials, an agricultural by-product, were identified as a potential adsorbent material for wastewater treatment in this study. Batch experiments were carried out for the sorption of methyl orange onto Olive Solid Wastes (OSW) particles. The operating variables studied were initial solution pH, initial dye concentration, and OSW dose. Equilibrium data were fitted to Freundlich isotherm equation. The monolayer sorption capacity of OSW for methylene blue sorption was found to be 101 mg/g. The sorption kinetics was found to follow pseudo second order kinetic model

High adsorption capacity of thermally treated solid olive wastes to treat olive mill wastewater

In this study, solid olive wastes were suggested as adsorbents for olive mill wastewater (OMWW) clean-up. These solid olive wastes underwent thermal treatment by two-step process: carbonization at 300°C and 400°C, then physical activation at 800°C and 1000°C. Characterizations were determined by FTIR, TGA/DTA, and N2 Adsorption-Desorption techniques. The efficiency of these new bio-adsorbents was verified on OMWW. Adsorption kinetics experiments were realized at room temperature and diluted OMWW (1/100 v/v). Evaluation of obtained activated carbons (ash, iodine value, and moisture) shows a good activity and stability in weight according to the thermogravimetric analysis. Moreover, the textural results of BET surface area showed a high area for activated carbons prepared from olive stones at 300°C/800°C (SBET = 208 ± 0.3 m2/g) and olive flesh at 400°C/1000°C (SBET = 77 ± 0.8 m2/g). The adsorption rates of OMWW were 91% after 120 min and 95.3% after 60 min contact time at pH = 2.0, respectively. At the end, the pH increased to neutral value. Thus, these bio-adsorbents from solid waste of olive industry can be efficient adsorbents for their liquid effluent clean-up.

Carbon-dots conductometric sensor for high performance gas sensing

In this paper the first example of using C-dots (CDs) as sensing nanomaterial for monitoring low concentrations of NO2 in ambient air is reported. In the logic to support a green circular economy, CDs were prepared from a natural low cost precursor consisting in olive solid waste (OSW) by a simple pyrolysis process combined with chemical oxidation. Characterization data showed the formation of spherical CDs with dimensions in the narrow size range from 0.5 to 5 nm and charged with functional groups (COO- (carboxylate), C-O-C (epoxide) and C-OH (hydroxyl) imprinting excellent water colloidal dispersion. The nanomaterial was used to fabricate and test a conductometric gas sensor (CDs-sensor) that was found to exhibit excellent performances in terms of high and selective response to sub-ppm concentration of NO2 at low temperature (150 °C), low limit of detection (LOD) of 50 ppb, good reproducibility and stability over use and aging. To the best of our knowledge, this is the first example reported in the literature of CDs high performances gas sensing material. Results here presented pave the way for a new class of a carbon nanomaterial for gas sensing to be applied in the field of environmental monitoring.

Effect of Fresh and Fermented Olive Solid Waste and Cow Manure on Zinc Forms in Calcareous Soil and Wheat Plant Productivity

A field experiment was conducted at the farm of Abu Jarash in Agricultural College, using different rates of olive solid waste and cow manure, as follows: (control, Mineral fertilizer +NPK, fresh olive solid waste100%, fresh olive solid waste 75%+ cow manure 25%, fresh olive solid waste 50%+ cow manure 50%, fermented olive solid waste 100%, fermented olive solid waste 75%+ cow manure 25%, fermented olive solid waste 50%+ cow manure 50%, cow manure 100%) the Zink ground fertilizers added for all previous treatments, and cultivation of wheat, the forms of zinc were followed by serial extraction and the study led to the following results: the fermented olive solid waste 100% treatment was Superiority in the amount of zinc forms as following: (total, soluble, exchanged, linked with carbonate, linked with organic matter linked with iron and manganese oxides and residual) the amounts of Zinc were (114.14, 0.19048, 1.0710, 6.329, 9.433, 21.04, 76.10) mg/kg in the same previous order. While the zinc values in the control treatment were (62.90, 0.03847, 0.6081, 3.29, 6.083, 15.03, 37.2) mg/kg for the same forms and in the same previous order. The fermented olive solid waste treatment 100% had the highest yield (5.980) ton/h. The control treatment had the lowest value (3.987) ton/h.

A computational investigation of olive oil residues combustion in a vertical furnace

The paper presents a numerical investigation of combustion of pulverised olive waste and its impregnated samples. Olive oil by-products, mainly olive solid waste (OSW) and olive mill wastewater (OMWW) mixtures that are called impregnated solid waste (ISW) are investigated for different mixing ratios. The investigation is carried out by an in-house two-dimensional CFD code based on the finite volume method, developed for this purpose. The model is first validated by comparisons to the experimental data and predictions of other authors. Subsequently, it is applied to the cases of present interest, predicting the efficiency of the thermal process, species and temperature distributions. The combustion behaviour of ISW is compared with that of the original OSW under the same conditions. The findings of the present study shows that a beneficial effect of using ISW is observed, as the addition of OMWW leads to a decrease of carbon oxides production. Furthermore, the OMWW addition does not have a negative effect on their firing quality since the different samples exhibit quite close temperature profiles. Obtained results are important for the investigation the possibility of using olive residues as an alternative energy source in olive producing countries.

Short-term impacts of pomace application and Pseudomonas bacteria on soil available phosphorus

Abstract This study was conducted with the aim of investigating phosphorus release from pomace or solid olive waste in the presence of phosphorus solubilizing Pseudomonas bacteria. A multi-level factorial experiment with complete randomized design was employed in three replications. A calcareous soil was mixed with 2 and 4 g pomace per 100 g soil (W2 and W4, respectively) and inoculated with indicator and soil isolated Pseudomonas sp. (106 cell g−1) (Pf and Pi, respectively). Soil without pomace and Pseudomonads were also included as control (W0Pn). Mixtures incubated in sterile and non-sterile conditions for 4 months. Sampling was carried out at 0, 2, 7, 14, 28, 42, 56, 86 and 120 days and some soil biochemical properties were measured. The effects of pomace, bacteria, incubation time and their interactions were significant on pH, EC, basal respiration, organic carbon (OC), available phosphorus (Pava) and phosphatase activity (p ≤ 0.01). Pomace increased soil OC content in both non-sterile and sterile conditions. The maximum amount of Pava in non-sterile mixtures was observed in W4Pi (133.25 mg kg−1). Pomace and phosphorus solubilizing bacteria addition to soil increased phosphatase activity. Although Pava concentration was highest in W4 treatments during the incubation period, its trend was ascending in W2 treatments. It seems that 2 g pomace per 100 g soil is enough for improving biological properties and phosphorus availability. Overall, the application of pomace with P-solubilizing bacteria can be a solution to increase soil available P level, reduce dependency on chemical P fertilizers and sustainable management of such solid wastes.

Potential for Production of Biochar-Based Fertilizers from Olive Mill Waste in Mediterranean Basin Countries: An Initial Assessment for Spain, Tunisia, and Greece

Olive mill wastes continue to be a management challenge due to the large volumes produced, particularly due to their toxicity and impacts on the environment. Thermal conversion through pyrolysis or hydrothermal carbonization techniques can detoxify wastes while conserving nutrient contents. In this work, we produced up-to-date data on olive mill waste flows in Spain, Tunisia, and Greece and characterized representative samples in the laboratory. Assays of thermal conversion of olive mill wastewaters and solid wastes were also performed to understand biochar yields and final properties, and the total quantities of nutrients contained were estimated. Of particular note were the quantities of potassium in Tunisian wastewaters, representing 0.6% of the total mass and an annual flow of approximately 5000 t, and in the Spanish solid wastes, an average of 1.7% of the total mass is potassium, representing an annual flow of approximately 23,000 t. Concerning phosphorus, Spanish solid wastes had the highest contents (0.1%), double that of other countries’ wastes. Annually, olive mill wastes from the three countries are estimated to contain approximately 35 × 103 tons of potassium and 2.6 × 103 tons of phosphorus. With this resource converted to biochar, each year more than 700 km2 of soils could be enriched in 0.2% carbon with biochar at an application rate of 7 t ha−1.