Open AccessArticle

Potential for Using Composts Produced from Agri-Food Industry Waste as Biocomponents of Liquid and Solid Fuels

Aneta Sienkiewicz

Paweł Cwalina

^1,*

Sławomir Obidziński

Małgorzata Krasowska

¹,

Małgorzata Kowczyk-Sadowy

Alicja Piotrowska-Niczyporuk

and

Andrzej Bajguz

Department of Agri-Food Engineering and Environmental Management, Bialystok University of Technology, Wiejska 45E, 15-351 Białystok, Poland

Department of Biology and Plant Ecology, Faculty of Biology, University of Bialystok, Ciolkowskiego 1J, 15-245 Bialystok, Poland

Author to whom correspondence should be addressed.

Energies 2024, 17(24), 6412; https://doi.org/10.3390/en17246412

Submission received: 20 November 2024 / Revised: 13 December 2024 / Accepted: 18 December 2024 / Published: 19 December 2024

(This article belongs to the Special Issue Advanced Studies in Thermochemical Conversion of Solid Wastes into Energy Products)

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Abstract

The growing awareness of the depletion of fossil fuels and numerous environmental issues have led to increased interest in finding natural components that can be used to produce various types of fuels. In this study, composts made from the organic fraction of agri-food waste (i.e., two composts produced in a bioreactor and one obtained from a Municipal Waste Disposal Facility) were evaluated for the first time as potential sources of additives for fuel production. The presence of fatty acid methyl esters was determined using gas chromatography–mass spectrometry (GC-MS/SIM), while the calorific value and heat of combustion of the samples were measured in accordance with the PN-EN ISO 1928:2002 standard using a calorimeter. Chromatographic studies identified the presence of 33 compounds, predominantly unsaturated esters. The highest ester content was noted in the compost obtained from the company, while the lowest content was found in the compost containing grass, buckwheat husk, and apple pomace. Of the studied raw materials, the highest calorific value and heat of combustion on a dry matter basis were observed for the compost containing grass, buckwheat husk, and apple pomace, while the lowest values were recorded for the compost obtained from the company. Based on the obtained results, it can be concluded that composts could serve as biocomponents of fuels.

Keywords:

organic fertilizers; post-production residues; biofuel; solid fuels; circular economy

1. Introduction

In the face of global challenges related to climate change, the depletion of natural resources, and growing energy needs, the search for sustainable energy sources has become a priority for many countries [1]. Sustainable production of biofuels from organic waste is becoming one of the most promising solutions [2,3]. Not only does bio-waste processing help reduce the amount of waste going to landfills, but it also enables the production of energy in the form of biogas, bioethanol, or biodiesel [4,5]. Biocomponents obtained from composts are ecological energy sources that can support sustainable development and reduce dependence on fossil fuels [6,7].

Composting is a natural process involving the decomposition of organic materials, transforming waste into a valuable fertilizer. The process involves plant residues (e.g., grass or leaves), kitchen waste (e.g., vegetable and fruit leftovers), sawdust, paper, and other residues from agri-food processing. The finished compost can be used as an organic fertilizer for plants, enriching the soil with nutrients and improving its structure. Thus, composting is not only a way to reduce waste but also to improve soil quality and support plant growth [8,9]. In addition to their traditional use as fertilizers, composts can also be utilized as biocomponents in the production of liquid and solid fuels [10]. In this context, it is necessary to consider the potential for various uses of composts, as well as their environmental and economic benefits.

Composts made from agri-food waste are rich in nutrients, but their properties and compositions may vary depending on the type of materials used. They contain, among others, carbon, nitrogen, phosphorus, and potassium, which makes them a valuable raw material [11]. However, where composts contain contaminants such as heavy metals, microplastics, or toxins, or where excess compost is a problem, incineration may be a more appropriate option than soil application. In the context of biofuels, their energy properties and the content of fatty acid methyl esters (FAMEs) may contribute to improving the combustion efficiency [12]. These esters are derivatives of fatty acids and may occur in composts in various compositions, especially when composts contain materials rich in fats. These esters may come from kitchen scraps or organic materials containing fats, e.g., seeds [13]. The presence of FAMEs in composts may affect the fertilizing value of compost, in which case they are a source of energy for microorganisms that decompose organic matter and may affect the structure of the compost and the water retention capacity. It is important to strive for a balanced composition in the composting process, avoiding excess fatty materials, which may disturb biological processes [14,15].

Composts with the appropriate content of fatty acid methyl esters can be used as solid biofuels in the process of producing pellets or briquettes [16]. In terms of liquid biofuels, composts from agri-food waste can be processed through fermentation or transesterification, which allows for the production of biodiesel. Biodiesel production from vegetable oils is mainly carried out through transesterification. The process consists of the oil reacting with alcohol (usually methanol or ethanol) in the presence of a catalyst. As a result of this process, fatty acid methyl esters (biodiesel) are produced, with glycerin as a by-product. Biodiesel can be used as fuel in diesel engines, often in mixtures with traditional diesel oil. Its use helps reduce emissions of CO2 and other pollutants, including nitrogen oxides and particulate matter [17,18,19]. Therefore, the content of fatty acid methyl esters in composts may influence their properties, but their sustainable use remains important [20,21,22].

For the reasons discussed above, the composting process not only enables the efficient management of organic waste but also transforms it into a valuable product that can be used as biofuel. The use of composts as biocomponents for fuels contributes to the reduction of greenhouse gas emissions, as it allows for the recycling of organic waste and the reduction of its storage in landfills. In addition, composts support soil biodiversity and improve soil quality, which has a positive impact on ecosystems [23].

There have been some studies on the content of fatty acid methyl esters (FAMEs) in agro-food by-products, such as grape by-products (e.g., pomace, stalks, bunches) [24,25], potato, carrot, orange, and banana peels [26,27,28], and brewer’s spent grain [29,30]. However, only a few studies have addressed the content of FAMEs in composts [31]. Witaszek et al. [32] examined the calorific value of four composts obtained from grass, walnut, reed, and a mixture of leaves and silage. The available data suggest that the use of compost for energy purposes through combustion is possible [33,34].

This article aims to investigate the possibilities of using composts obtained from agro-food waste in the production of biocomponents, focusing on their chemical properties, ecological benefits, and challenges related to their use in the energy industry. In this study, composts produced from the organic fraction of waste obtained from the agro-food sector (i.e., two composts produced in a bioreactor and one compost obtained from the Municipal Waste Disposal Plant) were assessed as potential sources of additives for fuel production.

2. Materials and Methods

2.1. Composts

The composts were formulated in a laboratory bioreactor with engineered aeration using the organic fraction of agri-food industry waste and residues from fruit and vegetable processing (Table 1). The composted wastes were collected from a facility located in the Podlaskie Voivodeship (Poland).

Table 1 presents the compositions of the tested composts, both those produced in a bioreactor and those obtained from the company. To evaluate the impact of thermal processing, the organic compost was additionally subjected to the process of pelleting under laboratory conditions. A detailed description of the composting process is presented in the study by Sienkiewicz et al. [35]. The compost blends were formulated considering their fundamental characteristics, such as pH, dry matter content, and contents of organic matter and elements such as nitrogen, phosphorus, potassium, and carbon left over from the waste processing. Details on the physical and chemical parameters of specific agri-food processing residues and the obtained composts have been previously documented in the literature [35].

2.2. Fatty Acid Methyl Ester Analysis

For the measurement of the FAMEs, 0.5 g of compost was extracted with hexane in the presence of a methanol–potassium hydroxide (KOH) mixture acting as a catalyst. A total of 33 FAMEs were identified in the compost samples using gas chromatography–mass spectrometry in the selected ion monitoring mode (GC-MS/SIM) (Table 2). A detailed description of the transesterification procedure and analytical methods is presented in the study by Sienkiewicz et al. [12]. Four replicates were performed for each compost sample.

2.3. Determination of Calorific Value and Heat of Combustion

The calorific value and the heat of combustion were determined according to the PN-EN ISO 1928:2002 [36] standard using a KL-12Mn calorimeter (Bydgoszcz, Poland) from Precyzja-Bit.

The calorific value and the heat of combustion were determined using Equation (1):

L H V = H H V - 24.43 (w + 8.94 H^{a}) [M J \cdot {k g}^{- 1}]

(1)

where

LHV—calorific value (lower heating value) [MJ∙kg⁻¹];
HHV—heat of combustion (higher heating value) [MJ∙kg⁻¹];
w—moisture content of the sample [%];
H^a—hydrogen content of the sample [%];
24.43—coefficient accounting for the heat of water vaporization at 25 °C in pellets with a 1% water content;
8.94—coefficient accounting for the stoichiometry of the hydrogen combustion reaction (quantitative changes).

2.4. Statistical Analysis

The presence of significant differences in the FAMEs, calorific value, and heat of combustion were assessed using one-way analysis of variance (ANOVA). The normality and homogeneity of variance were checked prior to ANOVA using the Shapiro–Wilk and Levene tests, respectively. Differences among the mean values were determined using Tukey’s honest significant difference (HSD) test. The level of statistical significance was set at p < 0.05. Principal component analysis (PCA) of the FAMEs was performed to build a model that explains the relationships among the analyzed variables. A resulting biplot was created using the two main components, i.e., PC1 and PC2, which together explain 73.5% of the total variance. All statistical analyses of the data were performed using STATISTICA 13.3 software (TIBCO Software Inc., Palo Alto, CA, USA).

3. Results and Discussion

3.1. Identification and Composition of the Fatty Acid Methyl Esters

Analysis using gas chromatography–mass spectrometry in the selected ion monitoring mode (GC-MS/SIM) quantified the presence of up to 33 out of the 37 analyzed FAMEs. In all the analyzed compost samples, 9 MUFAs, 10 PUFAs, and 14 SFAs were detected (Table 3, Table 4 and Table 5).

The compositional analysis of the studied compost samples revealed that the amount of MUFA methyl esters (26.48–51.76%) exceeded that of PUFA and SFA fatty acids (Figure 1). The highest share of MUFAs was identified in the organic compost-pellets (51.76%), whereas the lowest MUFA amount was observed in the organic compost (26.48%). MUFAs are fatty acids with one unsaturated carbon bond. The most common ones are oleic acid (18:1n9) and palmitoleic acid (C16:1n7), and there are many rarer types of MUFAs [37]. The analyzed composts also exhibited distinct shares of PUFAs and SFAs. The highest share of PUFAs was noted in the garden compost (39.43%), while the lowest was observed in the buckwheat husk compost (23.19%). Some agricultural by-products are potential sources of 18-carbon PUFAs, particularly linoleic acid (C18:2n6), a precursor to arachidonic acid. The highest share of SFAs was noted in the buckwheat husk compost (49.35%), while the lowest SFAs were observed in the organic compost-pellets (14.01%). According to Ferreira [27], polyunsaturated fatty acids (PUFAs) are the dominant group in grape pomace (72.7%), grape bunches (54.3%), and brewer’s spent grain (59.0%). In carrot peels, monounsaturated fatty acids (MUFAs, 47.3%) predominate, while in grape stems (46.2%), sediments (from 50.8 to 74.1%), and potato peels, saturated fatty acids (SFAs, 77.2%) are the most abundant.

The dominant FAMEs included C18:1n9c fatty acid, as well as C18:3n6 and C17:0 (Table 3, Table 4 and Table 5). The organic compost-pellets exhibited the highest content of C18:1n9c, while the organic compost had the highest concentrations of C18:3n6 and C17:0. Other FAMEs, i.e., C14:1, C17:1, C18:1n9t, C22:1n9, C24:1n9, C20:2, C20:3n6, C20:4n6, C20:5n3, C22:2n6, C22:6n3, C10:0-C16:0, C18:0, and C20:0-C24:0, contributed minimally to the overall FAME composition, as reflected by their low contents (i.e., less than approx. 100 µg∙g⁻¹ _dw, Table 3, Table 4 and Table 5).

The highest concentration of total FAMEs was found in the organic compost-pellets (2055.33 µg∙g⁻¹ _dw, Table 6), while the lowest concentration was determined for the buckwheat husk compost (443.68 µg∙g⁻¹ _dw, Table 6). The total FAME contents in the garden compost and organic compost were at similar levels (Table 6).

Bekier et al. [31] found that the total amount of fatty acids significantly decreased during composting. They noted an increased share of saturated fatty acids, which indicates their greater resistance to decomposition compared to unsaturated forms.

Hachicha et al. [38] observed a reduction in the lipid fraction by at least 95% when composting olive mill sludge with poultry manure. Unsaturated fatty acids, especially polyunsaturated fatty acids, were the most degraded (55% reduction), leading to an increase in the content of saturated fatty acids.

The composition of fatty acid methyl esters (FAMEs) derived from cherry stone waste showed a high ratio of unsaturated to saturated fatty acids [39]. Similarly, herbal waste contained a higher amount of unsaturated FAMEs compared to saturated ones, where the main polyunsaturated FAME was linoleic acid, while the dominant saturated FAME was palmitic acid [12].

PCA analysis enabled the clustering of analyzed compost samples, preserving a high level of explained variance. In this analysis, the number of variables was reduced to the two principal components (PC1 and PC2, respectively), which may suggest that the dataset of 33 FAMEs is highly correlated and reducible (Figure 2). Comparing the sample positions on the graph with the component forms and factor loadings revealed that the buckwheat husk compost (with negative coordinates on the first axis) was characterized by higher contents of certain fatty acids, i.e., C10:0-C14:0, C14:1, C20:4n6, C22:0, C22:6n3, and C23:0, based on their factor loadings along the first axis. The organic compost-pellets (with positive coordinates on the second axis) were characterized by higher contents of C18:0, C18:1n9c, C18:2n6t, C18:2n6c, C20:0, C20:2, C21:0, and C24:0, based on their factor loadings along the second axis. On the other hand, garden compost and organic compost (with positive coordinates on the first axis) were characterized by a higher content of C18:3n6 based on the factor loading of this fatty acid on the first axis.

3.2. Calorific Value and Heat of Combustion

Table 7 presents the heat of combustion and calorific value results for the tested composts.

The results show that the buckwheat husk compost exhibited the highest calorific value (17.24 MJ∙kg⁻¹) and heat of combustion (18.8 MJ∙kg⁻¹). Such high values of the energy properties of the compost are due to the low ash content and the slight decomposition of the buckwheat husk. According to Joka-Yildiz et al. [40], who studied the energy suitability of buckwheat husk, its calorific value was 17.01 MJ∙kg⁻¹, while its heat of combustion was 18.44 MJ∙kg⁻¹. A slightly higher value of heat of combustion (17.79 MJ∙kg⁻¹) was found for the buckwheat husk studied by Kulokas et al. [41], while the ash content was 3.87%.

Compared to the buckwheat husk compost, the organic and garden composts were characterized by significantly worse energy properties. The organic compost exhibited a heat of combustion of 10.09 MJ∙kg⁻¹ and a calorific value of 9.54 MJ∙kg⁻¹. The garden compost had the lowest calorific value and heat of combustion, at 8.32 and 8.81 MJ∙kg⁻¹, respectively. The recommended range for energy recovery from solid waste suggested in other studies is 7.5 to 12.5 MJ∙kg⁻¹ [42,43]. Fetene et al. [43], who conducted a study on the possibility of managing various solid wastes for energy purposes, reported that garden waste had a HHV of 16.4 MJ∙kg⁻¹ and a LHV of 5.2 MJ∙kg⁻¹. They also investigated the suitability of food waste for energy purposes, finding that it had a lower HHV (11.1 MJ∙kg⁻¹) compared to garden waste, while the LHV was 1.6 MJ∙kg⁻¹, due to the high moisture content of the selected waste. According to Budzyński and Bielski [44], the energy values of rapeseed, mustard, and linseed straw waste are 16–16.5 MJ∙kg⁻¹.

The low LHV of the tested composts is due to the very high ash content of >55% in two of the cases. Consequently, these composts cannot be used as fuel without pretreatment to reduce the non-combustible content.

4. Conclusions

FAME identification was performed to study composts produced from the organic fraction of waste obtained from the agri-food sector as potential sources of additives in fuel production. The presence of 33 compounds was demonstrated in the tested composts, while the most abundant group was unsaturated esters. The organic compost-pellets showed the highest total concentration of FAMEs, while the buckwheat husk compost exhibited the lowest concentration. The buckwheat husk compost had the highest calorific value and heat of combustion, as well as the lowest ash content. In contrast, the organic and garden composts exhibited significantly poorer energy properties and, therefore, cannot be used as fuel without preliminary processing to reduce the content of non-combustible substances. The research findings suggest that the compost sourced from a local company could serve as a natural additive in liquid fuel production, whereas composts made from grass, buckwheat husk, and apple pomace could be utilized as a biocomponent for solid fuels. In summary, the best solution is to use compost as fertilizer wherever possible to support soil regeneration and carbon sequestration. Incineration or other methods of energy recovery should be considered as a last resort for low-quality waste or unused surpluses.

Author Contributions

Conceptualization, A.S. and S.O.; data curation, A.S., A.P.-N., P.C. and M.K.-S.; formal analysis, A.S. and A.B.; investigation, M.K.-S., P.C. and M.K.; methodology, S.O., P.C., A.S. and A.P.-N.; resources, M.K. and A.B.; supervision, S.O. and A.S.; validation, S.O., A.P.-N., A.S., M.K.-S. and A.B.; visualization, A.S., M.K.-S. and P.C.; writing—original draft, M.K.-S., M.K. and P.C.; writing—review and editing, M.K.-S. and A.S. All authors have read and agreed to the published version of the manuscript.

Funding

This work was carried out as part of a team project no. WZ/WB-IIS/5/2023 and was financed by the Ministry of Education and Science as part of a grant for maintaining research potential awarded to the Faculty of Civil Engineering and Environmental Sciences, Bialystok University of Technology.

Data Availability Statement

The data are contained within the article.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Fatty acid methyl ester composition of the analyzed composts obtained from agri-food industry waste.

Figure 2. Biplot of FAME contents in the compost samples, showing the first two principal components (PC1 and PC2) of the PCA model that together explain 73.5% of the total variance, i.e., 41.85% and 31.64% for PC1 and PC2, respectively. The blue biplot vectors indicate the strength and direction of factor loading for all the analyzed fatty acids. 1—garden compost, 2—buckwheat husk compost, 3—organic compost, 4—organic compost-pellets.

Table 1. Composition of the analyzed composts.

Compost	Composition
Produced in a bioreactor
Garden compost	Green waste (grass, leaves, branches)
Compost from agricultural and food processing residues	Grass, buckwheat husk, fruit pomace
Obtained from company
Organic compost	Green waste
Organic compost-pellets	Green waste

Table 2. FAME standards used in GC-MS analysis of compost samples.

Type of Fatty Acid	Systematic Name	Common Name of FAME	Abbreviation
MUFA	Myristoleic acid methyl ester	Myristoleic acid	C14:1
	cis-10-Pentadecanoic acid methyl ester	Pentadecanoic acid	C15:1
	9-Hexadecenoic acid methyl ester	Palmitoleic acid	C16:1
	cis-10-Heptadecenoic acid methyl ester	Heptadecenoic acid	C17:1
	trans-9-Octadecenoic acid methyl ester (Z)	Elaidic acid	C18:1n9t
	9-Octadecenoic acid methyl ester I	Oleic acid	C18:1n9c
	cis-11-Eicosenoic acid methyl ester	Gondoic acid	C20:1
	13-Docosenoic acid methyl ester (Z)	Erucic acid	C22:1n9
	15-Tetracosenoic acid methyl ester (Z)	Nervonic acid	C24:1n9
PUFA	9,12-Octadecadienoic acid methyl ester (E,E)	Linolelaidic acid	C18:2n6t
	9,12-Octadecadienoic acid methyl ester (Z,Z)	Linoleic acid	C18:2n6c
	all-cis-6,9,12-Octadecatrienoic acid	γ-Linolenic acid	C18:3n6
	9,12,15-Octadecatrienoic acid methyl ester (Z,Z,Z)	Linolenic acid	C18:3n3
	cis-11,14-Eicosadienoic acid methyl ester	Eicosadienoic acid	C20:2
	cis-11,14,17-Eicosatrienoic acid methyl ester	Eicosatrienoic acid	C20:3n3
	cis-8,11,14-Eicosatrienoic acid methyl ester	Dihomo-γ-linolenic acid	C20:3n6
	5,8,11,14-Eicosatetraenoic acid methyl ester (all-Z)	Arachidonic acid	C20:4n6
	cis-5,8,11,14,17-Eicosapentaenoic acid methyl ester	Eicosapentaenoic acid	C20:5n3
	cis-13,16-Docasadienoic acid methyl ester	Docosadienoic acid	C22:2n6
	4,7,10,13,16,19-Docosahexaenoic acid methyl ester (all-Z)	Cervonic acid	C22:6n3
SFA	Butyric acid methyl ester	Butyric acid	C4:0
	Hexanoic acid methyl ester	Caproic acid	C6:0
	Octanoic acid methyl ester	Caprylic acid	C8:0
	Decanoic acid methyl ester	Capric acid	C10:0
	Undecanoic acid methyl ester	Undecylic acid	C11:0
	Dodecanoic acid methyl ester	Lauric acid	C12:0
	Tridecanoic acid methyl ester	Tridecylic acid	C13:0
	Tetradecanoic acid methyl ester	Myristic acid	C14:0
	Pentadecanoic acid methyl ester	Pentadecylic acid	C15:0
	Hexadecanoic acid methyl ester	Palmitic acid	C16:0
	Heptadecanoic acid methyl ester	Margaric acid	C17:0
	Octadecanoic acid methyl ester	Stearic acid	C18:0
	Eicosanoic acid methyl ester	Arachidic acid	C20:0
	Heneicosanoic acid methyl ester	Heneicosylic acid	C21:0
	Docosanoic acid methyl ester	Behenic acid	C22:0
	Tricosanoic acid methyl ester	Tricosylic acid	C23:0
	Tetracosanoic acid methyl ester	Lignoceric acid	C24:0

MUFA—monounsaturated fatty acid, PUFA—polyunsaturated fatty acid, SFA—saturated fatty acid.

Table 3. MUFA contents in composts obtained from agri-food industry waste. The data represent the means (n = 4) ± standard deviations. The lowercase letters indicate statistical differences at p < 0.05 according to Tukey’s post hoc test.

MUFA	Garden Compost	Buckwheat Husk Compost	Organic Compost	Organic Compost-Pellets
MUFA	[µg∙g⁻¹ _dw]
C14:1	30.97 ± 1.35 a	48.58 ± 1.46 b	38.22 ± 6.88 a	32.18 ± 0.72 a
C15:1	120.66 ± 2.92 c	5.90 ± 0.61 a	80.18 ± 3.93 b	6.55 ± 0.51 a
C16:1	252.56 ± 5.63 d	4.30 ± 0.16 a	28.19 ± 3.56 b	97.16 ± 3.69 c
C17:1	15.56 ± 0.30 c	3.44 ± 0.04 a	3.75 ± 0.42 a	4.97 ± 0.28 b
C18:1n9t	60.17 ± 2.78 d	10.09 ± 0.50 b	6.34 ± 0.59 a	22.55 ± 0.55 c
C18:1n9c	50.63 ± 1.73 b	21.83 ± 3.23 a	200.36 ± 10.91 c	879.25 ± 16.83 d
C20:1	104.65 ± 2.66 c	4.04 ± 0.19 a	93.49 ± 5.28 b	4.26 ± 0.18 a
C22:1n9	4.01 ± 0.11 a	4.48 ± 0.80 a	2.55 ± 0.06 b	3.86 ± 0.74 a
C24:1n9	28.24 ±1.79 c	19.19 ± 0.26 b	12.54 ± 0.76 a	13.16 ± 0.32 a

Table 4. PUFA contents in composts obtained from agri-food industry waste. The data represent the means (n = 4) ± standard deviations. The lowercase letters indicate statistical differences at p < 0.05 according to Tukey’s post hoc test.

PUFA	Garden Compost	Buckwheat Husk Compost	Organic Compost	Organic Compost-Pellets
PUFA	[µg∙g⁻¹ _dw]
C18:2n6t	49.03 ± 3.54 c	7.59 ± 0.22 a	18.27 ± 2.17 b	142.16 ± 3.83 d
C18:2n6c	59.63 ± 3.26 c	7.85 ± 0.28 a	17.79 ± 1.26 b	138.34 ± 5.66 d
C18:3n6	393.89 ± 7.50 a	4.20 ± 0.38 b	476.63 ± 49.11 a	355.69 ± 163.13 a
C18:3n3	118.85 ± 5.45 c	4.59 ± 0.60 a	35.41 ± 2.73 b	5.17 ± 0.30 a
C20:2	1.75 ± 0.08 a	2.13 ± 0.24 a	1.52 ± 0.35 a	10.15 ± 1.15 b
C20:3n6	3.86 ± 0.15 a	3.95 ± 0.10 a	2.82 ± 0.22 b	3.36 ± 0.35 c
C20:4n6	14.23 ± 0.97 a	22.34 ± 0.40 c	15.89 ± 0.68 b	14.84 ± 0.43 a
C20:5n3	1.82 ± 0.11 ab	2.22 ± 0.03 b	1.64 ± 0.16 ab	1.61 ± 0.04 ab
C22:2n6	16.53 ± 0.87 a	19.47 ± 0.17 a	12.37 ± 0.41 a	12.99 ± 0.53 a
C22:6n3	20.81 ± 1.50 b	28.53 ± 0.10 c	19.02 ± 0.20 a	19.15 ± 0.28 a

Table 5. SFA contents in composts obtained from agri-food industry waste. The data represent the means (n = 4) ± standard deviations. The lowercase letters indicate statistical differences at p < 0.05 according to Tukey’s post hoc test.

SFA	Garden Compost	Buckwheat Husk Compost	Organic Compost	Organic Compost-Pellets
SFA	[µg∙g⁻¹ _dw]
C10:0	24.41 ± 0.69 a	36.26 ± 0.85 b	23.78 ± 0.55 a	24.10 ± 0.12 a
C11:0	10.22 ± 0.25 a	14.89 ± 0.19 b	10.66 ± 0.46 a	10.53 ± 0.41 a
C12:0	19.93 ± 0.47 a	30.21 ± 0.79 b	21.32 ± 0.92 a	21.06 ± 0.81 a
C13:0	9.50 ± 0.34 a	13.80 ± 0.25 c	10.15 ± 0.57 a	11.91 ± 0.22 b
C14:0	19.42 ± 0.55 a	28.04 ± 0.90 c	23.33 ± 0.94 b	18.77 ± 0.27 a
C15:0	1.55 ± 0.11 a	0.12 ± 0.01 a	34.77 ± 18.89 b	2.39 ± 0.12 a
C16:0	57.60 ± 2.86 c	1.37 ± 0.39 a	4.72 ± 0.54 b	1.12 ± 0.03 a
C17:0	167.51 ± 7.19 c	2.86 ± 0.05 a	483.90 ± 16.23 d	55.83 ± 25.24 b
C18:0	4.04 ± 0.14 c	1.17 ± 0.03 b	0.65 ± 0.20 a	12.70 ± 0.35 d
C20:0	35.44 ± 1.89 a	50.32 ± 0.89 c	43.81 ± 2.18 b	58.18 ± 0.89 d
C21:0	14.49 ± 0.53 a	23.12 ± 1.49 c	19.71 ± 1.12 b	37.18 ± 0.89 d
C22:0	7.34 ± 0.67 a	9.86 ± 0.54 b	7.39 ± 0.84 a	6.16 ± 0.43 a
C23:0	0.86 ± 0.11 a	1.46 ± 0.03 b	0.97 ± 0.13 a	1.01 ± 0.18 a
C24:0	5.45 ± 0.20 a	5.48 ± 0.30 a	6.10 ± 0.25 a	27.01 ± 1.65 b

Table 6. Sum of mean FAME content (± SD) in composts obtained from agri-food industry waste, with and without distinction for MUFAs, PUFAs, and SFAs.

Composts	∑ MUFAs ± SD	∑ PUFAs ± SD	∑ SFAs ± SD	∑ FAMEs ± SD
Composts	[µg∙g⁻¹ _dw]
Garden compost	667.46 ± 19.29	680.40 ± 23.43	377.75 ± 15.99	1725.61 ± 58.71
Buckwheat husk compost	121.85 ± 7.25	102.87 ± 2.53	218.96 ± 6.79	443.68 ± 16.57
Organic compost	465.61 ± 32.38	601.35 ± 57.28	691.27 ± 43.81	1758.23 ± 133.47
Organic compost-pellets	1063.93 ± 23.80	703.45 ± 175.70	287.95 ± 31.60	2055.33 ± 231.10

Table 7. Heat of combustion and calorific value results for the tested composts. The lowercase letters indicate statistical differences at p < 0.05 according to Tukey’s post hoc test.

Type of Raw Material	HHV [MJ∙kg_d.m.⁻¹]	LHV [MJ∙kg_d.m.⁻¹]	Ash Content [%]
Garden compost	8.81 ± 0.11 a	8.32 ± 0.03 a	65.23 ± 0.05 c
Buckwheat husk compost	18.8 ± 0.1 c	17.24 ± 0.09 c	4.66 ± 0.06 a
Organic compost	10.09 ± 0.07 b	9.54 ± 0.07 b	58.97 ± 0.06 b

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Sienkiewicz, A.; Cwalina, P.; Obidziński, S.; Krasowska, M.; Kowczyk-Sadowy, M.; Piotrowska-Niczyporuk, A.; Bajguz, A. Potential for Using Composts Produced from Agri-Food Industry Waste as Biocomponents of Liquid and Solid Fuels. Energies 2024, 17, 6412. https://doi.org/10.3390/en17246412

AMA Style

Sienkiewicz A, Cwalina P, Obidziński S, Krasowska M, Kowczyk-Sadowy M, Piotrowska-Niczyporuk A, Bajguz A. Potential for Using Composts Produced from Agri-Food Industry Waste as Biocomponents of Liquid and Solid Fuels. Energies. 2024; 17(24):6412. https://doi.org/10.3390/en17246412

Chicago/Turabian Style

Sienkiewicz, Aneta, Paweł Cwalina, Sławomir Obidziński, Małgorzata Krasowska, Małgorzata Kowczyk-Sadowy, Alicja Piotrowska-Niczyporuk, and Andrzej Bajguz. 2024. "Potential for Using Composts Produced from Agri-Food Industry Waste as Biocomponents of Liquid and Solid Fuels" Energies 17, no. 24: 6412. https://doi.org/10.3390/en17246412

APA Style

Sienkiewicz, A., Cwalina, P., Obidziński, S., Krasowska, M., Kowczyk-Sadowy, M., Piotrowska-Niczyporuk, A., & Bajguz, A. (2024). Potential for Using Composts Produced from Agri-Food Industry Waste as Biocomponents of Liquid and Solid Fuels. Energies, 17(24), 6412. https://doi.org/10.3390/en17246412

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