Opportunities and Potential for Energy Utilization from Agricultural and Livestock Residues in the Region of Thessaly

Abstract

In recent years, due to the circular economy, the use of green energy forms, such as biofuels and biogas from anaerobic digestion of fermentable materials (e.g., agricultural and livestock residues) has entered our lives. According to the International Energy Agency it is estimated that the needs in 2040 will be 48% higher than in 2012 so all political decisions have converged on an urgent need for the use of more and more renewable and green energy. Considering the overall economic activity of these sectors in the region of Thessaly, the aim of this study is to highlight the residues from agricultural and livestock activities in the primary sector and calculate the annual biomass production, the methane and biogas potential, the electrical and thermal energy that can be produced from these wastes, as well as the solid residue that can be used to improve the soil of the region. The study was based on data referring to the years 2015 to 2020. The production of livestock and agricultural residues, averaged over the above six-year period in the study area, was estimated at approximately 4.8 × 10⁶ t·yr.⁻¹, with livestock residues accounting for 83% and agricultural residues for 17%. Furthermore, the total residues can produce an average biogas potential of approximately 4.7 × 10⁶ m³·yr.⁻¹, while the amount of electricity that can be produced ranges from 708–1091 GWh·yr.⁻¹, and the corresponding thermal energy from 1112–1577 GWh·yr.⁻¹. As a result of the complete anaerobic digestion process, a solid residue could also be obtained for the improvement of the region’s soil, which translates into a quantity in the range of 4.01 × 10⁴ to 5.10 × 10⁴ t·yr.⁻¹.

1. Introduction

Renewable energy refers to energy produced by sources, such as the sun, the wind, and water. Agriculture is one of the largest biological sectors that produce the highest amount of biomass, which can be an important input for the bioeconomy [1]. The utilization of green energy sources, such as biofuels and biogas from anaerobic digestion of fermentable materials (such as agricultural and animal leftovers), has become more prevalent recently thanks to the circular economy. The need to decouple from fossil fuels has become increasingly urgent in recent years. First and foremost, because of the depletion of fossil fuel supplies but also because using green and renewable energy sources reduces the carbon footprint, lowering the emissions of greenhouse gases and CO₂ into the atmosphere.

According to the International Energy Agency, it is estimated that the energy needs in 2040 will be 48% higher than in 2012 [2], so all political decisions in recent years have converged on an urgent need for the use of more renewable and green energy, with their financing increasing every year. One of these forms, with different characteristics from fossil fuels, is the potential of biomass, which can be used as an energy source. Recently, many different types of research have focused on determining biomass potential with policies being developed on it because it emits fewer greenhouse gases [3].

In Greece, in the last fifteen years, the use of anaerobic digestion plants has been increasing, firstly because it is an available raw material for their operation, secondly because they are efficient, since they produce thermal and electrical energy, which they sell, and thirdly because they are among the companies that produce the least amount of greenhouse gases, implementing a sustainable development in the economy and a sustainable environment [4]. Biogas as a fuel, produced by anaerobic digestion, implementing the circular economy, is a promising fuel and an alternative form of energy that has several advantages [5]. The utilization of biomass, either through thermochemical conversion or biological processes, is also a pathway for renewable energy production and can be a significant fraction of the RES energy mix. Anaerobic digestion (AD) is a method whereby organic-biodegradable waste, such as agricultural plant waste, food waste, sewage sludge, livestock waste, secondary crop waste, and others, are converted into a valuable energy source while decreasing their volumes [4]. The biodegradation of agricultural and livestock residues takes place under anaerobic conditions, with the action of bacteria in four stages under which the microorganisms work together and co-operatively similar to a well-tuned machine, producing biogas. Both nuisances and odors in biogas plants are minimal and apart from the final product, which is biogas, a solid and a liquid end product, useful for agricultural land, is produced. The solid can be used to improve the soil structure while the liquid can be used for the liquid fertilization of fields by farmers. Agricultural and livestock residues are an abundant and an ideal resource for anaerobic digestion. On the other hand, large quantities of them are left unused every year while they could be exploited through anaerobic digestion. As such, they are placed unevolved a number of times on the ground and without a uniform strategy from the state for their exploitation. In addition, they often contaminate the soil and aquifers and end up on our plates through the food chain. As a matter of common practice, agricultural residues are most often burned when they could be used as a cheap raw material for the operation of biogas plants.

The Greek agricultural sector is an essential part of the economy. Thus, significant amounts of livestock and agricultural waste are produced yearly [6]. In addition, the abundance of livestock and agricultural residues could replace up to 35% of the annual electricity consumption by using them as feedstock [5]. Therefore, the value of these materials and the calculation of the biogas production potential are essential. Agricultural residues (biomass) are crop residues that remain in the field after the harvesting of arable crops or the pruning of trees where leaves, branches, straws, stalks, peels, etc. are found. Livestock waste is the waste left by animals after the digestion of food and urine, commonly known as manure. According to these quantities, the biogas potential could be calculated. Regarding the biomass from agricultural residues, this depends on the type of plant, the cultivation treatments applied, the soil, and the climate of the area where it is grown [7].

2. Materials and Methods

2.1. Study Area

The study area concerns the region of Thessaly and specifically the prefectures of Karditsa, Larissa, Magnesia, and Trikala, which are in the center of Greece. According to the Hellenic Statistical Authority (ELSTAT), in 2019 there were 60,251 farms in the agricultural sector employing 103,233 people. Livestock farms refer to farming for both meat and milk, and regarding all the main types of animals, such as cattle, sheep, goats, pigs, turkeys, and chickens. The horticulture sector refers to vegetables (e.g., tomato, cucumber, watermelon, melon, pumpkin, peppers, eggplant, and potato), large-scale crops (e.g., durum wheat, soft wheat, maize, oats, and rye), legumes (e.g., beans, lentils, and chickpeas), and industrial crops ( e.g., cotton, tobacco, and oilseeds). Finally, tree crops (e.g., apple, pear, quince, cherry, apricots, peaches, plums, kiwi, pomegranate, figs, and lotus) are included. According to the Hellenic Statistical Authority, in 2012 Greece’s agricultural sector consumed 5% of the produced electricity. In comparison, in 2012, the Thessaly region consumed 21% of its total electricity demands for its agricultural activities, indicating that a significant amount of energy is necessary to strengthen the agricultural sector in that region [8]. As can be seen, the region of Thessaly has an abundance of crops and livestock, and its economy is largely dependent on agricultural and livestock production. It should also be noted that several processing plants for agricultural products are active in the region.

2.2. Assessment of Agricultural Residues

Agricultural residues include anything left in the field after harvesting fruits, such as leaves, shoots, fruit casings, roots, and any residue generated by cultural treatments, such as tree pruning. All of these can be used through appropriate treatment and transformed into organic fertilizer by two methods [9]. One is through aerobic digestion, i.e., to be decomposed under the influence of O₂, while the other method uses anaerobic digestion where the decomposition is carried out under conditions of O₂ deficiency [10]. For example, some plants, such as wheat, oats, and rye leave behind straw, stalks, and fruit husks as residues; maize stalks, leaves and cobs, and cotton leave behind stalks; legumes leave behind stalks and fruit shells. The availability of these residues every year is abundant, and it is important to exploit them through anaerobic digestion, producing biogas, and applying them to the circular economy for sustainable development and the environment [11]. However, a major drawback of using these wastes is the difficulty and often the inability of collecting them [5].

According to measurements that have been made, plant residues have a calorific value, for example, olive, pear, apricot, peach, and vine have 19.0, 18.7, 17.8, 18.8, and 18.7 MJ·kg⁻¹, respectively [12]. The chemical composition of agricultural residues is wide and case-specific studies are needed. The theoretical biomass potential is the total amount of residue that can be collected to produce energy, which is expressed in Joules. Under anaerobic conditions and in four phases (hydrolysis, acidogenesis, acetogenesis, and methanogenesis) [13], biomass is transformed by bacterial action into CH₄ and CO₂, which is burned in cogeneration engines for electrical and thermal energy production to subsequently benefit from their use. The process of separating CO₂ from biogas is called upgrading; it improves the quality and the heating value (calorific value) of the biogas by up to 39 MJ·m⁻³. With the appropriate treatment, the upgraded biogas can be used as a substitute for natural gas [14], feedstock to produce value-added products, and as a substrate in fuel cells. The final application of the biogas depends upon the national framework of subsidies, policies, and the availability of heat and gas grids [15]. The proper management of residues is an important factor, and in a case of a no management system, or if one does exist but is ineffective, then it can cause pollution and contamination of soil, water, and air [13,16,17]. For agricultural residues, there is a need for the calculation of the availability of the total amount, and the amount of agricultural residues depends on the type of crop, the area cultivated, the cultivation treatments, and the climatic conditions of the region. Therefore, in this research, data from the information systems of the Hellenic Payment and Control Agency for Guidance and Guarantee Community Aid (O.P.E.K.E.P.E) for the period 2015–2020 and from the four prefectures of Thessaly were collected, and as a result the hectares of crops cultivated in these years was found.

According to [18], the theoretical calculation of agricultural residues is given by Equation (1), where PARr is the production of residues from the annual crops (t), CA is the crop area (ha), AP is the crop yield (t·ha⁻¹), RtP is the residue ratio per product (−), and Av is the availability of the residues (–). The above variables are defined for each different type of crop, i (plant or tree).

$$PARr={{\displaystyle \sum }}^{ }\left(C{A}_i·A{P}_i·Rt{P}_i·A{v}_i\right)$$

(1)

In the case of the ratio of the residues to the product is unknown then Equation (2) was used:

$$PARr={{\displaystyle \sum }}^{ }\left(C{A}_i·R{Y}_i·A{v}_i\right)$$

(2)

where RY is the quantity of residues per hectare (t). The calculation of the residues (prunnings) from tree crops is performed through Equation (3), where PARt is the pruning residues (t), TNum is the quantity of trees per hectare (trees·ha⁻¹), and Pr is the rate of production of residues per tree (t).

$$PARt=\left(C{A}_i·TNu{m}_i·P{r}_i·A{v}_i\right)$$

(3)

In the case of the quantity of the residues per hectare and the residue ratio per product are known then Equation (4) was performed.

$$PARt={{\displaystyle \sum }}^{ }\left(C{A}_i·R{Y}_i·A{v}_i\right)$$

(4)

In the region of Thessaly, most of the most known plants are cultivated and the region has an area of 14,036 km² with 50% of the area consisting of mountainous and semi-mountainous massifs while the other 50% is plain [19]. In this study, we selected most of the cultivated plants of Thessaly. Firstly, according to the average yields of the crops, and based on the area of each plant species, the area was isostatically calculated, and the plants were grouped for the calculation of the final residue amounts in these groups. The grouping was performed not only for the common calculation factors for the related species, but also because each group that was created has its own economic value. Thus, some plants were grouped while others that have a distinct value to the region are presented individually. The first (I) category includes horticultural vegetables, and the grouping was performed according to the relatedness of the species as follows: Cucurbitaceae (pumpkin, watermelon, melon, cucumber), Solenoids (tomato, pepper, eggplant), Winter vegetables (broccoli, cabbage, cauliflower), and Miscellaneous vegetables (bean, onion, garlic, okra), potato, and industrial tomato. In the second (II) category large-scale plants, such as maize, durum wheat, other cereals (soft wheat, oats, barley, rye), and edible legumes (beans, chickpeas, lentils) are included. The third (III) category consists of industrial plants, such as cotton, sugar beet, tobacco, and oilseeds (sunflower, rapeseed). The fourth (IV) category consists of tree crops, such as Stone fruits (cherry, apricot, cherry plum, plum, peach), Pome fruits (pear, apple, quince), Acorns (hazelnut, walnut, almond), vines, olives, and other various trees (kiwi, lotus, muskmelon, pomegranate, fig).

Table 1. Amount of agricultural residues in the prefecture of Karditsa in 2015.

Cultivation Species	Cultivated Area	Residue/ Product—RtP	Availability—Av	Residue Production—RY	Crop Yield—AP	Production of Vegetable Residue
	(ha)	(–)	(–)	(t)	(t·ha−1)	(t)
Horticultural–Vegetables
Cucurbitaceae	272	0.4	0.4	-	65	2832
Solenoids	435	0.4	0.4	-	60	4179
Winter vegetables	28	0.4	0.4	-	55	245
Miscellaneous vegetables	79	0.4	0.4	-	25	317
Potatoes	27	0.4	0.4	-	33	142
Industrial tomato	519	0.4	0.4	-	70	5809
Large scale plants
Maize	2502	-	0.5	7.17	-	8968
Durum wheat	11,161	-	0.4	2.97	-	13,260
Other cereals	10,676	-	0.4	2.55	-	10,889
Edible legumes	235	1.58	0.4	-	1.7	252
Industrial plants
Cotton	44,293	2.1	0.5	-	2,5	116,268
Sugar beet	77	0.42	0.7	-	10	226
Tobacco	1150	1	0.73	-	2.25	1888
Oilseeds	26	2.2	0.5	-	2	58
Tree Crops
Stone fruits	19	-	0.8	5.88	18	90
Pome fruits	21	-	0.8	5.88	15	101
Acorns	189	1.9	1.6	0.8	5	241
Viniculture	352	0.65	0.5	-	25	2863
Oliveculture	118	1.55	0.8	-	2	292
Other tree crops	73	2	0.8	-	25	2927
					Total	171,847

contains the plant residues for the prefecture of Karditsa, in the year 2015.

The amounts of agricultural residues from the various annual crops (maize, cotton, wheat, tomato, watermelon, etc.) and the prunings, resulting from the cultivation of the perennial plants (cherry, apricot, pear, apple, etc.) are significant. These amounts vary every year and depend on the types of plants grown [20].

Similarly, for the other prefectures we have a total of ~4.3 × 10⁵ t·yr.⁻¹ for Larissa, 1.2 × 10⁵ t·yr.⁻¹ for Magnesia, and 0.9 × 10⁵ t·yr.⁻¹ for Trikala. The total quantity for the produced agricultural residues of all four prefectures for the period 2015–2020 is presented in Figure 1.

2.3. Assessment of Livestock Residues

For the livestock residues, we can estimate the amount of manure per animal species if we know the number of animals. From the live weight of the animal and the number of animals we can calculate the total weight for each animal species. Then, we can calculate the daily volume of waste with a factor to find the daily production in liters for each animal species and multiplying by the specific weight we can then estimate the daily weight of manure [8]. The animal species used were cows of different ages, pigs, sheep, goats, turkeys, and hens. Accordingly, livestock waste is available in large quantities in the region of Thessaly, and there is an increasing trend in recent years.

Table 2. Amount of livestock waste in the prefecture of Karditsa in the year 2015.

Species	Weight of Animals	Number of Animals	Total Animal Weight	Calculation Parameter	Special Weight	Waste Amount
(–)	(kg)	(–)	(kg)	(lt·kg−1 LW *)	(kg·lt−1)	(kg·day−1)	(t·yr.−1)
–	–	×103	×105	×10−2	–	×104	×104
Cattle < 1 month	70	0.22	0.15	5.3	0.977	0.08	0.03
Cattle 1—6 months	140	1.61	2.25	5.3	0.977	1.16	0.43
Cattle 6—24 months	450	3.68	16.6	5.3	0.977	8.58	3.13
Cattle > 24 months	600	5.91	35.5	8.4	1.010	30.1	10.9
Pigs	170	8.71	14.8	5.8	0.977	8.40	3.06
Sheep and goats	60	204	123	4.0	0.977	47.9	17.5
Turkeys	7.5	4.00	0.30	5.6	1.060	0.18	0.06
Hens	2.8	2.64	0.07	5.6	1.060	0.04	0.02
						Total	~35.1 × 104

* LW = Live weight of animal population.

contains the parameters and estimations for the prefecture of Karditsa for the year 2015.

For the rest of the prefectures, we have a total of ~1.9 × 10⁶ t·yr.⁻¹ for Larissa, ~0.5 × 10⁶ t·yr.⁻¹ for Magnesia, and ~0.95 × 10⁶ t·yr.⁻¹ for Trikala. The total quantity for the entire Thessaly Region for the period 2015–2020 is presented in Figure 2.

3. Results and Discussion

3.1. Theoretical Calculation of Biomethane Potential and Biogas Potential of Plant Residues

For the estimation of the biogas potential in agricultural residues, both in tree (perennial) and annual crops, we first need to calculate the corresponding methane potential (MP) [8]. Thus, for perennial crops, where the residues are mostly prunings, the tree crops’ methane potential (TCMP) is calculated using Equation (5):

$$TCMP=M{P}_{pr}·0.73·PR·1000 \left(\mathrm{kg}·{\mathrm{t}}^{-1}\right)$$

(5)

where TCMP is the tree crop methane potential per year (m³·yr.⁻¹), MP_pr is the methane potential per kg of residue (pruning) (m³·kg⁻¹ of residue), and PR is the quantity of residues (prunings) produced per tree crop species (t·yr.⁻¹).

As far as other crops are concerned (cotton, cereals, horticultural, potatoes, corn, etc.), commonly known as annual crops, hay, leaves, roots, and stems are considered residues. The annual crop methane potential (ACMP) is given using Equation (6):

$$ACMP=M{P}_{pr}·P{R}_{res}·1000 \left(\mathrm{kg}·{\mathrm{t}}^{-1}\right)$$

(6)

where ACMP is the annual crop methane potential per year (m³·yr.⁻¹), MP_pr is the annual crop methane potential per kg of residue (m³·kg⁻¹ of residue), and PR_res is the quantity of residues produced per type of annual crop (t·yr.⁻¹).

Since we know the methane potential for both perennial and annual crops, we can calculate the biogas potential of anaerobic digestion using the following formula:

$$BiP=\frac{MiP·100}{\%C{H}_4}$$

(7)

where BiP is the biogas potential of residues of plant origin (m³·yr.⁻¹), MiP is the Methane potential for residues of plant origin (m³ CH₄·yr.⁻¹) [21], and PR_res is the quantity of residues produced per type of annual crop (t·yr.⁻¹). The production of biogas is proportional to the amount of plant residues, with the results presented in

Table 3. Calculation of biogas potential for plant residues in Karditsa Prefecture year 2015.

Cultivation Species	Plant Residue Production	MP	Methane Production	% CH4	Biogas Potential
(–)	(t·yr.−1)	(m3·kg−1 residue)	(m3 CH4·yr.−1)	(–)	(m3·yr.−1)
–	×103	–	×105	–	×105
Horticulture–Vegetables
Cucurbitaceae	2.83	0.18	5.10	55	9.27
Solenoids	4.18	0.18	7.52	55	13.7
Winter vegetables	0.24	0.18	0.44	55	0.80
Miscellaneous vegetables	0.32	0.18	0.57	55	1.04
Potatoes	0.14	0.18	0.26	55	0.46
Industrial tomato	5.81	0.18	10.4	55	19.0
Large scale plants crop
Maize	8.97	0.27	24.2	59	4.10
Durum wheat	13.3	0.36	47.7	55	8.68
Other cereals	10.9	0.28	30.5	55	5.54
Edible legumes	0.25	0.04	0.10	60	0.17
Industrial plants
Cotton	116	0.18	20.9	55	38.0
Sugar beet	0.23	0.10	0.23	58	0.39
Tobacco	1.89	0.18	3.40	55	6.18
Oilseeds	0.06	0.18	0.10	55	0.19
Tree Crops
Stone fruits	0.09	0.18	0.12	55	0.21
Pome fruits	0.10	0.28	0.21	55	0.38
Acorns	0.24	0.18	0.32	55	0.58
Viniculture	2.86	0.28	5.85	55	10.6
Oliveculture	0.29	0.18	0.38	55	0.70
Other tree crops	2.93	0.18	3.84	55	6.99
Stone fruits	-	0.18	-	55	-
Total	172	–	35.1	–	63.4

.

For the other prefectures, we have for the Biogas Potential a total of ~1.6 × 10⁸ m³·yr.⁻¹ for Larissa, ~0.4 × 10⁸ m³·yr.⁻¹ for Magnesia, and ~0.3 × 10⁸ m³·yr.⁻¹. The total quantity for the entire Thessaly Region for the period 2015–2020 is presented in Figure 3.

3.2. Theoretical Calculation of Thermal and Electrical Energy for Agricultural Residues

In the case of AD, heat and electricity cogeneration is applied, where the heat produced is used for consumption in the biogas plant and/or for other uses (e.g., greenhouse heating), while the methane is burned in an internal combustion engine, converting it into electricity [20,22]. The electricity produced is made available through a fixed line supply to the public electricity company (PPC) with an economic benefit and revenue for the biogas plant. Combined heat and power internal combustion engines have an efficiency between 75–90%, of which 55–65% is attributed to thermal energy (THE) and 35–45% to electricity (EE), with the lower calorific value (LCV) of methane being at 10 kWh·m⁻³ [7]. Therefore, the thermal energy produced will be:

$$THEPRO=\% THE efficiency·LCV$$

(8)

$$PARr=\% EE efficiency·LCV$$

(9)

The theoretical values for the generated electricity and thermal energy in all four prefectures in GWh·yr.⁻¹ are presented in

Table 4. Electricity & thermal energy produced for the year 2015 in the four prefectures of Thessaly.

Prefecture	EE		THE
	Min 35%	Max 45%	Min 55%	Max 65%
	(GWh·yr.−1)
Karditsa	92.04	142.00	144.63	205.11
Larisa	237.25	366.04	372.82	528.73
Magnisia	59.89	92.40	94.11	133.47
Trikala	51.43	79.36	80.82	114.62

below for the year 2015.

Whereas, for the period 2015–2020, for the entire Region of Thessaly, are presented in Figure 4. In Figure 5, the mean annual electric and thermal energy using agricultural residues for the Region of Thessaly are presented. From 2015–2020, the mean electric energy that can be produced using agricultural residues ranges from 515–560 Gwh·yr.⁻¹, while thermal energy ranges from 770–837 Gwh·yr.⁻¹.

3.3. Calculation of Solid Residue of Agricultural Residues

Considering that the efficiency of the AD ranges, according to [8], between 55–70%, and the soil amendment production factor is equal to 0.05 of the total volatile solids, we can calculate the total volatile solids and the amount of soil amendment produced, according to the percentage of the volatile solids per crop. The produced soil amendment for the period 2015–2020 in t·yr.⁻¹ for the Region of Thessaly is presented in Figure 6.

3.4. Theoretical Calculation of Biogas, Electricity, and Thermal Energy of Livestock Residues

For the calculation of biogas, we will rely on the data presented in

Table 5. Quantity of biogas produced per animal species from manure.

Animal Species	Organic Content	Biogas [m3·kg−1 VS *]	Average Values [m3·kg−1 VS *]
Sheep and Goats	Proteins, fat carbohydrates	0.30–0.40	0.35
Cattle	Proteins, fat carbohydrates	0.20–0.30	0.25
Poultry	Proteins, fat carbohydrates	0.35–0.60	0.50
Pigs	Proteins, fat carbohydrates	0.25–0.50	0.35

* VS: Volatile solids.

, according to [23].

Based on the assumptions for the agricultural residues, we calculated the cogeneration of both the electrical and thermal energy, and the amount of potentially produced soil amendment. Therefore, Figure 7 presents the biogas potential from the livestock residues for the period 2015–2020, while Figure 8 and Figure 9 present the amount of cogeneration of both the electricity and thermal energy for the period 2015–2020 for the Region of Thessaly, and the mean annual electric and thermal energy using livestock waste for the Region of Thessaly. From 2015–2020, the mean electric energy that can be produced from livestock waste ranges from 348–376 Gwh·yr.⁻¹, with thermal energy ranging from 520–562 Gwh·yr.⁻¹.

3.5. Calculation of Solid Residue of Livestock Residues

For the calculation of the solid residue from the livestock residues, we followed the same methodology as the agricultural residues and are presented in Figure 10 for the Region of Thessaly for the period 2015–2020.

The quantity of agricultural waste from the different annual crops, such as maize, cotton, wheat, tomato, and watermelon, as well as prunings from perennial plant cultivation, such as cherry, apricot, pear, and apple, and manure from animal husbandry, are so significant that we can use them, under the right circumstances, to generate energy [24]. Huge amounts of agricultural waste and animal excrement (manure) are dumped on the ground or piled up outside livestock pens, which releases enormous amounts of methane and carbon dioxide into the air [25]. The generation of renewable energy must be hastened since climate change has started to manifest itself in recent years, and these wastes are one of the most readily available and plentiful raw materials. A sustainable and clean solution to the world’s energy crisis is sought through EU regulations, which seek to gradually phase out fossil fuels and increase the proportion of renewable energy in yearly energy consumption. By employing this kind of biomass for anaerobic digestion, the circular economy may be implemented with a zero-carbon footprint, reducing emissions of greenhouse gases into the atmosphere [21,26].

Thessaly is a typical example of a region in Greece with strong economic activity in the primary sector. Because there are significant amounts of unused agricultural and animal waste in the area, they have the potential to revitalize and raise the region’s proportion of renewable energy sources [27,28]. In this research region, the output of livestock and agricultural residues was predicted to be 4.8 × 10⁶ t·yr.⁻¹ on average for the six-year period 2015–2020, with animal residues accounting for 83% and agricultural residues for 17%. Given that anaerobic digestion is the process employed, the total leftovers have an average biogas potential of 4.7 × 10⁶ m³·yr.⁻¹, while the potential for producing electricity ranges from 708–1091 GWh·yr.⁻¹, and the potential for producing heat energy from 1112–1577 GWh·yr.⁻¹. A solid residue that ranges in quantity from 4.01 × 10⁴ to 5.10 × 10⁴ t·yr.⁻¹ might be acquired from the complete anaerobic digestion process for the purpose of improving the soil in the area. Therefore, it is clear that there is a large amount of biomass in the Thessaly region that is underutilized but could be used for anaerobic digestion to produce energy in the context of renewable energy, laying the groundwork for a sustainable but also more environmentally friendly method of energy production [21].

4. Conclusions

The region of Thessaly in Greece presents an opportunity for energy utilization using agricultural residues and livestock waste through anaerobic digestion. The average agricultural residues were approximately 0.81 × 10⁶ t·yr.⁻¹, while the average livestock waste was 4 × 10⁶ t·yr.⁻¹ for the period 2015–2020. The significant economic activity in the primary sector in Thessaly results in the production of large quantities of unexploited biomass with biomethane and biogas potential. By utilizing anaerobic digestion, biogas can be produced and combusted to generate electrical and thermal energy, contributing to the increased use of renewable energy sources and a more sustainable and environmentally friendly way of energy production. The proposed anaerobic digestion technology could potentially yield 4.8 × 10⁶ t·yr.⁻¹ of biogas in the Thessaly region, producing an estimated 708–1091 GWh·yr.⁻¹ of electricity, which is the primary desired product. Furthermore, the process of anaerobic digestion can also yield a solid residue that can be used to improve the soil in the region. Overall, this case study highlights the potential of the Thessaly region for the production of green energy and the importance of utilizing biomass resources to create a more sustainable future.

However, apart from electrical energy, thermal energy can be produced using cogeneration in significant quantities and in fact in larger quantities than electricity. Thermal energy can be used to heat a greenhouse or a small settlement near a biogas plant. Thus, it is evident that Thessaly could viably exploit its renewable energy sources under an environmentally friendly and an economically viable way. Future research might focus on combining industrial waste, livestock manure, and agricultural leftovers to create heat and electrical energy through anaerobic digestion.