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Article

Evaluation of Changes in the Chemical Composition of Grasses as a Result of the Methane Fermentation Process and Biogas Production Efficiency

by
Bogusława Waliszewska
1,
Hanna Waliszewska
1,2,
Mieczysław Grzelak
3,
Leszek Majchrzak
4,*,
Eliza Gaweł
5,
Maciej Murawski
3,
Agnieszka Sieradzka
1,
Iryna Vaskina
6 and
Agnieszka Spek-Dźwigała
1
1
Department of Chemical Wood Technology, Poznań University of Life Sciences, Wojska Polskiego 38/42, 60-637 Poznań, Poland
2
The National Centre for Research and Development, Chmielna 69, 00-801 Warszawa, Poland
3
Department of Grassland and Natural Landscape, Poznań University of Life Sciences, Dojazd 11, 60-656 Poznan, Poland
4
Agronomy Department, Poznań University of Life Sciences, Dojazd 11, 60-632 Poznań, Poland
5
Department of Forage Crop Production, Institute of Soil Science and Plant Cultivation—State Research Institute, Czartoryskich 8, 24-100 Puławy, Poland
6
Department of Biosystem Engineering, Poznań University of Life Sciences, Wojska Polskiego 48, 60-637 Poznań, Poland
*
Author to whom correspondence should be addressed.
Energies 2024, 17(16), 4100; https://doi.org/10.3390/en17164100
Submission received: 5 July 2024 / Revised: 13 August 2024 / Accepted: 13 August 2024 / Published: 18 August 2024
(This article belongs to the Special Issue Sustainable Energy Development in Liquid Waste and Biomass)
Browse Figures
Versions Notes

Abstract

:
Methane fermentation, which is one of the key processes in biogas production, plays an important role in the conversion of biomass to energy. During this process, changes occur in the chemical composition of organic feedstocks, including the chemical composition of grasses. The assessment of these changes is crucial for the efficiency and productivity of biogas production. The material for this study comprised fully mature grass blades with leaves and inflorescences and was collected from extensively used meadows and pastures, as well as cultivated and set-aside areas in the Wielkopolskie Voivodeship, the communes of Białośliwie and Trzcianka, Poland. The aim of this study was to compare methane fermentation efficiency in nine grass species and identify the biomass component involved in biogas production. The results indicate that the fermentation process, as expected, changed the cellulose content. The lignin content of the grasses before fermentation varied more than the cellulose content. The content of holocellulose (sum of carbohydrate components) in the grasses ranged from 59.77 to 72.93% before fermentation. Methane fermentation significantly reduced the carbohydrate content in the grasses, with a low degree of polymerization. Grassland biomass-based biogas production is a viable alternative to conventional fossil fuels.

1. Introduction

Grasses from extensively managed meadows and pastures are a common source of animal feed. However, in modern livestock farming, the feed of choice has changed from species-rich forage obtained from natural grasslands typically low in energy content to cultivated crops and high-energy feed concentrates. There are vast areas of underutilized grassland that need to be managed [1]. Globally, as the focus on alternative energy sources increases and mineral fertilizer prices soar, grassland biomass could be used for biogas production. The digestate produced from agricultural biogas plants [2,3] can be used as a fertilizer that positively influences the growth and development of grasses and the soil environment. The production of biogas from biomass, waste, or by-products is recognized as renewable energy [4,5]. In Austria and Germany, about 50% of agricultural biogas plants use grass silage as a biogas source [6]. Biogas plants are RESs (Renewable Energy Sources) installations that are completely independent of weather conditions, season, or precipitation and, considering the current energy market situation, are increasingly common and gaining importance.
The amount and composition of the biogas obtained from different grasses depends on several factors such as the type of bacteria used, process condition (temperature), type of substrate, and its chemical composition [7,8]. Biogas typically comprises about 55% methane, 45% carbon dioxide, and minor amounts of other components [9]. To optimally utilize biomass for renewable energy, Pilarski et al. [10] propose the production of bioethanol and biogas simultaneously from corn, since it is one of the most widely cultivated crops in the world and has many applications, ranging from animal and human nutrition to biofuel production. The biomass produced by corn (leaves, stalks, and ears) is used in biogas plants, while the grain is used for ethanol production. The resulting distillery digestate is reused for biogas production.
In the context of the global challenges of climate change and the demand for more sustainable forms of energy, understanding and developing grass fermentation is an important step towards achieving the Sustainable Development Goals. By deepening our understanding of the mechanisms of this process and identifying potential strategies to optimize it, we can collectively strive to create greener and more efficient energy production systems using the wealth of natural resources that are grasses.
The anatomy and chemical composition of plant biomass within the same species vary greatly. This variation is influenced by several factors: growing conditions, plant developmental stage, and its morphological parts. Understanding the chemical composition of the raw material is integral to optimizing its use. In a literature review on the influence of chemical composition on the calorific value of biomass and the correlation of the individual components, the authors report that these are very important indicators [11]. In addition, policies in the agricultural sector are driving environmentally friendly biomass energy production systems. This further emphasizes the role that cultivated grasslands can play in sustainable biogas production [12]. This study focuses on the biogas production potential of different grass species growing under different conditions.
In this study, nine grass species were investigated as a potential source of biogas. The structural and plant by-product components were analyzed and the effect of the anaerobic digestion process on the change in their respective content was also analyzed. These analyses helped identify the components primarily involved in biogas production and how they affect the composition and yield of the digestate. The species diversity of grasses in terms of their suitability for fermentation and process optimization strategies to increase biogas production efficiency is also discussed.

2. Materials and Methods

2.1. Material Collection

The material for this study was collected from extensively used meadows and pastures, as well as cultivated and set-aside areas during the 2020 growing season. The material comprised fully mature grass blades with leaves and inflorescences from the area of the Wielkopolskie Voivodeship; the communes of Białośliwie and Trzcianka. Nine grass species were selected for this study. These were reed fescue (Festuca arundinacea Schreb.); brome grass (Bromus inermis Leyss.); perennial ryegrass (Lolium perenne L.); westerwold ryegrass (Lolium multiflorum var. westerwoldicum); meadow fescue (Festuca pratensis Huds.); meadow ryegrass (Alopecurus pratensis L.); meadowgrass (Poa pratensis L.); meadow timothy (Phleum pratense L.); and soft hair (Bromus hordeaceus L.). The harvested grasses were placed in an air-conditioned laboratory until constant humidity was achieved. For chemical analyses, the raw material was manually cut into small pieces and then ground in a Retsch SM 200 laboratory cutting mill. The milled raw material was sieved to separate the analytical fraction with a particle size of 0.1–0.4 mm. The raw material prepared in this way was used for further testing.

2.2. Chemical Composition

Structural and adventitious components were determined using standard assay methods:
-
Cellulose was determined according to Seifert using dioxane and acetylacetone [13];
-
Lignin was determined according to Tappi using 72% sulfuric acid [14];
-
Holocellulose was determined using sodium chlorite [15];
-
Extractives were determined in a Soxhlet apparatus using 96% ethanol [16];
-
Ash was determined according to DIN 51731;
-
Hemicelluloses were calculated arithmetically based on the difference between holocellulose and cellulose. Hemicellulose content was calculated based on the difference between the contents of holocellulose and cellulose.

2.3. Batch Test

The research experiments on biogas production (batch test) were carried out in the Ecotechnologies Laboratory (Department of Biosystems Engineering, PULS)—the largest Polish biogas laboratory (encompassing over 260 reactors working in temporary or permanent mode). The fermenters used for this experiment were used within the last 15 years for analyzing the methane production efficiency of over 3500 different substrates.
Methane fermentation was performed in 2 dm3 glass reactors according to DIN 38 414-S8 and the guidance of VDI 4630 published by the Association of German Engineers in Dresden.
In order to proceed correctly with the biogas efficiency analysis, it was important to maintain the methodological proportions of tested substrates and inoculum. For this purpose, he following analyses were indispensable: dry matter (PN-75 C-04616/01) and organic dry matter (PN-Z-15011-3). The mentioned analyses were crucial for the calculation of the methane efficiency of the checked materials expressed in units like m3/Mg FM (fresh matter); m3/Mg DM; and m3/Mg ODM.
Approximately 13 g of each grass species with about 1100 g of digestate (rich in methanogenic bacteria with dry matter content of 2.7–2.9% and ash content of 28–30%) was used in the experiment. The experiment was conducted in a multi-chamber bio-fermenter (Figure 1). The materials were placed in the reactors and then flooded with digestate. The reactors, purged with nitrogen (to create anaerobic conditions), were placed in a water bath at 39 °C ± 1 (mesophilic fermentation) to ensure optimal conditions for the process. Biogas yield from each chamber was transferred to cylindrical store-equalizing reservoirs that were filled with liquid resistant to gas solubility [17,18]. The daily measurements of produced gases (methane, carbon dioxide) were made every 24 h, with an accuracy of 0.01 dm3.
The gas yield was analyzed using an infrared sensor for methane and carbon dioxide measurement and by an electrochemical sensor for oxygen measurement (Gas analyzer—GA5000 GeoTech company, Hong Kong, China). The calibrations of the GA5000 analyzer were made every 7 days using the calibration gases (65% CH4 and 35% CO2 presented in one mixture).
The results are presented on a dry matter basis as the average of 3 samples after deduction of the background, which was digestate.
According to the norm DIN 38 414-S8, the criterion to finish the methane production test from analyzed substrates was the time when daily gas generation reached the level of less than 1% of the total production obtained during the whole experiment.
After the fermentation process, the chemical composition of the digestate was examined using the same determinations as for the raw test material. The results are presented on a dry matter basis as the average of 3 samples.
All analyses were performed using R Statistical Software (v4.4.0-“Puppy Cup”) [19] using the agricolae package [20].

3. Results and Discussion

Below, Table 1 shows the cellulose, lignin, holocellulose, and hemicellulose content of selected grasses before fermentation and after fermentation. The cellulose content ranged from 35.17 to 36.92%, with L. westerwoldicum having the lowest content (31.34%) and B. inermis having the highest content (38.65%). Slightly higher amounts of cellulose (34%) in bagasse leaves (determined by the Kürschner–Hoffer method) were reported by Tapia-Maruri et al. [21]. Similar differences in the content of α-cellulose in genotypes of different grass species were shown by Rahaman et al. [22]. For instance, they reported 13.10–40.76% α-cellulose in Sorghum bicolor, 35.2140.98% in Arundo donax, and 17.20–27.28% in Pennisetum purpureum.
The fermentation process, as expected, altered the cellulose content. The loss of cellulose mass varied widely, depending on the grass species. The smallest loss was observed in L. perenne (2.71%) and L. westerwoldicum (2.97%), while the largest was observed in A. pratensis (19.06%) and B. inermis (18.86%). A slight loss of 7.47% was observed in B. hordeaceus. The loss of cellulose content in the remaining species ranged from 12.51 to 15.28% (Figure 2).
The lignin content of the grasses before fermentation varied more than that of cellulose. It ranged from 12.44% for B. hordeaceus to 17.70% for Alopecurus pratensis (Table 1). For most species, the lignin content ranged from 15.58% to 17.02%. A very low lignin content (only 4.81%) in bagasse leaves was determined by Tapia-Maruri et al. [21]. Perhaps their modified method of determining lignin influenced the amount. Large discrepancies in lignin content, ranging from 13.41% to 26.25%, were shown by Rahaman et al. [22] in the genotypes of six grass species tested. Even the same species showed different contents of lignin. For instance, the lignin content in Saccharum spontaneum ranged from 17.20% to 23.01%, while in Arundo donax it ranged from 18.77% to 22.40%. After the fermentation process, significantly higher amounts of lignin were observed. For most grasses, the amount of lignin in the digest was 44–45%, with the exception of Phl. pratense (39.67%) and L. perenne (41.5%). The increased lignin content in the digestate is due to the mass loss of carbohydrate compounds during the fermentation process. The apparent increase in lignin content ranged from 133 to 200% (Figure 3).
The content of holocellulose before fermentation ranged from 59.77% to 72.93% (Table 1). L. westerwoldicum had the lowest content, while B. horeaceus had the highest content. The holocellulose content in the majority of the species ranged from 63% to 69%. After the fermentation process, the holocellulose content ranged from about 22% to 29%. Only L. westerwoldicum showed a reduction in holocellulose content to 15%.
The analysis carried out showed that the content of hemicelluloses in the grasses before fermentation ranged from 28% to 36.5% (Table 1). These values are higher than previously reported values and could have a positive effect on the fermentation process. Rahaman et al. [22], studying six grass species, determined the content of hemicelluloses to be between approximately 12% and 20%. According to Rahaman et al. [22], Saccharum spontaneum had the highest hemicellulose content (20.19%), while Arundo donax had the lowest hemicellulose content (11.97%).
The methane fermentation process significantly reduced the content of low-polymerized carbohydrates in the grasses. The concentration of hemicelluloses after fermentation ranged from 8.78% in Phl. pretense to 19.54% in F. arudinacea. The percentage loss of hemicelluloses during the fermentation process ranged from 39.32% in F. arudinacea to almost 70% in Phl. pretense (Figure 2). P. pratensis and L. perenne also showed a significant loss of hemicelluloses (68.83% and 67.92%, respectively).
Table 2 shows the content of ethanol-extractable substances in the grasses before and after the fermentation process. Analysis of the mean values of extractives and ash showed statistically significant differences for all components.
Before fermentation, the content of ethanol-extractable substances in the different grass species ranged from 12.02% to 25.04%. After the fermentation process, the amount of ethanol-extractable compounds ranged from 5.61% in B. hordeaceus to 7.63% in P. pratensis. The other grasses contained between 6.24% and 6.91% of these substances after fermentation. Analysis of the results showed that the loss of ethanol-extractable substances quantitatively was comparable to the decrease in the content of hemicelluloses. The loss ranged from 48.09% in the case of B. inermis to as much as 73.60% in L. westerwoldicum.
Table 2 also shows the ash content of the grasses before and after methane fermentation. Before fermentation, as with the extractives, there was a wide variation in ash content among species, ranging from 4.21% to 9.46%. Ash content depends on various factors, and the wide variability found in this study is comparable to other studies. Depending on the development stage of the plant, Herrmann et al. [23] found between 7% and 16% ash in ryegrass mixture, between 4% and 10% in Sorghum bicolor, and between 10 and19% in Helianthus annuus. The same authors showed ash content ranging from 7% to 11% in meadow fescue.
After the fermentation process, higher amounts of ash were observed in the residue than in the fresh plant material. Its amount in the digest ranged from 30.60% to 45.12%. This was more than 5–9 times the amount of mineral compounds in fresh grasses. Such a large increase in ash concentration in the assayed material was due to the addition of a fermentation inoculant, the composition of which cannot be disclosed due to analysis and potential industrial use.
The potential to produce biogas with a high methane content is an important quality parameter for plant biomass used as biogas feedstock. The main factor influencing the amount of methane yield that can be obtained under favorable process conditions in biogas plants is the choice of plant species [23]. Tilman et al. [24] concluded that biofuels derived from low-input native perennial grasses can produce more useful energy and reduce greenhouse gas emissions and agrochemical pollutants compared to arable crops such as maize or soya.
In Table 3, the authors show the data of dry matter and organic dry matter of the studied grass species. The dry matter ranged from 89.85% to 92.98%. Gobena et al. [25] found that the average dry matter of different grasses was about 92.78%. Waliszewska et al. [26] found that the average dry matter content of different grass species was about 93.53%. Both cited publications show that the authors obtained higher dry matter content in the studied grass species than this study. This could be due to the different storage conditions for the samples or the ability of the plant to retain water.
The content of organic compounds in the dry matter of the studied grass species ranges from 87.10% to 94.93%. The lowest content of organic compounds was observed in L. perenne, while the highest content was observed in A. pratensis, F. pratensis and B. inermis. Platače and Adamovičs [27] examined timothy and meadow fescue in their study. They observed dry matter organic compounds in the range of 92.98% to 95.01% for timothy and 93.12% to 93.95% for meadow fescue. These values are comparable to the current study.
Amaleviciute-Volunge et al. [28] studied different grass species and reported biogas yields ranging from 63.2 to 114.3 dm3∙kg−1 FM. Chiumenti et al. [29], who studied perennial grasses, reported a biogas yield of 164.6 dm3∙kg−1 FM and a methane yield of −87.4 dm3∙kg−1 FM. Scarlat et al. [30] found that the methane yield of grass was 55–128 dm3∙kg−1 FM. Slightly higher biogas yields of 510–560 l/kg VS were obtained by Kasulla et al. [31], with approximately 60% methane from the napier grass hybrid. Similar biogas quantities of 540–580 L/kg VS were reported from extensive grassland in a study by Korres et al. [12]. Species from which more than 400 m3∙Mg−1 VS of biogas can be obtained are feasible to consider as biogas feedstock. The results of the present study show that many grass species from Polish grasslands can be used for biogas production.
Analyzing the data shown in Figure 4, no correlation was found between the holocellulose content and the amount of biogas obtained during the fermentation process.
The species L. westerwoldicum, containing only 59.8% holocellulose, yielded more than 400 m3·Mg1 VS of biogas, while B. hordeaceus, with the highest content (almost 73%) of holocellulose, produced only 381 m3·Mg−1 VS of biogas. There was also no correlation between the lignin content of the grasses and biogas production (Table 1 and Table 4).
The grass species B. hordeaceus containing the least lignin (12.44%) among the grasses tested had the lowest biogas yield. It is likely that other biomass components, e.g., phenolic substances with complex chemical structure, may have an inhibitory effect on biogas production. According to literature reports, high methane production can be obtained from plants with low lignin content and high amounts of non-structural carbohydrates and soluble and easily degradable cellular components [32,33]. The authors of the present study, based on the results obtained from nine grass species, do not unequivocally support such a claim. The amount of biogas produced may depend on many other factors, hence each species should be studied individually.

4. Conclusions

The process of anaerobic digestion for biogas production results in significant changes in the structural and incidental biomass components of the grass species studied. Low-polymerized carbohydrates (hemicelluloses) were degraded to the greatest extent. Lignin was the least degradable and most prominent biomass component in the digestate.
The lack of correlation between carbohydrate and lignin content and the biogas yield suggests that only a comprehensive study of the chemical composition of the biomass can predict which species will be most favorable in terms of suitability for biogas production.
The high biogas production and methane content of the biogas indicate that grasses from Polish meadows could be an alternative source of biogas from renewable sources.
Given the well-known anaerobic digestion technology and the need for rural development and sustainable energy production, biogas production from grasses is an attractive solution that meets many legal, agronomic, and environmental requirements.

Author Contributions

Conceptualization, B.W. and M.G.; methodology, M.G.; software, H.W.; validation, L.M., E.G. and M.M.; formal analysis, B.W.; investigation, M.Gresources, M.G; data curation, B.W.; writing—original draft preparation, M.M.; writing—review and editing, L.M.; visualization, A.S.; supervision, A.S.-D.; project administration, B.W.; funding acquisition, B.W.; supervision of research, I.V. All authors have read and agreed to the published version of the manuscript.

Funding

The research conducted from budget of the Department of Chemical Wood Technology and the Department of Grassland and Natural Landscape at the Poznan University of Life Sciences. The publication was financed by the Polish Minister of Science and Higher Education as part of the Strategy of the Poznan University of Life Sciences for 2024–2026 in the field of improving scientific research and development work in priority research areas.

Data Availability Statement

The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.

Acknowledgments

The authors are grateful for support provided by the Poznan University of Life Sciences, Poland, including technical support and materials used for field experiments.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Scheme of bio-fermenter for biogas production research (3-chamber section): 1—water heater with temperature regulator, 2—water pump, 3—insulated conductors of calefaction liquid, 4—water coat, 5—bio-fermenter with charge capacity 2 dm3, 6—sampling tubes, 7—biogas transporting tube, 8—gas sampling valve, 9—biogas volume-scale reservoir.
Figure 1. Scheme of bio-fermenter for biogas production research (3-chamber section): 1—water heater with temperature regulator, 2—water pump, 3—insulated conductors of calefaction liquid, 4—water coat, 5—bio-fermenter with charge capacity 2 dm3, 6—sampling tubes, 7—biogas transporting tube, 8—gas sampling valve, 9—biogas volume-scale reservoir.
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Figure 2. Mass loss of cellulose, holocellulose, and hemicelluloses because of the methane fermentation process [%].
Figure 2. Mass loss of cellulose, holocellulose, and hemicelluloses because of the methane fermentation process [%].
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Figure 3. Apparent increase in lignin content as a result of the fermentation process [%].
Figure 3. Apparent increase in lignin content as a result of the fermentation process [%].
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Figure 4. Amount of biogas and methane [m3·Mg−1 VS] obtained vs. holocellulose [%].
Figure 4. Amount of biogas and methane [m3·Mg−1 VS] obtained vs. holocellulose [%].
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Table 1. Main components of selected grass species with statistically significant differences before and after methane fermentation (Tukey’s test). Mean values with standard deviation for each species are presented (statistically significant at p < 0.01).
Table 1. Main components of selected grass species with statistically significant differences before and after methane fermentation (Tukey’s test). Mean values with standard deviation for each species are presented (statistically significant at p < 0.01).
Grass SpeciesCellulose [%]Lignin [%]Holocellulose [%]Hemicellulose [%]
BeforeAfterBeforeAfterBeforeAfterBeforeAfter
Methane Fermentation
Festuca arundinacea35.56 cd ± 0.1131.11 b ± 0.4617.28 ab ± 0.3644.86 a ± 0.1867.43 bc ± 0.4344.56 ab ± 0.5431.87 b ± 0.5113.45 ab ± 0.61
Bromus inermis38.65 a ± 0.5331.36 b ± 0.1414.89 e ± 0.3444.62 a ± 0.2268.40 b ± 0.4442.67 bc ± 0.5629.75 bc ± 0.7111.31 bcd ± 0.70
Lolium perenne34.28 e ± 0.1433.35 a ± 0.2715.58 de ± 0.1841.50 b ± 1.3265.48 bcd ± 1.3543.36 bc ± 1.2031.20 b ± 1.2310.01 cd ± 1.47
Lolium westerwoldicum31.34 f ± 0.0230.41 bc ± 0.1916.12 bcde ± 0.3944.55 a ± 0.0659.77 e ± 0.6344.44 ab ± 0.6928.43 c ± 0.6214.03 a ± 0.73
Festuca pratensis35.17 d ± 0.1229.96 c ± 0.2315.90 cde ± 0.2444.26 a ± 0.7263.69 d ± 0.6841.66 bcd ± 0.1528.52 c ± 0.6011.70 abc ± 0.38
Alopecurus pratensis36.42 bc ± 0.2629.48 c ± 0.1417.70 a ± 0.9244.72 a ± 0.2568.97 bc ± 2.1941.20 cd ± 0.7732.55 b ± 2.0211.72 abc ± 0.78
Poa pratensis36.13 bc ± 0.0331.37 b ± 0.7316.71 abcd ± 0.1545.32 a ± 0.1571.42 a ± 0.2342.37 bc ± 0.6435.29 a ± 0.2011.00 bcd ± 1.25
Phleum pretense36.92 b ± 0.5231.28 b ± 0.5017.02 abc ± 0.2539.67 c ± 0.4965.48 cd ± 0.6040.06 d ± 2.6028.56 c ± 0.788.78 d ± 1.18
Bromus hordeaceus36.39 bc ± 0.4533.67 a ± 0.4412.44 f ± 0.2244.74 a ± 0.4172.93 a ± 0.6247.01 a ± 0.4136.54 a ± 0.5713.34 ab ± 0.78
a, b, c, d, e, f—homogeneous groups.
Table 2. Change in extract and ash content with statistically significant differences due to fermentation (Tukey’s test). Mean values with standard deviation for each grass species are presented (statistically significant for p < 0.01).
Table 2. Change in extract and ash content with statistically significant differences due to fermentation (Tukey’s test). Mean values with standard deviation for each grass species are presented (statistically significant for p < 0.01).
Grass SpeciesExtraction Substances [%]Ash [%]
BeforeAfterBeforeAfter
Methane Fermentation
Festuca arundinacea15.95 cd ± 0.90 6.32 bc ± 0.275.39 f ± 0.02 44.40 a ± 0.47
Bromus inermis12.02 f ± 0.626.24 c ± 0.078.57 b ± 0.0244.61 a ± 0.01
Lolium perenne17.04 c ± 0.506.55 bc ± 0.226.14 e ± 0.0134.21 d ± 0.33
Lolium vesterwoldicum25.04 a ± 0.356.61 bc ± 0.359.46 a ± 0.0241.08 b ± 0.20
Festuca pratensis20.77 b ± 0.146.71 bc ± 0.307.40 c ± 0.5441.97 b ± 0.26
Alopecurus pratensis14.19 de ± 0.256.83 bc ± 0.264.51 g ± 0.0138.77 c ± 0.61
Poa pratensis16.01 c ± 0.34 7.63 a ± 0.124.21 g ± 0.0238.10 c ± 0.24
Phleum pretense15.76 c ± 0.306.91 b ± 0.036.33 e ± 0.0230.60 e ± 0.14
Bromus hordeaceus12.46 ef ± 0.81 5.61 d ± 0.116.93 d ± 0.0645.12 a ± 0.14
a, b, c, d, e, f—homogeneous groups.
Table 3. The content of dry matter and organic dry matter in different grass samples.
Table 3. The content of dry matter and organic dry matter in different grass samples.
Grass SpeciesDM [%]ODM [%]
Festuca arundinacea91.2193.00
Bromus inermis90.8094.61
Lolium perenne92.9887.10
Lolium westerwoldicum90.6192.30
Festuca pratensis92.0794.73
Alopecurus pratensis91.1694.93
Poa pratensis89.8591.65
Phleum pretense90.9692.35
Bromus hordeaceus91.2492.38
Table 4. The content of methane and overall biogas yield in different grass samples.
Table 4. The content of methane and overall biogas yield in different grass samples.
Grass SpeciesMethane Yield
[m3·Mg−1 VS]		Biogas Yield
[m3·Mg−1 VS]
Festuca arundinacea239.36437.89
Bromus inermis232.45429.24
Lolium perenne187.80356.94
Lolium westerwoldicum220.62406.15
Festuca pratensis229.56423.08
Alopecurus pratensis229.16425.97
Poa pratensis219.34415.40
Phleum pretense205.62396.58
Bromus hordeaceus211.00381.36
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Waliszewska, B.; Waliszewska, H.; Grzelak, M.; Majchrzak, L.; Gaweł, E.; Murawski, M.; Sieradzka, A.; Vaskina, I.; Spek-Dźwigała, A. Evaluation of Changes in the Chemical Composition of Grasses as a Result of the Methane Fermentation Process and Biogas Production Efficiency. Energies 2024, 17, 4100. https://doi.org/10.3390/en17164100

AMA Style

Waliszewska B, Waliszewska H, Grzelak M, Majchrzak L, Gaweł E, Murawski M, Sieradzka A, Vaskina I, Spek-Dźwigała A. Evaluation of Changes in the Chemical Composition of Grasses as a Result of the Methane Fermentation Process and Biogas Production Efficiency. Energies. 2024; 17(16):4100. https://doi.org/10.3390/en17164100

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Waliszewska, Bogusława, Hanna Waliszewska, Mieczysław Grzelak, Leszek Majchrzak, Eliza Gaweł, Maciej Murawski, Agnieszka Sieradzka, Iryna Vaskina, and Agnieszka Spek-Dźwigała. 2024. "Evaluation of Changes in the Chemical Composition of Grasses as a Result of the Methane Fermentation Process and Biogas Production Efficiency" Energies 17, no. 16: 4100. https://doi.org/10.3390/en17164100

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