Potential of bioethanol production from olive mill solid wastes

Polymers without Petrochemicals: Sustainable Routes to Conventional Monomers

Access to a wide range of plastic materials has been rationalized by the increased demand from growing populations and the development of high-throughput production systems. Plastic materials at low costs with reliable properties have been utilized in many everyday products. Multibillion-dollar companies are established around these plastic materials, and each polymer takes years to optimize, secure intellectual property, comply with the regulatory bodies such as the Registration, Evaluation, Authorisation and Restriction of Chemicals and the Environmental Protection Agency and develop consumer confidence. Therefore, developing a fully sustainable new plastic material with even a slightly different chemical structure is a costly and long process. Hence, the production of the common plastic materials with exactly the same chemical structures that does not require any new registration processes better reflects the reality of how to address the critical future of sustainable plastics. In this review, we have highlighted the very recent examples on the synthesis of common monomers using chemicals from sustainable feedstocks that can be used as a like-for-like substitute to prepare conventional petrochemical-free thermoplastics.

Olive oil industry: a review of waste stream composition, environmental impacts, and energy valorization paths

The olive oil production is a key economic sector for the producing countries, mainly in the Mediterranean region. However, the worldwide increasing oil production led to the generation of huge amounts of wastes detrimental for the environment. Therefore, efficient and sustainable management of olive industry wastes has recently acquired significant interest in the scientific research community. In the actual world energy context, various studies dealt with the valorization of the solid/liquid waste streams obtained from the discontinuous/continuous extraction of olive oil for energy purposes. The application of waste-to-energy treatments to these effluents can turn them out into an important energy resource. This review article presents the main used oil extraction techniques and their related research developments. The characterization of the generated wastes and the factors behind their bad environmental impacts are highlighted. Relevant research works related to biochemical and thermochemical conversion of olive mill wastes are extensively reviewed and discussed in terms of product yields and composition. A recent update of the studies addressing olive industry waste applications for energy production is also given. This investigation revealed a lack of studies in relation to the hydrothermal processing of olive mill wastes. Despite their suitability for this process (e.g., high moisture content), few papers have investigated the hydrothermal conversion of these waste streams. This scientific gap opens a very interesting research direction, which has to be further investigated.

Olive Pomace and Pâté Olive Cake as Suitable Ingredients for Food and Feed

Olive oil extraction generates several by-products that represent an environmental issue, mainly for Mediterranean countries where olive oil is mostly produced. These by-products represent an ecological issue for their phenolic components, such as oleuropein, hydroxytyrosol, and tyrosol. However, olive oil by-products can be treated and properly exploited in different fields for their health-promoting properties, and they represent great potential for the food and beverage, cosmetic, and pharmaceutical industries. Furthermore, recovery and treatment processes can contribute to efficient waste management, which can enhance the sustainability of the olive oil industry, and in turn, lead to relevant economic benefits. The solid waste, i.e., olive pomace, could be considered to be a suitable matrix or primary resource of molecules with high added value due to their high phenolic content. Olive pomace, at different moisture contents, is the main by-product obtained from two- or three-phase extraction systems. A commonly used centrifugal extraction system, i.e., a multiphase decanter (DMF), does not require the addition of water and can generate a new by-product called pâté or olive pomace cake, consisting of moist pulp that is rich in phenols, in particular, secoiridoids, without any trace of kernel. Although several reviews have been published on olive wastes, only a few reviews have specifically focused on the solid by-products. Therefore, the aim of the present review is to provide a comprehensive overview on the current valorization of the main solid olive oil by-products, in particular, olive pomace or pâté olive cake, highlighting their use in different fields, including human nutrition.

Reaction Mechanism of the Microwave-Assisted Synthesis of 5-Hydroxymethylfurfural from Sucrose in Sugar Beet Molasses

5-hydroxymethylfurfural (HMF) stands out among the chemical products derived from biomass as a building block in the chemical industry. The conventional production of HMF is usually carried out from fructose, glucose, or other monosaccharides as feedstock, but sugar beet molasses, a by-product of the sugar industry containing sucrose (45–55%), is promising. This exploratory study used three aqueous stock solutions and one biphasic system as the sources of sucrose. The dehydration of sucrose to 5-hydroxymethylfurfural was assisted by microwave heating and subcritical water conditions. The maximum yield of HMF was 27.8 mol % for the aqueous solution of synthetic sucrose at 80 min of treatment. Although HMF yield was 7.1 mol % in the aqueous sugar beet molasses solution, it increased 2-fold after clarification (15.1 mol %) and 1.6-fold in the biphasic system (11.4 mol %). These are favorable outcomes since this is an exploratory investigation. The pseudo-first-order model fitted experimental data from the conversion of the sucrose from the stock solutions, and kinetic parameters were estimated and compared. The estimated reaction rate constant showed that inversion of sucrose is faster than fructose dehydration to HMF, but the latter reaction was the rate-determining step only for the biphasic system. The maximum partition coefficient value was four between 40 min and 60 min of reaction, calculated at room temperature. These predictions help investigators to estimate conversions and selectivity when pilot plants need to be simulated.

Applications of bioactive compounds extracted from olive industry wastes: A review

The wastes generated during the olive oil extraction process, even if presenting a negative impact for the environment, contain several bioactive compounds that have considerable health benefits. After suitable extraction and purification, these compounds can be used as food antioxidants or as active ingredients in nutraceutical and cosmetic products due to their interesting technological and pharmaceutical properties. The aim of this review, after presenting general applications of the different types of wastes generated from this industry, is to focus on the olive pomace produced by the two-phase system and to explore the challenging applications of the main individual compounds present in this waste. Hydroxytyrosol, tyrosol, oleuropein, oleuropein aglycone, and verbascoside are the most abundant bioactive compounds present in olive pomace. Besides their antioxidant activity, these compounds also demonstrated other biological properties such as antimicrobial, anticancer, or anti-inflammatory, thus being used in formulations to produce pharmaceutical and cosmetic products or in the fortification of food. Nevertheless, it is mandatory to involve both industries and researchers to create strategies to valorize these byproducts while maintaining environmental sustainability.

Recovering Apple Agro-Industrial Waste for Bioethanol and Vinasse Joint Production: Screening the Potential of Chile

Bioethanol production has increased in demand as a replacement for conventional fuels. This work studies the use of apple pomace, which corresponds to 45% (w/w) of dehydrated apple production, as a reliable and inexpensive source for bioethanol production. Additionally, the vinasse obtained from the process as a byproduct is analyzed. Apple pomace has important properties for energy purposes, with high soluble sugar (6%–8%), organic compounds and low protein content. The carbohydrates were consumed in 99.3% in 144 h at a temperature of 30 °C and in a yeast Saccharomyces cerevisiae (YSC) concentration of 0.10 g/L. The bioethanol purity produced, 99.5% (v/v), was quantified by gas chromatography and calorific value (23.21 MJ/kg). This high purity, which fulfills the EN 15376, ASTM D 4806 Standard, allows its use as a fuel and oil additive. Moreover, it can be stated that vinasse obtained from alcohol distillation is a compound that has physicochemical values like other vinasses. Finally, Chile, as the most important exporting country of dehydrated apples in the world, has great potential to take advantage of the use of this raw material for bioethanol and vinasse production.

Pistacia lentiscus extract enhances mammary epithelial cells' productivity by modulating their oxidative status

We assessed the potential of phenolic compounds from Pistacia lentiscus (lentisk) to enhance production of milk constituents in bovine mammary epithelial cells (MEC). MEC were exposed to 0 (control), 1 or 10 ppm of polyphenols from lentisk ethanolic extract (PLEE) for 24 h. PLEE were absorbed by the MEC plasma membrane, but also penetrated the cell to accumulate in and around the nucleus. PLEE increased triglyceride content in the cell and its secretion to the medium, and significantly increased intracellular lipid droplet diameter. Compared to control, PLEE increased dose-dependently the lactose synthesis, secretion of whey proteins, and contents of casein. To evaluate mitochondrial activity under pro-oxidant load, MEC were preincubated with PLEE and exposed for 2 h to H₂O₂. Exposure to H₂O₂ increased the proportion of cells with impaired mitochondrial membrane potential twofold in controls, but not in PLEE-pre-treated cells. Accordingly, proton leakage was markedly decreased by PLEE, and coupling efficiency between the respiratory chain and ATP production was significantly enhanced. Thus, lentisk polyphenols divert energy to production of milk fat, protein and lactose, with less energy directed to cellular damage control; alternatively, PLEE enables MEC to maintain energy and oxidative status under extreme metabolic rate required for milk production and secretion, and reduces the limitation on energy required to support production.

Circular economy in olive oil production - Olive mill solid waste to ethanol and heavy metal sorbent using microwave pretreatment

Olive mill solid waste (OMSW) is an abundant agricultural waste without viable solution. The effects of OMSW different pretreatments (microwave or autoclave), different additives (water, formic, or sulfuric acid), and utilization of different saccharification enzymes (Cellic® CTec2 or Accellerase® 1500) were tested on saccharification process and sugar release, and on fermentation inhibitors formation and ethanol production. Microwave treatment with formic acid resulted in highest saccharification rates (90% of cellulose fraction) and fermentation yields (15.9 g/L ethanol), although loss of sugars and fermentation inhibitors production was notable. Microwave with water treatment resulted in less saccharification and ethanol (9.6 g/L). To facilitate economical process and to extract maximum value, solid remnants after saccharification were tested as heavy metal sorbent. Microwave with water resulted in the best sorbent, followed by microwave with formic acid. Addition of sulfuric acid, to either microwave or autoclave, resulted in very poor saccharification and absorbance capacity. Therefore, combination of ethanol and sorbent production from OMSW are suggested.

Biomethane recovery from olive mill residues through anaerobic digestion: A review of the state of the art technology

Residues from production of olive oil are generated yearly in great amounts, both in liquid and solid forms. Different waste treatment systems were proposed in literature, to minimize environmental pollution while raising the energy recovery. Anaerobic digestion is one of the available routes to recover energy from waste via production of biogas while reducing organic load and pollutants to the environment. The use of farming and agro industrial wastes as co-substrate in anaerobic digestion can induce benefits related to the simultaneous treatment of different wastes. In particular, co-digestion can significantly enhance the process stability as well as the bio-methane generation. This work aims at reviewing the latest achievements in anaerobic digestion of olive mill residues, focusing on the aspects that can mostly favor the process, principally from a technical but also from an economical point of view. For the mono-digestion processes, methane yields up to 419 L_CH4 kg_VS^-1 were reported for olive mill wastewaters (Calabrò et al. 2018), while a production of 740 L_CH4 kg_VS^-1 was achieved when digesting olive mill solid waste together with olive mill wastewater and milk whey (Battista et al. 2015). An increase up to 143% in the methane yield was also reported when the feedstock was subjected to a 5 days aeration before digesting it in a semi-continuous stirred tank reactor (González-González and Cuadros 2015).

Exploitation of olive oil mill wastewaters and molasses for ethanol production using immobilized cells of Saccharomyces cerevisiae

An alcoholic fermentation process is described, involving molasses, the main by-product of the sugar industry, blended with crude olive oil mill wastewaters (OOMWs) and immobilized Saccharomyces cerevisiae cells on delignified cellulosic material (DCM). For comparison, fermentations with free cells were also carried out. Initially, the optimum blending mixture for molasses dilution was sought after, while at a second step repeated batch fermentations at a temperature range 5-30 °C were performed to monitor the operational stability of the system. A 1/1 ratio of OOMWs/tap water blending mixture and cell immobilization resulted in higher fermentation parameters. Ethanol concentration and daily productivity values recorded at temperatures ≥ 20 °C (up to 67.8 g L^-1 and 67.6 g L^-1 d^-1, respectively) could be adopted by the industrial sector, although the decline in fermentation efficiency observed, probably due to the toxicity effects of OOMWs. Finally, the potential of OOMWs treatment for ethanol production is highlighted and assessed.

Production of biochar from olive mill solid waste for heavy metal removal

Commercial activated carbon (CAC) and biochar are useful adsorbents for removing heavy metals (HM) from water, but their production is costly. Biochar production from olive solid waste from two olive cultivars (Picual and Souri) and two oil production process (two- or three-phase) and two temperatures (350 and 450°C) was tested. The biochar yield was 24-35% of the biomass, with a surface area of 1.65-8.12m²g^-1, as compared to 1100m²g^-1 for CAC. Picual residue from the two-phase milling technique, pyrolysed at 350°C, had the best cumulative removal capacity for Cu⁺², Pb⁺², Cd⁺², Ni⁺² and Zn⁺² with more than 85% compared to other biochar types and CAC. These results suggest that surface area cannot be used as a sole predictor of HM removal capacity. FTIR analysis revealed the presence of different functional groups in the different biochar types, which may be related to the differences in absorbing capacities.

Hydrolysis of olive mill waste to enhance rhamnolipids and surfactin production

The aim of this work was to demonstrate the effectiveness of hydrolysis pretreatment of olive mill (OMW) waste before use as a carbon source in biosurfactant production by fermentation. Three hydrolysis methods were assessed: enzymatic hydrolysis, acid pretreatment plus enzymatic hydrolysis, and acid hydrolysis. Fermentation was carried out using two bacterial species: Pseudomonas aeruginosa and Bacillus subtilis. Our results showed that the enzymatic hydrolysis was the best pretreatment, yielding up to 29.5 and 13.7mg/L of rhamnolipids and surfactins respectively. Glucose did not show significant differences in comparison to enzymatically hydrolysed OMW. At the best conditions found rhamnolipids and surfactins reached concentrations of 299 and 26.5mg/L; values considerably higher than those obtained with non-hydrolysed OMW. In addition, enzymatic pretreatment seemed to partially reduce the inhibitory effects of OMW on surfactin production. Therefore, enzymatic hydrolysis proved to effectively increase the productivity of these biosurfactants using OMW as the sole carbon source.

A review of olive mill solid wastes to energy utilization techniques

In recent years, the utilization of olive industry by-products for energy purposes has gained significant research interest and many studies have been conducted focused on the exploitation of olive mill solid waste (OMSW) derived from the discontinuous or continuous processing of olive fruits. In this review study, the primary characteristics of OMSW and the techniques used to define their thermal performance are described. The theoretical background of the main waste-to-energy conversion pathways of solid olive mill wastes, as well as the basic pre-treatment techniques for upgrading solid fuels, are presented. The study aims to present the main findings and major conclusions of previously published works undertaken in the last two decades focused on the characterization of olive mill solid wastes and the utilization of different types of solid olive mill residues for energy purposes. The study also aims to highlight the research challenges in this field.

Biorefinery based on olive biomass. State of the art and future trends

With currently more than nine million hectares, olive tree cultivation has spread worldwide, table olives and olive oil as the main products. Moreover, a number of by-products and residues derived from both tree cultivation and the process of industrial olive oil production, most having no practical applications, are obtained yearly. This paper reviews the research regarding these by-products, namely biomass from olive tree pruning, olive stones, olive pomace and wastewaters obtained from the process of olive oil production. Furthermore, a wide range of compounds has been identified and can be produced using a broad definition of the term biorefinery based on olive tree biomass. As an example, this paper reviews ethanol production as one of the main proposed applications, as well as research on other value-added products. Finally, this paper also assesses recent technological advances, future perspectives and challenges in each stage of the process.