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Article

Transforming Wine By-Products into Energy: Evaluating Grape Pomace and Distillation Stillage for Biomass Pellet Production

by
Miguel Oliveira
1,2,
Bruno M. M. Teixeira
2,
Rogério Toste
2 and
Amadeu D. S. Borges
1,2,3,*
1
CQ-VR, Chemistry Research Centre-Vila Real, University of Trás-os-Montes e Alto Douro, 5001-801 Vila Real, Portugal
2
Laboratory of Thermal Sciences and Sustainability, University of Trás-os-Montes e Alto Douro, 5001-801 Vila Real, Portugal
3
Engineering Department, University of Trás-os-Montes e Alto Douro, 5001-801 Vila Real, Portugal
*
Author to whom correspondence should be addressed.
Appl. Sci. 2024, 14(16), 7313; https://doi.org/10.3390/app14167313
Submission received: 15 July 2024 / Revised: 10 August 2024 / Accepted: 13 August 2024 / Published: 20 August 2024
(This article belongs to the Special Issue Advanced Plant Biotechnology in Sustainable Agriculture)
Browse Figure
Versions Notes

Abstract

:
The by-products of the wine industry represent a global production of 10.5 to 13.1 million tons of wine pomace annually. This study examines the chemical composition and energy potential of wine pomace and distillation stillage, evaluating their suitability for pellet production within ENplus® standards. Proximate analysis, elemental analysis, and calorimetric analysis were conducted on samples of the two by-products collected in a local Distillery in Portugal. The results reveal that wine pomace has a higher volatile matter content (62.695%) than distillation stillage, which, however, has lower ash content (3.762%) and higher fixed carbon (31.813%). Calorimetric analyses show that distillation stillage has a superior low heating value compared to wine pomace, with values exceeding 19 MJ/kg. Both by-products, however, exceed ENplus® limits for ash (≤0.70), nitrogen (≤0.3), and sulfur (≤0.04) content, presenting challenges for use as high-quality fuel pellets. Combining these biomasses with other materials could reduce the pollutant content of the pellet and improve efficiency. This study highlights the need for pre-treatment strategies to lower ash content and enhance combustion. Policy support for sustainable practices is essential to optimize the use of wine pomace and distillation stillage as renewable energy sources.

1. Introduction

The wine industry is one of the largest agro-industrial sectors in the world [1]. The International Organization of Vine and Wine estimates that in the year 2022, around 25.99 billion liters of wine were produced worldwide. In the same period, the Portuguese wine industry produced 680 million liters, producing hundreds of tons of grape pomace resulting from the crushing and pressing stages carried out in wine production [2,3,4,5].
Grape pomace is composed primarily of grape skins, seeds, and stems, each contributing uniquely to bioenergy production. The high cellulose and hemicellulose content in grape pomace provides substantial substrates for bioethanol production through fermentation, where these polysaccharides are broken down into fermentable sugars. Lignin, another significant component, enhances the biomass’s calorific value, making it suitable for bio-oil production through pyrolysis. The phenolic compounds, including flavonoids, tannins, and anthocyanins, offer antioxidant properties that can inhibit microbial activity, preserving the biomass during storage and enhancing its viability for bioenergy applications [6,7].
However, the utilization of grape pomace for bioenergy presents challenges. The high lignin content requires complex and energy-intensive pretreatment processes to break down the rigid plant cell walls, posing a significant disadvantage. Moreover, the variable composition of grape pomace, influenced by grape variety and winemaking processes, can lead to inconsistencies in bioenergy yield. Despite these challenges, the inherent advantages such as high energy content, waste utilization, and the antioxidant properties that aid in biomass preservation, underscore the potential of grape pomace as a valuable resource for sustainable bioenergy production [6,7]. There are two distinct types of grape pomace. Pomace derived from pressing grapes before fermentation begins, a method commonly used in white wine production, is called fresh pomace. The pomace obtained from pressing grapes after the fermentation process, which is typical in red wine production, is called fermented pomace [5]. Estimates indicate that every 6 liters yields approximately 1 kg of grape pomace, which represents a global production of 10.5 to 13.1 million tons of grape pomace annually [8]. This by-product of wine production is mainly made up of skins, stems, and seeds [3,9,10,11]. Estimates indicate that each ton of grape pomace contains approximately 430 kg of skins, 250 kg of stems, and 230 kg of seeds [12].
Much of this by-product of wine production has been applied as an organic soil improver, as it contains significant amounts of organic matter and is rich in nutrients [13,14,15]. However, due to the continuous application of agricultural by-products in agricultural fields, soils are becoming increasingly saturated, posing a significant challenge for large producers in determining the appropriate disposal methods for grape pomace [16,17]. This saturation can lead to nutrient imbalances, reduced soil fertility, and potential environmental contamination. As a result, producers must explore sustainable disposal and utilization options, such as composting, biogas production, or developing new markets for grape pomace-based products, to mitigate these challenges and ensure environmental compliance.
Due to technological improvements in a variety of fields, grape pomace has emerged as a valuable resource with a variety of value-added uses that can be utilized as a functional compound in the pharmaceutical and cosmetic sectors or for distillation and obtaining pomace spirit, an alcoholic beverage that has its origins in Portugal [3,4,8,18]. Pomace spirit is obtained through the distillation of grape pomace and is considered a strong drink with a high alcohol content. This potent spirit can be used as a culinary ingredient, adding depth and complexity to various dishes, particularly in sauces, marinades, and desserts. Additionally, pomace spirit is often enjoyed on its own as a digestif or incorporated into cocktails, providing a unique and robust flavor profile that enhances the overall drinking experience and stops the fermentation process in the production of fortified wines like Port wine [17,18]. To produce pomace spirit, the pomace is placed in a still, where it is carefully heated and distilled [19,20]. During this process, the liquid and volatile components of the pomace are separated from the solid by-products. The heat causes the alcohol and other volatile compounds to evaporate, which are then condensed back into liquid form, yielding the potent spirit. This method not only extracts the valuable alcoholic components but also concentrates the flavors and aromas present in the pomace, resulting in a distinctive and robust beverage. Additionally, the distillation process generates a new by-product, which includes the remaining solid by-products and any non-volatile compounds, often used in various agricultural or industrial applications [21]. Therefore, it has become important to chemically analyze the by-products of wine and pomace brandy production with a focus on sustainable use. This analysis helps in identifying valuable components that can be repurposed, thereby contributing to a circular economy [22,23]. By finding innovative ways to utilize these by-products, such as converting them into biofuels, we can reduce primary energy consumption. This shift promotes renewable energy sources over fossil fuels, leading to more environmentally friendly and sustainable production practices in the wine and pomace brandy industries [23].
Currently, most of the energy produced in Europe comes from non-renewable sources like gas, coal, and oil [24]. Due to the increasing global energy demand, it has become crucial to establish measures and policies aimed at transitioning to a more sustainable energy system [25], as fossil fuel-based energy production is the primary contributor to global greenhouse gas (GHG) emissions [26]. This paradigm shift has resulted in a new appreciation for biomass, such as wood and its derivatives, traditionally reserved for cooking and heating, as possible alternative fuels to reduce GHG emissions on a global scale [27]. Nevertheless, using such materials for energy production presents challenges. The relatively high moisture content and generally low density of these materials, compared to more regularly used fossil fuels, make the direct usage of raw, unprocessed biomass unviable [27,28]. To address these issues, innovative processing techniques are being developed to improve the efficiency and feasibility of biomass as a renewable energy source. These include drying and densification processes that enhance the energy content and ease of handling of biomass fuels. By investing in such technologies, we can better harness the potential of biomass, contributing to a more diversified and sustainable energy portfolio [29,30].
As such, transforming these biomasses into usable fuel is crucial if they are to be used in the production of energy. This is usually conducted through a pellet production process, which generally follows a series of steps, starting with a drying process followed by a series of pre-processing methods, namely a size reduction, in which the biomass is compacted through compression and impact forces or through a longer contact interaction such as attrition [31]. Afterward, a series of treatments are usually applied to the resulting materials like torrefaction, a mild pyrolysis process where the biomass is heated in an inert atmosphere, typically between 200 °C and 300 °C. This results in the dehydration and decarboxylation of the biomass, making it more brittle and enhancing its grindability. The main advantages of torrefaction include increased energy density, improved storage properties, and reduced biological activity. However, it has the disadvantages of requiring additional energy input for the process and potential emissions of volatile organic compounds [31,32,33]. Steam Explosion involves subjecting the biomass to pressurized hot steam for a period of time and then rapidly depressurizing it. This treatment disrupts the structure of the biomass, making it more accessible for further processing. The advantages of steam explosion include enhanced pellet durability and mechanical strength, as well as increased surface area for subsequent chemical reactions. The disadvantages include the complexity of the equipment and the potential loss of some volatile components [31,32,33]. Hydrothermal carbonization is a process where biomass is treated with water at elevated temperatures and pressures, leading to the formation of a carbon-rich material. This method is particularly suitable for materials with high moisture content, such as wet agricultural residues. The advantages include the production of a stable, high-energy-density product, and the ability to handle wet feedstock directly. However, the disadvantages include the need for high-pressure equipment and the generation of a wastewater stream that requires treatment. Biological treatment involves exposing the biomass to microorganisms that break down the recalcitrant components of the biomass. This method can be advantageous due to its low energy requirements and the potential for bioconversion into valuable products. However, it is often a slower process and can be less predictable due to variations in microbial activity and environmental conditions [31,32,33]. These advanced treatments significantly improve the efficiency and utility of biomass as a renewable energy source. By refining the raw materials through these processes, we can create biomass fuels that are more energy-dense, easier to transport and store, and capable of producing lower emissions when used. This holistic approach to biomass utilization helps address the limitations of raw biomass and maximizes its potential as a sustainable alternative to fossil fuels.
The biomass is then finally turned into pellets ranging from 6 mm up to 40 mm in size, as per literature [32], permitting its use for energy generation [28]. In the context of wine by-products, understanding the production of these biomass pellets is important, specifically the few nuances related to the utilization of mixed biomass pellets. These are pellets produced through the usage of biomass materials other than wood, normally by reusing biomass from agricultural wastes. If worked upon properly, these pellets can possibly achieve energy release and heating values similar to standard wood pellets [34,35]. However, mixed biomass pellets tend to contain problematic amounts of sulfur and chlorine, which is concerning due to the effects these chemicals have on both the equipment upon which they are used and the environment [35]. In the case that the values exceed the commercially recommended standard set by independent pellet certification schemes it is suggested that the biomass should be mixed in with other materials in order to improve its content properties [35]. The need to sometimes combine different materials in order to produce adequate pellets does present itself as an opportunity to reutilize biomasses such as wood shavings, sawdust and other wastes that may have been produced in a variety of industries [28,35]. Keeping this in mind, this study aims to set a basis of understanding for wine pomace and distillation stillage as viable biomasses for energy production in the pellet fabrication industry, and how it can contribute towards diminishing the environmental impact of the agricultural waste products resulting from the wine industry.

2. Material and Methods

2.1. Samples

The analyzed samples were collected in a distillery, located in the Douro region, in the northern part of Portugal. There were collected samples after the pressing and crushing stages in the wine production process (wine pomace), as well as after the distillation process in the production of pomace brandy (distillation stillage). Both samples were properly identified and labeled before being placed in airtight bags in order to preserve them and avoid any external contamination. The grapes used for the production of these winery by-products were exclusively red varieties, specifically Touriga Nacional, Touriga Franca, and Tinta Roriz.
The analyses were conducted at the Thermal Sciences and Sustainability Laboratory of the University of Trás-os-Montes and Alto Douro and comprised the following steps: drying, proximate analysis, elemental analysis, and calorimetric analysis.

2.2. Sample Drying

Wine pomace and distillation stillage samples were placed on trays inside a Termaks TS 8136 oven from Norway set to a temperature of 30 °C to simulate natural air drying conditions in the most accurate way possible and avoid further operational costs. The samples were regularly monitored, with mass measurements recorded at consistent intervals. This process continued until significant variations in mass were no longer observed, indicating that the samples had reached a stable, dry state. This drying step is crucial to ensure accurate and consistent data in subsequent analyses by eliminating the variable of moisture content, which can affect the weight and the overall composition of the pomace [36,37]. Maintaining a low drying temperature of 30 °C helps to prevent any thermal degradation or loss of volatile compounds, thereby preserving the integrity of the samples for further testing [36,37].

2.3. Thermo-Chemical Characterization

2.3.1. Proximate Analysis

In sterilized and pre-weighed crucibles, approximately 1 g of each sample was meticulously collected and placed in a Protherm PLF 110/6 muffle furnace from Turkey under specific conditions as described in Table 1. Each sample underwent three repetitions to ensure precision and reliability in the analysis.
For moisture content determination, the samples were heated at 105 °C for 2 h to effectively remove water. Volatile matter analysis involved a multi-stage heating process at 950 °C: initially, 2 min with the furnace door open to release volatiles, followed by 3 min with the door half-closed to gradually increase the temperature, and finally, 6 min with the door fully closed to complete the volatilization process, with crucibles covered throughout to ensure accurate measurement of volatile matter. For ash content determination, samples were incinerated at 750 °C for 6 h to ensure thorough combustion of organic material, leaving behind only inorganic ash.

2.3.2. Elemental Analysis

Samples weighing between 2 and 3 mg were meticulously collected into an aluminum capsule for subsequent elemental analysis using a Thermo Scientific Flashsmart elemental analyzer from the United Sates of America (USA) to determine the percentage of Carbon (C), Hydrogen (H), Nitrogen (N), Sulfur (S), and Oxygen (O) present in a sample (CHNS analysis). The analytical conditions for these tests are detailed in Table 2.
The CHNS analysis involved subjecting the samples to a high combustion reactor temperature of 950 °C, ensuring thorough oxidation. The reduction reactor, although not utilized, maintained a temperature of 400 °C to balance the thermal environment between the two reactors. Meanwhile, a stable oven temperature of 65 °C provided optimal conditions for sample preparation.
During the analysis, each sample spent 12 s within the reactor, with precise oxygen injection lasting 5 s. The gas fluxes were carefully controlled throughout: 140 mL/min of drag gas facilitated sample movement, while 250 mL/min of oxygen and 100 mL/min of reference gas ensured accurate combustion and calibration.

2.3.3. Calorimetry

The heating value analysis was conducted by igniting samples under strictly controlled conditions within an oxygen atmosphere, utilizing the advanced capabilities of the isoperibolic calorimeter Parr 6400 from Moline, IL, USA.
To ensure accuracy and reliability, each sample underwent rigorous testing with three replications. The controlled environment of the oxygen atmosphere within the calorimeter ensures consistent combustion conditions, essential for the precise determination of the heating values of the samples.

2.4. Normalization

Tests were conducted in accordance with ISO 18134-1:2015 Solid biofuels—Determination of moisture content—Oven dry method—Part 1: Total moisture [38], ISO 16948:2015 Solid biofuels—Determination of total content of carbon, hydrogen and nitrogen [39], ISO 18123:2015 Solid biofuels—Determination of the content of volatile matter [40], ISO 18122:2015 Solid biofuels—Determination of ash content [41] and ISO 18125:2017 Solid biofuels—Determination of calorific value [42].

2.5. Statistical Analysis

Statistical analysis was performed using Microsoft Excel 16.88 (24081116). A t-test was employed to compare the means of different groups within the study.
The choice of the t-test was based on its suitability for comparing the means of two independent samples, which is critical for evaluating differences in the chemical composition and energy potential between grape pomace and distillation stillage.
The results provided p-values, which were used to determine the statistical significance of the observed differences. A p-value less than 0.05 was considered statistically significant, indicating that the differences in means were unlikely to have occurred by chance. This approach allowed for a rigorous evaluation of the data, supporting the study’s findings with quantitative evidence.

3. Results and Discussion

3.1. Drying

Both materials experience a rapid mass loss in the early phase of the drying process, with wine pomace showing a slightly higher loss compared to distillation stillage. Figure 1 shows the mass loss in percentage over time of the samples, the time axis is labeled in terms of the square root of time. As time progresses, the rate of mass loss for both materials decreases, with their respective curves converging. During the intermediate period, the behavior of wine pomace and distillation stillage remains similar, though wine pomace consistently demonstrates a marginally higher mass loss. By the final phase of the drying process, both materials reach a stable state. The overall trends indicate that wine pomace undergoes a slightly higher total mass loss than the distillation stillage sample recording a loss of water mass of around 65%, while the wine pomace showed a lower value, with a loss of 58.77%. These results are in accordance with the literature [5], which indicates that the water content in grape pomace can vary within a range of 60–70%.

3.2. Proximate Analysis

Distillation stillage has a moisture content of 5.454%, slightly higher than the 5.268% moisture content of wine pomace (Table 3). The small difference can be attributed to the evaporation of water during the distillation process, which results in a relatively higher moisture content in the distillation stillage. Low moisture content is advantageous for energy recovery because it means less energy is required to evaporate the water during combustion or thermal conversion processes, making both samples suitable in this regard. The volatile matter content, which represents the portion of the biomass that vaporizes when heated and is indicative of the material’s combustibility, is 58.97% for distillation stillage and 62.695% for wine pomace. Wine pomace’s higher volatile matter content suggests that it may have a higher potential for energy release during combustion. Ash content, the non-combustible residue remaining after combustion, is 3.762% for distillation stillage and 6.359% for wine pomace. Lower ash content is preferable for energy recovery since it reduces the amount of residue and fouling in combustion systems. In this case, distillation stillage has a significant advantage with its lower ash content. Fixed carbon, which contributes to the char left after volatile matter is released and is an important factor for sustained combustion, is 31.813% for distillation stillage and 25.677% for wine pomace. The higher fixed carbon content in distillation stillage indicates a greater potential for sustained energy release through slower-burning carbon residues.
When comparing these findings with the study by [43], which analyzed grape stalks and grape pomace, similar patterns emerge. Grape stalks had a moisture content of 7.20%, volatile matter of 71.6%, ash content of 5.20%, and fixed carbon of 16.0%. Grape pomace had 5.40% moisture, 70.2% volatile matter, 6.40% ash, and 18.0% fixed carbon. The distillation stillage and wine pomace from this study has lower moisture and volatile matter contents than the grape stalks and grape pomace analyzed by [43], but the fixed carbon content in this distillation stillage is significantly higher, indicating a superior potential for sustained energy release.
The t-test results from the proximate analysis reveal that significant differences exist between the two materials in volatile matter content (p-value equal to 0.00112), ash content (p-value equal to 0.000348), and fixed carbon content (p-value equal to 0.0000418). However, there is no significant difference in moisture content (p-value equal to 0.105).
In summary, both distillation stillage and wine pomace show promise for energy recovery. Distillation stillage has advantages with lower ash content and higher fixed carbon, suggesting more efficient combustion with less residue. Wine pomace, with higher volatile matter content, may offer a quicker and more intense initial energy release. The choice between the two would depend on the specific requirements of the energy recovery process, such as the need for rapid energy release versus sustained combustion with minimal residue.

3.3. Elemental Analysis

Distillation stillage has a nitrogen content of 2.57%, which is slightly higher than the 2.494% found in wine pomace (Table 4). The carbon content of distillation stillage is 54.928%, which is greater than the 52.099% in wine pomace. Carbon content is directly related to the calorific value of the biomass; thus, distillation stillage has a higher potential energy output due to its higher carbon percentage [44,45]. Hydrogen content, another critical factor for energy release during combustion, is 6.725% in distillation stillage, which is higher than the 5.669% in wine pomace [45]. This indicates that distillation stillage may have a higher energy release potential. Sulfur content in distillation stillage is 0.153%, which is significantly higher than the 0.043% found in wine pomace. Lower sulfur content in wine pomace suggests it is more environmentally friendly, as it would result in fewer SOx emissions during combustion [44]. The oxygen content is 31.862% for distillation stillage and 33.337% for wine pomace. Lower oxygen content generally correlates with higher calorific value, implying that distillation stillage might have a slightly higher energy density compared to wine pomace [44,45].
Comparing these results with the findings from [43], grape stalks contained 48.1% carbon, 5.8% hydrogen, 1.3% nitrogen, 0.4% sulfur, and 44.4% oxygen. Grape pomace had 53.5% carbon, 5.7% hydrogen, 2.5% nitrogen, 0.1% sulfur, and 38.2% oxygen. This distillation stillage’s higher carbon and hydrogen contents suggest a higher potential calorific value, consistent with the trends observed in [43], where higher elemental carbon and hydrogen correlate with higher energy output.
The t-test results from the elemental analysis reveal that statistically significant differences are observed in carbon (p-value equal to 0.00242), hydrogen (p-value equal to 0.00951), and sulfur content (p-value equal to 0.0171) between the two materials. Nevertheless, there is no significant difference in nitrogen (p-value equal to 0.707) content, and the difference in oxygen content (p-value equal to 0.0964) is not statistically significant. This indicates that while the materials differ significantly in several elemental compositions, nitrogen and oxygen contents do not.
In summary, both distillation stillage and wine pomace show promise for energy recovery. Distillation stillage has advantages with lower ash content and higher fixed carbon, suggesting more efficient combustion with less residue. This makes it well-suited for direct combustion and pyrolysis processes, which convert the organic material into bio-oil, syngas, and biochar through high-temperature treatments. These processes benefit from the high energy density of distillation stillage, resulting in efficient energy recovery [46]. Wine pomace, with higher volatile matter content, may offer a quicker and more intense initial energy release but, often requires pretreatment to enhance its energy potential due to its lower carbon content and higher levels of nitrogen and sulfur. Enzymatic hydrolysis is commonly used to break down the complex carbohydrates in wine pomace into fermentable sugars, which can then be converted into bioethanol through microbial fermentation. This biological treatment process is advantageous as it operates under milder conditions compared to thermal methods, reducing energy input and preserving the structural integrity of the biomass. However, the variability in the composition of wine pomace, influenced by grape variety and winemaking processes, can lead to inconsistencies in bioenergy yield [46]. The choice between the two would depend on the specific requirements of the energy recovery process, such as the need for rapid energy release versus sustained combustion with minimal residue.

3.4. Calorimetric Analysis

Distillation stillage has a high heating value (HHV) of 20.544 MJ/kg, which is higher than the HHV of wine pomace at 19.741 MJ/kg (Table 5). The HHV measures the total energy content of the fuel, including the energy contained in the water vapor formed during combustion [44,45]. The higher HHV of distillation stillage indicates that it has a greater overall energy content compared to wine pomace.
Similarly, the low heating value (LHV) of distillation stillage is 19.109 MJ/kg, compared to the LHV of wine pomace at 18.514 MJ/kg. The LHV represents the net energy content of the fuel, excluding the energy lost as latent heat in water vapor [44]. The higher LHV of distillation stillage suggests that it provides more usable energy upon combustion than wine pomace. The higher values for both HHV and LHV in distillation stillage compared to wine pomace suggest that distillation stillage has a superior energy recovery potential [44,45].
The t-test results from the calorimetric analysis reveal that statistically significant differences are found in both the HHV (p-value equal to 0.000135) and the LHV (p-value equal to 0.0000249). This suggests that the two materials have distinct differences in their calorific values, which are unlikely to be due to random variation.
Overall, distillation stillage offers a higher energy yield than wine pomace, as indicated by its higher HHV and LHV. This makes distillation stillage a more efficient choice for energy recovery processes, providing more energy per kilogram of biomass [44]. Wine pomace, while slightly lower in energy content, still presents a viable option for energy recovery, but with a lower energy yield compared to distillation stillage.

3.5. Framing within ENplus® Parameters

ENplus® is an independent certification scheme for wood pellets that ensures their quality and performance for heating purposes [47]. It sets stringent standards for the production, logistics, and trading of wood pellets, helping to guarantee their reliability and efficiency as a renewable energy source. To evaluate the potential of wine pomace and distillation stillage as alternative sources for pellet production, it is essential to compare their properties against the ENplus® standards. This comparison helps determine whether these biomasses can meet the quality requirements for commercially viable wood pellets, ensuring their reliability and efficiency as renewable energy sources. The ENplus® pellet classes are divided into 3 groups: A1, A2, and B (Table 6) [47].
Both samples have moisture contents well below the ENplus® thresholds, indicating suitability for energy recovery in terms of moisture. However, their ash contents significantly exceed the maximum limits set by all ENplus® classifications, which could pose challenges for their use as fuel according to these standards. Therefore, incorporating a pre-treatment step, such as leaching, is necessary to enhance the efficiency and effectiveness of the energy recovery process [48].
The nitrogen content in both samples is also higher than the ENplus® limits, raising concerns about potential NOx emissions during combustion [49].
Distillation stillage has a sulfur content that exceeds all ENplus® classification limits, which could lead to higher SOx emissions, while wine pomace meets the A2 and B standards but not the A1 limit [47,49]. Despite these challenges, both samples exceed the minimum LHV requirement set by ENplus®, indicating their high energy recovery potential [47].
In summary, while distillation stillage and wine pomace exhibit favorable moisture content and high LHV for energy recovery, their high ash, nitrogen, and sulfur contents may limit their suitability under ENplus® standards, particularly for the higher quality classifications. In order to make these materials viable for production, it is recommended to mix them with sawdust from a suitable type of wood [50]. This combination enhances their suitability for combustion by improving their heating value and reducing the high concentrations of nitrogen, sulfur, and ash found in both wine pomace and distillation stillage. For example, spruce sawdust could be used in the mixing process. From the [51] results it is possible to estimate the amount of sawdust needed for the mixture to meet ENplus® certification standards. For distillation stillage pellets, the mixture should contain approximately 8.38% of the sample for an A1 classification, 21.74% for an A2 classification, and around 31.85% for a B classification. For wine pomace, the mixture should have about 4.95% or less sample for an A1 classification, 22.28% for an A2 classification, and approximately 36.24% for a B classification.

4. Conclusions

This study explored the potential of utilizing wine pomace and distillation stillage, by-products of the wine industry, as sustainable sources for pellets production. The findings indicate that both materials exhibit promising characteristics for energy recovery, each with distinct advantages and challenges.
The drying behavior of wine pomace and distillation stillage showed effective profiles, reaching stable states with minimal moisture content. Wine pomace exhibited a slightly higher mass loss than distillation stillage, which showed a lower moisture content (5.454%), and ash content (3.762%) compared to wine pomace, making it a preferable candidate for pellets due to the reduced residue after combustion. However, wine pomace had higher volatile matter content (62.695%), suggesting a more intense initial energy release during combustion.
Distillation stillage has higher carbon (54.928%) and hydrogen content (6.725%) than wine pomace, correlating with a higher heating value and energy output. This was confirmed by the calorimetric analysis. However, distillation stillage also had higher sulfur content (0.153%), potentially leading to more SOx emissions.
The results underscore the viability of wine pomace and distillation stillage as alternative bioenergy sources, contributing to waste valorization and sustainability in the wine industry.
Future research should focus on optimizing pretreatment processes to address the high ash content in both biomasses, improving the overall yield and consistency of bioenergy production. Investigating methods to reduce sulfur content in mixed biomass pellets can enhance their environmental compatibility and reduce potential equipment corrosion and environmental pollution. Conducting pilot-scale studies to validate laboratory findings and assess the economic feasibility of large-scale implementation of bioenergy production from these wine by-products is crucial. Furthermore, exploring additional value-added applications of grape pomace and distillation stillage in pharmaceutical, cosmetic, and agricultural sectors can promote a circular economy and reduce reliance on fossil fuels.

Author Contributions

Writing—Original Draft: M.O., R.T. and B.M.M.T.; Investigation: M.O. and B.M.M.T.; Formal analysis: M.O. and B.M.M.T.; Writing—Review & Editing: M.O. and A.D.S.B.; Conceptualization: A.D.S.B.; Methodology: A.D.S.B.; Data Curation: A.D.S.B.; Validation: A.D.S.B.; Resources: A.D.S.B.; Supervision: A.D.S.B. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Pretorius, I.S. Tailoring wine yeast for the new millennium: Novel approaches to the ancient art of winemaking. Yeast 2000, 16, 675–729. [Google Scholar] [CrossRef] [PubMed]
  2. Base de Datos|OIV. Available online: https://www.oiv.int/es/what-we-do/data-discovery-report?oiv (accessed on 12 February 2024).
  3. Devesa-Rey, R.; Vecino, X.; Varela-Alende, J.L.; Barral, M.T.; Cruz, J.M.; Moldes, A.B. Valorization of winery waste vs. the costs of not recycling. Waste Manag. 2011, 31, 2327–2335. [Google Scholar] [CrossRef]
  4. Dwyer, K.; Hosseinian, F.; Rod, M. The Market Potential of Grape Waste Alternatives. J. Food Res. 2014, 3, 91. [Google Scholar] [CrossRef]
  5. Oliveira, R.M.C. Valorização do Bagaço de Uva: Avaliação da Potencialidade de Produção de Biogás. Master’s Thesis, Universidade da Beira Interior: Covilhã, Portugal, 2011. [Google Scholar]
  6. Onache, P.A.; Geana, E.-I.; Ciucure, C.T.; Florea, A.; Sumedrea, D.I.; Ionete, R.E.; Tița, O. Bioactive Phytochemical Composition of Grape Pomace Resulted from Different White and Red Grape Cultivars. Separations 2022, 9, 395. [Google Scholar] [CrossRef]
  7. Watrelot, A. Ongoing Research: Grape Pomace, Midwest Grape and Wine Industry Institute—Iowa State University. 2021. Available online: https://www.extension.iastate.edu/wine/ongoing-research-grape-pomace/ (accessed on 29 July 2024).
  8. Gómez-Brandón, M.; Lores, M.; Insam, H.; Domínguez, J. Strategies for recycling and valorization of grape marc. Crit. Rev. Biotechnol. 2019, 39, 437–450. [Google Scholar] [CrossRef]
  9. González-Centeno, M.; Rosselló, C.; Simal, S.; Garau, M.; López, F.; Femenia, A. Physico-chemical properties of cell wall materials obtained from ten grape varieties and their byproducts: Grape pomaces and stems. LWT Food Sci. Technol. 2010, 43, 1580–1586. [Google Scholar] [CrossRef]
  10. Mateo, J.J.; Maicas, S. Valorization of winery and oil mill wastes by microbial technologies. Food Res. Int. 2015, 73, 13–25. [Google Scholar] [CrossRef]
  11. Genisheva, Z.; Macedo, S.; Mussatto, S.I.; Teixeira, J.A.; Oliveira, J.M. Production of white wine by Saccharomyces cerevisiae immobilized on grape pomace. J. Inst. Brew. 2012, 118, 163–173. [Google Scholar] [CrossRef]
  12. Dávila, I.; Robles, E.; Egüés, I.; Labidi, J.; Gullón, P. The Biorefinery Concept for the Industrial Valorization of Grape Processing By-Products. In Handbook of Grape Processing By-Products; Elsevier: Amsteram, The Netherlands, 2017; pp. 29–53. [Google Scholar] [CrossRef]
  13. Borta, A.-M.; Sturza, R. Ways of Application of the Circular Bioeconomy in the Wine Industry. J. Eng. Sci. 2024, 30, 124–146. [Google Scholar] [CrossRef]
  14. Korkie, L.; Janse, B.; Viljoen-Bloom, M. Utilising Grape Pomace for Ethanol Production. S. Afr. J. Enol. Vitic. 2017, 23, 31–36. [Google Scholar] [CrossRef]
  15. Negreanu-Pirjol, T.; Negreanu-Pirjol, B.-S.; Artem, V.; Ranca, A.; Ciocan, M.; Popoviciu, D.R. Chapter V Grape Pomace—A Promising Biocomponent as Biostimulant and Eco-Fertilizer. A Review. In Agricultural Studies on Different Subjects; Çiğ, A., Ed.; Iksad Publishing House: Ankara, Turkey, 2021. [Google Scholar]
  16. Bustamante, M.; Said-Pullicino, D.; Paredes, C.; Cecilia, J.; Moral, R. Influences of winery–distillery waste compost stability and soil type on soil carbon dynamics in amended soils. Waste Manag. 2010, 30, 1966–1975. [Google Scholar] [CrossRef]
  17. Muhlack, R.A.; Potumarthi, R.; Jeffery, D.W. Sustainable wineries through waste valorisation: A review of grape marc utilisation for value-added products. Waste Manag. 2018, 72, 99–118. [Google Scholar] [CrossRef]
  18. Infovini|O Portal Do Vinho Português|Glossário. Available online: http://www.infovini.com/classic/pagina.php?l=B&codPagina=28&pg=2 (accessed on 3 May 2024).
  19. Cortés, S.; Fernández, E. Differentiation of Spanish Alcoholic Drinks, Orujo, Obtained from Red and White Grape Pomace Distillation: Volatile Composition. Int. J. Food Prop. 2011, 14, 1349–1357. [Google Scholar] [CrossRef]
  20. García-Lomillo, J.; González-SanJosé, M.L. Applications of Wine Pomace in the Food Industry: Approaches and Functions. Compr. Rev. Food Sci. Food Saf. 2017, 16, 3–22. [Google Scholar] [CrossRef]
  21. López-Vázquez, C.; Bollaín, M.H.; Berstsch, K.; Orriols, I. Fast determination of principal volatile compounds in distilled spirits. Food Control 2010, 21, 1436–1441. [Google Scholar] [CrossRef]
  22. Antonić, B.; Jančíková, S.; Dordević, D.; Tremlová, B. Grape Pomace Valorization: A Systematic Review and Meta-Analysis. Foods 2020, 9, 1627. [Google Scholar] [CrossRef]
  23. Curiel-Fernández, M.; Bueno-Herrera, M.; Guadalupe, Z.; Ayestarán, B.; Pérez-Magariño, S. Chemical Characterization of Polysaccharide Extracts Obtained from Pomace By-Products of Different White Grape Varieties. Molecules 2023, 28, 6770. [Google Scholar] [CrossRef] [PubMed]
  24. Martins, F.; Felgueiras, C.; Smitková, M. Fossil fuel energy consumption in European countries. Energy Procedia 2018, 153, 107–111. [Google Scholar] [CrossRef]
  25. Chang, M.; Thellufsen, J.Z.; Zakeri, B.; Pickering, B.; Pfenninger, S.; Lund, H.; Østergaard, P.A. Trends in tools and approaches for modelling the energy transition. Appl. Energy 2021, 290, 116731. [Google Scholar] [CrossRef]
  26. Johnsson, F.; Kjärstad, J.; Rootzén, J. The threat to climate change mitigation posed by the abundance of fossil fuels. Clim. Policy 2019, 19, 258–274. [Google Scholar] [CrossRef]
  27. Hoefnagels, R.; Junginger, M.; Faaij, A. The economic potential of wood pellet production from alternative, low-value wood sources in the southeast of the U.S. Biomass Bioenergy 2014, 71, 443–454. [Google Scholar] [CrossRef]
  28. Japhet, J.A.; Tokan, A.; Kyauta, E.E. A Review of Pellet Production from Biomass Residues as Domestic Fuel. Int. J. Environ. Agric. Biotechnol. 2019, 4, 835–842. [Google Scholar] [CrossRef]
  29. Sarker, T.R.; Nanda, S.; Meda, V.; Dalai, A.K. Densification of waste biomass for manufacturing solid biofuel pellets: A review. Environ. Chem. Lett. 2023, 21, 231–264. [Google Scholar] [CrossRef]
  30. Alazaiza, M.Y.D.; Ahmad, Z.; Albahnasawi, A.; Nassani, D.E.; Alenezi, R.A. Biomass processing technologies for bioenergy production: Factors for future global market. Int. J. Environ. Sci. Technol. 2024, 21, 2307–2324. [Google Scholar] [CrossRef]
  31. Onochie, U.P.; Ighodaro, O.O.; Kwasi-Effah, C.C.; Unuereopka, O.J. A Comprehensive Review on Biomass Pelleting Technology and Electricity Generation from Biomass. J. Energy Technol. Environ. 2019, 1, 38–49. [Google Scholar]
  32. Pradhan, P.; Mahajani, S.M.; Arora, A. Production and utilization of fuel pellets from biomass: A review. Fuel Process. Technol. 2018, 181, 215–232. [Google Scholar] [CrossRef]
  33. Vigants, H.; Priedniece, V.; Veidenbergs, I.; Blumberga, D. Process Optimization for Pellets Production. Energy Procedia 2017, 113, 396–402. [Google Scholar] [CrossRef]
  34. Nunes, L.J.R.; Matias, J.C.O.; Catalão, J.P.S. Mixed biomass pellets for thermal energy production: A review of combustion models. Appl. Energy 2014, 127, 135–140. [Google Scholar] [CrossRef]
  35. Miranda, T.; Montero, I.; Sepúlveda, F.J.; Arranz, J.I.; Rojas, C.V.; Nogales, S. A Review of Pellets from Different Sources. Materials 2015, 8, 1413–1427. [Google Scholar] [CrossRef]
  36. Havlík, J.; Dlouhý, T.; Pitel’, J. Drying Biomass with a High Water Content—The Influence of the Final Degree of Drying on the Sizing of Indirect Dryers. Processes 2022, 10, 739. [Google Scholar] [CrossRef]
  37. Williams, C.L.; Emerson, R.M.; Tumuluru, J.S. Biomass Compositional Analysis for Conversion to Renewable Fuels and Chemicals. In Biomass Volume Estimation and Valorization for Energy; InTech: London, UK, 2017. [Google Scholar] [CrossRef]
  38. ISO 18134-2:2017; (E) Solid Biofuels-Determination of Moisture Content-Oven Dry Method-Part 2: Total Moisture—Simplified Method. ISO: Geneva, Switzerland, 2017.
  39. ISO 16948:2015; (E) Solid Biofuels-Determination of Total Content of Carbon, Hydrogen and Nitrogen. ISO: Geneva, Switzerland, 2015.
  40. ISO 18123:2015; (E) Solid Biofuels—Determination of the Content of Volatile Matter. ISO: Geneva, Switzerland, 2015.
  41. ISO 18122:2015; (E) Solid Biofuels-Determination of Ash Content. ISO: Geneva, Switzerland, 2015.
  42. ISO 18125:2017; (E) Solid Biofuels-Determination of Calorific Value. ISO: Geneva, Switzerland, 2017.
  43. Deiana, A.; Gimenez, M.; Rómoli, S.; Sardella, M.; Sapag, K. Batch and Column Studies for the Removal of Lead from Aqueous Solutions Using Activated Carbons from Viticultural Industry Wastes. Adsorpt. Sci. Technol. 2014, 32, 181–195. [Google Scholar] [CrossRef]
  44. Hartmann, H. Solid Biofuels, Fuels, and Their Characteristics. In Encyclopedia of Sustainability Science and Technology; Springer: New York, NY, USA, 2017; pp. 1–36. [Google Scholar] [CrossRef]
  45. Wang, L.; Wu, M.; Pang, Y.; Xu, J.; Li, X.; Chen, Y. Upgrading of Diammonium Hydrogen Phosphate on Wood and High-Value as an Efficient Derived Carbon. BioEnergy Res. 2023, 16, 2604–2615. [Google Scholar] [CrossRef]
  46. Mikucka, W.; Zielińska, M. Distillery Stillage: Characteristics, Treatment, and Valorization. Appl. Biochem. Biotechnol. 2020, 192, 770–793. [Google Scholar] [CrossRef]
  47. ENplus®, History of ENplus®, ENplus Pellets. 2022. Available online: https://enplus-pellets.eu/history/ (accessed on 29 May 2024).
  48. Basu, P. Biomass Gasification, Pyrolysis and Torrefaction: Practical Design and Theory, 2nd ed.; Academic Press: London, UK, 2013. [Google Scholar]
  49. Nussbaumer, T. Primary and Secondary Measures for the Reduction of Nitric Oxide Emissions from Biomass Combustion. In Developments in Thermochemical Biomass Conversion; Springer: Dordrecht, The Netherlands, 1997; pp. 1447–1461. [Google Scholar] [CrossRef]
  50. Siyal, A.A.; Mao, X.; Liu, Y.; Ao, W.; Jiang, Z.; Wahab, N.; Ran, C.; Zhang, R.; Liu, G.; Dai, J. Pellet production from furfural residue and sawdust: Evaluating the characteristics and quality of pellets and their dependency on process parameters. Biomass Bioenergy 2021, 149, 106087. [Google Scholar] [CrossRef]
  51. Kantová, N.; Holubčík, M.; Čaja, A.; Trnka, J.; Jandačka, J. Analyses of Pellets Produced from Spruce Sawdust, Spruce Bark, and Pine Cones in Different Proportions. Energies 2022, 15, 2725. [Google Scholar] [CrossRef]
Applsci 14 07313 g001
Figure 1. Oven drying curves at 30 °C.
Figure 1. Oven drying curves at 30 °C.
Applsci 14 07313 g001
Table 1. Test conditions for elemental analysis.
Table 1. Test conditions for elemental analysis.
TemperatureTime Interval
Moisture105 °C2 h
Volatile Matter950 °C2 min with open door
3 min with door half closed
6 min with door fully closed
Ashes750 °C6 h
Table 2. CHNS test conditions.
Table 2. CHNS test conditions.
Temperatures
Combustion reactor temperature:950 °C
Reduction reactor temperature (not being used):400 °C
Oven temperature:65 °C
Time intervals
Total analysis time:720 s
Time in which the sample falls into the reactor:12 s
Oxygen injection time:5 s
Gas fluxes
Drag gas:140 mL/min
Oxygen:250 mL/min
Reference:100 mL/min
Table 3. Proximate Analysis of distillation stillage and wine pomace (dry basis).
Table 3. Proximate Analysis of distillation stillage and wine pomace (dry basis).
SampleMoisture (%)Volatile Matter (%)Ash (%)Fixed Carbon (%)
Distillation stillage5.454 ± 0.11858.97 ± 0.2653.762 ± 0.12931.813 ± 0.018
Wine pomace5.268 ± 0.02762.695 ± 0.0576.359 ± 0.03825.677 ± 0.093
Table 4. Elemental Composition of distillation stillage and wine pomace (dry basis).
Table 4. Elemental Composition of distillation stillage and wine pomace (dry basis).
SampleN (%)C (%)H (%)S (%)O (%)
Distillation stillage2.57 ± 0.30154.928 ± 0.5316.725 ± 0.2510.153 ± 0.03231.862 ± 0.948
Wine pomace2.494 ± 0.05552.099 ± 0.4695.669 ± 0.1050.043 ± 0.01233.337 ± 0.541
Table 5. HHV and LHV of distillation stillage and wine pomace (air-dried basis).
Table 5. HHV and LHV of distillation stillage and wine pomace (air-dried basis).
SampleHHV (MJ/kg)LHV (MJ/kg)
Distillation stillage20.544 ± 0.03719.109 ± 0.024
Wine pomace19.741 ± 0.02518.514 ± 0.032
HHV—High heating value, LHV—Low heating value.
Table 6. Threshold values of parameters in accordance with ENplus® system [47].
Table 6. Threshold values of parameters in accordance with ENplus® system [47].
Moisture (%)Ash (%)N (%)S (%)LHV (MJ/kg)
ENplus® A1≤10.0≤0.70≤0.3≤0.04≥16.5
ENplus® A2≤10.0≤1.20≤0.5≤0.05≥16.5
ENplus® B≤10.0≤2.00≤1.0≤0.05≥16.5
Distillation stillage5.454 ± 0.1183.762 ± 0.1292.57 ± 0.3010.153 ± 0.03219.109 ± 0.024
Wine pomace5.268 ± 0.0276.359 ± 0.0382.494 ± 0.0550.043 ± 0.01218.514 ± 0.032
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Oliveira, M.; Teixeira, B.M.M.; Toste, R.; Borges, A.D.S. Transforming Wine By-Products into Energy: Evaluating Grape Pomace and Distillation Stillage for Biomass Pellet Production. Appl. Sci. 2024, 14, 7313. https://doi.org/10.3390/app14167313

AMA Style

Oliveira M, Teixeira BMM, Toste R, Borges ADS. Transforming Wine By-Products into Energy: Evaluating Grape Pomace and Distillation Stillage for Biomass Pellet Production. Applied Sciences. 2024; 14(16):7313. https://doi.org/10.3390/app14167313

Chicago/Turabian Style

Oliveira, Miguel, Bruno M. M. Teixeira, Rogério Toste, and Amadeu D. S. Borges. 2024. "Transforming Wine By-Products into Energy: Evaluating Grape Pomace and Distillation Stillage for Biomass Pellet Production" Applied Sciences 14, no. 16: 7313. https://doi.org/10.3390/app14167313

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