Biofuel pellets from spent coffee grounds

doi:10.21203/rs.3.rs-1551835/v1

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Research Article

Biofuel pellets from spent coffee grounds

https://doi.org/10.21203/rs.3.rs-1551835/v1

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posted 13 Apr, 2022

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The research is aimed at solving the urgent problem of food industry waste disposal on the example of using spent coffee grounds. The storage of coffee industry waste leads to the loss of potentially valuable raw materials. As one of the most promising solutions, this article considers the use of coffee grounds as the main component for fuel composition with the addition of a binder in the form of crushed cardboard and paper waste. The elemental composition, physical and mechanical properties of fuel pellets and the highest specific heat of coffee biomass and fuel composition based on it were determined in the laboratory studies. It is shown that the waste from coffee production is low in ash and has a high fuel cell content, as well as a high specific heat of combustion. The use of spent coffee grounds as raw materials for biofuel pellets production can be considered as an effective way of processing spent coffee grounds and increasing the value of coffee industry waste.

Coffee

Biofuel

Cardboard

Paper

Recycling

Waste

The scientific novelty of the work lies in the determination of a new composition intended for the preparation of biofuel pellets for various types of power plants. The invention relates to compositions intended for the preparation of environmentally friendly fuel pellets for various types of power plants. Compressed biomass pellets include dried waste coffee grounds and waste paper and cardboard. The proposed pellets made from compressed biomass have a significant resource-saving effect by reducing the need for wood. Another advantage when using pellets from pressed biomass is the useful disposal of waste by involving it in economic circulation with the prospect of using it in various types of power plants: pellet boilers, fireplaces for space heating, in field conditions, etc.

Spent coffee grounds represent a wet solid residue formed after brewing coffee, and in most cases its disposal is carried out without any intermediate actions for valorisation of materials and energy recovery. Spent coffee grounds are a very favorable raw material for the production of biofuel briquettes and pellets: this biomass is energy efficient, widely available and helps to reduce the amount of waste entering landfills. Moreover, from an economic point of view, the use of local energy resources is more preferable than the use of imported fuel.

Energy supply from biomass resources not only promotes fuel diversification, but also reduces air pollution, since biomass resources contain relatively low sulfur and heavy metal content compared to fossil fuels such as coal [1]. Many types of low-demand carbon-containing products or waste can be used for the production of thermal energy. The most accessible and technically studied method of processing the above-mentioned low-demand products and waste is briquetting them with binders [2].

The purpose of this study is to develop a method for producing biofuel pellets from spent coffee grounds.

The main objectives of the conducted research are:

1 Study of the main thermal characteristics of spent coffee grounds as a potential raw material for the production of biofuel pellets;

2 Selection of the substance acting as a binding component and its quantity for the manufacture of biofuel pellets from coffee;

3 Study of the basic physical and chemical, mechanical and calorific properties of biofuel pellets from spent coffee grounds, waste paper and cardboard;

4 Determination of the amount of the main polluting substances formed during the process of pellets combustion.

The scientific novelty of the work consists in determining a new composition intended for the preparation of biofuel pellets for various types of powerplants. Pellets from pressed biomass are made from dried spent coffee grounds, waste paper and cardboard.

The proposed pellets from pressed biomass have a significant resource-saving effect by reducing the need for wood. Also, the advantage of using pellets from pressed biomass is the disposal of waste by involving them in economic turnover with the prospect of use in different types of powerplants: pellet boilers, fireplaces for heating rooms, in field conditions, etc.

Laboratory tests were carried out at the shared core facilities of the St. Petersburg Mining University (Fig. 1).

*provided by the authors

In one of the coffeehouses, 10 samples of used coffee grounds were taken in order to assess the possibility of its use as a raw material for biofuel pellets (Table 1). The samples differed in the presence or absence of caffeine, roasting (light or dark) and grinding size (fine, medium or coarse). A mixture of three medium-ground roasts was also taken, because is in this form that most of the coffee waste in espresso machines is formed.

Table 1

Description spent coffee grounds samples*
Sample number	Grinding	Type of spent coffee grounds
1	Fine	Decaffeinated (dark roast)
2	Medium
3	Coarse
4	Fine	Light roast
5	Medium
6	Coarse
7	Fine	Dark roast
8	Medium
9	Coarse
10	Medium	The blend of dark roast, light roast and decaffeinated coffee
*provided by the authors

The samples of spent coffee grounds were dried to an air-dry state. At the first stage of the research, the main characteristics of coffee biomass were studied, such as moisture content, volatile matter content, ash content and elemental composition. For this purpose, thermogravimetric and elemental analysis of spent coffee grounds were performed.

Thermogravimetric analysis was carried out using a thermogravimetric analyzer LECO TGA-701. Determination of moisture content, ash content and yield of volatile substances was carried out in accordance with GOST R 53357 − 2013 (ISO 17246:2010) (Fig. 2).

^{*provided by the authors}

Table 2 shows that the moisture content in the samples varied from 7.1 to 7.9%.

Table 2

Moisture content in spent coffee grounds, %*
	Blend	Decaffeinated	Dark roast	Light roast
Fine grinding		7.1	7.6	7.9
Medium grinding	7.4	7.3	7.8	7.1
Coarse grinding		7.3	7.1	7.7
*provided by the authors

Table 3 shows that the ash content ranges from 1.1 to 3.2%, and the smallest amount of ash is that of dark-roasted coffee. The coffee blend is characterized by average values.

Table 3

Ash content of spent coffee grounds, %*
	Blend	Decaffeinated	Dark roast	Light roast
Fine grinding		2.3	1.8	1.7
Medium grinding	2.0	1.8	1.2	3.1
Coarse grinding		1.9	1.1	1.5
*provided by the authors

The content of volatile substances varies from 79.0–82.4% (Table. 4), and the lowest volatile content was found in decaffeinated coffee.

Table 4

Volatile yield of spent coffee grounds, %*
	Blend	Decaffeinated	Dark roast	Light roast
Fine grinding		79	80.3	82.4
Medium grinding	81.8	79	80.8	80.5
Coarse grinding		79.2	81.9	81.9
*provided by the authors
Then an elemental analysis was carried out and the contents of carbon, hydrogen and nitrogen in the samples of spent coffee grounds were determined (Table 5). The properties of fuel are largely determined by its chemical composition – the content of carbon, hydrogen, oxygen, nitrogen and sulfur [3]. The carbon, hydrogen and nitrogen contents in the spent coffee grounds were measured using a LECO CHN628 elemental analyzer. The analysis was carried out in accordance with the methodology of GOST 32979 − 2014 (ISO 29541:2010).

The amount of carbon in the samples was 55.7–58.0%, hydrogen − 7.6–7.9%, nitrogen − 2.1–2.5% (Table 5).

Table 5

Content of nitrogen, hydrogen and carbon in spent coffee grounds, %*
	Blend	Decaffeinated	Dark roast	Light roast
C	57.2	58	57.4	55.7
H	7.6	7.9	7.6	7.7
N	2.5	2.3	2.3	2.1
*provided by the authors
The highest specific heat of combustion of the samples was measured using a calorimeter for determination of the caloric content of solid fuels and the amount of thermal energy IKA C 2000 in accordance with GOST 147–2013. The combustion energy of a fuel sample is determined by burning the sample in compressed oxygen medium. The amount of heat released during combustion is proportional to the amount of the combustion energy of the substance.

The results of sample combustion are presented in Table 6.

Table 6

The highest specific heat of combustion of spent coffee grounds*
Type of coffee	The highest specific heat of combustion, MJ/kg	Lowest heat of combustion, MJ/kg
Decaffeinated (dark roast)	22.5	20.6
Light roast	20.8	19.0
Dark roast	22.6	20.8
Blend	22.6	20.8
*provided by the authors

The lowest heat of combustion of spent coffee grounds was calculated by the formula:

\({Q}_{i}^{a}\) =\({Q}_{s}^{a}\)-24.42\(\bullet \left({W}^{a}+8.94{H}^{a}\right)\),

where 24.42 represents vaporisation heat at 25°С per 1% of the water release, KJ/kg.

8.94 is the conversion coefficient of the mass fraction of hydrogen to water;

\({W}^{a}\) - the mass fraction of moisture of the analytical sample, %;

\({H}^{a}\) - the mass fraction of hydrogen in the analytical sample, %.

The results of the analyses allow us to conclude that coffee grounds have a low ash content, a high content of fuel elements and a relatively high heat of combustion, therefore, the use of spent coffee grounds as raw material for biofuel pellets can be considered as an effective way of recycling coffee industry waste.

Literature review and patent search

Coffee is the second most sold commodity after oil and the second most consumed beverage after water [4]. It is estimated that 3.5 billion cups of coffee are consumed worldwide every day. It is grown in more than 70 countries, producing more than 16 billion pounds of coffee beans annually [5]. Developing countries produce more than 90% of the world's coffee, generating income for approximately 25 million small farmers [6].

However, coffee production generates a lot of coffee waste and by-products, which, on the one hand, could be used for other purposes (as a sorbent for removing heavy metals and dyes from aqueous solutions, in the production of fuel pellets or briquettes, as a substrate for the production of biogas, bioethanol or biodiesel, a substrate for growing mushrooms, a source of natural phenolic antioxidants, composting material, in the production of reusable cups, etc. On the other hand, they are a potential source of serious environmental pollution.

The main solid by-products of coffee cultivation and preparation are spent coffee grounds, by-products of coffee fruits and residues of grain processing (coffee husk, peel, pulp) [5].

In addition to landfill disposal, there are other disposal options: use for animal feeding, production of organic compost or fertilizers, anaerobic digestion, or solid fuel production. Оther applications have been considered recently, including the use for the removal of heavy metals, the extraction of valuable compounds, the use as raw materials for the production of activated carbon and the production of bioethanol [7].

Spent coffee grounds are lipid-containing organic waste which has a huge potential for the production of biofuels. Depending on the geographical location, the average oil content in the spent coffee grounds ranges from 7.5 to 20.6%. 12% is considered the average oil content in the spent coffee grounds [4]. The lipid content of spent coffee grounds in terms of dry weight ranges from 7 to 27.8%, which is significant compared to other main types of biodiesel raw materials, such as rapeseed oil (37–50%), soybean oil (20%) and palm oil (20%) [8].

Coffee biodiesel has been proved to reduce CO₂ emissions by 80.5% compared to hydrocarbon diesel fuel during its life cycle. Moreover, the efficiency of converting the energy of raw materials into fuel energy in the case of coffee biodiesel was 10% higher than that of gasoline diesel [9].

Currently, the development of global initiatives that contribute to the creation of waste streams with an increase in value, also known as the increase of the cost of waste, has become one of the main strategies for managing food waste while boosting resource efficiency and reducing environmental pressure [10]. For example, in one of the studies [11], an experimental proposal "Waste to Energy" is being developed and analyzed to achieve a circular economy, which consists in the fact that the reuse of spent coffee grounds provides energy for the roasting phase of coffee preparation.

The composition of the coffee grounds-based fuel and the method of its production were patented [12]. The authors propose a composition for a coffee grounds-based fuel containing dried spent coffee grounds (54% by weight); vegetable fat (23%); brown sugar (20%); corn syrup (2%); in this case, vegetable fat and brown sugar are mixed together and slowly brought to a boil. Then the resultant mixture is removed from the fire, the dried spent coffee grounds are mixed with the resultant mixture, then corn syrup is added to the resultant mixture it and the resultant mixture is poured and pressed into a mold for final molding. When the mixture has cools to room temperature, it is removed from the mold for use. The advantages of this composition are that it does not use wax as an ingredient, so it is easier and cheaper to produce, and also such fuel has a more intense and longer combustion than coffee grounds-based fuel that uses wax as an ingredient. The disadvantage is the relatively high cost of vegetable fat and similar products, which can affect the overall retail value.

There is also another composition of a solid fuel based on coffee. The present invention [13] is a solid combustible fuel composition, the main part of which is represented by dry spentcoffee grounds formed into high-density pellets, synthetic logs or other products for fueling a fire. A homogeneous mixture containing at least 50% coffee and 30% or less by weight of a combustible binder is pressed and extruded in the form of logs.

The solid fuel production process involves the initial drying of the spent coffee grounds to the optimal moisture content, then any required additives (paraffin binders) are mixed with particles and the resulting mixture is given the desired shape under pressure. The mixture is compressed to a density of 650 to 1250 kg/m3

The present composition has the following advantages: the used coffee grounds have a higher calorific value than dry hardwood, as well as a higher ratio of volatile and bound carbon; the composition is a homogeneous mixture with a homogeneous particle size distribution.

There is also a solid fuel composition based on coffee and sawdust. Patent [14] is a solid fuel composition of spent coffee grounds and/or waste green coffee beans, sawdust and wax binder for the manufacture of firewood to provide better flame output power, and a sound similar to the sound of natural wood burning. The fuel composition is produced by combining coffee waste (coffee grounds or green coffee bean waste, or any combination thereof in dried or wet form) with sawdust (any wood-based particles, including sawdust, flat chips, wood chips, crushed fiberboard, crushed wax plate, shredded paper, etc.) and a combustible wax binder (any petroleum or vegetable wax, which is a solid substance at temperatures below 45°C and almost completely burns in case of ignition). The component of coffee waste is added to a container for mixing in an amount from 1–50% of the total mass of the fuel composition. The combustible wax binder, in an amount from 35–65% by weight of the entire fuel composition, is melted in a separate container. Sawdust is added to the mixing container and mixed with the coffee waste. After that, the melted hot wax binder is added, and the mixture is stirred to disperse the wax completely. Then the fuel composition is fed into an extruder equipped with a nozzle suitable for the extrusion of logs, and the fuel composition is extruded and cut into segments of the appropriate length.

There is also an invention [15], which is compressed products, usually in the form of briquettes and/or pellets that include substantial amounts of biomass as raw materials. These products can be used in co-firing powerplants, for animal bedding, in absorbent products, in landscaping and home heating. The compressed base consists of biomass and a second component, which contains another material (it may optionally be biomass), acting as a binder. The biomass can be represented by soybean planting material, sage, wood products, corn and sunflower planting material, various paper and cardboard products. The second component may include starch, plastic, fish oil, bicarbonate of soda, lime, paraffin, vegetable oil, coffee grounds and animal fat.

The accredited shared core facilities of St. Petersburg Mining University has developed a composition for the preparation of biofuel pellets for various types of powerplants.

The following additives were considered as a binder: starch, microcellulose, sugar syrup and crushed cardboard and paper waste. These binders and spent coffee grounds were mixed in proportions 1:99, 2:98, 5:95, 10:90 and 20:80, and the resulting mixtures were tried to be pressed into pellets using a Carver 4350L manual press. By experimental way, it was found that only cardboard and paper have the necessary adhesive properties in order for the resulting mixture to be pressed into pellets and retain its shape (Table 7).

Table 7

Selection of a binder
Binder	The binder content of the composition, %
Binder	1	2	5	10	20
Starch	-	-	-	+	+
Microcellulose	-	-	-	+	+
Sugar syrup	-	+	+	-	-
Shredded cardboard and paper waste	+	+	+	+	+
*provided by the authors
Note: "+" - the mixture can be pressed into pellets, "-" - the mixture cannot be pressed into pellets

To form strong pellets, a binder was added to the dried spent coffee grounds (Fig. 3). As a binder, shredded waste paper and cardboard without impregnation and coatings, unpolluted, (FCCO code 40510000000) belonging to hazard class V are used. Waste paper and cardboard are formed as a result of unpacking raw materials and equipment from cardboard containers and in the course of office work. Paper and cardboard waste is formed as a result of unpacking of raw materials, materials and equipment from cardboard containers and in the course of clerical activities and office work.

^{*provided by the authors}

Waste paper and cardboard are crushed in a shredder to a particle size of no more than 5 mm. Then the dried spent coffee grounds are mixed with crushed paper and cardboard waste in a powder mixer or in a crusher. Coffee and the binding component were taken in proportions 100:0, 99:1, 98:2, 95:5, 90:10 and 80:20 in order to identify the optimal ratio.

The resultant mixture was pressed into pellets with a diameter of 12 mm and a length of 20 ± 1 mm using a Carver 4350 L manual press with a press power of 3 tons.

The destruction of pellets during their transportation and loading and unloading reduces the efficiency of their use during combustion and makes it difficult to automate the process of fuel supply to combustion plants. In this regard, the mechanical strength of the pellets obtained was determined using a drum to determine the mechanical strength in accordance with GOST 34090.1–2017 (ISO 17831-1:2015). It was estimated as 93–98% with 5–10% of binder (Table 8).

Table 8

The test results of mechanical properties of pellets from pressed biomass*
Binder content	0%	1%	2%	5%	10%	20%
Mechanical strength, %	-*	96.2	93.4	92.7	98.6	95.5

*provided by the authors

Next the thermal characteristics of pellets were studied. Thermogravimetric analysis of the obtained biofuel pellets from spent coffee grounds and waste paper and cardboard was carried out using the LECO TGA-701 thermogravimetric analyzer. Determination of moisture content, ash content and yield of volatile substances was carried out in accordance with GOST R 53357 − 2013 (ISO 17246:2010).

The highest specific heat of combustion of pellets was also measured using a calorimeter for determination of caloric content of solid fuels and the amount of thermal energy (IKA C 2000) (Table 9). The highest specific heat of combustion of pellets was 22–24 MJ/kg (in terms of the lowest heat of combustion − 20.2–22.2 MJ/kg). These are relatively high values. Spent coffee grounds can therefore be successfully used as raw materials for obtaining solid fuel composition and manufacturing biofuel pellets.

Table 9

Test results of thermal properties test of pellets from pressed biomass*
Binder content	0%	1%	2%	5%	10%	20%
Moisture content, %	7.4	5.7	5.3	5.4	6.9	4.3
Ash content, %	1.8	2.0	2.0	2.1	2.3	2.5
Volatiles, %	80.6	79.7	79.9	80.0	80.7	80.6
The highest specific heat of combustion, MJ/kg	22.6	24.0	24.0	23.6	23.3	22.0
Lowest heat of combustion, MJ/kg	20.8	22.2	22.2	21.8	21.5	20.2

*provided by the authors

Next, the composition of the released gases formed during the combustion of fuel pellets from compressed biomass was determined. The samples were combusted in the furnace of the LECO CHN-628S analyzer, the resulting exhaust gases were identified using the ECOLAB gas analyzer, designed for automatic continuous or periodic measurement of concentrations of harmful substances in atmospheric air, in the air of the working area and in technological processes in order to protect the environment. The gas analyzer is equipped with sensors for measuring concentrations of carbon monoxide, methane, ammonia, hydrogen sulfide, nitrogen monoxide, nitrogen dioxide and aliphatic saturated hydrocarbons (C1-C10) (Table 10).

Table 10

Test results of properties of pellets from pressed biomass during combustion*
Binder content	0%	1%	2%	5%	10%	20%
CO₂, mg/g	-**	142.15	144.23	156.44	164.81	185.1
CO, mg/g	-**	0.21	0.21	0.21	0.23	0.24
NO, mg/g	-**	0.58	0.58	0.6	0.61	0.65
NO₂, mg/g	-**	0.21	0.22	0.22	0.24	0.27
** dried spent coffee grounds without the addition of a binder cannot be pressed
*provided by the authors

Recycling coffee industry waste can bring significant environmental and economic benefits. In general, the studied coffee samples differ slightly in the parameters studied and all varieties of spent coffee grounds can potentially be used as raw materials for biofuel pellets. However, it is most advisable to use the spent mixture formed in espresso machines, since it is the most accessible and easy to collect, and also has good fuel characteristics.

The data obtained as a result of thermogravimetric and elemental analysis of combustion in a calorimeter were checked for the normality of the distribution using Lilliefors and Shapiro-Wilkes tests' criteria (Table 11). The evaluation of the differences between the samples depending on the type of coffee and the size of the grinding was carried out using the ANOVA one-factor analysis of variance for the normal distributed parameters and the Kraskel-Wallis criterion for parameters that do not obey the normal distribution law (Table 12).

Table 11

Checking the distribution of values of measured parameters for normality*
Variable	Lilliefors test	The Shapiro–Wilk test
Moisture	p > .20	0.416331
Volatiles	p > .20	0.445170
Ash	p < .05	0.045795
Ash recalculated to dry basis	p < .05	0.045097
Volatiles recalculated to dry basis	p > .20	0.627864
Carbon, %	p < .10	0.011560
Hydrogen, %	p > .20	0.201074
Nitrogen, %	p < .05	0.002611
Heat of combustion	p < .05	0.025884
*provided by the authors
Note: the values of p-value < 0.05 are marked in red, which allow rejecting the hypothesis of the normality of the distribution

Table 12

Analysis of comparison of parameters depending on the type of coffee or grinding*
Criteria for checking the equality of the samples	Predictor	Moisture	Volatiles	Ash	Ash recalculated to dry basis	Volatiles recalculated to dry basis	Carbon	Hydrogen	Nitrogen	Highest specific heat of combustion, J/g
Kruskal–Wallis test, p	Type of coffee			0.02	0.03		0.00		0.17	0.12
Kruskal–Wallis test, p	Grinding			0.32	0.32		0.98		0.20	0.34
One-way ANOVA, p	Type of coffee	0.17	0.00			0.00		0.00
One-way ANOVA, p	Grinding	0.71	0.52			0.61		0.90
*provided by the authors
Note: the values of p-value < 0.05 are marked in red, which allows rejecting the hypothesis that the samples belong to one general population

Depending on the size of the grinding, the sample parameters do not significantly differ in any of the parameters. The volatile components content is significantly lower in decaffeinated used coffee. The ash content is significantly lower in dark roasted coffee. The carbon content is significantly higher in decaffeinated samples and lower in light roasted coffee samples. Decaffeinated coffee also had a higher content of hydrogen and nitrogen compared to coffee with caffeine. Dark roasted coffee has the highest values of the highest heat of combustion, significantly lower values are characteristic of light roasting.

Thus, the size of the grinding does not affect the characteristics of the spent coffee. Despite the revealed statistically significant differences in the characteristics of the samples, it can be concluded that it is inappropriate to separate the collection of spent coffee grounds by roasting types and the presence or absence of caffeine. In a mixture of three types of spent coffee, decaffeinated coffee and light-roasted coffee make up a small fraction of the total mass of the grounds (up to 10–15%), so the characteristics of the coffee mixture are slightly inferior to the spent dark-roasted coffee.

The results of analyses and experiments show that pellets from spent coffee grounds have a high fuel potential and mechanical strength, low ash and moisture content. For comparison, in the paper by Pashkevich, M.A., Petrova, T.A., Sverchkov, I.P [16], the lowest specific heat of combustion, ash content, the content of the main fuel elements and the ash content in the watered waste of coal enrichment were determined. It was revealed that the watered coal waste contains about 60% of carbon, 23% of ash, and the lowest specific heat of combustion of the coal sample is 18.5 MJ/kg. The authors found that the most effective way to dispose of the coal waste under consideration is to use it as a water-coal fuel at power stations.

During the combustion of pellets, the amount of CH₄, H₂S, SO₂ and hydrocarbons released was below the detection limit, and the amount of CO₂, CO, NO and NO₂ generated per unit weight is less than that of traditional organic fuels.

It is established that the most optimal content of the binder is 5–10%. When adding a smaller amount of crushed cardboard and paper, it is difficult to control the uniformity of mixing coffee and a binder, and when adding more binder, the characteristics of biofuel pellets decrease significantly: the higher specific heat of combustion decreases, more carbon dioxide and nitrogen oxides are released, ash content increases.

According to the results of testing samples of pellets from pressed biomass, a classification was assigned according to the following parameters: origin (3, fruit biomass), diameter D and length L, mm (D12, D (12 ± 1.0) mm and 3.15 mm < L⩽50 mm), moisture content, M (M08,⩽8%), ash content, A (A3.0, ⩽3.0%), mechanical strength, DU (DU95.0-92.0, < 95,0%), the yield of volatile matters, VM (81%) in accordance with GOST 33103.1–2017 "Solid biofuel. Technical characteristics and fuel classes" (introduced 01.01.2018).

The development of global initiatives that contribute to the creation of waste streams with an increase in their value, also known as the increase the cost of waste, has become one of the main strategies for managing food waste while increasing resource efficiency and reducing environmental pressure [1].

Energy supply from biomass resources not only increases fuel diversification, but also reduces air pollution, since biomass resources contain relatively low sulfur and heavy metal content compared to fossil fuels such as coal [10].

Based on the results of the work carried out, it can be concluded that the spent coffee grounds have low ash content, high carbon, hydrogen and nitrogen content. By adding the binder to the dried spent coffee grounds, durable biofuel pellets were formed which have a high specific heat of combustion and mechanical strength. The use of spent coffee grounds as raw material for biofuel pellets can be considered as an effective way of recycling coffee industry waste and increasing the valorisation of spent coffee grounds.

Based on the results of the conducted research, a solution is proposed for the disposal of spent coffee grounds and waste paper and cardboard by manufacturing a composition for environmentally friendly biofuel pellets. This approach may be of interest to many coffee industry companies. For example, in January 2020, Starbucks announced a "long-standing commitment to become a resource-saving company," and one of the strategies was to find better ways to manage their waste [17]. Using spent coffee grounds as biofuel can be an excellent option for sustainable waste management for the company along with other environmental initiatives.

The work was carried out on the basis of the laboratory and experimental base of the accredited shared core facilities of high-tech equipment of St. Petersburg Mining University.

Funding The research was carried out at the expense of a subsidy for the fulfillment of the state task in the field of scientific activity for 2021 No. FSRW-2020-0014.

Data availability Data used in this paper was derived from publicly available information and the result of ongoing research. No personal or sensitive information was used.

Declarations

Conflict of interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Human or animal rights No animals were involved in this study.

Consent for participate No human subjects were involved in this study.

Consent for publication No human subjects were involved in this study.

Authors and Afliations

Yuri D. Smirnov¹, Ivan P. Sverchkov¹, Rushania I. Gabdullina¹

¹Saint-Petersburg Mining University, Saint Petersburg, Russian Federation

e-mail: [email protected]

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Biofuel pellets from spent coffee grounds

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