Effect of Composted Organic Waste on Miscanthus sinensis Andersson Energy Value

Abstract

At the time of rising urbanization and population growth, the search for renewable energy sources to ensure sustainable development is of extreme importance. The aim of this research was to determine the effects of different proportions of composted organic materials, i.e., mushroom substrate and municipal waste, on Chinese silver grass (Miscanthus sinensis Andersson) energy value. A three-year field experiment was established on experimental plots in the east-central part of Poland. Various treatment combinations, each introducing 170 kg N·ha⁻¹ to the soil, had a positive effect on the energy parameters of Chinese silver grass biomass. The highest calorific value (17,964 kJ·kg⁻¹) was noted for plants treated with mushroom compost on its own (MSC100%).

1. Introduction

The global increase in greenhouse gas emissions observed recently and the need to ensure energy security have prompted the search for environmentally friendly sources of renewable energy [1]. Biomass is increasingly used as a source of sustainable fuel. The amount needed for it to supplement global annual electricity demand is expected to reach 360 million tons [2]. Composting waste organic materials is one of the oldest and most environmentally friendly methods of their utilization [3]. Both spent mushroom substrate and municipal waste are by-products of human economic activity and human existence. Composting organic waste is a safe way to dispose it, and as an organic fertilizer, it can be used to enrich the soil, which in turn can increase the value of energy crops [4]. Organic fertilizers are a safer alternative to mineral ones in the soil environment. Their components are released slowly, and, in effect, nutrient balance in the soil is maintained for a longer time. Humic acids in organic waste compost stimulate soil microorganisms that have a positive effect on soil structure [5].

The most common energy crops, subject to many studies, are osier willow (Salix vinimalis), giant miscanthus (Miscanthus x giganteus), and tuberous sunflower (Helianthus tuberosus) [6,7]. Despite the fairly extensive literature on the above species, little attention has been paid to Chinese silver grass (Miscanthus sienensis Andersson), a plant with many economic possibilities, which is also used as an energy crop (biofuels, thermal energy). Additionally, its cultivation increases organic carbon content in the soil, and it does not compete with plants cultivated for food production [8]. Thus far, research has mainly focused on Miscanthus x giganteus, a hybrid of Miscanthus sacchariflorus and Miscanthus sinensis. A perennial grass species, Miscanthus x giganteus is cultivated in Europe due to its high yield (10–25 t/ha of dry matter), but it is not resistant to low temperatures and water shortages in the same way that Miscanthus sinensis Andersson is. Miscanthus sinensis is not as sensitive to low temperatures, heavy metal contamination, or stress factors as are other hybrid species [9]. It combines such features as high yields, low demand for nutrients and water, phytoremediation potential, and an ability to adapt to adverse environmental conditions [10]. For this reason, Miscanthus sinensis Andersson is one of the most beneficial species of its genus [11]. In order to maximize the amounts of Miscanthus sinensis biomass used for energy purposes, it is necessary to focus on the assessment of factors determining its yield [12].

2. Materials and Methods

2.1. Experiment Description

In the spring of 2018, an experiment was established on plots with an area of 2 m², with three replications and randomly selected blocks. The research material was Chinese silver grass (Miscanthus sinensis Andersson), a perennial species. In the three-year experiment, the research factors were years of research and combinations of organic fertilizers, applied according to the following scheme:

• Control plot (no treatment);
• MWC_100% (3.49 kg per plot; 17.450 Mg·ha⁻¹);
• MWC_75% (2.62 kg per plot; 13.100 Mg·ha⁻¹) + MSC_25% (1.40 kg per plot; 7 Mg·ha⁻¹);
• MWC_50% (1.74 kg per plot; 8.700 Mg·ha⁻¹) + MSC_50% (2.80 kg per plot; 14 Mg·ha⁻¹);
• MWC_25% (0.87 kg per plot; 4.350 Mg·ha⁻¹) + MSC_75% (4.20 kg per plot; 21 Mg·ha⁻¹);
• MSC_100% (5.60 kg per plot; 28 Mg·ha⁻¹).
• Here, MWC is the municipal waste compost, and MSC is the mushroom substrate compost.

2.2. Determination of Soil and Organic Waste Properties

Before establishing the experiment, representative soil samples were collected from the top layer of the soil (0–30 cm) in order to assess its physical and chemical properties. In the soil material the following were determined:

−

Granulometric composition by the Bouyoucos–Casagrande aerometric method modified by Prószyński in accordance with the Polish Standard PN-R-04033 [13] and with the Grain Size Classification of Soils and Mineral Formations according to PTG 2008 [14];

−

pH value in H₂O and in 1 mol/L KCl by the potentiometric method;

−

Total hydrolytic acidity and the sum of basic cations (S) by the Kappen method on the basis of which the value of soil sorption capacity (T) and the degree of base saturation were calculated;

−

Total carbon, nitrogen, and hydrogen content by elemental analysis (The PerkinElmer 2400 Series II CHNS/O Elemental Analyzer 2400 (PekinElmer, Shelton, CT, USA), with the Thermal Conductivity Detector);

−

Total (in the calculations assumed as total, but in reality similar to it) content of Ni, Cu, Cr, Zn, Pb, Cd, K, and P (after wet mineralization of soil samples with aqua regia) by optical emission spectrometry at Eurofins OBiKŚ Poland Ltd. in Katowice, Poland, the former Centre for Environmental Research and Control [15].

The pH value of the soil was 6.81, and its total nitrogen and carbon concentration was 39.40 and 2.85 g·kg⁻¹DM, respectively. As a result of deep tillage and intensive fertilizer treatment, their content was high and typical for cultured soils. At the start of the experiment, the total content of heavy metals (Cr, Cd, Cu, and Ni) in the soil was several times lower than the amounts provided by the Regulation of the Minister of the Environment [16]. On the other hand, the content of Zn and Pb was within the standards.

In the representative samples of mushroom compost and municipal waste compost the following were determined:

−

Dry matter by drying of the sample at 105 °C until a constant mass was obtained;

−

pH in H₂O and in 1 mol/L KCl by the potentiometric method;

−

Total nitrogen content (Nt) by the modified Kjeldahl method with samples mineralized with concentrated sulfuric acid (VI) in the presence of a selenium mixture [17];

−

Organic carbon content (Corg) by the oxidation-titration method [18];

−

Total content of macroelements (P and K) and heavy metals (Co, Pb, Cd, Cr, Zn, and Ni) by inductively coupled plasma optical emission spectrometry (ICP-OES) after mineralization of soil samples with aqua regia [15].

2.3. Determination of Biomass Composition

Plants were harvested in January 2019 and 2020 and in February 2021, and the yield of fresh matter was determined. Each year, after shredding and grinding, samples were sent to the Energy Company in Siedlce, where the following were determined:

−

Ash content (PN-ISO 1171:2002) [19];

−

Heat of combustion (PN-G-04513:1981) [20];

−

Calorific value in the dry state (PN-91/G-04510) [21], with the conversion factor to dry state, according to the Polish Standard PN-91/G-04510, being 1.04;

−

Cellulose, hemicellulose, and lignin content by near-infrared reflection spectroscopy (NIRS) using the NIRFlex N-500 (Büchi Labortchnik AG, Flawil, Switzerland), apparatus at the Institute of Technology and Life Sciences in Falenty, with the content of the fiber fraction being used to calculate the amounts of cellulose, hemicellulose, and lignin [22].

2.4. Meteorological Conditions

Meteorological data were provided by the Institute of Meteorology and Water Management–National Research Institute in Warsaw, the Hydrological and Meteorological Station in Siedlce. These data were used to calculate Sielyaninov’s hydrothermal coefficient (K) for each month of the growing season. The values of the coefficient were grouped into classes of weather conditions in order to determine extremely dry and extremely wet periods affecting the growth of Miscanthus sinensis [23]. The combined effects of monthly precipitation and air temperature were assessed by means of Sielyaninov’s hydrothermal coefficient (K), calculated according to the following formula:

$$\mathrm{K}=\frac{\mathrm{P}}{0.1\mathrm{Ʃ}\mathrm{t}}$$

where P is the monthly precipitation, and Ʃt is the sum of daily air temperatures for a given month [24].

To assess the hydrothermal conditions, the following ranges of Selyaninov’s hydrothermal coefficient (K) were used:

K ≤ 0.4 to extremely dry (ss);

0.4 < K ≤ 0.7 very dry (bs);

0.7 < K ≤ 1.0 dry (s);

1.0 < K ≤ 1.3 quite dry (ds);

1.3 < K ≤ 1.6 optimal (o);

1.6 < K ≤ 2.0 quite wet (dw);

2.0 < K ≤ 2.5 wet (w);

2.5 < K ≤ 3.0 very wet (bw);

K > 3.0 extremely wet (sw) [23].

2.5. Statistical Processing

The results were statistically processed using the analysis of variance for a two-factor experiment. The significance of the effect of experimental factors on the value of the features was determined on the basis of the F Fisher–Snedecor test. The value of LSD_0.05 (for a detailed comparison of means) was calculated using Tukey’s test. Statistica StatSoft 13.1 was used for calculations [15].

3. Results

The values of Sielyaninov’s coefficient (K) indicated that the most favorable weather conditions for Chinese silver grass (Miscanthus sinensis Andersson) were in the 2018 growing period (

Table 1. Values of Selyaninov’s hydrothermal coefficient (K) between 2018 and 2020.

Year	Month
	April	May	June	July	August	September	October
2018	1.07 ds	0.50 bs	1.38 o	1.58 o	0.44 bs	0.92 s	1.52 o
2019	0.32 ss	2.83 bw	0.44 bs	0.72 s	1.21 ds	1.01 ds	0.62 bs
2020	0.29 ss	3.24 sw	3.02 sw	0.69 bs	1.09 ds	1.06 ds	2.73 bw

ss—extremely dry; bs—very dry; s—dry; ds—quite dry; o—optimal; bw—very wet; sw—extremely wet.

) and less beneficial in 2019 and 2020. In 2018, the beginning of the growing period was quite dry and very dry, but June, July and October were optimal for plant growth and development.

The dry matter content of mushroom compost was 30%, with a much higher value of 68% for municipal waste compost (

Table 2. Selected properties of organic waste materials (g·kg⁻¹DM).

Organic Waste	pH	DM (%)	Corg	C:N	N	P	K
MWC	7.10	68	236	14.93	14.30	17.32	25.4
MSC	6.4	30.00	284	13.59	20.9	8.86	11.21

). The pH value of mushroom compost was 6.41, close to neutral, while for municipal waste compost, it was neutral (7.10). According to Vitti et al. [25], pH of good-quality compost should range from 6.0 to 7.8.

According to Madej et al. [26], composted waste plant materials contain up to 450 g·kg⁻¹ of dry matter, with the N concentration ranging from 13 to 15 g·kg⁻¹DM, the P concentration ranging from 2.19 to 4.81 g·kg⁻¹DM, and the K concentration being 4.98 g·kg⁻¹DM. In the present experiment, a much higher content of macronutrients was noted. Mushroom compost and municipal waste compost contained 20.9 g·kg⁻¹ and 14.30 g·kg⁻¹ of N, 8.86 g·kg⁻¹ and 17.32 g·kg⁻¹ of P, and 11.21 g·kg⁻¹ and 25.4 g·kg⁻¹ of K, respectively. In particular, mushroom compost contained higher amounts of N (20.9 g·kg⁻¹) than did municipal waste compost, and in municipal waste compost, more P and K was noted. Despite these differences, the C:N ratio values were similar for both kinds of organic waste.

Compared to the values provided by the BN-89/9103-09 Polish Standard [27], the content of heavy metals (

Table 3. Content of selected heavy metals in organic waste materials (mg·kg⁻¹DM).

Organic Waste	Co	Pb	Cd	Cr	Zn	Ni
MWC	3.58	78.4	2.08	34.12	623.2	15.6
MSC	0.415	3.98	0.287	3.08	156.9	4.84

) was at a relatively low level and did not exceed permissible amounts. It was much lower in mushroom compost than in municipal waste compost. However, quality parameters of both organic materials were satisfactory, with neutral pH, relatively high nutrient content, and moderate heavy metal content. Mladenov [28] reported similar results.

Because of its low hygroscopic moisture in the analytical state, biomass was found suitable to be used for energy purposes (

Table 4. Hygroscopic moisture content of Miscanthus sinensis biomass in the analytical state (%).

Treatment (A)	Year of Research (B)			Average
	2018	2019	2020
	Hygroscopic Moisture (%)
Control plot	4.55	3.24	5.98	4.59
MWC100	4.79	3.08	5.94	4.60
MWC75 + MSC25	4.80	3.04	5.77	4.54
MWC50 + MSC50	4.99	3.03	6.40	4.81
MWC25 + MSC75	4.85	3.08	6.11	4.68
MSC100	4.92	3.03	6.52	4.82
Mean	4.82	3.08	6.12	4.67

LSD_0.05; A—treatment, A—NS; B—year of research, B—1.390; AxB, BxA—interaction, AxB—NS, BxA—NS.

). If moisture of a material increases, its caloric value decreases. According to the literature, the average calorific value of dry hay is 18 MJ·kg⁻¹, but when moisture content increases to 70%, it decreases to 4 MJ·kg⁻¹ [29]. As regards biomass conversion into biogas, plants with lower moisture content (dried grass or straw) are of higher energy values [30]. In the present experiment, the average moisture content of Miscanthus sinensis was 4.67%, with much higher values than those in the analytical state observed by Kowalczyk-Juśko [31] for some other energy crops (Helianthus tuberosus–9.7%, Spartina pectinata–13.5%, Miscanthus sacchariflorus–7.2%). The moisture content of Miscanthus x giganteus in the dry state is 9.21% [32]. The most favorable moisture content for the process of combustion is 6–8% [33]. Its value depends on the leaf-to-stem ratio of fresh biomass, as leaves contain more water than do stems [34]. Organic fertilizers applied to Chinese silver grass did not affect the moisture level of hygroscopic biomass, but it varied over the years of research. The most favorable value of 3.08% was noted in the second year.

The highest percentage of hygroscopic moisture (4.82%) was noted on the plot where the highest dose of mushroom compost was applied. The lowest value (4.54%) was found for plants treated with 75% municipal waste compost and 25% mushroom compost applied together. However, differences in the hygroscopic moisture of Miscanthus sinensis biomass between fertilized plots were not statistically significant. On the other hand, hygroscopic moisture content varied significantly over the years of research.

An important element in the assessment of an energy crop is its ash content. According to the literature, when ash content increases by 1%, the heat of combustion decreases by 0.2 kJ·kg⁻¹ [35]. Dradrach et al. [36] reported that ash content in Miscanthus sinensis was 4.74%. In the present experiment, its average three-year value was 4.45% (

Table 5. Ash concentration of Miscanthus sinensis dry matter (%).

Treatment (A)	Year of Research (B)			Mean
	2018	2019	2020
	Ash Concentration (%)
Control plot	5.36	3.55	4.69	4.53
MWC100	7.14	2.73	3.88	4.58
MWC75 + MSC25	6.85	3.35	3.77	4.66
MWC50 + MSC50	6.23	3.17	4.24	4.55
MWC25 + MSC75	5.58	2.86	4.26	4.23
MSC100	4.43	2.78	5.31	4.17
Mean	5.91	3.07	4.35	4.45

LSD_0.05; A—treatment, A—NS; B—year of research, B—1.148; AxB, BxA—interaction, AxB—NS, BxA—NS.

). In dry-state samples, the highest amount (5.91%) was recorded in the first year, while the lowest in the second, at 3.07%. The differences in ash content between years of research were statistically significant. Unlike the year of research, treatment combinations did not significantly affect ash content in Miscanthus sinensis biomass. Compared to other species, Miscanthus sinensis ash content is not high. For Miscanthus sacchariflorus, it is 4.3%, with 7% in rapeseed, and, for comparison, in bituminous coal, it is 22% [18,37,38]. In the present experiment, no interaction concerning ash content between years and treatments was observed.

In the experiment conducted by Eiland et al. (2021), the ash content of Chinese silver grass biomass was 79% higher in the first year than in the second [39]. Kalembasa reported that ash content in the biomass of Miscanthus sinensis was 5.2% [40], and in another study, high ash content was found to have a negative effect on biomass calorific value [41]. Gołąb-Bogacz et al. (2021) reported that nitrogen fertilizers increased the ash content of Miscanthus biomass [41]. In Miscanthus sinensis intended for energy purposes, ash content should be as low as possible. In a good quality plant material, it should range from 2 to 4% [42]. In the present experiment, the highest critical value with more than 7% of ash in dry matter was recorded in the first year in plants treated with urban waste compost.

The heat of combustion of Miscanthus sinensis biomass in the dry state significantly varied over the years research (

Table 6. Heat of combustion of Miscanthus sinensis biomass in the dry state (kJ·kg⁻¹DM).

Treatment (A)	Year of Research (B)			Mean
	2018	2019	2020
	Heat of Combustion (kJ·kg−1DM)
Control plot	19,324	17,076	19,148	18,516
MWC100	18,849	19,148	19,390	19,129
MWC75 + MSC25	18,863	18,648	19,476	18,996
MWC50 + MSC50	19,397	17,272	19,613	18,761
MWC25 + MSC75	19,125	17,955	19,629	18,903
MSC100	19,034	18,913	19,657	19,201
Mean	19,099	18,169	19,485	18,918

LSD_0.05; A—treatment, A—25.952; B—year of research, B—14.734; AxB, BxA—interaction, AxB—44.950, BxA—36.090.

). According to Dradrach et al. [36], for Miscanthus sinensis biomass, it was 17,472 kJ·kg⁻¹DM. In the present experiment, the average value across treatment combinations and years of research was higher, at 18,918 kJ·kg⁻¹DM. The highest heat of combustion was noted in 2020 (19,485 kJ·kg⁻¹) and the lowest in the second year (2019), at 18,169 kJ·kg⁻¹. It was expected that organic fertilizers, compared to control, would significantly increase the heat of combustion. The recorded values were similar to those of Miscanthus x. giganteus, whose calorific value was reported to be 18.79 kJ kg⁻¹DM [43].

The differences between years of research were statistically significant. Mushroom and municipal waste composts significantly increased the Miscanthus sinensis heat of combustion. The highest value (19,201 kJ·kg⁻¹) was on the plots treated with mushroom compost on its own and with municipal waste compost also on its own (19,129 kJ·kg⁻¹). As a three-year average, the lowest heat of combustion amounting to 18,516 kJ·kg⁻¹ was noted in the dry-state sample from the control plot.

Porvaz [44] reported that the calorific value of Miscanthus sinensis ranged from 17 to 19 MJ/kg. In the present research, similar values were noted. The overall average calorific value of Miscanthus sinensis biomass (

Table 7. Calorific value of Miscanthus sinensis biomass in the dry state (kJ·kg⁻¹).

Treatment (A)	Year of Research (B)			Mean
	2018	2019	2020
	Calorific Value (kJ·kg−1)
Control plot	18,102	15,831	17,918	17,284
MWC100	17,650	17,803	18,149	17,867
MWC75 + MSC25	17,661	17,401	18,232	17,765
MWC50 + MSC50	18,187	16,022	18,377	17,529
MWC25 + MSC75	17,907	16,702	18,393	17,667
MSC100	17,800	17,658	18,434	17,964
Mean	17,884	16,903	18,250	17,679

LSD_0.05; A—treatment, A—89.900; B—year of research, B—51.039; AxB, BxA—interaction, AxB—155.711, BxA—125.019.

) was 17,679 kJ·kg⁻¹. Treatment with composts significantly affected the calorific value of Miscanthus sinensis. Statistically significant differences were noted between control plants and those growing on plots treated with composts. As a three-year average, dry-state samples of control plants were of the lowest calorific value, at 17,284 kJ·kg⁻¹. Plants with the highest calorific value (17,964 kJ·ha⁻¹) were from the plot treated with mushroom compost on its own (MSC100%). Significant differences in calorific value were also noted between the years of the experiment, with the lowest in the first and second, with values of 17,884 kJ·ha⁻¹ and 16,903 kJ·ha⁻¹, respectively.

The chemical composition of plant biomass has a direct impact on its calorific value and on its processing to produce energy. The main components determining the value are multimolecular biopolymers such as cellulose (35–48%), hemicellulose (22–30%), and lignin (15–27%), used in a complex process to produce bioenergy [45]. Their content ensures that it is possible to obtain energy or liquid and gaseous fuels from biomass [46]. The hypothesis put forward in the experiment assumed that varied combinations of organic fertilizers, each introducing 170 kg N ha⁻¹ to the soil, would affect the chemical composition of Miscanthus sinensis. The content of lignin is particularly important because lignin-derived methoxyphenols are the main component of smoke in the initial stage of combustion [47]. According to Chupakhin et al., for the best calorific value, Miscanthus sinensis should contain 41–45% cellulose, 20.6–33% hemicellulose, and 19.0–23.4% lignin [12].

Roszkowski [48] argues that high lignin yield has an impact on biomass calorific value. In the present experiment, treatment affected lignin content and, at the same time, biomass calorific value. The three-year average of the Miscanthus sinensis lignin concentration was 7.93% (

Table 8. Lignin content in Miscanthus sinensis biomass (% DM).

Treatment (A)	Year of Research (B)			Mean
	2018	2019	2020
	Lignin (%)
Control	7.35	8.59	7.68	7.87
MWC100	7.22	8.43	7.89	7.85
MWC75 + MSC25	7.60	8.66	8.26	8.17
MWC50 + MSC50	7.50	8.47	7.96	7.98
MWC25 + MSC75	7.24	8.67	8.39	8.10
MSC100	7.18	8.06	7.49	7.62
Mean	7.35	8.48	7.95	7.93

LSD_0.05; A—treatment, A—0.280; B—years of research, B—0.159; AxB, BxA—interaction, AxB—0.486, BxA—0.390.

). As regards treatment groups, the biomass of Miscanthus sinensis produced the most lignin in response to the combination of municipal waste compost with mushroom compost in proportions of 25:75 and 75:25. In the first year, the highest (7.60%) was noted on the plot treated with a mixture of municipal waste compost (75%) and mushroom compost (25%). In the second and third year, the highest lignin concentration, with 8.67% and 8.39%, respectively, was in response to municipal waste compost (25%) applied together with mushroom compost (75%), i.e., in inverse proportion. As an average of treatment combinations, the highest percentage of lignin was noted in the second year of the experiment (8.48%) and the lowest in the first (7.35%).

The content of lignin noted in the experiment was very low. Chupakhin et al. reported that Miscanthus sinensis is a species with a low lignin content of 8% as its average value [12]. Low lignin content is a desirable feature in bioethanol production, but it depends on many factors [11]. Liu et al. highlighted the multidimensional genetic background of Miscanthus sinensis and the unexplained molecular processes determining its parameter values and its resistance to abiotic stress factors [10].

Neither treatment nor years of research significantly affected Miscanthus sinensis cellulose content (

Table 9. Cellulose content of Miscanthus sinensis biomass (% DM).

Treatment Combinations (A)	Years of Research (B)			Mean
	2018	2019	2020
	Cellulose (%)
Control	44.44	47.87	44.34	45.55
MWC100	44.67	47.27	44.61	45.52
MWC75 + MSC25	44.37	46.93	45.00	45.44
MWC50 + MSC50	45.52	47.59	44.63	45.92
MWC25 + MSC75	45.65	46.77	46.74	46.39
MSC100	47.21	45.72	43.72	46.46
Mean	45.31	47.03	44.84	45.88

LSD_0.05; A—treatment, A—NS; B—year of research, B—NS; AxB, BxA—interactions, AxB—NS, BxA—NS.

). There was no interaction between them either. As an overall average, the cellulose percentage in the biomass was 45.88% DM, which was within the range of 40–55% and can be regarded as high content in lignocellulosic biomass. In the study by Chupakhin et al., cellulose content, with an average value of 40.6%, and biomass yield increased each year of research [12]. This was not consistent with the results obtained in the present experiment.

Neither treatment combinations of mushroom and municipal waste composts nor year of research significantly affected hemicellulose content in Miscanthus sinensis biomass (

Table 10. Hemicellulose content in Miscanthus sinensis biomass (% DM).

Treatment (A)	Year of Research (B)			Mean
	2018	2019	2020
	Hemicellulose (%)
Control	27.85	35.44	32.60	31.96
MWC100	30.85	35.14	31.90	32.54
MWC75 + MSC25	26.71	34.24	31.55	30.84
MWC50 + MSC50	29.49	35.18	32.18	32.28
MWC25 + MSC75	30.64	33.82	33.43	32.63
MSC100	30.51	33.10	29.88	31.80
Mean	23.30	34.49	31.92	32.01

LSD_0.05; A—treatment, A—NS; B—year of research, B—NS; AxB, BxA—interaction, AxB—NS, BxA—NS.

). As an average effect of treatment groups and years of cultivation, the hemicellulose concentration was 32.01%. Sun and Cheng [49] noted that the share of cellulose in lignocellulosic biomass was 40–55%, with 24–40% being hemicellulose. Thus, the content determined in the experiment was within the above ranges. Chupakhin et al., found that the average content of hemicellulose was 30.2%, and they also noted that some Miscanthus species contained high levels of cellulose and hemicellulose and low levels of lignin and ash [12].

4. Conclusions

According to the research factors, the treatment of plants with 100% mushroom compost resulted in the most favorable energy value (the highest calorific value and heat of combustion, the lowest ash content, the highest cellulose content). Organic fertilizers, each combination introducing 170 kg N·ha⁻¹, increased the calorific value of Miscanthus sinensis biomass. The highest (17,964 kJ·kg⁻¹) was noted on the plot treated only with mushroom compost (MSC100%). The lowest, gradually decreasing during the three-years of research, was on the control plot. Organic fertilizer treatment slightly increased the heat of combustion of Miscanthus sinensis biomass. In response to municipal waste compost (MWC100%), it was 19,129 kJ·kg⁻¹DM, with 19,201 kJ·kg⁻¹DM for plants treated with mushroom compost (MSC100%). Ash content in plants, as a negative factor during biomass combustion, was at a moderate level (4.45%), decreasing with years of research. Different treatment combinations did not significantly affect ash content in Miscanthus sinensis biomass. Unlike the amount of lignin, which changed across years and treatments, the content of cellulose and hemicellulose did not vary significantly. At 7.93%, the lignin content was extremely low, which is desirable for the production of bioethanol. Calorific value, hygroscopic moisture, and ash content significantly varied over the years of the experiment. Some results of the Miscanthus sinensis biomass chemical composition (extremely low lignin and high hemicelluloses amounts) differed from what had been expected, so it is necessary to continue research in this area.