Thermochemical properties and life cycle assessment of waste spent coffee grounds

Theoklitos Klitou; Kyriaki Koumenidou; Michalis Menicou; Paris A Fokaides

doi:10.1038/s41598-026-54060-8

. 2026 May 21;16:23283. doi: 10.1038/s41598-026-54060-8

Thermochemical properties and life cycle assessment of waste spent coffee grounds

Theoklitos Klitou ¹, Kyriaki Koumenidou ¹, Michalis Menicou ¹, Paris A Fokaides ^1,^2,^✉

PMCID: PMC13402803 PMID: 42168459

Abstract

Spent coffee grounds (SCGs) represent a widely available organic residue with significant potential for energy valorization. This study evaluates the feasibility of converting SCGs into fuel pellets. Thermochemical characterization indicated promising properties for energy recovery and informed the development of a subsequent life cycle assessment (LCA). A cradle-to-gate LCA, performed using the ILCD methodology, assesses four pelletization scenarios: a baseline grid-powered process, sun drying, photovoltaic electricity supply, and their combination.The results identify drying and transportation as the dominant contributors to environmental impacts. The combined sun drying and photovoltaic scenario achieves the lowest impacts across all assessed categories, reducing greenhouse gas emissions and fossil resource depletion by more than 50% compared to the baseline.A sensitivity analysis was conducted on key parameters, including moisture content (25%, 50%—baseline scenario, and 75%), electricity supply based on alternative European grid mixes, and transportation distance for both the collection of SCGs and the distribution of pellets. The analysis highlights the importance of balanced moisture content, the influence of electricity generation profiles, and the benefits of reduced transportation distances on overall environmental performance.A preliminary cost–benefit perspective is also presented to outline key economic considerations, forming the basis for a more detailed techno-economic assessment in future work.

Keywords: Spent coffee grounds, Pelletization, LCA, Waste management, Biomass combustion

Subject terms: Energy science and technology, Engineering, Environmental sciences, Materials science

Introduction

In today’s fast-paced world, energy powers our everyday lives, but the reliance on fossil fuels is quickly losing its appeal. As technology evolves and the global population grows, energy demands continue to rise, bringing sustainable alternatives into focus. Traditional fuels not only harm the environment but are also depleting at an unsustainable rate. Renewable Energy Sources (RES) have emerged as critical, eco-friendly solutions for the future. Among them, biomass stands out as a particularly promising option, offering the potential to help the EU achieve its environmental targets while simultaneously reducing waste and pollution. This transition marks a significant step toward a cleaner and more sustainable future^1–4.

Coffee is undoubtedly one of the most widely consumed beverages globally, with an estimated 2.25 billion cups consumed daily⁵. In Cyprus, coffee holds a prominent place in everyday life, deeply embedded in social and cultural traditions. Although the country’s spent coffee ground (SCG) output is modest in comparison to major coffee-consuming nations, the consistent growth in local consumption presents a promising opportunity for valorization. SCGs are increasingly recognized as a valuable secondary resource, contributing to sustainable waste management and circular economy initiatives. By reimagining coffee waste as a renewable input for bioenergy or material applications, Cyprus can adopt innovative, environmentally responsible practices that align with international sustainability trends while leveraging its local consumption habits.

The last five (5) years, 2018 to 2024, the out-of-home volume for roasted coffee in Cyprus grew steadily, increasing from 1.30 million kilograms in 2018 to an expected 1.26 million kilograms in 2024⁶. This upward trend is projected to continue, reaching 1.44 million kilograms by 2029. In the τ table below (Table 1), the per capita consumption of roast coffee from 2018 to July 2024 (actual data) is shown, along with projections through 2029. The figure highlights a decline in 2020, likely due to external factors as the COVID-19 pandemic, followed by a recovery in subsequent years. Consumption is expected to stabilize at around 0.9 kg per capita from 2027 onward. Given the current data and future projections, the valorization of spent coffee grounds (SCGs) in Cyprus presents a substantial and advantageous opportunity⁶.

Table 1.

Per capita consumption of roast coffee from 2018 to July 2024 (actual data) and projections from 2025 to 2029, measured in kilograms per person per year⁶.

Volume per capita (roast coffee) (Kg)	Year
0.85	2018
0.87	2019
0.67	2020
0.70	2021
0.73	2022
0.76	2023
0.78	2024
0.81	2025
0.83	2026
0.86	2027
0.89	2028
0.89	2029

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Beyond their market potential, Spent Coffee Grounds (SCGs) are increasingly catching the eye of eco-conscious innovators. With their impressive calorific value, SCGs are being repurposed as a sustainable energy source, making waves in biofuel production and green energy solutions. The circular economy thrives through the valorization of spent coffee grounds (SCGs), which bridges the gap between coffee culture and renewable energy. Repurposing SCGs offers a sustainable and economically viable solution to reducing waste while harnessing their latent potential. This approach aligns with the UN Sustainable Development Goals #6 (Clean Water and Sanitation), #7 (Affordable and Clean Energy), and #12 (Responsible Consumption and Production), contributing to a greener and more responsible future⁵ .

As comprehensively reviewed by Campos-Vega et al. (2015), early innovation efforts prior to 2005 were largely centered on the selective extraction of individual high-value constituents from spent coffee grounds (SCGs), including oils, flavor compounds, terpenes, and alcohols. In more recent years, research has increasingly shifted toward bioenergy production and biorefinery concepts, positioning SCGs as a versatile feedstock for fuels, chemicals, and materials. Despite this expanded research landscape, the review highlights that practical implementations have remained largely fragmented, with most valorization pathways targeting single components rather than the holistic utilization of the SCG matrix. Consequently, integrated fractionation strategies capable of systematically exploiting carbohydrates, lipids, phenolic compounds, nitrogenous compounds, minerals, caffeine, and Maillard-derived brown compounds within a unified industrial framework are still scarce. As illustrated in Fig. 1, SCGs constitute a chemically rich and multifunctional biomass, underscoring the significant yet underexploited potential for fully integrated, multi-product valorization approaches beyond conventional first-generation waste management routes^.

Spent coffee grounds (SCGs) are an abundant agro-industrial biomass residue generated during the brewing and processing of coffee. According to Campos-Vega et al.⁷, SCGs exhibit a complex chemical composition that includes carbohydrates, lipids, proteins, phenolic compounds, minerals, caffeine, and Maillard-derived brown compounds, supporting their classification as a high-potential lignocellulosic biomass feedstock. Unlike dedicated energy crops, SCGs are continuously available and low-cost, as they arise from an existing food supply chain, making them particularly attractive within circular economy frameworks. Their compositional diversity enables multiple valorization pathways, including bioenergy production and the recovery of value-added compounds, while simultaneously addressing waste management and environmental sustainability challenges.

The circular potential is evident in the repurposing of SCGs, as a source of energy, turning a waste product into a valuable resource. However, it is important to consider the efficiency of these biofuel processes and their overall environmental impact.

Despite the significant expansion of research in recent years, there remains a notable deficiency in publications addressing fuel pellets and their combustion in heating applications. This gap becomes more pronounced when considering studies specifically focused on fuel pellets made from spent coffee grounds (SCGs) and the processes involved in their production. Although the publication rate in this niche area is inconsistent, the overall trend suggests a gradual increase in interest. Notably, only one published paper to date has focused on the life cycle assessment (LCA) of fuel pellets made from SCGs².

This paper investigates the potential for the sustainable reuse of spent coffee grounds (SCGs) as fuel pellets, examining both the characteristics of SCGs and their combustion properties, as well as the life cycle assessment (LCA) of the pelletization process.

Theoretical background/literature review

Research on spent coffee grounds (SCGs) and their potential applications is increasingly gaining attraction. As is shown in the Fig. 2, over the past five years, the number of publications on this topic has steadily risen, reflecting a growing interest in their diverse uses. The production of these studies has yet to stabilize, indicating a dynamic field ripe for innovation.

Research in this area weaves through a rich tapestry of disciplines, all converging around a shared focus on environmental impact and sustainability. A thematic network has been crafted (Fig. 3) to spotlight recent explorations (2018–2024) into Spent Coffee Grounds (SCG), mapping out the tightly interlinked fields that gravitate toward this topic. As depicted in the figure, SCG appears at the heart of research themes like Biomass, Waste Management, Sustainable Development, and the Circular Economy, revealing an eco-conscious shift that reimagines “waste” as a resource in the journey toward a more sustainable, circular future.

Fig. 3 — Thematic network map on spent coffee grounds for the last five (5) years (2018–2024).

Spent Coffee Grounds (SCGs) find themselves intricately connected to a constellation of themes, including biomass, feedstock, food waste, biochar, biodiesel, waste management, and waste incineration—signaling a nuanced exploration into the valorization of coffee waste. The biofuel nexus links with emerging themes that underscore a heightened interest in sustainable bioenergy solutions, such as waste management, life cycle assessment, and environmental impact. Waste Management and Sustainable Development further align with the circular economy, forming a cohesive narrative around resource regeneration.

The thematic map reveals a vision for SCGs as transformative assets in a circular bioeconomy. These processes not only mitigate climate change but also reduce landfill dependency, cut carbon emissions, minimize resource consumption, and advance sustainable development. Yet, for SCGs to fully realize their potential as eco-friendly assets, further research and practical implementation remain essential.

From 1977, with the first ever published study of the possible reuse of SCGs, until the 2000s, studies were rare and fluctuating, in contrast with the last years where the interest is growing and the number of publications is going up⁸.

Recent advancements in technologies for valorizing spent coffee grounds (SCGs) encompass processes such as anaerobic digestion, pyrolysis, liquefaction, gasification, oil extraction, fermentation, and various other methods aimed at producing value-added products, including compost, adsorbents, antioxidants, and nutrients [5]. The potential end uses of SCGs are shown in the following Fig. 4. SCGs are a rich source of bioactive compounds with antioxidant, antimicrobial, and anti-inflammatory properties, valuable in various industries (Zuorro and Lavecchia et al.⁹ . Anaerobic digestion of SCGs produces methane-rich biogas and nutrient-rich fertilizer, though expanding feedstock to include all food waste from cafes and restaurants could enhance its efficacy. A 2023 study (Vitale et al., 2023) shows that Expresso Coffee By-products can be used as natural fertilizers¹⁰.

Fig. 4 — End uses for spent coffee grounds (SCGs).

Through the application of innovative recycling techniques, SCGs can function as sustainable biobased fertilizers to address the growing demands of an expanding global population. However, when generated in substantial quantities, SCGs present significant environmental concerns due to the increased oxygen demand required for their decomposition and the presence of harmful compounds such as caffeine, tannins, and polyphenols. As a result, SCGs are not widely applicable for large-scale composting and are often disposed of in landfills, leading to considerable economic and environmental implications⁵. Conversely, bioenergy derived from SCGs has garnered significant attention in recent years due to their non-seasonal availability and widespread distribution, offering a promising alternative for sustainable energy applications.

Mushroom growth medium

Additionally, studies (Carrasco-Cabrera et al., 2019) showed that Spent Coffee Grounds (SCG) serve as an effective substrate for cultivating edible mushrooms, particularly oyster mushrooms, offering comparable nutritional quality and yields to traditional substrates, though large-scale implementation remains limited¹¹. Also, studies have shown that using SCG as a growth substrate provides mushrooms with the same nutritional quality and yields as mushrooms grown on substrates currently utilized by the mushroom industry, such as straw¹². Furthermore, the mushrooms generated have neither caffeine nor tannins, and the fungus is expected to partially break down the toxins in the SCG¹³. SCG seems to be an excellent substrate for mycelia development but not for mushroom growth in one research¹⁴. Oyster mushrooms tend to be the best type for growing on SCG, as they are reasonably easy to grow and more resistant to changing environmental conditions¹⁵.

Bioactive compounds

Coffee beans are a rich tapestry of bioactive compounds, including phenolic compounds, melanoidins, diterpenes, xanthines, and vitamin precursors. Each contributes uniquely to coffee’s potential health benefits. For instance, chlorogenic acids—the predominant element in coffee seeds—have been associated with reduced risks of atherosclerosis, diabetes, and several cancers^16,17. Melanoidins, formed in the roasting process, exhibit an impressive array of health-promoting effects: they have been shown to inhibit bacterial growth in the colon, possess anti-inflammatory and antiglycative properties, and may even help thwart tumor growth and metastasis^18,19. Though conventional brewing only partially extracts these compounds, spent coffee grounds (SCG) remain a compelling, underutilized source of bioactive elements. Studies have unearthed a wealth of antioxidants within SCG, boasting a high phenolic content that rivals conventional sources²⁰. Yet, despite mounting evidence supporting SCG’s value in the food and pharmaceutical sectors, a standardized, scalable method for its utilization has yet to take root in industry.

Fuel pellets

Turning raw solid biomass material into pellets has a high potential for energy usage. Spent coffee grounds (SCGs) hold significant potential as an energy source through their conversion into fuel pellets and various biofuels. Because of the high efficiency of the combustion, the coffee pellets have a high calorific value content with a low amount of non-usable material remaining (ash) and negligible carbon monoxide emissions. The pellets, on the other hand, have a high moisture content, low bulk density, and mechanical resilience. The densification process, which compresses biomass into pellets with higher energy density, offers a promising way to enhance the energy potential of SCG. The global market for fuel pellets (FPs) is expanding as these densified solids serve as a renewable substitute for coal in electricity and power generation, as well as residential and district heating. By transforming SCGs into fuel pellets, we can contribute to climate change mitigation, reduce landfill waste, lower carbon emissions, and decrease freshwater eutrophication. This study aims to assess the total environmental impact of the pelletization process.

The combustion characteristics of spent coffee grounds (SCGs), repurposed as biofuel pellets, reveal a promising alternative energy source with a blend of efficiency and environmental responsibility. During testing²¹, conducted in accordance with the CYS EN 303-5:2012 standard¹⁴, SCG pellets demonstrated impressive combustion efficiency, maintaining an average of 89%. CO emissions, which initially registered at 1166.3 ppm, steadily declined to 317.3 ppm as the flame temperature increased, a testament to the robust combustion dynamics facilitated by high temperatures and optimized oxygen flow. Flue gas temperatures rose consistently, underscoring the pellets’ stable heat output.

These coffee-derived pellets not only met but exceeded European emissions standards for Class 3 boilers, proving their viability as a cleaner, more sustainable energy source²². Their low carbon monoxide emissions, coupled with high flame efficiency and minimal ash residue, mark them as an ideal candidate for environmentally conscious heating solutions. While aspects such as bulk density and moisture content present opportunities for refinement, the overall performance of SCG pellets highlights their potential in the world of biofuel—a sustainable energy choice with a touch of artisanal charm (The combustion).

Spent Coffee Grounds (SCGs) can be processed into a variety of biofuels, including biohydrogen, biobutanol, biodiesel, bio-oil, bioethanol, biogas, and hydrocarbon fuels. Technologies such as pyrolysis demonstrate promise in producing high-quality biofuels and biochar, thereby addressing the fuel crisis and contributing to climate change mitigation efforts. However, further research is required to ensure that SCG pellets comply with standards for density, mechanical stability, hydrophobicity, and energy content. Additionally, the environmental sustainability of biodiesel production is variable; while it is generally viewed as more sustainable than fossil fuels, its advantages may be compromised by the choice of feedstock and production methods, particularly when deforested land or significant chemical inputs are utilized^22–24.

Methodology

Materials

Coffee grounds from an espresso machine sample given by Coffee Island were used in this investigation. The sampling was performed according to the procedures described in EN 14780:2017²⁵. Solid biofuels were placed in air-tight plastic containers. Each sample was labelled with a unique identification number and the date/ time of sampling before being transferred to the laboratory.

Analysis

In this section, a comprehensive account of the tests conducted to characterize spent coffee grounds, is provided, accompanied by detailed explanations of the techniques employed for each test. The conducted tests are listed below:

Moisture content.
Ash content.
Calorific value.
C, H, N content.

Moisture content determination

The moisture content of the prepared general analysis samples was determined according to the procedure described in EN 18134-3:2015²⁶. The samples were placed in the drying furnace (SNOL 20/300) and dried at 105 °C in air atmosphere to achieve constancy in mass. The moisture content was then calculated from the recorded mass loss of the sample using an analytical balance (KERN ABT 220-5DM). The following procedure is demonstrated in Moisture content measurement of solid biofuels 2015.

Ash content determination

During the ash content analysis of the samples, the ash content was determined using a high-temperature laboratory furnace (SNOL 4/1100) and KERN ABT 220-5DM analytical balance, following the standardized procedure outlined in EN 18122:2015²⁷. The results are reported on a dry basis, considering the calculated moisture content of the samples.

Calorific value measurement

The calorific value of the obtained sub-samples was estimated according to EN 18125:2017²⁸, Calorific value measurement of solid biofuels using bomb calorimetry 2015, using a Parr 1341 Oxygen Bomb Calorimeter. A calibration of the calorimeter took place prior to the experimental runs using certified benzoic acid pellets, with known calorific value.

C, H, N content measurement

The total carbon (C), Hydrogen (H) and Nitrogen (N) content of the samples, was determined according to the procedure described in EN 16948:2015²⁹. The tests were conducted using a Perkin Elmer 2400 Series II CHN analyser, which was calibrated prior to the measurements using appropriate substances, i.e., acetanilide, as indicated by the manufacturer. The total C, H, and N content in dry basis was calculated by considering the moisture content of the sample. The following procedure is demonstrated in Elemental analysis of Solid Biofuels 2015.

Life cycle assessment

The Life Cycle Assessment (LCA) consists of four essential phases. Phase 1: Scope and Definition outlines the goals and boundaries of the assessment. Phase 2: Life Cycle Inventory collects data on the inputs and outputs of the system. Phase 3: Impact Assessment evaluates the environmental impacts based on the inventory data. Finally, Phase 4: Interpretation connects the findings to the original objectives, ensuring the results offer meaningful insights into sustainability.

The objective of this LCA study is to evaluate the environmental implications of the pelleting process in Cyprus, which utilizes spent coffee grounds to produce pellets for residential heating. The entire biomass chain has been prioritized, from the transportation of waste from its creation site to the transfer of manufactured pellets to sales destinations. Spent coffee grounds refer to coffee grounds after they have been used; they are the waste product of the espresso coffee extraction process. The system’s primary role is to produce EN 17225-6:2021 (International Organization for Standardization, 2021) certified non-woody pellets for non-industrial applications.

System boundaries

Figure 5 shows a schematic representation of the stages of the biomass pelleting process chain that are included in the scope of the study: transportation of wet waste from the production points to the central management center, feeding, drying, pelleting, cooling, packaging, and distribution of pellets from the management centers back to sale points of the final products. The use of materials and energy for the construction of the employed machinery and infrastructure is excluded from the system boundaries due to its minimal contribution to the overall impact³⁰.

Fig. 5 — LCA analysis of the SCG pelletization process³¹.

Impact categories

The Sphera LCA software³², as well as the ISO 14040:2006 + A1:2020³³ and ISO 14044:2006 + A1:2018 + A2:2020³⁴ standards, were utilized to implement the LCA in this study. In this work, the International Reference Life Cycle Data System (ILCD) guidelines methodology is applied to execute the life cycle impact assessment (LCIA). The ILCD has released ‘Recommendations for Life Cycle Impact Assessment in the European context’ which chooses the methodology which has been evaluated as the best within the impact category (ILCD handbook recommendations for Life Cycle Impact Assessment 2011)³⁵. In this paper, the ReCiPe 2016 v1.1 method was chosen to address the environmental impact categories for this pelletization process.

ReCiPe 2016 v1.1 is a harmonized life cycle impact assessment (LCIA) method that translates elementary flows from a Life Cycle Inventory (LCI) into a limited set of environmental impact scores using characterization factors, and it is designed in a way that provides a comprehensive impact assessment at both midpoint and endpoint levels³⁶. It encompasses a broad spectrum of environmental impact categories, addressing issues relevant to human health, ecosystem quality, and resource scarcity³⁶.

The choice of specific impact categories for reporting, such as Climate Change, Fine Particulate Matter Formation, Fossil Depletion, Freshwater Eutrophication, Human Toxicity (cancer and non-cancer), Land Use, and Terrestrial Acidification, is often guided by their widespread environmental significance, direct relevance to human and ecosystem health, and their frequent prioritization in scientific publications and policy discussions^37,38. These categories help identify the most environmentally friendly option/scenario by ensuring a holistic evaluation of environmental performance, which is crucial for informed decision-making in various applications, from food production to waste management and construction^31,39.

I.
Climate Change (Kg CO2 eq.): This category quantifies the contribution of greenhouse gas emissions to global warming, expressed in kilograms of carbon dioxide equivalents.
II.
Fine Particulate Matter Formation (Kg PM2.5 eq.): This indicator assesses the potential for the formation of fine particulate matter in the atmosphere, which can negatively affect human respiratory health, measured in kilograms of PM2.5 equivalents.
III.
Fossil Depletion (Kg oil eq.): This category represents the depletion of fossil resources due to their extraction and consumption, typically measured in kilograms of oil equivalents.
IV.
Freshwater Eutrophication (Kg P eq.): This category evaluates the potential for nutrient enrichment in freshwater systems, leading to excessive algal growth and oxygen depletion, expressed in kilograms of phosphorus equivalents.
V.
Human Toxicity, cancer (Kg 1,4-DB eq.): This category assesses the potential for substances to cause carcinogenic effects on human health, quantified in kilograms of 1,4-dichlorobenzene equivalents.
VI.
Human Toxicity, non-cancer (Kg 1,4-DB eq.): This category evaluates the potential for substances to cause non-carcinogenic adverse effects on human health, also quantified in kilograms of 1,4-dichlorobenzene equivalents.
VII.
Land Use (Annual crop eq.yr): This category measures the impact of land occupation and transformation, often expressed in annual crop equivalents per year, reflecting the agricultural productivity lost or altered.
VIII.
Terrestrial Acidification (Kg SO2 eq.): This indicator assesses the potential for emissions to contribute to soil and water acidification, which can harm terrestrial ecosystems, measured in kilograms of sulfur dioxide equivalents.

Alternative scenarios

The Life Cycle Assessment (LCA) was initially conducted on the existing palletization process. Following the analysis and evaluation of the preliminary results, the subprocesses with the greatest environmental impact were identified.

Based on these findings, a series of hypothetical scenarios was developed in which one or more parameters were modified, and the environmental burden of each scenario was calculated.

Initially, four different energy supply scenarios were used to evaluate the manufacturing process’s energy consumption. Next, the moisture content of the spent coffee grounds and the electricity use, considering grid mixes from four European regions, were analyzed, as described below.

Energy consumption

The three selected and assessed scenarios in addition to the current one are presented in the table below (Table 2).

Table 2.

ReCiPe 2016 v1.1 environmental impact categories.

ReCiPe 2016 v1.1 impact category (Unit)

Climate change (kg CO₂ eq.)

Climate change, biogenic (kg CO₂ eq.)

Fine particulate matter formation (kg PM₂.₅ eq.)

Fossil resource scarcity (kg oil eq.)

Water consumption (m³)

Freshwater ecotoxicity (kg 1,4-DCB eq.)

Freshwater eutrophication (kg P eq.)

Human carcinogenic toxicity (kg 1,4-DCB eq.)

Human non-carcinogenic toxicity (kg 1,4-DCB eq.)

Ionising radiation (kBq Co-60 eq to air)

Land use (m²a crop eq.)

Marine ecotoxicity (kg 1,4-DCB eq.)

Marine eutrophication (kg N eq.)

Mineral resource scarcity (kg Cu eq.)

Photochemical ozone formation, terrestrial ecosystems (kg NOx eq.)

Photochemical ozone formation, human health (kg NOx eq.)

Ozone depletion (kg CFC-11 eq.)

Terrestrial acidification (kg SO₂ eq.)

Terrestrial ecotoxicity

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The LCA results for each scenario are discussed in the following section, where a comparative analysis identifying the most environmentally promising solution is presented.

Sensitivity analysis

Moisture content

The moisture content of the Spent Coffee Grounds (SCGs) was defined as a variable parameter in the analysis. A baseline scenario was set at 50% moisture, based on experimental measurements. Two additional scenarios were considered in the framework of a sensitivity analysis of the process: a low-moisture case at 25% and a high-moisture case at 75%. The functional unit was fixed at 1 tonne of produced coffee pellets; therefore, the quantity of SCGs required varies depending on the moisture content. As the moisture increases, a larger mass of raw material is needed, while lower moisture results in a smaller required input mass. The process most affected by this variation is drying, and the associated electricity consumption is calculated based on the mass of the input material, which is directly determined by its moisture content.

Electricity, alternative grid

Electricity supply was treated as a variable parameter by examining different grid mixes. The baseline scenario used Cyprus’s (CY) electricity grid, while other scenarios represented various European regions, selecting specific countries as representative examples.

The electricity supply scenarios were defined as follows:

Baseline scenario – Cyprus (CY).
Central and Eastern Europe – Poland (PL).
Northern Europe – Sweden (SE).
Southern Europe – Greece (GR).
Western Europe – France (FR).

The selected countries were used as representative cases for their respective regions.

Transportation distance

Transportation distance was also treated as a variable parameter. The distance travelled by the truck for the collection of spent coffee grounds and the distribution of coffee pellets was subjected to a sensitivity analysis. A baseline scenario of 100 km was defined, along with two alternative scenarios at 80 km and 120 km, representing a ± 20% variation.

Cost-benefit analysis

A preliminary techno-economic analysis (TEA) was conducted to provide an initial assessment of the economic performance of the proposed process. The analysis considers the main cost components, including capital expenditures (CAPEX) related to equipment, installation, and infrastructure, as well as operational expenditures (OPEX), such as electricity consumption, transportation, labor, and maintenance. The evaluation is based on simplified assumptions appropriate for an early-stage analysis, without the application of a detailed discounted cash flow model. his approach allows for the identification of the main cost drivers and provides an indicative understanding of the economic implications of the system. A comprehensive techno-economic analysis, including detailed financial modeling and levelized cost indicators, is beyond the scope of the present study and is planned for a subsequent stage of the research.

Results and discussion

Thermochemical properties

All analyses were conducted twice, and the average values were reported. Table 3 displays the results of the sample analyses alongside two references from the literature. Reference 1⁴⁰ presents the findings of a mixture of Coffee arabica spent coffee grounds naturally dried in the sun, with a moisture content reaching 8.22%. Reference 2⁴¹ provides the results of 100% Arabica spent coffee grounds of varying origins, with an average moisture content of approximately 52%, dried in a well-ventilated area.

Table 3.

Description of the four pelletization scenarios assessed in the Life Cycle Assessment.

Baseline scenario		The pelletization process is carried out using electricity obtained from the grid provided by a state-owned supplier
Scenario 1: sun drying		In the pelletization process, the drying of coffee waste is carried out using solar radiation, while the remaining processes use electricity from the grid provided by a state-owned supplier
Scenario 2: photovoltaics		The entire pelletization process is carried out using energy from photovoltaic panels
Scenario 3: sun drying and photovoltaics		The entire process, except for the drying of coffee residues, is carried out using photovoltaic panels. The drying process is powered by solar radiation

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The standard EN ISO 17225-6:2021 specifies the minimum standards for non-woody pellets.

The moisture content of the tested samples was calculated (i.e., on an as-determined basis, Mar) to be greater than 12 w%, exceeding the permitted limits specified in Table 4. Due to the significant moisture content retained in the coffee, this exceeded the allowable limit. However, it is feasible to allow the used coffee grounds to naturally dry in the sun, achieving a moisture mass share of 12% or less.

Table 4.

Reference specifications for pellets.

	Unit	EN standard	Sample			References
	Unit	EN standard	1	2	Average	1[9]	2[10]
Moisture content, M_ad	[w%]	EN ISO 18134-1:2015	54.21	53.37	53.79	Dried 8.22	52
Ash, A_d	[w%]	EN ISO 18122:2015	2.23	3.33	2.80	1.59	1.47
Net Calorific value, q_{p, net, d}	[MJ/kg]	EN ISO 18125:2017	20.75	21.19	20.97	19.74	21.26
Carbon content, C_d	[w%]	EN ISO 16948:2015	47.81	46.06	46.94	50.26	56.73
Hydrogen content, H_d	[w%]	EN ISO 16948:2015	6.31	6.30	6.31	6.29	7.11
Nitrogen content, N_d	[w%]	EN ISO 16948:2015	0.46	2.41	1.44	2.21	2.83
Oxygen (by diff.), Od	[w%]	–	45.42	45.23	45.31	31.37	33.19

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• ad: as determined basis.

• d: dry basis.

• p, net, d: constant pressure, net, dry.

As for the ash content of the tested samples, the findings study revealed that the sample’s ash content meets the standards of the EN ISO 17225-6:2021 standard, which specifies a maximum allowable value of 10% on a dry basis. The ash level of pellets produced from biomass feedstock mixes should not exceed 10% by weight.

The net calorific value of the spent coffee grounds sample is acceptable, ranging from 20.75 to 21.19 MJ/kg, and exceeds the minimum standard of 14.5 MJ/kg specified in Table 4.

In terms of elemental analysis, the results, showed that the Nitrogen content level of sample 1 was within the permitted limits shown in Table 4, on contrast with the second sample (sample 2) that was not. The average Nitrogen content of the sample was 1.44 w%, which is lower than the maximum allowable value of 2.0 w%.

Environmental aspect – life cycle assessment

Scope and system boundaries

Following the definition of the system boundaries, the Life Cycle Inventory (LCI) was compiled. It includes detailed information on the transportation of Spent Coffee Grounds (SCG) to the processing facility, the associated energy and mass balances throughout the pelletization process, and the subsequent distribution of the produced coffee pellets to commercial outlets. The system boundaries of this study follow a cradle-to-gate approach, encompassing the collection and transportation of SCG, the drying, grinding, and compression stages involved in pellet production, as well as the transport of the final product to the point of sale. The analysis excludes the use phase of the pellets and their end-of-life treatment, as these lie beyond the defined scope of the current assessment.

Life cycle inventory (LCI) – data collection

Table 5 below shows the data utilized for the LCA implementation for this study. The information was gathered via empirical investigations, machinery manufacturers, or was derived from the Sphera LCA database.

Table 5.

Reference specifications for SCG pellets.

Class	Unit	Non-woody pellets EN ISO 17225-6
Class	–	A	B
Moisture content, M^a_ar	(w%)	≤ 12	≤ 15
Nitrogen content, N_d	(w%)	≤ 1.5	≤ 2.0
Ash, A_d	(w%)	≤ 6.0	≤ 10.0
Net Calorific value, q_{p, net, d}	(MJ/kg)	≥ 14.5	≥ 14.5
^aWet basis

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Table 5 summarizes the inventory data used for the LCA in this study. Data were obtained from empirical measurements, machinery manufacturers’ specifications, and the Sphera LCA database. The functional unit of the study is defined as 1000 kg (1 tn) of produced coffee pellets. This unit serves as the reference basis for all calculations, ensuring consistency when comparing environmental and economic results across scenarios.

Transportation from coffee shops to management centre

The study models the collection of Spent Coffee Grounds (SCGs, 2014 Kg) from Coffee Island coffee shops in the Nicosia district. The management center, located at Frederick University premises in Nicosia, is defined as the starting and ending point of the collection tour. The total travel distance for the collection tour is estimated at 100 km, representing the distance the truck travels to collect the coffee grounds from the selected shops. Figure 6 provides an indicative map where the collection points and the management center are marked.

The same coffee shops are assumed to serve as the final points of sale for the produced pellets (i.e. 1000 kg) after processing; therefore, the same travel distance and route are assumed for pellet distribution in the model.

Means of transportation and fuel consumption

Transportation to and from the management center is modeled using a diesel-fueled truck. Diesel consumption is calculated using an existing process from the Sphera LCA database for a Euro V t truck. This process is parameterized by the total distance travelled and the transported mass and returns the corresponding diesel consumption per tour. The truck is assumed to return empty to the management center.

As mentioned in our study Environmental evaluation of biomass pelleting using life cycle assessment (2016)⁴², the values regarding the total fuel consumption for the investigated scenarios were obtained using the transportation distance of predefined collection locations to the plant (GoogleMAPS data) and by utilizing an existing process in the Sphera LCA database for a Euro V truck (Table 6; Fig. 5).

Table 6.

Life cycle inventory (LCI).

Process and inputs	Value	Units description	Data source
Transport from coffee shops to the management centre	2014	Kg of SCGs
Diesel	13.36	Kg calculated considering the cargo weight and real distance	Sphera LCA database
Transportation distance	100	km	Google maps
Feeding mass	2014	Kg of SCGs entering the system
Drying mass loss	1007	Kg
Drying grid electricity	435.1	MJ	Empirical Data
Pelleting grid electricity	273.4	MJ	Empirical Data
Cooling and screening mass loss	7	Kg	Empirical Data
Cooling grid electricity	12.5	MJ	Empirical Data
Transport from management centre to sale points (i.e. coffee shops)	1000	kg
Transportation distance	100	km	Google maps
Diesel	6.64	kg	Sphera LCA database

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Impact assessment

The environmental impact assessment was conducted using Sphera LCA software, applying the ILCD methodology and following ISO 14,040 and 14,044 standards. The analysis focused on eight midpoint impact categories: Climate Change (Kg CO2 eq.), Fine Particulate Matter Formation (Kg PM2.5 eq.), Fossil Depletion (Kg oil eq.), Freshwater Eutrophication (Kg P eq.), Human Toxicity, cancer (Kg 1,4-DB eq.), Human Toxicity, non-cancer (Kg 1,4-DB eq.), Land use (Annual crop eq.yr), Terrestrial Acidification (Kg SO2 eq.).

Results for the baseline scenario (1000 kg of SCG pellets produced) indicate that Climate Change was 252.50 kg CO₂eq, with the drying phase contributing the largest share due to high electricity consumption. Fine Particular Matter Formation was equal to 0.305 Kg PM2.5 eq., and the fossil depletion was 69.396 Kg oil eq, primarily linked to energy and transport inputs. The human toxicity, cancerous and non-cancerous, was equal to 1.952 and 17.599, respectively. In addition, the Freshwater eutrophication and the Terrestrial acidification were 4.83E-04 kg P eq.and 0.961 kg SO2 eq. lastly the Land use was equal to 6.946 annual crop eq. yr. The results are summarized in the Table 7 below.

Table 7.

ILCD recommendations LCA results for the selected impact categories of the baseline scenario.

Env. impact category	Value
Climate change (Kg CO2 eq.)	252.50
Fine particulate matter formation (Kg PM2.5 eq.)	0.302
Fossil depletion (Kg oil eq.)	69.396
Freshwater eutrophication (Kg P eq.)	4.83E-04
Human toxicity, cancer (Kg 1,4-DB eq.)	1.952
Human toxicity, non-cancer (Kg 1,4-DB eq.)	17.599
Land use (annual crop eq.yr)	6.940
Terrestrial acidification (Kg SO2 eq.).	0.961

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Table 8 presents the key emissions associated with the pelletization process. Among them, airborne pollutants such as carbon dioxide (CO₂), sulfur dioxide (SO₂), and nitrogen oxides (NOₓ) emerged as the primary contributors across most impact categories. The drying and transportation stages were identified as the most environmentally intensive, highlighting the critical need for energy-efficient interventions. These results provide the rationale for the alternative mitigation scenarios examined in Sect. 3.2.4.

Table 8.

Data of emissions.

Coffee pellets
Inputs
Wet waste coffee (kg)	2014
Non-renewable energy resources (MJ)	69.76
Material resources in total	20611.29
Non-renewable elements	0.1229
Non-renewable resources	14.77
Renewable resources	20596.40
Outputs
Coffee pellets ((kg)	1000
Emissions
Emissions to air (kg))	4637
Inorganic emissions to air (kg)	3785
Carbon monoxide (CO) (kg)	0.1126
Carbon dioxide (CO2) (kg)	223.1
Nitrogen oxides (NOx) (kg)	0.2544
Sulphur dioxide (SO2) (kg)	0.7019
Particles to air (kg)	0.02964
Emissions to fresh water (kg)	17319.67
Emissions to sea water (kg)	43.45
Emissions to agricultural soil (kg)	5.20E-5
Inorganic emissions to agricultural soil (kg)	0.0011

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The initial results indicate that drying coffee residues collected from retail stores requires the most energy and, consequently, has the greatest environmental impact. In response, the research team developed three alternative scenarios aimed at mitigating this impact as much as possible. The three selected and examined alternatives are presented in Table 2. In addition, the research team evaluated other pelletization-related parameters to assess their influence on environmental impact.

Life cycle assessment results