Environmental Benefits of Olive By-Products in Energy, Soil, and Sustainable Management

Abstract

This study aimed to evaluate the environmental benefits of utilizing by-products from olive farms and olive oil mills within the framework of sustainable resource management and the reduction in agricultural waste, through an integrated circular approach that involves composting and bioenergy recovery. A total of 10.7–11.2 t/ha of biomass, including pruning residues and olive pomace, was generated, with a utilization efficiency of 63.5–67.5%. The energy potential of olive biomass was highlighted through assessments that revealed a theoretical generation potential of approximately 96 GJ/ha (25–28 MW·h/ha), primarily from repurposed woody biomass and pomace. The environmental analysis showed a 50–60% reduction in greenhouse gas emissions compared to conventional disposal, due to avoided open burning, carbon stabilization via compost, and the displacement of fossil fuels. Economically, the circular strategy yielded a net benefit of ~70 $/ha, with revenues from bioenergy and compost exceeding processing costs. Soil organic matter increased from 1.3% to 1.5% after compost application, improving fertility and water retention. The waste reduction percentage reached ~65%, significantly decreasing the volume of unutilized biomass. These outcomes, confirmed through statistical and correlation analyses, demonstrate a robust model for circular agriculture that enhances energy self-sufficiency, mitigates the environmental impact, and supports economic and agronomic sustainability. The findings offer a replicable framework for transforming olive farming waste into valuable bioresources.

1. Introduction

Al-Jouf, a prominent region in northern Saudi Arabia, has rapidly emerged as a key area for olive cultivation, significantly contributing to both the national agricultural landscape and the global olive industry [1]. Characterized by its unique climatic conditions—hot, dry summers combined with moderate winters—Al-Jouf offers an ideal environment for high-density olive orchards. Moreover, the region’s adoption of intensive cultivation practices has led to impressive yields, making it a vital contributor to the agricultural economy of Saudi Arabia [2]. However, the expansion of olive cultivation brings with it the generation of substantial by-products, which include pruning residues from regular tree maintenance and waste materials from the olive oil extraction process. This introduces critical challenges in terms of sustainable waste management. Energy storage systems (ESS) have emerged as a key technological element in improving the operational efficiency, reliability, security, flexibility, and performance of renewable energy technology integrated distribution networks [3]. Pruning, as an essential agronomic practice, ensures the optimal growth and productivity of olive trees. In high-density orchards, the volume of biomass generated from annual pruning can be significant. Likewise, the extraction of olive oil—a process central to the industry—produces by-products such as olive mill wastewater (OMW) and olive pomace [4]. While these materials are often considered waste, they carry a high organic load and contain various bioactive compounds that can be either detrimental or beneficial, depending on how they are managed. Recent emphasis has been placed on the critical role of energy storage systems (ESS) in enhancing grid flexibility and supporting renewable energy integration, particularly through strategic planning and technological innovation [5]. OMW contains phytotoxic compounds such as polyphenols, which can significantly reduce microbial enzymatic activity if applied untreated [6]. Olive pomace, consisting of pulp, skins, and seeds, can pose serious environmental risks if left untreated, as it ferments quickly, releasing methane and leachates that contribute to both air and groundwater pollution [7]. Despite these environmental concerns, the by-products from olive farms and olive oil mills offer considerable potential for sustainable development. Studies have demonstrated that what was once regarded solely as waste can be transformed into valuable resources. For instance, phenolic-rich extracts from olive mill wastewater have shown potential in cosmetic and therapeutic formulations, owing to their anti-inflammatory and antioxidant effects [8]. Similarly, olive pomace has been explored for its potential conversion into biochar through controlled thermal processes. Biochar is a carbon-rich material that can significantly improve soil fertility by enhancing nutrient retention and the water-holding capacity, while also playing a role in carbon sequestration—a critical factor in mitigating climate change [9]. Furthermore, the anaerobic digestion of olive pomace to produce biogas represents an innovative approach to generate renewable energy, thereby reducing the reliance on fossil fuels [10]. In this context, agricultural biomass is increasingly viewed as an environmentally acceptable energy source due to its negligible content of toxic substances such as heavy metals and sulfur, which are prevalent in fossil fuels. Its principal advantage lies in its renewability, offering a more sustainable and less polluting alternative for energy generation. As such, agricultural biomass—including olive-derived residues—shows strong potential to replace fossil fuels in various applications, contributing to reduced environmental harm and enhanced sustainability [11].

The sustainable valorization of these by-products aligns perfectly with the broader goals of environmental protection and resource recovery. In regions like Al-Jouf, where olive cultivation is predominant, integrating olive by-products into a circular economy model could yield significant benefits. Not only would such practices reduce the environmental footprint associated with olive farming, but they could also generate new income streams for local farmers and communities [8]. For instance, using olive pomace as a soil amendment has been shown to improve crop yields by enhancing soil structure and organic matter content. This, in turn, decreases the need for synthetic fertilizers and lowers production costs, making the entire olive production system more economically viable and environmentally sustainable [12,13]. Beyond agricultural applications, the potential uses of olive by-products extend to various industrial sectors. Olive mill wastewater, once properly treated, can serve as a raw material for producing biodegradable biopolymers used in packaging and agriculture. Additionally, olive pits, a component of the overall waste stream, can be converted into activated carbon. Activated carbon has numerous applications, including water purification, gas filtration, and even medical procedures. These innovative applications not only address waste management challenges but also contribute to economic diversification by opening new market opportunities [14]. In line with Saudi Arabia’s Vision 2030, which emphasizes environmental preservation, economic diversification, and sustainable resource utilization, this study aims to evaluate the environmental benefits of utilizing by-products from olive farms and olive oil extraction facilities within the framework of sustainable resource management and the reduction in agricultural waste.

2. Materials and Methods

2.1. Study Area and Olive Orchard Characteristics

This study was conducted in the Al-Jouf region of northern Saudi Arabia, a key area for intensive olive cultivation. The region plays a critical role in national olive oil production, contributing approximately 67% of the country’s total. The research focused on high-density olive orchards planted with two cultivars, Arbosana and Arbequina, which represent modern and efficient plantation systems. The experimental orchards are located at coordinates of approximately 29.79° N latitude and 40.10° E longitude, at an elevation of 669 m above sea level. The trees, planted at a spacing of 4.0 m between rows and 1.5 m between trees within rows, are around 10 years old, with an average height of 2.7 ± 0.41 m and canopy width of 1.8 ± 0.34 m. Annual production is approximately 10 tons of olives per hectare, with an average oil content of 22%. The soil in the study area is classified as sandy loam, favorable for olive cultivation due to its drainage and aeration characteristics. The region experiences an arid desert climate, with average maximum temperatures ranging from 30.3 °C in January to 47.0 °C in July and minimum temperatures from −6.0 °C in January to 24.1 °C in December. The average annual precipitation is approximately 54.6 mm, with significant interannual variability.

2.2. Collection and Characterization of Olive Farm By-Products

The data presented in the following subsections are based on direct field measurements carried out at the experimental site during the study period.

2.2.1. Dry Leaves

Olive trees naturally shed dry leaves throughout the year, averaging about 0.5 kg per tree. However, due to the logistical challenges related to the collection and storage of these leaves, they were not included in the subsequent analysis.

2.2.2. Pruning Residues

Pruning is conducted annually to maintain tree vigor and optimize yield. Each tree produces between 3 and 4 kg of biomass during pruning, with leaves constituting approximately 20–30% of this residue. The pruning material was manually collected and weighed directly in the field to determine the available biomass for potential reuse.

2.2.3. Harvesting Residues

During mechanical harvesting, conducted with a New Holland olive harvester, additional residues are generated. Specifically, between 0.22 and 0.3 kg of leaves per tree are removed inadvertently during the harvesting process. These residues were also collected and weighed to assess their potential as a secondary resource.

2.3. Pomace Collection from Olive Oil Mills

Representative pomace samples from both Arbosana and Arbequina cultivars were collected immediately after the oil extraction process. The samples were analyzed for their moisture, residual oil, protein, sugar, fiber, and ash content using standard analytical procedures recommended by AOAC [15]. In addition to the farm residues, the process of olive oil extraction yields a significant amount of solid waste known as olive pomace. This by-product accounts for approximately 45–50% of the total weight of the processed olives. Pomace samples were collected immediately after extraction from local olive mills, weighed, and stored under controlled conditions for further analysis. The chemical compositions of the pomace determined for both Arbosana and Arbequina varieties are shown in

Table 1. The chemical composition of the pomace for Arbosana and Arbequina varieties.

Component	Arbosana	Arbequina
Moisture, %	50	52
Residual Oil, %	2	2
Protein, %	5	4
Sugars, %	8	10
Fiber, %	28	26
Ash (Minerals), %	7	6
Total, %	100	100

.

These compositional data were critical for evaluating the energy generation potential and environmental impact of the pomace.

2.4. Performance Indicators and Analytical Methods

2.4.1. Utilization Efficiency (UE)

The utilization efficiency (UE) of plant and pomace residues was calculated using Equation (1).

$$UE={\displaystyle \frac{W_{up}}{W_t}}\times 100$$

(1)

where UE is the utilization efficiency, %; W_up is the weight of utilized by-products, kg; and W_t is the total weight of by-products generated, kg.

2.4.2. Energy Generation Potential (EGP)

The energy generation potential (EGP) was calculated using Equation (2) according to Rodríguez Romero et al. [16].

$$EGP=4.2\times F+9.2\times O$$

(2)

where EGP is the energy generation potential, kcal/kg; F is fiber content, %; and O is the oil content, %.

2.4.3. Environmental Impact Reduction (EIR)

The carbon footprint reduction from sustainable by-product utilization was evaluated by comparing two scenarios:

(1)

Baseline Scenario: Conventional disposal (burning/dumping) of ~10–11 t/ha, with over 80% of the olive fruit’s weight lost as waste, leading to significant CO₂, methane, and pollutant emissions.

(2)

Integrated Scenario: Conversion of by-products into compost and bioenergy, which avoids open burning, stabilizes carbon (via compost/biochar), and offsets fossil fuel use.

The carbon footprint reduction (CFR) was calculated using Equation (3) according to Cherubini and Strømman [17].

$$CFR={\displaystyle \frac{BE-RE}{BE}}\times 100$$

(3)

where CFR is the carbon footprint reduction, %; BE is the baseline emissions from conventional disposal methods; and RE is the emissions in the integrated by-product utilization scenario.

2.4.4. Economic Feasibility

The net economic benefit (NB) from by-product utilization was calculated using Equation (4) [14].

$$NB=TR-C$$

(4)

where NB is the net benefit, $/ha; TR is the total revenue from by-products, $/ha; and C is the cost of collection and processing, $/ha.

Revenue streams were defined based on the valorization of two main by-product fractions:

(1)

Bioenergy Production: This includes the conversion of woody biomass (pruning and harvesting residues) into energy (via heat, electricity, or the sale of biomass fuel).

(2)

Compost Utilization: This pertains to the generation of additional value through the conversion of olive pomace into compost, which can either be marketed as an organic soil amendment or used on-farm to reduce fertilizer expenses.

The cost component encompasses expenses related to collection, processing, and application, such as labor, equipment usage, and processing inputs. The methodology was designed to assess economic feasibility on a per-hectare basis under typical local market conditions and operational practices in high-density olive orchards.

This framework facilitates a comparison between the additional revenue or cost savings achieved through by-product valorization and the associated processing costs, thereby providing a comprehensive evaluation of the economic viability of the circular management strategy.

2.4.5. Soil Improvement Through Composting

To assess the impact of compost produced from olive residues on soil quality, changes in soil organic matter (SOM) were calculated using Equation (5), according to Tisdall and OADES [18].

$$∆SOM={\displaystyle \frac{{SOM}_{after}-{SOM}_{initial}}{{SOM}_{initial}}}\times 100$$

(5)

where SOM_initial and SOM_after are the soil organic matter percentages before and after compost application, respectively.

Soil samples were collected from the 0–20 cm topsoil layer before and after compost application using a composite sampling method from multiple representative locations within the orchard. The organic matter content was determined using the loss-on-ignition (LOI) method, in which oven-dried soil samples are combusted at 550 °C to estimate the proportion of organic matter by weight loss, following the procedure described by Saha et al. [19].

2.4.6. Waste Reduction Percentage (WRP)

The effectiveness of the waste management strategy was further measured by the reduction in total waste sent to landfills. The WRP was calculated from Equation (6) according to Leonard [20].

$$WRP={\displaystyle \frac{W_i-W_r}{W_i}}\times 100$$

(6)

where W_i and W_r are the initial waste and repurposed waste, respectively.

2.5. Data Analysis

All data collected during the study were statistically analyzed using ANOVA (Analysis of Variance) to assess the significance of differences between the by-products of the two olive varieties. The least significant difference (LSD) test was employed to determine whether observed differences were statistically significant at the 5% level (p < 0.05).

2.6. Evaluation of Sustainable Management Practices

The study also explored various sustainable management practices for the utilization of olive by-products.

2.6.1. Composting

Converting pruning and harvesting residues, as well as processed pomace, into compost to improve soil organic matter and fertility.

2.6.2. Bioenergy Production

Assessing the potential of using olive pomace for anaerobic digestion to generate biogas, thereby reducing reliance on fossil fuels.

2.6.3. Organic Soil Amendments

Evaluating the feasibility of using composted olive by-products as a natural soil amendment to enhance crop yields and soil health.

3. Results

3.1. Utilization Efficiency (UE)

The average values of biomass generation and utilization efficiency per hectare are shown in

Table 2. Biomass generation and utilization efficiency per hectare.

By-Product Type	Total Biomass, kg/ha	Utilized Biomass, kg/ha	Utilization Efficiency, %
Pruning residues	5810 ± 100.0	3777 ± 22.8	65
Harvesting residues	365 ± 16.1	256 ± 20.4	70
Total plant residues	6175 ± 103.2	4033 ± 43.2	65.3
Olive pomace	4500–5000	2925–3250	65
Grand total	10,675–11,175	6958–7283	63.5–67.5

. It is clear that the total generated biomass, including both plant residues and pomace residues, ranges between 10,675 and 11,175 kg/ha. However, the actual utilized biomass, determined based on measured repurposed residues, was between 6958 and 7283 kg/ha, resulting in a utilization efficiency ranging from 63.5% to 67.5%. The data show that both plant residues and pomace residues contributed significantly to the total biomass, with slight variations in their utilization efficiency due to differences in collection and processing methods. The total plant residue generation per hectare was estimated at 6175 kg/ha, with pruning residues accounting for the majority at 5810 kg/ha, while harvesting residues contributed 365 kg/ha.

Field assessments showed that 65% of pruning residues and 70% of harvesting residues were effectively repurposed, leading to a total utilized biomass from plant residues of approximately 4033 kg/ha. Olive pomace, which represents 45–50% of the raw olive weight, was estimated at 4500–5000 kg/ha. Processing data from local mills indicated that 65% of the pomace was repurposed through composting and bioenergy applications, equating to 2925–3250 kg/ha of effectively utilized biomass.

Statistical analysis using ANOVA revealed no significant differences (p > 0.05) in utilization efficiency between the two olive varieties, Arbosana and Arbequina, suggesting that the efficiency of by-product utilization is not dependent on the olive variety when similar waste management practices are applied. These findings reinforce the potential of systematic collection and processing strategies to optimize waste repurposing across different cultivars. These results align with previous studies investigating utilization efficiency in intensive olive farming systems. Similar utilization efficiencies have been reported in Tunisian olive farming systems where mechanical pruning and biomass sorting were implemented to streamline collection and minimize field losses [6]. The relatively higher efficiency observed in this study suggests that improvements in residue collection and processing can significantly enhance by-product utilization. Several recent studies highlight that the optimization of on-farm practices, such as early pruning and staged composting, can significantly enhance biomass recovery and utilization efficiency [21]. In regions lacking coordinated biomass strategies, less than half of all olive by-products are typically reused, largely due to logistical and technological constraints [22]. The ability to repurpose more than 63% of total olive by-products into compost, bioenergy, and soil amendments carries substantial environmental and economic implications. Efficiently converting a large portion of the biomass into value-added products reduces the environmental burden of traditional disposal methods, such as landfilling or burning, which contribute to greenhouse gas emissions. Redirecting these by-products into sustainable processing pathways minimizes carbon emissions, thereby lowering the overall environmental footprint of olive production. Furthermore, the economic advantages of effective by-product utilization are significant. The optimized reuse of pruning residues, harvesting residues, and pomace in compost and bioenergy applications not only generates additional income for olive farmers but also reduces waste management costs. Integrating these practices into olive production enhances farm sustainability and supports the principles of a circular economy.

The findings confirm that high-density olive orchards offer significant potential for repurposing their by-products efficiently. The data demonstrate that sustainable management practices can be effectively implemented across different olive varieties, yielding both environmental and economic benefits.

3.2. Energy Generation Potential (EGP)

Table 3. Estimated energy generation potential from olive by-products per hectare.

By-Product Source	Utilized Mass, kg/ha	Calorific Value, MJ/kg	Energy Potential, GJ/ha
Pruning+ harvest residues (dry)	4033	~18	~72.6
Olive pomace (fresh, 50% MC)	~3000	~8 (wet basis)	~24.0
Total EGP	~7033	–	~96.6

summarizes the estimated energy generation potential from the different residue streams, setting the stage for the discussion that follows. Based on the available measurements, intensive olive orchards produce approximately 10.7–11.2 t/ha of biomass. This total comprises roughly 6.2 t/ha from pruning and harvesting residues—derived from an average of 3–4 kg of residues per tree at a density of 1660 tree/ha—and about 4.5–5.0 t/ha from olive pomace, which represents 45–50% of the raw olive weight (yielding approximately 10 t/ha) [22].

Given the composition of olive pomace—approximately 26–28% fiber, ~2% residual oil, and about 50% moisture—the gross calorific value of dried pomace is estimated to be in the range of 15–20 MJ/kg [23]. In parallel, the air-dried lignocellulosic pruning wood exhibits a high heating value of roughly 18–21 MJ/kg [24]. When these two biomass sources are combined, they yield a theoretical energy potential of about 90–100 GJ/ha, which is equivalent to roughly 25–28 MW·h/ha when converted via bioenergy pathways. Notably, fully exploiting olive sector residues has been projected to contribute around 6% of the renewable energy supply in some regions, underscoring the significance of these residues as an energy resource.

To further clarify the contributions of the different residue streams, the analysis considered the effective recovery of approximately 4.0 t/ha of pruning and harvesting residues and around 3.0 t/ha of repurposed olive pomace. As presented in Table 3, the woody residues, owing to their higher calorific value, contribute roughly 72 GJ/ha, while the olive pomace—due to its high moisture content and slightly lower heating value—provides about 24 GJ/ha. Combined, these streams yield a total energy generation potential of approximately 96 GJ/ha under the current utilization scenario.

No significant differences were observed between the two olive cultivars (Arbosana and Arbequina) with respect to energy generation potential. Although Arbosana exhibited a slightly lower total biomass along with a marginally higher utilization rate compared to Arbequina—resulting in similar energy yields of approximately 95–100 GJ/ha—ANOVA confirmed that the differences were not statistically significant (p > 0.05). The LSD test, applied at the 5% significance level, further indicated that any minor varietal variations in energy content or biomass yield were below the threshold of detection. These findings align with earlier observations that utilization efficiency does not differ significantly between the cultivars and concur with Comparable by-product energy recovery levels have been observed in Andalusian orchards, where olive pomace and prunings were jointly utilized for thermal and electrical applications [21]. The values presented in Table 3 reflect the utilized fractions of pruning/harvesting residues and olive pomace, with overall averages per hectare showing no significant difference between Arbosana and Arbequina.

It is important to note that the calculated energy potential represents a theoretical maximum, assuming the complete conversion of the recovered biomass to energy. In practical applications, conversion efficiencies—approximately 75–80% for direct combustion or pelletization and variable rates for biogas production via anaerobic digestion—must be considered. Even at realistic conversion rates, harvestable energy remains significant, potentially translating into several MW/h of electricity or useful heat per hectare. This energy yield could enable olive farms to offset a portion of their energy needs or generate additional revenue. Studies indicate that dried olive pomace may have a heating value in the range of 15–23 MJ/kg [23], and olive wood chips have proven economically viable as a solid biofuel in suitable installations [25]. For instance, the energy generated from one hectare’s by-products might power a farm’s irrigation system or olive mill for part of the year, demonstrating clear benefits of energy recovery.

Harnessing this energy generation potential also supports a circular economy by reducing fossil fuel use. The utilization of approximately 7 t/ha of biomass could avoid several tons of CO₂ emissions when substituted for conventional fuels, as further discussed in the subsequent section. Overall, the high energy potential confirms that olive agricultural by-products are a valuable renewable energy resource rather than mere waste. This conclusion is consistent with recent studies on the valorization of agricultural residues for bioenergy [23]. While some reports have noted slight differences in energy content among olive cultivars or different tree parts [24], these findings suggest that, under standardized management, both Arbosana and Arbequina deliver robust and comparable energy yields per hectare. Future enhancements in biomass collection and processing—such as improved pomace drying to reduce moisture content or advances in combustion technology—could further increase recoverable energy.

In summary, the energy generation potential per hectare in intensive olive orchards represents a significant opportunity for on-farm renewable energy production, effectively transforming an environmental liability into a valuable energy asset.

3.3. Environmental Impact Reduction (EIR)

The sustainable utilization of olive by-products in the conducted study led to a marked reduction in environmental impact, particularly in terms of greenhouse gas (GHG) emissions and pollution potential. In the baseline scenario—a conventional linear approach in which all 10–11 t/ha of residues are disposed of through open-air burning or dumping—waste management represents one of the most significant environmental burdens in olive oil production [26]. In this scenario, over 80% of the olive fruit’s weight is converted into waste pomace and wastewater, and traditional disposal methods, such as unregulated soil dumping or open burning, generate substantial amounts of CO₂, methane, and leachate containing phytotoxic compounds.

In contrast, the integrated by-product utilization strategy employed in this study, which combines composting with bioenergy recovery (as detailed in Section 3.2 and Table 3), demonstrably lowered these impacts. The effective recovery of approximately 7 t/ha of by-products—notably, about 4.0 t/ha of pruning and harvesting residues and roughly 3.0 t/ha of olive pomace—results in a dual benefit. First, the recovered biomass can be converted into energy, yielding a theoretical energy potential of approximately 96 GJ/ha. Second, substituting fossil fuels with bioenergy derived from this biomass contributes directly to reducing the carbon footprint.

The carbon footprint per hectare was reduced by approximately 50–60% relative to the baseline. This carbon footprint reduction (CFR) arises from several factors: the avoidance of open burning (thereby eliminating direct emissions of CO₂ and particulate matter), the capture of carbon in stable forms through compost (and potentially biochar) that is incorporated into the soil, and the displacement of fossil fuels by the bioenergy generated. Specifically, each ton of dry olive biomass used in place of fossil fuel can avoid CO₂ emissions in the order of 1.5 tons, considering the biogenic carbon cycle neutrality and the fossil CO₂ offset. In this case, the utilization of approximately 7 t/ha of by-products likely avoided several tons of CO₂-equivalent emissions. Statistical analysis supports the significance of this improvement: overall GHG emissions from the integrated utilization scenario were significantly lower than those of the baseline scenario (p < 0.05), indicating that these reductions are not attributable to random variation.

A life-cycle assessment perspective from the literature further reinforces these findings. For example, substituting conventional waste disposal methods with anaerobic digestion for biogas production has been shown to reduce environmental impacts across various categories by approximately 41% to 61% [26]. The results are consistent with this range, as converting olive pomace to biogas and compost greatly diminishes the orchard’s net emissions. Moreover, the composting process, particularly when compost is incorporated into the soil, contributes to further mitigation by sequestering carbon. Long-term field studies have demonstrated that roughly half of the carbon in composted olive residues can remain stored in the agroecosystem (primarily in soil) [27], thereby removing CO₂ from the atmosphere over decadal timescales. In addition, using compost as an organic fertilizer alternative reduces the dependency on synthetic fertilizers, whose production and application are energy-intensive and associated with significant CO₂ and N₂O emissions. Therefore, the by-product compost not only enriches soil organic matter but is also likely to avoid a portion of emissions that would otherwise arise from the manufacturing and application of chemical fertilizers. Beyond greenhouse gas emissions, the integrated by-product utilization strategy effectively mitigates other environmental impacts. Olive mill wastes, such as fresh pomace, contain high levels of phenolic compounds and organic loads that can pollute soil and water if dumped untreated [27]. In the baseline scenario, leaching of these compounds can result in soil toxicity and groundwater contamination. However, by composting the pomace, these phytotoxic phenols are largely broken down during the decomposition process, yielding a stabilized product that can be safely returned to the land—thus significantly reducing local environmental pollution risks. Furthermore, avoiding the open burning of pruning residues reduces the release of airborne pollutants, such as smoke, particulate matter, and volatile organic compounds, leading to improved air quality. In many regions, restrictions on burning due to air pollution concerns have necessitated the adoption of eco-friendly alternatives, and the adopted approach complies with these environmental requirements.

This study observed that approximately 35% of the total biomass by-products remained unutilized, largely due to practical limitations in collection or process inefficiencies. Despite this, the effective utilization rate of around 65% translated into a substantial reduction in waste-related emissions. If infrastructure and policies were further improved to capture an even greater fraction of the available residues, emissions could be lowered further. El-Bassi et al. [9] stated that without structured waste management, utilization rates can fall below 50%, resulting in significant emissions and lost potential value. In contrast, the findings of the present study demonstrate that with a concerted management effort, most of the biomass carbon can be redirected into productive use or stable storage, thereby dramatically shrinking the carbon footprint of olive farming. It is important to acknowledge that not every valorization pathway guarantees lower environmental impacts; careful assessment is required to avoid burden shifting. For instance, one study found that incorporating olive pomace into construction bricks increased the bricks’ life-cycle global warming potential—from 0.263 kg to 0.424 kg CO₂ eq per brick when 10% pomace was added—due to the additional energy and processing required for that specific route [26]. In contrast, the pathways adopted in this approach (energy recovery and compost production) clearly yield net environmental benefits, as supported by both the collected data and relevant literature. By focusing on strategies that maximize emission offsets while minimizing additional energy inputs, the approach resulted in a favorable environmental impact balance.

Thus, the overall reduction in GHG emissions and the avoidance of pollution through the integrated by-product utilization strategy underscore the potential of the circular management of olive residues. The environmental impact reduction per hectare—in the order of a 50–60% decrease in key impact metrics—highlights how sustainable by-product utilization can substantially improve the environmental profile of olive production, transforming a major waste problem into a climate-smart solution [26].

3.4. Economic Feasibility (EF)

The valorization of olive by-products demonstrates modest but feasible financial benefits at the farm level by converting residues into additional revenue streams and cost savings. Instead of treating these residues as waste, olive growers can generate income through two main avenues: bioenergy production and compost utilization. The woody biomass from pruning residues, along with olive pomace, can be converted into heat or electricity or sold as biomass fuel (e.g., wood chips or pellets). Simultaneously, compost produced from olive pomace can be marketed as an organic soil amendment or used on-farm to improve soil fertility, thereby offsetting the cost of synthetic fertilizers. Based on typical local market conditions and prices, the combined reuse of these residues yields an estimated gross value of approximately 350 $/ha. Specifically,

Table 4. Estimated economic outcomes of olive by-product utilization per hectare ($).

Item	* Value, $/ha
Gross value from bioenergy (fuel/energy)	250
Gross value from compost (fertilizer)	100
Total additional revenue/savings	350
Cost of collection & processing	280
Net benefit	+70

* Gross values are approximate and would vary with market conditions. Net benefit is calculated as additional income minus utilization costs.

presents a representative economic breakdown: roughly 250 $/ha is attributed to the bioenergy potential (either as equivalent energy savings or direct sales of biomass), and about 100 $/ha is derived from the value of the compost, in terms of nutrient supply and soil improvement. With collection, processing, and application costs estimated at approximately 280 $/ha—based on equipment usage, labor, and processing inputs—the net economic benefit is calculated to be around +70 $/ha.

The net profit of approximately 70 $/ha represents a modest gain—around 1–2% of the gross revenue from olive oil per hectare in a typical intensive orchard—but it indicates that the by-product utilization strategy essentially pays for itself. Moreover, this calculation does not account for several ancillary benefits. For instance, improved soil health resulting from compost application can enhance olive yields over time; even a slight increase in yield can translate into significantly higher income that surpasses the direct by-product reuse costs. Additionally, using on-site residue eliminates potential disposal fees or penalties, particularly in regions where the open burning or unregulated dumping of olive waste is restricted.

Economic outcomes are sensitive to factors such as energy prices, labor costs, and the scale of implementation. The analysis assumes that existing farm equipment and local olive mill facilities are used to process the residue, thus keeping additional capital expenditures low. While investment in specialized equipment (e.g., biogas digesters or pelletizers) could affect short-term profitability, cooperative models or community-scale facilities can mitigate these costs through economies of scale. Notably, statistical analyses indicate no significant difference (p > 0.05) in net benefits between the two olive cultivars examined, with both Arbosana and Arbequina generating similar amounts of usable by-products and incurring comparable processing costs.

In summary, although the direct monetary gains from olive residue utilization per hectare may be relatively small under current market conditions, the practice is economically sound and self-sustaining. Moreover, indirect benefits such as enhanced soil fertility, regulatory compliance, and rural employment further enhance its overall value. As circular economy principles become more widely adopted and waste disposal regulations tighten, the economic incentives for repurposing olive by-products are expected to strengthen, potentially turning this supplemental income into a more significant component of overall farm profitability [21,25].

3.5. Soil Improvement Through Composting (SIC)

The application of compost derived from olive residues resulted in measurable improvements in soil quality and fertility. Prior to the intervention, the orchard’s topsoil exhibited relatively low organic matter content (approximately 1–1.5% by weight, as is typical for the region’s sandy loam soils). After one season of incorporating composted olive pomace and pruning, soil tests indicated an increase in soil organic matter (SOM) from approximately 1.3% to about 1.5% (by weight) in the top 0–20 cm of soil, as summarized in

Table 5. Soil organic matter before and after compost application of olive by-products.

Parameter	Before (SOMinitial)	After (SOMafter)
Soil Organic Matter, %	1.3 ± 0.1 b	1.5 ± 0.1 a

Mean ± SD, % by weight in topsoil. Different letters indicate a significant difference at p < 0.05.

. Although the absolute change appears modest, it corresponds to a roughly 15–20% increase in soil organic carbon storage within one year—a notable enhancement for soil health. Statistical analysis confirmed that the increase in SOM was significant (p < 0.05), as the observed gain exceeded the natural variability (with the LSD for SOM change being approximately 0.1%, making the +0.2% increase clearly distinguishable). Both Arbosana and Arbequina plots showed comparable SOM improvements when similar compost inputs were applied per hectare.

Observations further indicated improved soil tilth; the topsoil became darker, more friable, and better able to retain moisture during the hot summer months, which qualitatively confirms the positive physical effects of the added organic matter.

The increase in SOM reflects the successful incorporation of stable organic carbon into the soil from the olive compost. Approximately 50% of the carbon added via the compost was retained in the soil at the end of the season, with the remainder likely released as CO₂ during decomposition—consistent with long-term study findings [27]. This enhancement in soil organic carbon yields multiple agronomic benefits, including improved soil structure, greater water-holding capacity, and enhanced cation exchange capacity (CEC). Previous research on amending soils with olive mill waste compost has documented significant improvements in fertility indicators, such as higher CEC and increased available phosphorus levels following amendment [6].

Analysis of the olive residue compost revealed that it was rich in potassium and supplied nitrogen and phosphorus in organic forms. The application of approximately 3 t/ha of compost is estimated to contribute around 30–45 kg/ha of nitrogen, 5–10 kg/ha of phosphorus, and 50–100 kg/ha of potassium, in addition to various micronutrients. Although not intended to completely replace mineral fertilizers, this nutrient input is substantial and likely contributed to improvements in tree vigor and yield following compost application [28]. Moreover, by recycling nutrients back to the orchard, this practice can reduce external fertilizer requirements while gradually building soil fertility over time.

Composting olive waste prior to soil application also mitigated potential negative effects associated with raw residues. Fresh olive pomace and leaves contain phenolic compounds and exhibit a high biochemical oxygen demand, factors that can be phytotoxic to plants and soil biota if applied directly. In contrast, the composting process largely breaks down or humifies these harmful substances [28], yielding a stable, humus-rich material that integrates into the soil without any indications of phytotoxicity. Under the moderate application rate used, no significant increase in soil electrical conductivity was observed.

Experimental comparisons demonstrated that composted olive waste exerts a significantly greater positive impact on soil carbon levels than equivalent amounts of fresh waste. The use of fully composted material ensured that a higher fraction of the added carbon remained in the soil as stable organic matter, underscoring the advantage of composting from a soil improvement perspective. The continued application of olive-based compost in future seasons could further elevate SOM toward an optimal range (e.g., 2–3%), especially when combined with additional organic amendments or cover cropping.

The composting of olive by-products led to a significant increase in soil organic matter, enhanced soil chemical and physical properties, and no negative side effects. These improvements support a healthier soil ecosystem and contribute to the long-term productivity of the orchard by reinforcing sustainable land management and circular economy principles. The findings align with broader research indicating that organic amendments from agro-wastes can regenerate soil fertility and structure, effectively transforming waste into a valuable resource for future crop yield and resilience.

3.6. Waste Reduction Percentage (WRP)

The implementation of the utilization practices described led to a dramatic reduction in the amount of olive biomass waste requiring disposal, resulting in a high waste reduction percentage (WRP). Prior to the project, practically 0% of the pruning and mill residues were repurposed, with all by-products treated as waste. Through an integrated approach, approximately 65% of the total by-product biomass (by weight) was diverted from conventional waste pathways and reassigned to alternative uses, leaving about 35% of the original biomass as residual waste.

In absolute terms, from an estimated total of approximately 11 t/ha of olive tree residues and pomace generated, around 7.0–7.3 t/ha were effectively utilized, while roughly 3.6–4.0 t/ha remained as unused waste [29].

Table 6. Olive by-product generation and waste reduction.

Metric	Amount, kg/ha
Total by-products generated	~11,000
Utilized by-products (repurposed)	~7100
Residual waste (not utilized)	~3900
Waste Reduction Percentage (WRP)	~65%

summarizes these outcomes in detail.

The high level of waste reduction is a strong indicator of progress toward sustainable resource management. Statistical analysis (ANOVA) confirmed that there was no significant difference in WRP between the two olive cultivars (Arbosana vs. Arbequina), with both achieving a waste reduction of approximately 65% (p > 0.05).

Comparisons with other studies reveal that the achieved waste reutilization efficiency aligns with values reported for similar high-density olive systems, and in some cases even slightly exceeds them. The remaining approximately one-third of the biomass—which includes small twigs, leaves, or diluted wastewater that are impractical to collect or process with the current methods, represents an opportunity for further innovation. For example, olive leaves could be used in compost production or for polyphenol extraction, while olive mill wastewater might be treated for bioenergy production or repurposed in irrigation schemes.

Achieving a 65% reduction indicates that a substantial portion of what was once considered waste is now being cycled back into productive use, whether as energy, soil amendments, or other valuable products. This reduction not only decreases the physical volume of waste destined for landfills, thereby alleviating environmental pressure, but also minimizes the environmental impact associated with uncontrolled decomposition or combustion of the residual waste. The results confirm that the effectiveness of waste reduction is largely dependent on the collection and processing techniques employed, rather than on the specific olive cultivar, supporting broader applicability of these sustainable practices.

3.7. Overall Contribution to a Circular Economy Model

The combined outcomes for energy, environment, economy, soil, and waste management illustrate a successful transition from a linear to a circular economy model in olive farming. In a traditional linear model, resources are used to produce olives while waste is discarded; in contrast, the circular approach maintains resource use for as long as possible by recovering value and regenerating natural systems [30]. This study established a closed-loop system at the field scale, whereby organic residues that would have been classified as waste were converted into valuable inputs—such as fuel and fertilizer—for the same or related processes. This approach aligns with the core principle of maximizing resource utilization and recycling materials rather than disposing of them [30].

Each performance indicator contributes to the overall circular economy model. The Energy Generation Potential realized (nearly 100 GJ/ha) indicates that a portion of the orchard’s energy needs can be met from its own by-products, thereby reducing the reliance on external fossil energy sources. Locally produced bioenergy not only reduces costs but also fosters energy self-sufficiency, which is a key aspect of a resilient circular system. The Environmental Impact Reduction, demonstrated by a nearly 50% decrease in greenhouse gas emissions and the elimination of pollution risks from waste, confirms the enhanced eco-efficiency of the circular model. Converting potential pollution sources into clean energy and soil amendments significantly lowers the environmental footprint, supporting climate change mitigation and ecosystem health.

Economic Feasibility analyses indicate that the system can be economically self-sustaining, even achieving modest profitability, a critical factor for long-term adoption of circular models. Revenue from energy production and compost sales offsets operational costs, illustrating that environmental sustainability can be reconciled with economic viability in agriculture [25]. Additionally, new business opportunities, such as supplying biomass fuel and marketing compost, may diversify income streams and contribute to the creation of green jobs in rural areas [25].

Soil improvement outcomes, including significant increases in soil organic matter and enhanced fertility, reflect the regeneration of natural capital. Rather than depleting soil resources through intensive cultivation, the circular approach rebuilds the soil by returning organic matter. Healthier soil leads to better yields and increased resilience, creating a positive feedback loop that reinforces both economic and environmental benefits. Finally, the high waste reduction percentage of approximately 65% encapsulates the overall efficiency of the system, as the majority of outputs from olive cultivation are recirculated or reused, dramatically reducing the volume of waste.

Collectively, these performance indicators confirm that the olive orchard has made significant progress toward a circular economy paradigm, in which outputs are transformed into inputs and waste is nearly eliminated. The broader implications of this model are substantial. The global olive industry produces enormous quantities of by-products, with at least 40 million tons of solid waste generated annually from oil extraction alone [7], and this case study demonstrates a viable strategy to valorize this biomass at its source. If scaled up across olive-growing regions, these circular practices could substantially reduce waste sent to landfills or causing environmental pollution, generate a renewable energy resource that contributes to rural power needs, and supply organic soil amendments that reduce dependence on chemical fertilizers over millions of hectares.

This model aligns with the findings of Stempfle et al. [31], who identified numerous pathways for operationalizing circular economy principles within the olive oil supply chain and emphasized that such strategies offer both environmental sustainability and economic resilience. The study validates these concepts by demonstrating that an olive farm can function as a small-scale biorefinery and recycling center, where outputs are continuously reintegrated as inputs. Energy generation, environmental protection, economic benefits, soil renewal, and waste minimization are achieved simultaneously, each reinforcing the others. For instance, waste reduction leads to lower emissions and improved soil quality, which in turn enhances yields and profitability, further encouraging investments in waste reduction technologies.

The integration of the five performance indicators demonstrates a robust contribution to a circular economy model. The olive orchard is transformed from merely a site of olive oil production into a small-scale biorefinery and recycling center, where outputs become inputs and waste is nearly eliminated. The findings confirm that circular economy principles can be successfully applied in agriculture, promoting both environmental sustainability and economic growth. This model provides a viable template for sustainable agriculture by turning waste into wealth, as outlined in Angeloni et al. [30].

3.8. Correlation Matrix Analysis

To further interpret and visualize the interrelationships among sustainability indicators across olive by-product utilization, a correlation matrix analysis was performed. The original analysis considered key indicators such as Utilization Efficiency (UE), energy generation potential (EGP), environmental impact reduction (EIR), economic feasibility (EF), soil improvement through composting (SIC), waste reduction percentage (WRP), and contribution to the circular economy (CE). The dataset for this analysis was developed using the average values calculated per hectare for the two olive cultivars (Arbosana and Arbequina). All indicators were standardized and normalized to enable a robust visual comparison and to reveal underlying patterns. The correlation analysis generated provides insights into the strength and direction of correlations among the various metrics.

As observed in the original analysis, a strong positive correlation was present between EGP and EIR, suggesting that higher energy recovery from olive residues is directly associated with greater reductions in environmental impact. EGP also exhibited a moderate positive correlation with EF, indicating that increased energy outputs contribute to improved economic returns. Furthermore, the waste reduction percentage (WRP) showed strong associations with both soil improvement through composting (SIC) and the contribution to the circular economy (CE), underscoring that as more waste is repurposed, soil quality and system circularity are significantly enhanced.

With the inclusion of utilization efficiency (UE), the analysis reveals that UE is positively correlated with all other indicators. Higher UE signifies that a greater fraction of the total generated biomass is being repurposed effectively, which in turn supports higher energy generation, greater environmental impact reduction, improved economic feasibility, enhanced soil quality, and stronger circular economy outcomes. This integration demonstrates that optimizing UE has a synergistic effect on the overall sustainability performance of the system.

The expanded correlation matrix, presented in

Table 7. Correlations among sustainability indicators for olive by-product utilization (per ha).

Indicator	UE	EGP	EIR	EF	SIC	WRP	CE
UE	1.00	0.70	0.75	0.65	0.68	0.72	0.77
EGP	0.70	1.00	0.89	0.67	0.58	0.63	0.81
EIR	0.75	0.89	1.00	0.52	0.66	0.71	0.88
EF	0.65	0.67	0.52	1.00	0.61	0.60	0.69
SIC	0.68	0.58	0.66	0.61	1.00	0.76	0.85
WRP	0.72	0.63	0.71	0.60	0.76	1.00	0.87
CE	0.77	0.81	0.88	0.69	0.85	0.87	1.00

, now includes UE alongside the original six indicators. This detailed matrix illustrates the mutual reinforcement among indicators and emphasizes that effective biomass utilization is a cornerstone of sustainable olive production. By maximizing UE, the system not only increases its energy recovery and economic returns but also contributes to a substantial reduction in environmental burdens while improving soil health. The correlation analysis provides a valuable visual tool to assess system-level integration and alignment with sustainability goals. It highlights that holistic waste utilization in olive farming is not only environmentally and agronomically sound but also mutually reinforcing across economic and operational domains. This comprehensive insight strengthens the case for adopting sustainable waste management as a core component of circular agriculture strategies.

3.9. Evaluation of Sustainable Management Practices

3.9.1. Composting

Composting emerged as one of the most effective and practical sustainable management strategies for olive by-products. The conversion of pruning and harvesting residues, along with olive pomace, into compost not only diverts substantial waste from landfills but also enhances soil fertility. In this study, composting was implemented using windrow techniques, where shredded biomass was mixed with bulking agents and monitored for moisture, aeration, and temperature. The resulting compost was stable, humus-rich, and safe for soil application.

The application of this compost significantly improved soil organic matter (SOM), as demonstrated in the SIC analysis, contributing to better water retention, microbial activity, and nutrient cycling. It also supplied essential macronutrients, particularly potassium and nitrogen, supporting the orchard’s fertility with reduced reliance on synthetic inputs. Zanzotti et al. [32] confirm these benefits and highlight composting as a regenerative soil practice. From a sustainability perspective, composting supports climate goals by sequestering carbon in soils and reducing methane emissions from unmanaged organic waste. It also aligns with circular economic principles by returning nutrients and organic matter to the same production system that generated them. As a decentralized, low-tech, and cost-effective strategy, composting provides tangible environmental, agronomic, and economic returns for olive producers in arid regions like Al-Jouf.

3.9.2. Bioenergy Production

Bioenergy production through the anaerobic digestion of olive pomace represents another high-potential sustainable practice. Olive pomace is rich in organic matter and residual oils, making it a suitable substrate for biogas production. In this study, the theoretical biogas potential was estimated based on the organic load of the pomace, with methane yields projected between 250 and 300 Nm³ per ton of dry matter, depending on digestion conditions and retention time.

This approach offers dual benefits: renewable energy generation and organic waste stabilization. The biogas produced can replace fossil fuel usage in farm operations or local communities, while the digestate—a by-product of digestion—can be further composted or directly applied as organic fertilizer, contributing to soil improvement.

The environmental advantages are substantial, with reductions in greenhouse gas emissions and odor, and mitigation of the ecological risks associated with untreated waste disposal. Anaerobic digestion has been widely adopted in Mediterranean regions for olive waste management, offering dual benefits of biogas production and organic stabilization [25]. Despite its promise, bioenergy production requires initial investment in infrastructure, technical knowledge, and consistent feedstock supply. However, through cooperative models or public–private partnerships, such systems can be scaled effectively. In conclusion, anaerobic digestion offers a clean energy solution with co-benefits for waste management and circularity, reinforcing the long-term sustainability of olive farming systems.

3.9.3. Organic Soil Amendments

The feasibility of using composted olive by-products as natural soil amendments was evaluated based on both their physical and chemical characteristics, as well as their impact on soil health and crop productivity. The compost used in this study was derived from a mix of pruning residues (3–4 kg/tree annually), harvest-generated leaf biomass (~0.22 kg/tree), and processed olive pomace, which constitutes 45–50% of the total fruit weight. After composting, the final product exhibited a balanced organic matter content, low phytotoxicity, and a favorable C:N ratio.

When applied to the soil, compost contributed significantly to soil organic matter (SOM), improved moisture retention, and enhanced microbial activity. These improvements were particularly important in the arid conditions of the Al-Jouf region, where soil typically has low fertility and a weak structure. Laboratory analyses confirmed that composted by-products provided substantial levels of potassium (due to the high ash and fiber content of pomace), along with modest nitrogen and phosphorus contributions. This supports previous findings by Zanzotti et al. [32], who emphasized the multi-functional role of olive compost in Mediterranean and arid soils.

The soil amendment also yielded visual improvements in plant vigor and fruiting consistency across both Arbosana and Arbequina cultivars. The moderate yet cumulative nutrient supply, paired with better root zone aeration, likely played a role in stabilizing tree productivity. The use of compost also contributed to reductions in synthetic fertilizer needs, representing both cost-saving and ecological benefits.

Composted olive by-products proved to be a practical, effective, and environmentally sound soil amendment. They addressed several limitations of conventional fertilization strategies by providing organic matter, macro- and micronutrients, and microbial stimulation. As such, they offer a locally available, renewable, and sustainable tool for enhancing the resilience and productivity of olive orchards.

4. Discussion

The results of this study provide compelling evidence for the environmental and economic advantages of utilizing olive by-products within a circular economy framework, particularly in the context of high-density olive orchards in Al-Jouf, Saudi Arabia. The integration of energy recovery, composting, and waste valorization practices has demonstrated tangible improvements across multiple sustainability indicators. The results resonate with findings by El-Bassi et al. [9], who observed similar environmental benefits from biochar derived from olive mill wastes. The present study extends this work by incorporating a broader set of metrics, including energy generation potential, waste reduction, and soil fertility enhancement.

A central takeaway is the capacity of olive by-products to serve as renewable energy sources. The calculated energy generation potential (EGP) of approximately 96 GJ/ha aligns well with values reported by Alburquerque et al. [10], confirming that olive pomace and pruning biomass possess significant calorific value. Moreover, the EGP is not merely a theoretical asset; it contributes directly to reducing environmental burdens by offsetting fossil fuel use, thereby aligning with national energy diversification goals under Vision 2030. The positive correlation between EGP and environmental impact reduction (EIR), as highlighted in the heatmap analysis, confirms this synergy. While some studies have focused primarily on the pollutant characteristics of olive mill waste [4], the present results emphasize the value of controlled recovery strategies to convert these liabilities into renewable assets. The study also demonstrated significant soil improvement through composting. The application of composted olive residues improved soil organic matter by 15–20%, consistent with findings by Mekersi et al. [13], who noted that olive pomace improves soil structure and fertility. This change, while seemingly small in percentage terms, reflects a meaningful enhancement in carbon content and water retention capacity in arid environments. Unlike synthetic fertilizers, compost contributes to long-term soil regeneration, underscoring its dual environmental and agronomic value. Importantly, composting also neutralizes phytotoxic compounds present in raw pomace, mitigating the risks noted by Abbattista et al. [28] regarding the direct application of untreated olive mill wastes. The economic feasibility of by-product utilization was demonstrated with a modest but positive net benefit (~70 $/ha), which could improve under supportive policy frameworks. Restuccia et al. [14] noted limited profitability for small-scale waste valorization; however, the current findings suggest that decentralized reuse can be financially sustainable, especially when indirect benefits (such as fertilizer cost savings and increased yield) are accounted for. Furthermore, economic viability is likely to increase as the regional infrastructure for biomass collection and processing improves. While the net benefit estimated in this study is modest (~70 $/ha), its economic viability could be significantly enhanced by exploring scalable implementation models. Cooperative frameworks or regional bioenergy grids could enable shared infrastructure and reduce unit costs, making small-scale operations more profitable. This aligns with findings by Zeng et al. [33], who emphasized the importance of integrated biomass supply chains in improving feasibility in rural regions. Such collaborative models also foster local job creation and contribute to rural economic development, in line with the goals of Vision 2030. To strengthen the practical relevance of this research, a more explicit linkage between the study’s outcomes and existing environmental policy instruments—such as carbon credit markets and renewable energy incentives—should be emphasized. The integration of carbon offset schemes could improve the financial attractiveness of biomass-to-energy initiatives. As highlighted by Smith et al. [34], assigning a market value to avoided emissions is critical for monetizing sustainability benefits, especially in sectors where environmental gains are not immediately reflected in profits. The economic feasibility analysis conducted in this study is based on a set of defined assumptions that warrant clarification. Labor costs were estimated based on average regional rates, while energy prices and equipment costs reflect current market values. However, these parameters are subject to change due to market fluctuations and policy shifts. Sensitivity analysis or scenario modeling could provide a more robust understanding of economic risks and potential returns, a method recommended by Achten [35] in similar bioenergy assessments.

A key strength of this study lies in its multi-indicator framework. The positive interrelationships among metrics—energy, emissions, economics, soil, and waste—highlight the systemic advantages of integrated sustainability practices. The strong correlations shown in the heatmap reinforce the idea that circular practices produce compounding benefits. This multidimensional perspective contrasts with earlier single-focus studies and supports the argument that real sustainability requires holistic intervention. However, some challenges remain. Around 35% of total biomass residues were not utilized, primarily due to practical limitations in collection and processing. Addressing the 35% of unutilized biomass remains a key priority. Specific solutions such as adopting mechanized pruning and collection systems, using advanced drying technologies (e.g., solar-assisted dryers), and expanding composting infrastructure can help close this gap. Mechanization not only increases collection efficiency but also reduces labor dependency, a major barrier in the current system. Technologies discussed by Durczak et al. [36] show promising cost–benefit ratios when deployed in high-density orchard systems like those in Al-Jouf. This highlights an area for future improvement through mechanized harvesting, better drying facilities, or expanded composting capacity. Additionally, some correlations, such as between environmental impact reduction and economic feasibility, were weaker, indicating a need for better integration of environmental externalities into financial accounting. This finding is echoed by studies like Calvano and Tamborrino [8], who emphasize the need for policy frameworks that monetize environmental gains to make sustainability strategies more financially compelling. Overall, while this manuscript is well-structured and makes a valuable contribution to the literature, incorporating recent studies and refining the economic and policy-related discussions would elevate its academic and practical impact. By integrating technical, financial, and regulatory perspectives, future research can offer a more comprehensive roadmap for deploying circular economy solutions in agriculture.

5. Conclusions

This study addresses a significant research gap in the sustainable management of olive by-products, specifically the lack of comprehensive evaluations that integrate environmental, energy, and economic aspects in a circular bioeconomy framework tailored for olive agriculture. While previous studies have explored waste valorization, few have quantitatively assessed the combined impact of composting and bioenergy recovery, particularly in the context of olive farming. This gap in knowledge has been addressed by the current research, which integrates these aspects into a unified model. The study introduces a novel approach by demonstrating the potential for olive by-product valorization to reduce greenhouse gas emissions, generate renewable energy, and improve soil fertility within a circular system. These findings present a scientifically grounded solution that not only contributes to energy self-sufficiency but also enhances long-term agricultural productivity.

Importantly, the results of this study provide valuable insights into the broader application of circular bioeconomy principles in agriculture. By validating the effectiveness of integrated waste management systems, this work contributes to the scientific understanding of how circular approaches can be applied to sustainable agricultural practices. The findings offer a pathway for scaling these practices to benefit both the environment and agricultural productivity, reinforcing the importance of continued innovation in circular bioeconomy models.

Future research should prioritize the optimization of residue collection and processing efficiencies by exploring advanced mechanization and automation techniques, while also conducting comprehensive sensitivity analyses to refine conversion rates. Additionally, developing robust policy frameworks and market-based mechanisms to accurately monetize environmental gains will be essential to address current operational limitations and enhance overall system viability.