Life Cycle Assessment of Biofuels Production Processes in Viticulture in the Context of Circular Economy

Abstract

Globally, as the population and the living standards expanded, so did the use of energy and materials. Renewable energy resources are being used to help address the energy issue and reduce greenhouse gas emissions (GHG). Because lignocellulosic biomass resources are widely available and renewable, various processes are used to convert these resources into bioenergy. In the current study, two production processes were evaluated, namely the transformation of vine shoot waste into value-added biofuels, i.e., pellets/briquettes and bioethanol. The life cycle assessment (LCA) technique was used for simulating and documenting the environmental performance of two biomass waste to biofuels pathways, possible candidates for closing loops in the viticulture production, according to the circular economy models. The SimaPro software was used to perform the LCA. The results show that the pellets/briquettes production process has a lower negative influence on the studied environmental impact categories compared to the production of bioethanol.

1. Introduction

The consumption of energy and materials increased globally with the population and the living standards, with harmful consequences, such as climate change (due to greenhouse gases), environmental degradation (due to atmospheric, soil, water, and food chain contamination), and fossil fuel reserves depletion, which set the priority on the fossil fuel phase-out and of the economy shifting to bioenergy [1,2,3]. Bioenergy from lignocellulosic biomass represents one of the main alternative sources of energy. Lignocellulosic biomass, a renewable resource, can be derived from various agricultural wastes [4], including vine shoot waste from viticulture [5], and it is primarily composed of cellulose, hemicellulose, and lignin [6]. Viticulture represents a major agricultural activity worldwide, occupying a global surface area of 7.3 million hectares in 2020, Romania being the 10th vineyard cultivator in the world and the 5th in Europe, with a surface area under vine of 190,000 hectares [7]. The waste from the vine cuttings consists of vine shoots generated in large quantities (between 2 and 4 tons/ha) annually [6,8]. Currently, there are several disposal techniques: storage of vineyard waste on the field, incorporation of crushed ropes into the soil, and burning on the field [8,9,10,11]. Among the mentioned elimination techniques, field burning is the most used after the cutting operation and is an important source of greenhouse gas emissions [12]. The valorization of these wastes through the production of biofuels can be an option to avoid the generation of greenhouse gas emissions and represents a sustainable solution to the burdens and costs faced by vineyard owners [13]. Additionally, turning waste into value-added products, instead of field use for mulching or disposal, can also create a new circular process in a linear production context [2,13]. Biomass waste can be a raw material used for feeding the biomass-to-biofuels pathways, and biofuels can be used directly in the vineyard. Such process sequences and loops implement the model of the circular economy for saving resources while reducing the negative environmental impacts and possibly the materials and energy costs [14,15,16].

Several studies investigated the techno-economic feasibility of transforming vineyard residues into biofuels. Regarding solid biofuel production from biomass, pellets and briquettes are the most common. In this regard, Zanetti et al. [17] assessed the quality of pellets produced from vineyard pruning residues; Duranay et al. [18] converted vine waste biomass into solid fuel via torrefaction, showing that the resulted product’s characteristics are similar to coal; Hamedani et al. [19] compared the pellets obtained from vine and olive biomass through the environmental impact of the entire production process; Picchi et al. [20] analyzed the potential of vineyard residues as combustion fuel in residential boilers and their environmental impact; Fernandez-Puratich et al. [21] assessed the energetic performance of vine chips from several varieties in comparison with pine pellets, underlying their advantages and disadvantages; Tenu et al. [22] investigated the quality parameters of briquettes obtained from vine tendrils and showed that these fulfill the requirements outlined in the standards from the field; Muzicant et al. [23] reported that combining vine shoots biomass with straw and hay enhances briquette quality and quantity. Furthermore, some studies assessed bioethanol production from vine shoot biomass waste, such as Senila et al. [24], who carried out an analysis to compare different production methods to obtain bioethanol through autohydrolysis, chlorite delignification, and simultaneous saccharification and fermentation. Basaglia et al. [25] analyzed the potential of several agro-food residues to be transformed into bioethanol, concluding that vine shoots and wheat straw were the most suitable. Davila et al. [26] studied the viability of producing bioethanol from hydrothermally processed vine shoots and lignin extraction, while Buratti et al. [27] analyzed the possibility of using steam explosion pretreatment to obtain ethanol by saccharification and fermentation.

To evaluate the environmental impact of biofuel production systems, research studies focusing on the life cycle assessment (LCA) technique was carried out. LCA is a standardized environmental tool that analyzes the inputs and the outputs throughout the life cycle phases (cradle to grave) [28]. Regarding biofuels evaluation from biomass waste, several studies exist in the literature, some focusing on different types of agricultural residues (straw, stalks, cobs, bagasse, husk, shoots), wood residues, and other biomass [29,30,31,32,33,34,35]. The first-generation biofuels generate issues such as energy consumption, food competition, environmental damages, energy inefficiency, and poor yields. Conversely, the lignocellulosic biomass has advantages, such as availability, abundance, and lower costs, which makes it a potential candidate to replace petro-fuels with eco-sustainable and cost-effective biofuels, but also to obtain other bioproducts, such as fermentable sugars, solvents, and drink softeners [36,37,38]. Biorefinery integration and, in particular, the hydrolysis process optimization through mitigating the energy inputs and GHG emissions, and by using fermentative cellulase and genetically engineered organisms or waste biomass, can increase the value of lignocellulosic biomass and reduce the ecological footprints [38].

The LCA study conducted by Pachon et al. [39], concerning two biorefinery scenarios concerning the sustainable use of vine shoots, concluded that lactic acid and furfural produced from the biochemical conversion of vine shoots reveal environmental benefits for the selected environmental impact categories in comparison with relevant reference systems. In the study of Gullón et al. [13], an assessment of the environmental impacts of the valorization of vine shoots was evaluated, considering five alternative valorization schemes, with different extraction, delignification, and hydrolysis routes, based on experiments and protocols carried out at semi-pilot scale. Biorefining systems are intensively demanding for chemicals and energy. Improving the efficiency and sustainability of the bio-refineries based on renewable waste raw materials is essential for obtaining high value-added compounds and processes, which depend on the desired purity of the final product.

Regarding pellets production, Ilari et al. [40] assessed the environmental impact of heat produced from vineyard pruning agripellets using LCA scenarios considering mobile or stationary pellet systems compared with other pellet and fossil alternatives. The main impact was caused by emissions and ash residues, affecting human health and ecosystem quality at almost similar levels to methane production, which had a higher impact on resources. Pellets production from olive and vine biomass, with different handling methods for biomass collection, following a cradle-to-gate perspective, was explored by another LCA study conducted by Hamedani et al. [19] to quantify and compare the environmental impacts. Olive pellets caused higher human, marine, and freshwater ecotoxicity and marine eutrophication, while vine pellets caused higher freshwater eutrophication and natural land transformation. The energy balance was more favorable for the olive than for the vine pellet, while fertilizers and pesticides had the highest impact on all categories.

In this context, the aim of the present study was to investigate and compare, using a life cycle assessment, two distinct pathways: bioethanol and pellets/briquettes production through the valorization of vine shoot waste and to evaluate the environmental sustainability of these processes. The findings of the current study would provide valuable information to policymakers in support of the circular economy implementation, as well as to different relevant stakeholders in viticulture in the pursuit of sustainability.

2. Materials and Methods

Life cycle assessment is a standardized method for analyzing the environmental performance of production systems during the phases of raw materials extraction and processing, production, logistics, circulation, and final disposal. The LCA methodology comprises four phases: (1), the goal and scope definition phase, with the objective setting and the analysis concern, the functional unit, and system boundary definition; (2), the inventory analysis phase (LCI), with a quantitative determining of the materials and the inputs and outputs of all the processes involved; (3), the impact assessment phase (LCIA) with the mapping of the unit flows impact potentials to the category indicators and factors of impact; and (4), the results interpretation phase [41,42,43,44].

In the current study, the potential environmental implications of bioethanol and pellets/briquettes production from vine shoot waste are assessed by implementing the standardized LCA methodology, following the principles and the framework of the ISO 14040 and ISO 14044 standards [45,46].

2.1. Goal and Scope Definition

The goal includes the rationale and audience of the assessment, and the scope establishes a functional unit and a boundary of the analyzed system. The main goal of the current study was to evaluate two pathways for producing bioethanol and pellets/briquettes from vine shoot waste using LCA, and to assess the environmental sustainability of these value-added products manufacturing flows.

Considering the study’s goal and scope, a functional unit of 1 kg of bioethanol and a functional unit of 1 kg of pellets/briquettes were established for the two production processes. The system boundaries were defined for a “cradle to gate” analysis, which includes all the process entries and the associated emissions for the bioethanol production (Figure 1) and the pellets/briquettes (Figure 2). The systems cover biomass transport and conversion and bioethanol production. The entries within and between the mentioned stages were taken into account.

The chopped and ground vine shoots were obtained and transported in October 2018 from the Research Station of the “Ion Ionescu de la Brad” University of Agricultural Sciences in Iasi, farm no. 3 “Vasile Adamachi”, where 8 vines varieties are grown (Sauvignon Blanc, Pinot Noir, Feteasca Regala, Feteasca Neagra, Feteasca Alba, Busuioaca de Bohotin, Muscat Ottonel, and Cabernet Sauvignon).

2.2. Life Cycle Inventory (LCI)

The LCI phase consists of gathering primary data, calculating the inputs and outputs within the product system boundary, and allocation. The inventory outcomes serve as inputs to the life cycle impact assessment phase. The collection of several sets of primary data was performed during the period October 2018–November 2019 (

Table 1. Life cycle inventory for bioethanol production (1 kg).

LCI Stage	Process	Amount	Unit
Input
Vine shoots	Transportation, freight, lorry 16–32	7185	kg/km
Autohydrolysis	Water	130	L
	Cellulose	6.73	kg
	Hemicellulose	3.35	kg
	Lignin	4.73	kg
	Electricity [Parr reactor]	74.0	kWh
Delignification	Cellulose	5.96	kg
	Hemicellulose	0.17	kg
	Lignin	4.32	kg
	Sodium chlorite	19.1	kg
	Water	77	kg
	Electricity	165	kWh
Simultaneous Saccharification and Fermentation (SSF)	Cellulose	4.52	kg
	Lignin	0.33	kg
	Enzymes	0.06	kg
	Water	50	L
	Electricity	390	kWh
Output
Autohydrolysis (solid phase)	Cellulose	5.93	kg
	Hemicellulose	0.17	kg
	Lignin	4.27	kg
Autohydrolysis (liquid phase)	Hemicellulose	1.26	kg
	By-products	2.79	kg
	Water	130	L
Delignification (solid phase)	Cellulose	4.12	kg
	Lignin	0.32	kg
Delignification (liquid phase)	Lignin + Water	80	kg
Simultaneous Saccharification and Fermentation (SSF)	Water + by-products	53.9	kg

and

Table 2. Life cycle inventory for pellets/briquettes production (1 kg).

LCI Stage	Process	Amount	Unit
S1-Baling shoots between rows	Diesel	9.3 × 10−3	kg
S2-Loading shoots in the trailer	Diesel	7.3 × 10−4	kg
S3-Transporting shoots at the end of the row	Diesel	1.7 × 10−3	kg
S4-Transport of shoots to the storage base	Diesel	1.3 × 10−3	kg
S5-Uploading shoots from the trailer	Diesel	7.3 × 10−4	kg
S6-Stacking shoots in the primary dryer	Diesel	6.3 × 10−4	kg
S7-Dehydration of the shoots	Electricity	1.89	kWh
S8-Chopping and grinding shoots	Electricity	2.3 × 10−2	kWh
S9-Pelletizing the wood material	Electricity	0.11	kWh

).

The bioethanol production process from vine shoot wastes includes three main stages: the pretreatment stage (autohydrolysis), the delignification stage, and the Simultaneous Saccharification and Fermentation process (SSF). The methodologies for all processes applied in bioethanol production from vine shoot waste were described in the study of Senila et al. [24]. The inputs characterized for each stage of the experiment and the afferent outputs are indicated in Table 1. The processes involved in obtaining pellets/briquettes consist of baling vine shoots between rows, loading vine shoots in the trailer, transporting vine shoots, storing vine shoots, uploading vine shoots from the trailer, stacking vine shoots in the dryer, dehydrating vine shoots, chopping and grinding vine shoots, and pelletizing the resulting material. All these were detailed in our previous studies [24,47,48], and the inventory data is presented in Table 2. The chemical composition of vine shoot waste was investigated and described in our previous publication [24]. The cellulose, hemicellulose, and lignin content were 42.4%, 22.6%, and 31.9%, respectively.”

2.3. Life Cycle Impact Assessment (LCIA)

The impact assessment refers to the process of understanding and evaluating the magnitude and importance of potential environmental impacts, as well as environmental impacts caused by the overall system of the product under study [45]. To assess the environmental impact, the global method ReCiPe Midpoint H and Endpoint H [49] was used with the help of the SimaPro software.

After completing the life cycle inventory assessment of biofuels derived from vine shoot waste, several impact categories on environmental factors were taken into account. The results are related to the selected midpoint impact categories of global warming (kg CO₂ eq), formation of fine particulate matter (kg PM_2.5 eq), human toxicity (kg 1,4-DCB eq), terrestrial ecotoxicology (kg 1.4-DCB), fossil resource scarcity (kg oil eq), water consumption (m³), freshwater eutrophication (kg P eq), and ecotoxicity (kg 1,4-DCB eq).

Regarding the production of 1 kg of bioethanol and 1 kg of pellets/briquettes from vine shoot waste, all flows were considered.

3. Results

Based on the inventoried data in the bioethanol and pellets/briquettes production processes, the impacts on the environmental categories were determined. The most significant impacts generated by the production of the mentioned biofuels are global warming, fine particulate matter formation, freshwater eutrophication and ecotoxicity, terrestrial ecotoxicity, fossil resource scarcity, water consumption, and human toxicity (Figure 3a,b). The human toxicity was calculated as the sum of the human carcinogenic and non-carcinogenic toxicity impacts obtained using the same ReCiPe method.

The results were expressed in percentages, according to the used nominalization indicator of the ReCiPe method applied with the help of the SimaPro software.

In bioethanol production, the main stage with the highest impact on the environment is represented by delignification, followed by SSF and autohydrolysis. The vine shoots have low impacts, lower than 10% for all impact cases. The possible impacts are generated by the consumption and burning of fuels used to transport the biomass from the field to the laboratory. The freshwater and terrestrial ecotoxicity are generated mostly (>80%) by the delignification stage due to the high amount of water, chemicals (sodium chloride), and energy consumption. The SSF process is mainly responsible for fine particulate matter formation, freshwater eutrophication, water consumption, global warming, human toxicity, and terrestrial ecotoxicity, especially due to the water, energy, and enzymes production and consumption. Autohydrolysis is responsible for less than 20% of the generated impact scenarios.

On the other hand, human toxicity, fossil resource scarcity, and freshwater ecotoxicity are the most significant impacts generated by pellets and briquettes production, mainly by the majority of the stages. In the last three stages, more than 40% of the generated impacts are represented by human toxicity and terrestrial ecotoxicity due to energy consumption. The rest of the stages, except baling strings, generate 30% terrestrial ecotoxicity, and 40% fossil resource scarcity and human toxicity, due to fossil fuel burning.

As seen in Figure 4, the SSF and delignification stages contribute mostly to the impacts, while the transportation of vine shoots has the lowest contribution. At the global warming impact, the SSF contributes with almost 180 kg CO₂ eq, the delignification with 140 kg CO₂ eq, the autohydrolysis with 34 kg CO₂ eq, and the vine shoots with less than 1.0 kg CO₂ eq. At the human toxicity impact, the entire process contributes with 16 kg 1.4-DCB (Dichlorobenzene), with 1.0 kg PM_2.5 eq for the fine particulate matter formation, 93 kg oil eq (45 and 40 kg oil eq from the SSF and delignification stage, <10 kg oil eq for the autohydrolysis and vine shoots stages). In the case of human toxicity, the delignification contributes with 5.6 kg 1.4-DCB, the SSF with 6.4 kg 1.4-DCB, and the first two stages with less than 1.3 kg 1.4-DCB. The high impact generated by the delignification stage on the freshwater ecotoxicity (0.427 kg 1.4-DCB) and the water consumption (2.99 m³) can also be observed in Figure 4.

The potential impacts caused by the production of 1 kg pellets/briquettes, for all nine stages of the process are presented in

Table 3. Life cycle impacts per kg of pellets/briquettes from all process stages.

Impact Category	Global Warming	Fine Particulate Matter Formation	Freshwater Eutrophication	Terrestrial Ecotoxicity	Freshwater Ecotoxicity	Fossil Resource Scarcity	Water Consumption	Human Toxicity
Unit	kg CO2 eq	kg PM2.5 eq	kg P eq	kg 1,4-DCB	kg 1,4-DCB	kg oil eq	m3	kg 1,4-DCB
S1	4.9 × 10−3	1.4 × 10−5	8.4 × 10−8	6.6 × 10−3	1.1 × 10−5	1.1 × 10−2	5.6 × 10−5	6.2 × 10−4
S2	3.9 × 10−4	1.1 × 10−6	6.6 × 10−9	5.2 × 10−4	8.5 × 10−7	9.0 × 10−4	4.4 × 10−6	4.8 × 10−5
S3	9.3 × 10−4	2.7 × 10−6	1.6 × 10−8	1.2 × 10−3	2.0 × 10−6	2.2 × 10−3	1.1 × 10−5	1.2 × 10−4
S4	6.7 × 10−4	1.9 × 10−6	1.1 × 10−8	8.9 × 10−4	1.5 × 10−6	1.5 × 10−3	7.6 × 10−6	8.3 × 10−5
S5	3.8 × 10−4	1.1 × 10−6	6.6 × 10−9	5.2 × 10−4	8.5 × 10−7	9.0 × 10−4	4.4 × 10−6	4.8 × 10−5
S6	3.3 × 10−4	9.6 × 10−7	5.7 × 10−9	4.5 × 10−4	7.3 × 10−7	7.7 × 10−4	3.8 × 10−6	4.2 × 10−5
S7	8.4 × 10−1	2.7 × 10−3	1.8 × 10−4	9.4 × 10−1	1.9 × 10−4	2.2 × 10−1	1.9 × 10−2	2.7 × 10−2
S8	1.0 × 10−2	3.3 × 10−5	2.2 × 10−6	1.1 × 10−2	2.3 × 10−6	2.6 × 10−3	2.4 × 10−4	3.3 × 10−4
S9	4.9 × 10−2	1.6 × 10−4	1.0 × 10−5	5.4 × 10−2	1.1 × 10−5	1.3 × 10−2	1.1 × 10−3	1.6 × 10−3

Note: S1- Baling shoots between roads; S2-Loading shoots in the trailer; S3-Transporting shoots at the end of the row; S4-Transporting shoots to the storage base; S5-Uploading shoots from the trailer; S6-Stacking shoots in the dryer; S7-Dehydrating the shoots; S8-Chopping and grinding shoots, and S9-Pelletizing the wood material.

. A significant contribution to the studied impacts is noticed in the case of the processes of dehydration (S7) of the vine shoots and of pelletizing of the wood material (S9). The contribution to global warming is represented by the following order S8 > S1 > S3 > S4 > S2 > S5 > S6, to the formation of fine particulate matter S8 > S1 > S3 > S4 > S2 > S5 > S6, to freshwater eutrophication S8 > S1 > S3 > S4 > S2 > S5 > S6, to terrestrial ecotoxicity S8 > S1 > S3 > S4 > S2 > S5 > S6, to freshwater ecotoxicity S1 > S8 > S3 > S4 > S2 > S5 > S6, to fossil resource scarcity S1 > S8 > S3 > S4 > S2 > S5 > S6, to water consumption S8 > S1 > S3 > S4 > S2 > S5 > S6 and to human toxicity S1 > S8 > S3 > S4 > S2 > S5 > S6.

The damage assessment was carried out based on the ReCiPe method. The results indicate that bioethanol production causes more damage than the pellets/briquettes (Figure 5a). Impacts on human health and the ecosystems are associated with 50% with the SSF process, 35% with the delignification, and 10% with the autohydrolysis. The vine shoots and the pellets/briquettes cause less than 10% of the damage to human health but also to the resources and ecosystems. Resources are damaged essentially by delignification (>60%), followed by the SSF (30%) and by the autohydrolysis (<10%). Vine shoots and pellets/briquettes contribute, like in the case of bioethanol production, with less than 10% of the negative impact related to the resources. Applying the single score analysis, which consists of normalizing, weighting, and aggregating several impact categories, as indicated in Figure 5b, human health is the most affected indicator compared to the ecosystems and resources.

4. Discussion

The current study leads to a comprehensive overview of the effects of bioenergy production processes. It shows the analysis of bioethanol and pellets/briquettes production with the help of the LCA, which is an effective technique for quantifying environmental impacts and improving environmental efficiency. Various studies have been published in which the LCA technique has been used to estimate the environmental impacts associated with the production of bioenergy from renewable resources [35,50,51,52,53,54,55,56]. However, only a few research studies on the environmental analysis of vine shoot biomass waste have been reported in the literature [13,19,20,39].

The production and use of biofuels can considerably reduce greenhouse gas emissions. According to Pachon et al. [39], the use of biofuels instead of fossil fuels results in lower emissions, indicating a 30–40% reduction in CO₂ emissions. Additionally, compared to gasoline, a decrease of up to 50% in fossil fuel usage might be attained [57]. The emissions reduction potential can vary significantly due to raw materials, biomass processing methods, the use of energy, chemicals, the scale of the experiment, and on-site infrastructure and conditions. Therefore, it is difficult to compare several biofuel production pathways, each study being very case-specific.

Regarding the comparison between the bioethanol production process and the pellets/briquettes production process, it was found that the pellets/briquettes production has a reduced environmental impact, while the overall impact of the bioethanol production was higher. In this context, dehydration of the shoots and pelletizing of the wood material contribute up to 2000 times more than the rest of the stages (Table 3). The dehydration and pelletizing of the wood material contribute to the global warming impact with 0.84 and 0.05 kg CO₂ eq, to the fine particulate matter formation with 2.7 × 10⁻³ and 1.6 × 10⁻⁴ kg PM_2.5 eq, 1000 times higher than the 8 stages. The contribution of the two processes to freshwater eutrophication is 1.8 × 10⁻⁴ and 1.9 × 10⁻⁴, respectively, more than 1 × 10⁻⁵ times and 1000 times than the contribution of the rest of the 8 stages. The contribution of the two processes to the ecotoxicology is 1.02 × 10⁻⁵ kg P eq and 1.1 × 10⁻⁵ kg 1.4-DCB, respectively, 1000 times more than the contribution of the other 8 stages. The water consumption is affected 1 × 10⁻⁴ times more by the hydration and pelletizing stages (2.0 × 10 ⁻² and 1.1 × 10⁻³ m³, respectively) than by the other 8 stages.

The terrestrial ecotoxicology could be caused by the dehydration and pelletizing stages, having contributions of 0.94 and 0.05 kg 1.4-DCB, respectively, almost 1800 times more significant than the contribution of the stages of stacking, uploading, and loading of shoots. Dehydration and pelletizing are responsible for the fossil resource scarcity, with contributions of 2.2 × 10⁻² and 1.3 × 10⁻² kg oil eq, respectively, while the other stages contribute with 7.7 × 10⁻⁴ to 1.1 × 10⁻² kg oil eq, respectively. The stages with the highest contribution to the human toxicity impact are the dehydration of shoots (2.7 × 10⁻³), followed by: the pelletizing of wood materials (1.6 × 10⁻³) and the shoots baling (6.2 × 10⁻⁴), chopping and grinding (3.3 × 10⁻⁴), transportation at the end of the field rows (1.2 × 10⁻⁴), then transportation to the storage base (8.3 × 10⁻⁵), loading in the trailer and uploading from the trailer (4.8 × 10⁻⁵) and eventually stacking them in the primary dryer (4.2 × 10⁻⁵).

The chopping and baling phases follow dehydration and pelletizing, but with an impact 100 times weaker, while the rest of the stages have even lower impacts. For example, for global warming, the chopping and baling stages contribute 0.01 and 0.005 kg CO₂ eq, while the other stages contribute less than 0.001 kg CO₂ eq. The chopping process contributes mainly to the fine particulate matter formation (with 3.3 × 10⁻⁵) and water consumption (with 2.4 × 10⁻⁴). The baling of strings contributes primarily to the fossil resource scarcity (with 0.01 kg oil eq), to the human toxicity (with 6.2 × 10⁻⁴), and to the freshwater ecotoxicity (with 1.1 × 10⁻⁵).

The pellets/briquettes production process has a lower contribution to the studied environmental impact categories compared to the bioethanol process, as indicated in Figure 4 and Table 3. In the former production process, there are no chemicals used, but only the energy consumption, which is significant in 2 processing stages (dehydration and pelletizing) and the use of fuels. Obtaining biofuels through this process is less harmful to the environment. Furthermore, storing the pellets/briquettes presents no risks compared to the special conditions required for the biofuels storage to prevent risks like altering the natural factors quality due to potential leakage of bioethanol into the soil and water sources.

Other studies indicate a higher contribution of the biofuels from biowastes production processes to the environmental degradation due to different technologies and the use of a larger list of chemicals [13,39,58]. For example, the technology used by Dávila et al. [26] consists of hydrothermal processing of vine shoots with the help of a steel Parr reactor, enzymatic hydrolysis of the waste, preparation of the inoculum and microorganisms, and the simultaneous saccharification and fermentation of the processed biomass. Jesus et al. [59] proposed cleaner alternatives for the delignification process (disrupting the lignocellulosic matrix, implying reagents and high quantities of water for neutralization), namely autohydrolysis in two sequential stages involving milder conditions. An alkaline delignification stage by using a microwave at different temperatures to better remove the lignin was suggested by Dávila et al. [60]. Using a microwave, the time, NaOH amount and temperature are reduced, increasing the delignification yield. The obtained solid residues are characterized by high glucan content and low hemicellulose and lignin content which could be a promising solid used in the SSF treatment. On the other hand, co-products are also obtained through production processes, which modify the environmental impact allocation. According to Pachon et al. [39], co-products of bioethanol, such as lactic acid and furfural, can be valorized from viticulture and vine shoots residues but with larger inputs (H₂SO₄, lime, methanol, NaCl) than the inputs in this study. Nevertheless, the contribution to the environmental impacts is high, participating with 3.26 kg CO₂ eq to the climate change, with 40.4 kg 1.4-DB eq to the human toxicity, with 69% to the freshwater eutrophication and with 52% to the water ecotoxicity, for the production of 1 kg of lactic acid [39]. Pergola et al. [50] used the LCA to analyze the effects on the environment through the use of sawdust and roundwood logs in the production of pellets. The results indicated that for obtaining 1 t of pellets, 38 and 83 kg of CO₂ eq are emitted into the atmosphere, contributing to the global warming impact category. The pelletizing process also contributes to the eutrophication impact with 0.002 and 0.005 kg P-PO₄-lim, respectively, and to the acidification impact with 1.36 and 2.71 kg SO₂ eq, respectively [50].

The total damage contribution (human health, ecosystems, and resources) of each of the two production pathways is higher than 17.5 Pt, according to the single score indicator (Figure 5b). The SSF contributes with 9.3 Pt, followed by the delignification (6.4 Pt), the autohydrolysis (1.8 Pt), the pellets/briquettes (0.05 Pt), and the vine shoots (0.002 Pt). The pellets/briquettes (comprising 10 stages) contribute 46 mPt to human health damage, 2.4 mPt to the ecosystems, and 0.21 mPt to resource depletion. Generally, it was noticed that stages S8 > S10 > S9 > S1 have the highest contributions, while S1 has the lowest contribution. Nonetheless, the bioethanol process, through the SSF (8.8 Pt), delignification (6.0 Pt), and autohydrolysis (1.7 Pt) stages, has the most significant contribution to the studied damages compared to the pellets/briquettes process.

In line with the vision of the Ellen McArthur Foundation [61] on the circular economy, the model environmentally analyzed in the present study closes loops, simultaneously maintaining the system value creation without significantly reducing the quality of the products, using more genuinely renewable energy and avoiding disposal, through optimizing the use of biomass waste in a circular process. This process enhances the efficiency in terms of energy, expenses, and environmental consequences, such as GHG emissions. The two value-added products could be used for the vineyard operations, producing some of the energy required for local consumption, to integrate these processes sustainably and achieve a circular economy.

Lignocellulosic biomass may also be used to produce Fischer-Tropsch products as an alternative way to obtain synthetic fuels. The Fischer-Tropsch process uses a thermochemical gasification process and generally requires high temperatures and pressures and the presence of catalysts, increasing greenhouse gas emissions [62].

To the best of our knowledge, no studies are conducted on the comparison between the two studied pathways. However, there are certain limitations concerning the feasibility of the biofuels from biomass waste, particularly vine shoots biomass, which will have to be addressed in future research. Besides the environmental impact, economic impact assessment would be necessary to determine the costs involved in the production processes of the two value-added products, namely bioethanol and pellets/briquettes. It is important to identify the process that provides an optimal solution from environmental and economic perspectives, notably given the worldwide challenge and effort toward circular economy and sustainability. A further limitation of the study consists of the fact that the findings are influenced by the laboratory scale of the experiment, as well as by the “cradle to gate” approach. In the case of a pilot or a larger scale experiment, the extension of the system boundary by including additional stages, such as wastewater treatment, would impact the calculations and the outputs, influencing the system’s environmental consequences. However, from a scientific, technical, and decisional point of view, the results of the study provide useful data in terms of agricultural and environmental management practices, closing the loop through efficient use of biomass waste in line with the principles of the circular economy.

5. Conclusions

The current study used the LCA technique to calculate the environmental impact of two processes, namely bioethanol and pellets/briquettes production, through the valorization of vine shoot waste. Compared to the bioethanol process, the pellets/briquettes production exhibited a smaller contribution to the evaluated environmental impact categories. Among the notable differences in the environmental characteristics, the main responsible stages in the case of bioethanol production are represented by the delignification, which generates high freshwater and terrestrial ecotoxicity due to the large quantities of water, chemicals, and energy consumed, and by the SSF process, which contributes mostly to the formation of fine particulate matter, freshwater eutrophication, water consumption, global warming, human toxicity, and terrestrial ecotoxicity. Regarding the pellets/briquettes production, human toxicity, fossil resource scarcity, and freshwater ecotoxicity are the most significant impacts, with the dehydration and the pelletization stages playing the most important role.

The production of biofuels from vine shoot waste would benefit the environment by reducing greenhouse gases, avoiding the negative effects of field burning and converting these wastes into value-added products. Using agricultural biomass waste can reduce the consumption of wood while avoiding deforestation. Additionally, instead of dedicated crops, it reduces land use, and it provides a solution faced by vineyard owners regarding the management of large amounts of biomass wastes.

The present study provides valuable information to support policymakers and different stakeholders involved in the viticulture field, facilitating the implementation of a circular economy and sustainability.