The Potential of Bioethanol from Agricultural Crop Residues: A Case Study of Algeria

Abstract

Due to the ever-increasing energy demand, Algeria’s sustainable energy crisis is a significant problem. Plant and crop residues can be a solution to this problem if they are used for bioethanol production, a viable alternative to fossil fuels. This study explores the potential of existing agricultural crop residues to overcome the sustainable energy crisis in Algeria. Agricultural residues such as cereals, roots and tubers, pulses, oil crops, vegetables, and fruits have great potential to solve the problem. The agricultural residues that are normally wasted can be utilized to produce bioethanol, which provides sustainable energy and also help to obtain a clean environment. It has been found that 1.65 million tons of bioethanol can be produced from Algeria’s available residues, which is equivalent to 44.10 petajoule of energy. Cereal and fruit residues contribute to most bioethanol generation, about 47.22% and 23.38%, respectively. In addition, bioethanol generated from residue can be used in Algeria’s transportation sector. Considering Algeria’s current energy condition, gasoline blended with ethanol such as E10 and E5 can be used in Algerian vehicles since no modification of vehicles is needed for utilizing these fuels. Research indicates that lignocellulosic biomass sources in Algeria, such as Alfa, olive pomace, and cereal straw, could provide up to 0.67 million tons of oil equivalent (Mtoe), representing approximately 4.37% of the energy consumption of the transport sector in Algeria. Algeria has the potential to produce up to 73.5 Mtoe and 57.9 Mtoe of renewable energy utilizing the energy crops. This study will also encourage relevant policymakers to develop sustainable energy policies that will enhance the renewable energy share in Algerian energy dynamics.

1. Introduction

Energy is considered as an indispensable part of human civilization as well as its development. Due to both rapid population growth and advancement in the fourth industrial revolution, energy consumption is increasing day by day [1]. Carbonaceous fossil fuel resources fulfill almost 75% of the world’s total energy demand. Nearly 60% of the greenhouse gas (GHG) emissions come from the energy consumption sector, which creates an adverse impact not only on the environment but also on the people on Earth [2,3]. Moreover, fossil fuel reserves are rapidly depleting, and sooner or later, they will reach their limit. For instance, at present, the world has oil and gas reserves until 2052 and 2088, respectively [4,5,6]. The excessive utilization of fossil fuels all around the globe is warming up the whole world. Moreover, byproduct gases of used natural gas are one of the main reasons for GHG emissions [7]. Upon realizing the adverse impacts of fossil fuel energy, to ensure a sustainable future, many countries are moving towards sustainable and renewable energy [8].

Energy production in Algeria heavily depends on carbonaceous fossil fuel resources, especially oil and natural gas resources, as over 93% of Algeria’s exports are oil and natural gas [9,10]. The high cost of resource imports poses a burden on Algeria. As there is no diversity in the energy scenario and a lack of sustainability, Algeria is trying to create new socio-economic dynamics around renewable energies. Algeria has already developed a master plan program to promote renewable energy, which aims for 22,000 MW of electricity to be generated from renewable resources [10,11]. This will reduce environmental pollution and generate energy in a sustainable way. In Algeria, the overall energy consumption is increasing day by day, which is evident from Figure 1 [12]. It shows that while the primary energy consumption was 1620 PJ in 2009, it increased by 920 PJ in 2019. The increasing trend of energy consumption is expected to continue.

As the energy demand is soaring day by day, more and more energy resources are being utilized to fulfill this, especially the coal and oil resources. The energy supply from various resources in Algeria is shown in Figure 2 [12]. Figure 2 shows that oil and natural gas supply the maximum energy demand, and coal and renewables supply a negligible amount of energy. Most importantly, considering 2018 to 2019, there is no increase in the share from renewable and coal energy.

Algeria, the largest country in Africa, has great potential for renewable energy sources, such as solar, geothermal, wind, and hydro-energy. Several researchers have investigated the potentiality of renewable energy resources in Algeria. Kaid et al. developed a new solar power station surveillance approach to solar PV in south Algeria. They performed their study on an area of 60 ha where 120,120 solar panels were placed [13]. Boudghene Stambouli et al. reviewed the renewable energy potential in Algeria and suggested that Algeria should increase harnessing power from these resources since they are more environment-friendly [14]. Nacer et al. analyzed renewable energy’s technical feasibility and economic viability in Algerian dairy farms. This study shows that their proposed system can generate $4.89\times {10}^8$ MJ/year and reduce greenhouse gas emissions by 80 million tons [15]. Roumanni et al. developed a new wind energy conversion system by considering the wind speed and environmental conditions of Adrar City, located in the south of Algeria. This research found that the sliding mode control (SMC) approach demonstrates the best performance [16]. Saba et al. developed an ontological solution for Energy Intelligent Management (OSEIM) for Ardar city, Algeria, which can save more than 4.5% of energy [17]. Akbi et al. analyzed the biomass potential in Algeria. It was found that urban waste is the most feasible resource for energy generation, and it can produce $6.06\times {10}^9$ MJ of energy through anaerobic digestion [18]. Kalloum et al. analyzed the performance of biogas production from municipal wastewater treatment sludge. This analysis exhibits an exergetic opportunity by generating 11.14 MJ of energy in the process [19]. Eddine et al. explored the potential of solid waste for energy generation in Algeria. In Algeria, per year, more than 10.3 × 10⁶ tons of municipal solid waste are generated. It was also found that 57% of the waste is disposed of in open dumps, 30% of the waste is burned in the open air, 10% is in controlled dumps and landfills, 2% is used for recycling, and only 1% is used for composting [20].

A few studies have been conducted regarding ethanol production in Algeria. Mehani et al. analyzed the biofuel generation from waste dates in South Algeria. This study also examined the characteristics of the produced fuel. They concluded that the low market value of common dates make them a good choice for producing industrial alcohol, and the process of generation is not convoluted [21]. The feasibility as well as the productivity of bioethanol production by anaerobic fermentation and distillation processes from the common date is also studied by researchers in Algeria. It is shown from the study that the distilled and rectified date juice produced ethanol 88° along with a sufficient production rate [22]. Another study led by Nabila et al. showed that in Algeria, the acid treatment of maize should be promoted, as this treatment favors bioethanol production [23]. Meryem et al. studied the possibility of energy production from the fruit waste of Adrar University by anaerobic bioconversion with yeast (Saccharomyces cerevisia). They found that from 100 g of waste, 35 mL of bioethanol can be produced. In addition, their research reveals that local natural resources have great potential for bioethanol production [24]. Gares et al. analyzed the potential of Algerian alfa (Stipa tenacissima), olive pomace, and cereal to produce bioethanol in Algeria [25]. While bioethanol production from crop residues has been widely studied globally, there is a lack of focused research on the specific challenges and opportunities associated with using agricultural residues in Algeria and the North African context. Although there have been studies on bioethanol production from biomass in other parts of the Mediterranean region, most focus on crops such as corn, wheat, or sugarcane and the yield optimization of conventional feedstocks like sugarcane or corn stover. However, in Algeria, there is limited research addressing the utilization of local agricultural residues, such as wheat straw, barley straw, and date palm residues.

In this study, all these residues are considered for bioethanol generation. But considering real-life scenarios we must consider the residue recovery ratio, as not all the residues can be extracted for energy generation, and an excess of this residue recovery can create adverse impacts on future yields [26]. All these previous studies either explored Algeria’s renewable energies on a general scale or just for some specific cities of Algeria. No insightful study has been found that can assess and analyze Algeria’s currently available agricultural residues, nor can it assess the potential of bioethanol generation from these available agricultural residues. This study will explore the potential of agricultural residue generation from various crops such as cereals, roots and tubers, pulses, oil crops, vegetables, and fruits in Algeria. Producing bioethanol from these wastes promotes the Algerian government’s ambitious goal to ensure sustainable energy and reduce fossil fuel emissions in various sectors of the Algerian economy.

2. Topography and Energy Status of Algeria

2.1. Demographic Information

Algeria has a population of over 43 million, and it is the tenth-largest country in the world, which is situated between latitude 35° and 38° N as well as longitude 8° and 12° E [10]. It has an overall area of 2,381,741 km², and the ‘Sahara’ desert occupies a significant portion of this land. There are three climate zones: the semi-arid zone in the High Plateaus region, the Mediterranean zone in the northern part, and the arid climate zone in the southern part of Algeria [14]. In Algeria, the mean annual temperature is 12 °C, and the mean precipitation varies annually from 150 mm to 500 mm. The southwestern region of Algeria has the highest wind energy potential, as the wind velocity is more than 6 m/s. Moreover, the average solar energy received is 1700 kWh/(m²/year) for the northern region and 2650 kWh/(m²/year) for the Sahara region of Algeria. Due to its geographical location, Algeria has a high renewable energy potential, such as wind, geothermal, biomass, and solar [27].

2.2. Bioenergy in Algeria

Bioenergy is an emerging solution for Algeria. The arable land area in Algeria is increasing every year; for instance, in 2017, 5,214,123 ha were cultivated, which was 158,547 ha greater than the previous year [28]. Forest reserves are estimated to provide 3700 ktoe of energy with a 10% recovery rate. Agricultural residues and urban waste provide 1.33 ktoe of energy as well. Maritime pine and eucalyptus are also considered useful energy harvesting plants found in Algerian forests [29]. Moreover, recent research predicted that $6.12\times {10}^9$ MJ of electricity can be generated by utilizing waste [14]. For bioenergy generation, municipal waste and industrial waste have the highest potential; while municipal waste consists of household and similar wastes, sewage sludge, and wastewater from treatment plants (WWTP), industrial waste generally consists of agricultural waste, vegetable waste, dairy industries waste, and oil waste [18]. The amount of household waste from other similar waste generation sources is constantly increasing in Algeria. For example, in 2012 households and similar wastes accounted for $10.3\times {10}^6$ tons, but in 2014 they increased to $11\times {10}^6$ tons [30]. Also, the per capita waste generation is rapidly increasing, and in 2025 it is expected to be 1.45 kg/Capita/Day [31]. Among these, 85% were domestic and commercial wastes, while 15% were generated by industry. By utilizing the maximum portion of these wastes they could be converted into electrical energy. In 2014, if proper measurements and technology were used, $8.7\times {10}^6$ tons of household waste and other similar wastes could have been converted to sustainable energy [18,32]. Sewage sludge from wastewater treatment plants is also a viable source of bioenergy in Algeria. As an organic substance, this waste can be utilized to produce both electricity and heat. The annual sludge production and dry substrate production in Algeria are 250 kt and 62.5 kt, respectively. Utilizing this massive amount of sludge, $1.39\times {10}^{98}$ MJ of electrical energy could be generated and 13.75 million m³ of biogas could be harnessed [18]. Among the industrial wastage, vegetable waters (amurca) and olive waste have a good potential for energy generation. In 2013, 258,800 m³ of vegetable waters as well as 129,400 kt of olive oil wastes were generated. Olive oil wastages and vegetable waters could produce $2.58\times {10}^9$ MJ and $6.38\times {10}^7$ MJ of electrical energy, respectively, in 2013 [18,33,34]. Poultry farming also generates 1314 kt of liquid manure as well as 125 kt of solid manure per year. Waste from milk processing as well as slaughterhouse waste has a good amount of bioenergy potential. In 2012, 47 kt of whey was produced from the dairy industries, generating $1.4\times {10}^7$ MJ of electrical energy in Algeria [28]. Considering municipal waste and industrial and agricultural wastages in 2013, $1.0176\times {10}^9$ m³ of biogas and $6.14\times {10}^9$ MJ of electrical energy could be generated in Algeria [18].

2.3. Bioethanol Generation

Biomass is considered a sustainable resource in many countries [35,36,37]. Biomass-based power plants are being recognized in various countries of the world to ensure sustainable energy for communities [38,39,40,41]. Approximately 26.5% of the electricity comes from renewable resources; however, among this, only 2.2% is supplied by bioenergy across the globe [42]. For sustainable electricity production, bioethanol can be used as a viable renewable energy source [43]. Utilizing the huge amount of bioenergy resources, Algeria could generate bioethanol for sustainable utilization. Various countries in the world are trying to produce biofuels from inexhaustible biomass, and bioethanol generation is gradually increasing.

As can be seen in

Table 1. Bioethanol production by different countries or regions in 2016 (in tons) [44].

Country	Tons
World	79,246,960
USA	45,597,500
Brazil	21,812,050
Europe	4,117,230
China	2,526,550
Canada	1,303,640
Rest of the world	3,889,990

, the USA leads the world in bioethanol production. Agricultural residues, such as cereal waste, pulses, oil crops, roots and tubers, vegetables, and fruit waste, have a higher potential for bioethanol production in Algeria [44]. Various elements such as ash, fixed carbon, nitrogen, hydrogen, oxygen, volatile matter, sulfur, cellulose, hemicellulose, and lignin are found in agricultural residues. The work of Zabed et al. provides the percentage of cellulose, hemicellulose, and lignin found in various agricultural residues [45]. The percentage of different elements like volatile matter, fixed carbon, ash contents, nitrogen, hydrogen, oxygen, high heating values, and sulfur found in agricultural residues can be obtained by a proximate and ultimate analysis. Agricultural residues have a heating value from 14.66 to 20.58 (MJ/kg), as well as a 14–24% fixed carbon content, 38–50% carbon, a 30–43% oxygen content, and a volatile content from 61.2 to 76.05% [1]. The calorific value of bioethanol is 26.70 MJ/kg, while the water content is 2.024 g kg⁻¹. At 15 °C the density of bioethanol is 790.0 kg/m³, while its kinematic viscosity is 1.130 mm²/s at 40 °C. Apart from this, the flashpoint of bioethanol occurs at 13 °C [46].

2.4. Technologies for Bioethanol Generation

The life cycle of bioethanol production from agricultural crops starts with the collection of crop residues, which are mainly the non-food parts of plants left after harvesting. Other key processes involve the preprocessing of the crop residues, hydrolysis, fermentation, and the final product.

Lignocellulose is the most abundant waste biopolymer material available on Earth. Carbohydrate polymers, such as cellulose and hemicellulose, as well as non-carbohydrate polymers comprise lignocellulose biomass [47]. Lignocellulose biomass residue is considered as a potential feedstock for sustainable fuel production [48]. Three major steps are required to convert agricultural residues to bioethanol: pretreatment, hydrolysis, and fermentation [1]. Among these three steps, the pretreatment is the costliest one, as there is the consideration of liquid handling, solid processing, and the treatment of carbon monoxide products. By improving the efficiency of this method, the production rate can be maximized while the total cost can be minimized [49,50]. Considering economic aspects, feedstock types, and ecological impacts, different pretreatment methodologies have been employed in various regions [51].

Typically, the pretreatment method is performed by dissolving recalcitrant, minimizing the particle size, and expanding the surface area for better bioethanol production. Pretreatment methods can be classified into four categories: physical, chemical, biological, and combined methods [52]. Among different physical methods, steam explosion, hydrothermal, and microwave-assisted pretreatments are mostly used. Other pretreatment methods such as milling, electron beam irradiation, photocatalysis, homogenization, and milling are infrequently used [53,54,55,56]. In the steam explosion method, vapor pressure is utilized, and substantial decompression is needed to deconstruct recalcitrant components of biomass. High-pressure saturated steam fractures the cell wall and releases the hemicellulose as well as lignin fractions. The steam explosion affects the physicochemical properties of lignocellulose biomass. Although it is highly energy efficient and has minimal environmental effects, the lignin removal rate is not satisfactory and produces noxious compounds [57,58,59]. Similarly to the steam explosion method, a microwave-assisted pretreatment is widely used in the process of lignocellulose biomass. Utilizing microwave heating, penetration occurs at the rigid structure of the lignocellulose biomass. Several studies have analyzed the microwave pretreatment and determined this pretreatment technology [60,61,62,63], which requires low activation energy [52].

The hydrothermal (liquid hot water) pretreatment is considered a physicochemical green pretreatment technology. In this method, high-pressure hot water at 160 °C–240 °C is supplied to lignocellulose material in order to maintain consistent material degradation. Although it has the advantages of a low-cost procedure as well as no use of chemical reagents, it consumes a sufficient amount of energy and water in the process [64,65].

In the context of chemical pretreatment technologies, the most prominent methods are alkaline, acidic, ionic liquid, and organic solvents. Acid pretreatment is a well-known method for treating lignocellulose biomass, where concentrated acids or diluted acids can be used for pretreating [52]. In dilute acid pretreatments, the acid consumption is lower, but a higher temperature is needed [66]. In the case of acid pretreatment technologies, phosphoric acid, acetic acid, and sulfuric acid cause disruption in the lignocellulose structure, especially breaking polysaccharide–lignin linkages and generating sugar [65,67]. It has significant drawbacks of inhibitor generation and high costs associated with the acid recovery process [68]. The alkaline pretreatment method is slow compared to other methods, but it is one of the simplest processes to generate bioethanol from lignocellulose biomass. In this method, lignin components present in the biomass can be removed efficiently while improving the surface area of the biomass [69,70]. For organic solvent pretreatment methods, phenols, acetone, amines, propionic acid, etc., can be used as an organic solvent to convert the lignocellulose material into lignin, cellulose, and hemicellulose, which will then be converted to bioethanol. Though various types of organic solvents can be used, ethanol and methanol are widely used owing to their high recovery rate and low cost compared to other organic solvents [71,72,73]. Although ionic liquid pretreatment requires a high amount of energy and a high percentage of wastage generation, it is one of the emerging technologies in pretreatment methods, as it can produce a high amount of sugars and carbohydrates, which can eventually generate bioethanol [74,75]. Currently, various types of ionic liquids are utilized for pretreatment, but acidic ionic liquid shows greater potential, as it has a profound impact on the depolymerization of the lignin component of biomass. However, researchers are now investigating how to reduce the overall cost and amount of waste generated from this method [76].

One of the advantages of the biological pretreatment method is that it does not require chemical recycling; therefore, this process is eco-friendly. Moreover, this process has a lower operating cost, a lower amount of inhibitor generation, and low energy consumption compared to other processes [77,78]. Typically, bacteria, fungal species, or enzymes are used in the biological pretreatment process. Phanerochaete chrysosporium, Trichoderma reesei, Trichoderma viride, and Aspergillus niger are normally used for fungi-based biological treatment processes. Clostridium sp., Cellulomonas sp., and Bacillus sp. are used in the bacteria-based biological treatment process. Cellulase, b-glucosidase, and xylanase are the most commonly used enzymes in the biological treatment process [79,80,81]. In the biological pretreatment process, disrupting the crystalline structure, lignin is omitted. Cellulolytic as well as hemicellulolytic microorganisms are utilized to produce sugars. The fungal pretreatment process is however slower than bacterial or enzymatic pretreatment processes [82,83].

Considering the problems of single-treatment technologies and lower efficiencies, combined methods have been proposed to improve the overall efficiency of the process. Various research projects have been conducted on combined pretreatment methods [84,85,86,87]. A combination of physical and chemical methods with a fungal pretreatment can overcome the problems of single pretreatment processes [52]; for instance, hydrogen peroxide with the steam pretreatment method increased the xylose and glucose yield [88]. In another study, a fungal and dilute acid pretreatment on olive tree waste causes a 51% increase in sugar generation [89]. The pretreatment is performed to remove the lignin and hemicellulose component from the biomass, as well as to hydrolyze separated cellulose to produce the sugar content. The sugar content is then fermented to produce bioethanol [1]. First, by breaking up the carbohydrate chains of cellulose, it is converted to sugar, and then in the fermentation process, it is converted to bioethanol because of microorganism activities [52]. The overall flow of the process of converting lignocellulose material to bioethanol is shown in Figure 3.

Different feedstocks follow different processes for pretreatment and their hydrolysis methods. The main components, pretreatment and hydrolysis methods, for bioethanol generation from different stocks are shown in

Table 2. Pretreatment and hydrolysis methods for bioethanol generation [90].

Feedstock	Main Components	Pretreatment Methods	Hydrolysis Methods
Cereals	Starch	Milling, gelatinization	α-amylase, glucoamylase
Roots/Tubers	Starch	Washing, chopping, gelatinization	α-amylase, glucoamylase
Pulses	Starch, protein	Dehulling, soaking, milling	α-amylase, glucoamylase, proteases
Oil Crops	Oil, protein	Oil extraction, milling	Cellulases, hemicellulases (meal)
Vegetables	Fiber, sugars	Washing, chopping, thermal	Cellulases, pectinases
Fruits	Simple sugars, pectin	Washing, crushing, pectinase	Direct fermentation, pectinases

[90].

3. Data and Methodologies

3.1. Agricultural Sector of Algeria

The agricultural sector provides 8% of the GDP of Algeria [25]. The area used for agricultural production varies annually. Figure 4 shows the hectares of land used for agricultural crop production in Algeria from 2011 to 2017 [28].

It is evident from Figure 4 that the overall trend of the used area for agricultural crop production gradually increased, though there is some reduction in 2014 and 2015. In 2014, the area used for agricultural production was the smallest for cereal production, which was 2,509,193 ha, while in 2015 the area used for cereal production was 2,686,254 ha. Due to this decrease in cereal production, the agricultural land usage was decreased.

3.2. Agricultural Crop Percentage

Despite being the tenth-largest country in the world, only 4% of Algeria’s land is cultivable. It produces various types of crops, which eventually create opportunities for various types of residues. Algeria’s main crops are cereals, oil crops, vegetables, various fruits, roots and tubers, and pulses [28]. In this study, these major agricultural crops’ production data from 2017 are analyzed to find their available residues, and results are compared in

Table 3. Crop area, production, and yield data [28].

Class	Crops	Area (ha)	Yield (hg/ha)	Production (Tons/Year)
Cereals	Barley	1,303,149	7441	969,696
	Maize	2025	13,007	2634
	Oats	87,816	7290	64,018
	Rice and paddy	155	20,179	313
	Sorghum	312	159,391	4973
	Wheat	2,118,469	11,501	2,436,503
Roots and Tubers	Potato	148,822	309,524	4,606,402
Pulses	Beans (dry)	1902	7781	1480
	Broad beans, horse beans (dry)	40,361	11,609	46,856
Oil Crops	Groundnuts	3666	27,745	10,171
	Olives	432,959	15,809	684,461
	Rapeseed	11,590	19,802	22,950
	Seed cotton	260	3077	80
	Sunflower seed	191	4501	86
Vegetables	Beans (green)	11,434	85,712	98,003
	Carrots and turnips	16,963	239,565	406,374
	Onions (dry)	48,301	294,054	1,420,310
	Pumpkins, squash, and gourds	13,085	235,278	307,861
	Tomatoes	23,977	536,467	1,286,286
Fruits	Apples	44,620	110,767	494,239
	Bananas	16	199,881	315
	Dates	167,643	63,143	1,058,559
	Grapefruit (including pomelos)	88	215,691	1897
	Grapes	69,569	81,441	566,579
	Lemons and limes	4234	183,646	77,757
	Oranges	49,942	203,025	1,013,951
	Tangerines, mandarins, clementines, and satsumas	14,414	173,902	250,669
	Watermelons	57,343	329,818	1,891,274

[28]. For the cereal class, barley, maize, oats, rice and paddy, sorghum, and wheat were considered. Potato was considered in the roots and tuber classification, and Algeria is the seventeenth largest producer of potatoes in the world [28]. For oil crops, groundnuts with shells, olives, rapeseed, cotton seed, and sunflower seeds were studied. Finally, for the vegetables list, beans (green), carrots and turnips, onions (dry), pumpkins, squash, gourds, and tomatoes are considered. And for fruits, apples, bananas, dates, grapefruit (including pomelos), grapes, lemons and limes, oranges, tangerines, mandarins, clementines, satsumas, and watermelons were investigated. Beans were considered in the pulse crop classification.

It can be seen from Table 3 that fruit generation is 5,355,240 tons and cereal generation is 3,478,137 tons, which are 30% and 20% of the whole crop production, respectively. Roots and tubers (Potato) and vegetables contribute 26% and 20% of the whole agricultural crop production. If we consider the land used for production, cereal contributes the most, since cereal crops use 3,511,926 ha of agricultural land, which contributes 75% of the total agricultural area. Oil crops contribute 10%, and vegetables contribute 9% of the total land used for agricultural crop production. Among cereal crops, barley and wheat are the most cultivable crops. Wheat is cultivated in 2,118,469 ha of the area and barley is cultivated in 1,303,149 ha of area. Other cereal crops are also cultivated, such as maize, oats, rice and paddy, and sorghum, but they are quite small in comparison to wheat and barley. Potato is considered the most important root and tuber crop in Algeria. In 2017, 148,822 ha of the area was cultivated for potato production, with a yield of 309,524 hg/ha. Among oil crops, olives contribute the maximum; 684,461 tons of olives were produced in 2017, which is 95% of the total oil crop production. Rapeseed is the second most produced oil crop. In 2017, 11,590 ha of agricultural lands were utilized to produce 22,950 tons of rapeseed, with a yield rate of 1980 kg/ha. Although groundnuts with shells, cotton seed, and sunflower seed are produced, we exclude their percentage due to small production. These crops contribute to the rest of the 2% of the oil crops. Fruits and vegetables are produced in a considerable amount in Algeria. In the context of vegetable crop production, onion (dry) contributes the most. Onion is produced in 48,301 ha of the area, producing 1,420,310 tons of onion (dry). This onion crop took up to 42% of the total land cultivated for vegetable crop production and produced 40% of the total vegetable crop generation. Though tomatoes are cultivated on 23,977 ha (21% of the total land used for vegetable production), they produce 1,286,286 tons of tomatoes, which is 37% of the overall vegetable generation in 2017. Beans (green), carrots and turnips, pumpkins, squash, and gourds are also produced in Algeria, but their contribution to the vegetable generation is less than 15% individually; 406,374 tons of carrots and turnips are produced, which contribute 12% of the total vegetable production.

In this study, several crops are considered the highest/greatest contributors to the food sector. Considering this, fruits, dates, grapes, watermelons, and oranges use 41%, 17%, 14%, and 12% of the total land, respectively. Though dates are produced in a larger area, regarding the total fruit production, they are behind watermelons. In 2017, 1,891,274 tons of watermelon were produced, which was 35% of the total fruit production considered in this study. Date and orange production comprised 20% and 19%, respectively, of the overall production of fruits in Algeria. The total amounts of grape and apple produced in 2017 were 568,476 tons and 494,239 tons, respectively, which were 11.5% and 9% of the total production of the fruits.

Various agricultural residues are generated from these crops and also from the subsequent process. Various types of crop residue that can be found from the agricultural crop are shown in

Table 4. Various types of crops residue from agricultural residues [21,24,25,91].

Crops	Types of Residues
Cereals	Stover, cobs, straw
Root and Tubers	Peel, cull, green immature potatoes
Pulses	straw
Oil Crops	Pomance, straw
Vegetables	Pomace, peel, cull,
Fruits	Peel, pomace, stem, bagasse, waste fruits

[21,24,25,91].

The main companies involved in bioethanol production in Algeria are shown in

Table 5. Different companies involved in bioethanol production in Algeria [92].

Company Name	Type of Activity	Notes
Sonatrach	National oil and gas company	Exploring biofuel production from oleaginous plants; no operational bioethanol plant.
Cevital	Conglomerate with interest in bioethanol	Plans to build a corn-based ethanol plant in Brazil; no bioethanol plant in Algeria.
Global Bioenergies	Biotechnology company	Developing renewable isobutene and bioethanol; no operational bioethanol plant in Algeria.
Petroser Services Algérie (PSA)	Oil and gas services company	No known involvement in bioethanol production.
Bioethanol Algérie	Proposed bioethanol company	No operational bioethanol plant yet

. There are already some companies developing and working on the bioethanol production, while some are proposed or future actions.

3.3. Residue Recovery and Bioethanol Generation

The availability of crop residue is one of the major factors determining the potential of bioethanol generation in Algeria. The measurement of the total amount of crop residue per unit of cropland is essential, and this includes the estimation of the actual amount of residue that can be used without hampering future yield and preventing land erosion [93]. Furthermore, energy from crop residues in various countries has been studied by various researchers [94,95,96,97]. For residue generation measurement, the residue to crop ratio coefficient is utilized in this study. Moreover, it is established from several studies that residue to crop coefficients can be used to extrapolate the available energy potential [93,94,98]. This extensive study is performed on most agricultural crops whose residue to the crop ratio is available in Algeria; therefore, from valid references, this study has taken available crop-to-residue ratio data to assess actual biomass residue.

The objective of this research is to report on the potential for energy production from crop residues based on Algeria’s agro-ecological regions’ true potential as evidenced by long-term data. Moreover, while recovering residues, environmental concerns and the future generation of residue must be considered, as extracting the excess amount of residue beyond the limit will cause erosion of land as well as hamper future production, which, in turn, create long-term adverse impacts. For developed countries, it is established by research that 35% of the residue can be extracted to ensure these above aspects [26]. This study has addressed this, and for residue recovery, 35% of the overall residue for every crop is considered in this study. Residue generation is found by multiplying the residue-to-crop ratio by the amount of crop production. Mathematically,

$${\mathrm{R}}_{\mathrm{g}}={\mathrm{A}}_{\mathrm{c}}\times {\mathrm{R}}_{\mathrm{C}}$$

(1)

where R_g = residue generation;

A_c = crop production;

R_c = residue to crop ratio.

The available residue that can be recovered is multiplied by the bioethanol conversion rate to find the amount of bioethanol that can be found in agricultural crops [1]. Mathematically,

$$\mathrm{B}={\mathrm{R}}_{\mathrm{g}}\times \mathrm{C}\mathrm{R}$$

(2)

where B = amount of bioethanol;

CR = conversion rate of bioethanol.

3.4. Economic Evaluation

The economic evaluation of converting agricultural crop residues to bioethanol involves assessing the financial feasibility and profitability of the entire process. This evaluation includes factors such as the cost of raw materials, processing costs, energy inputs, infrastructure requirements, market conditions, and potential revenue. The goal is to determine whether the bioethanol production process can generate positive economic returns and contribute to sustainability in both the agricultural and energy sectors.

The cost of raw materials depends on the availability, opportunity, and seasonality. It can be calculated from

$$\mathrm{Feedstock} \mathrm{cost}=\mathrm{Quanity}\times \mathrm{Per} \mathrm{unit} \mathrm{cost} \mathrm{of} \mathrm{feedstock}$$

(3)

The total processing cost involves the pretreatment, hydrolysis, fermentation, and waste management. Processing costs can account for a large proportion of the total production cost, so minimizing energy consumption and improving the efficiency of pretreatment, fermentation, and distillation are crucial for economic viability.

$$\mathrm{Processing} \mathrm{cost}=\sum \mathrm{Pretreament} \mathrm{cost}+\sum \mathrm{hydrolysis} \mathrm{cost}+\sum \mathrm{fermentation} \mathrm{cost}+\sum \mathrm{waste} \mathrm{management} \mathrm{cost}$$

(4)

Capital investments accounted for land, infrastructure development, maintenance, and upgrade. The revenue from bioethanol and coproducts can be calculated from

$$\mathrm{Revenue} \mathrm{from} \mathrm{bioethanol}= \mathrm{Amount} \mathrm{of} \mathrm{ethanol}\times \mathrm{per} \mathrm{unit} \mathrm{price}$$

(5)

$$\mathrm{Revenue} \mathrm{from} \mathrm{coproducts}=\sum (\mathrm{Quantity} \mathrm{of} \mathrm{by} \mathrm{products}\times \mathrm{per} \mathrm{unit} \mathrm{price})$$

(6)

The Net Present Value (NPV) is used to assess the profitability of bioethanol production over time. It is calculated as the difference between the present value of cash inflows and the present value of cash outflows:

$$\mathrm{N}\mathrm{P}\mathrm{V}={\sum }_{\mathrm{t}=1}^{\mathrm{n}}{\displaystyle \frac{{\mathrm{R}}_{\mathrm{t}}}{(1+\mathrm{i}{)}^{\mathrm{t}}}}-{\mathrm{C}}_{\mathrm{o}}$$

(7)

where R_t is revenue in time period t, i is discount rate, t is time period, n is total time, and C_o is initial capital investment.

The payback period is the time it takes for the investment to recover the initial capital expenditure through the net cash inflows:

$$\mathrm{Payback} \mathrm{period}={\displaystyle \frac{{\mathrm{C}}_{\mathrm{o}}}{\mathrm{Annual} \mathrm{net} \mathrm{cashflow}}}$$

(8)

Global fuel prices, government policies and subsidies, supply chains, and logistics play a key role in the economic evaluation for bioethanol production.

4. Results and Discussion

4.1. Agricultural Residues Recovery

The residue generated by these crops and residues that can be used for bioethanol generation found from Equation (1) is tabulated/calculated and presented in

Table 6. Residue generation from agricultural crops in 2017 [93,95,99].

Class	Crops	Residue (Tons/Year)	Residue Recovery (Tons/Year)	Residue to Crop Ratio
Cereals	Barley	1,309,089	458,181	1.35
	Maize	5162	1806	1.96
	Oats	90,905	31,816	1.42
	Rice, paddy	416	145	1.33
	Sorghum	12,154	4253	2.44
	Wheat	3,118,723	1,091,553	1.28
Roots and Tubers	Potato	1,842,560	644,896	0.4
Pulses	Beans (dry)	2812	984	1.9
	Broad beans, horse beans (dry)	89,026	31,159	1.9
Oil Crops	Groundnuts	21,359	7475	2.1
	Olives	1,437,368	503,078	2.1
	Rapeseed	48,195	16,868	2.1
	Seed cotton	168	58	2.1
	Sunflower seed	180	63	2.1
Vegetables	Beans (green)	39,201	13,720	0.4
	Carrots and turnips	162,549	56,892	0.4
	Onions (dry)	568,124	198,843	0.4
	Pumpkins, squash, and gourds	123,144	43,100	0.4
	Tomatoes	514,514	180,080	0.4
Fruits	Apples	988,478	345,967	2
	Bananas	630	220	2
	Dates	2,117,118	740,991	2
	Grapefruit (including pomelos)	3794	1327	2
	Grapes	1,133,158	396,605	2
	Lemons and limes	155,514	54,429	2
	Oranges	2,027,902	709,765	2
	Tangerines, mandarins, clementines, satsumas	501,338	175,468	2
	Watermelons	3,782,548	1,323,891	2

. Table 6 shows that from cereal crops, 4,536,452 tons of residues were generated in 2017, of which 68.75% came from wheat and 28.85% came from barley. From pulses, 91,838 tons of residues are produced in the same year. Potatoes, which fall in the category of roots and tubers, generated 1,842,560 tons in the year 2017. The maximum of the residues generated from the oil crops come from the olives, which is approximately 95%. The total oil crop residue is 1,507,270 tons. Onions and tomatoes are the top generators of residues, as in the case of vegetables. Tomatoes produce 514,514 tons of residue, which is almost 37% of the total vegetable residue of 1,407,533 tons. Onions produce 568,124 tons of dry residue, which makes them the top contributor to the vegetable residue. Among all the classes of crop residues, fruits produce most of the 10,710,480 tons. In these residues from fruits, watermelons, dates, and grapes contribute 35.3%, 19.76%, and 18.93% of the total fruit residues.

The amount of recovered crop residue from various classes of crops is shown in Figure 5. Considering the six classes of crops, the overall residue recovery is 7,033,647 tons. Among these, cereals, roots and tubers, pulses, oil crops, vegetables, and fruits produce 22.57%, 9.16%, 0.45%, 7.50%, 7.0%, and 53.29% of the total residue recovered. Considering all these crops, watermelons produce 1,323,891 tons that can be recovered for bioethanol production, which is the most for any single crop. Wheat comes in second by producing 1,091,553 tons of recoverable residues.

4.2. Agricultural Residue to Bioethanol

Different crops have a different bioethanol conversion rate. However, studies for all crop residues’ bioethanol conversion rates for Algeria are missing; therefore, in this study, we have taken valid bioethanol conversion rates of agricultural crops from the published literature, which are shown in

Table 7. Bioethanol conversion from residue (g/kg) and bioethanol yield (tons/year) [91,100,101,102,103,104,105,106,107].

Class	Crops	Bioethanol Conversion from Residue (g/kg)	Bioethanol (Tons/Year)
Cereals	Barley	498.91	228,591
	Maize	487.89	881
	Oats	498.91	15,873
	Rice, paddy	521.09	75
	Sorghum	498.91	2122
	Wheat	487.89	532,557
Roots and Tubers	Potato	166.479	107,361
Pulses	Beans (dry)	363.51	357
	Broad beans, horse beans (dry)	363.51	11,326
Oil Crops	Groundnuts	492.19	3679
	Olives	492.19	247,610
	Rapeseed	460.2	7762
	Seed cotton	492.19	28.9
	Sunflower seed	492.19	31
Vegetables	Beans (green)	363.51	4987.5
	Carrots and turnips	178.98	10,182.6
	Onions (dry)	327	65,021
	Pumpkins, squash, and gourds	416.05	17,931.9
	Tomatoes	50.67	9124
Fruits	Apples	190.149	65,785
	Bananas	175	38
	Dates	197.25	146,160
	Grapefruit (including pomelos)	53.652	71
	Grapes	53.652	21,278
	Lemons and limes	36.11	1965
	Oranges	134.919	95,760
	Tangerines, mandarins, clementines, satsumas	47.1	8264
	Watermelons	35.5	46,998

.

The hypothetical bioethanol conversion rate is based on the hemicellulose and cellulose content found in various agricultural residues [1]. By utilizing Equation (2), the bioethanol generation from agricultural residue has been calculated.

4.3. Contribution of Various Crops in Bioethanol Generation

It was found that 1.65 million tons of ethanol could be generated in 2017. The calorific value of 1 kg of bioethanol is 26.70 MJ/kg. As a result, overall, 44.10 PJ of energy could be produced from the generated bioethanol in 2017. Overall, the bioethanol generation from crop residues is shown in Figure 6. Though residues from cereal crops are less than those of fruits, in the case of bioethanol generation, the highest amount of bioethanol generated was from cereal crop residues. From the cereal crop residue, 780,102 tons of bioethanol could be generated, which is 47.22% of the crop residues’ overall bioethanol production. The next highest portion of bioethanol comes from fruit wastes, which contribute 23.38% of the overall bioethanol production from crop residues. The total bioethanol production of bioethanol from fruit waste is 386,323 tons. The oil crop residue produces 15.69%, and vegetable residues, as well as root and tuber residues, produced 6.49% of the total bioethanol production from agricultural crops.

Various countries produce lots of bioethanol from different types of agricultural crops. The USA is the top producer, with 77.74 kt of bioethanol from $1.05\times {10}^9$ kt of wheat waste. In Iran, from $4.3\times {10}^9$ kt wheat wastes, 1.88 kt of bioethanol can be produced [108,109].

In Algeria, from 2009 to 2018, the trend of oil consumption in the transportation sector is shown in Figure 7 [110]. In 2017, 14,204 ktoe of oil, which is equivalent to 594.69 PJ of energy, was consumed in Algeria’s transportation sector, and 85% of the goods and passengers used the road as their primary transport. The Algerian transport sector consists of 112,696 km of roads and 29,567 km of highways. Moreover, the number of vehicles in Algeria is increasing day by day. From 2003 to 2013, the road fleet size increased by 41% [111]. Light-duty vehicles comprise 63% of the total.

Table 8. Vehicles run by various fuels [111].

Fuel	Percentage of Vehicles Run of Fuels	Total Amount (ktoe)
Diesel	66%	8716
Gasoline	31%	4050
LPG	03%	366

shows the percentage of vehicles that used various types of fuels in Algeria.

Diesel and gasoline have an energy content of 50.04 MJ/L and 45.72 MJ/L, respectively [112], but these fuels have higher CO₂ emissions, which hinder the sustainable development goals of Algeria. Moreover, gasoline has a higher sulfur content, resulting in SO₂ pollution; although, mixing ethanol with gasoline could reduce the sulfur content as well as SO₂ emissions. Ethanol has a 15% higher combustion rate than gasoline [45]; thus, using bioethanol for the transportation sector can foster Algeria’s ambitious plan: renewable energy integration by 2030. Ethanol, which is widely used in the transport sector and is a colorless liquid, can cause less environmental pollution; moreover, it is low in toxicity and biodegradable; therefore, it has a promising future as it can be used as a fuel or fuel enhancer in Algeria. It has a 35% oxygen content, which means it can burn easily and reduce CO₂ emissions. As a result, it has positive implications. Because of ethanol’s high octane number, it can be used as a mixture with gasoline [113,114]. Typically in lighter vehicles, E85 (15% gasoline, the rest is bioethanol) is used [115]. The most commonly used bioethanol and fuel mix is ‘E10’, which comprises 10% ethanol and 90% petrol, and vehicle engines require no modification for using this [116]. Another mixture of bioethanol that can be used in the transport sector without vehicle modifications is ‘E5’, which is a blend of 5% ethanol and 95% gasoline. It can also be used in SI engines without any modification, which is proven by the study [117]. While a ton of ethanol produces 1.91 tons of CO₂, 1 ton of petrol emits 3.3 tons of CO₂. Though bioethanol emits CO₂, it is carbon neutral because the same amount of CO₂ is consumed during photosynthesis and released during combustion. This indicates that net CO₂ emissions from fossil fuels such as petrol and diesel are higher than bioethanol combustion [116]. In 2013, in the Algerian transport sector, 4 million TOE of energy was used, which is equivalent to 2698.22 kt of gasoline [118]. Utilizing E5 can reduce 134.91 kt of gasoline, while using E10 can reduce 269.82 kt of gasoline. Furthermore, considering the per ton price of gasoline in Algeria, USD 470.69, USD 63.5 million, and USD 127 million can be saved by using E5 and E10 in the transport sector [119]. Each ton of ethanol produces 1.39 tons less of CO₂ than per ton of gasoline, but 1 ton of Gasoline is equivalent to 1.5 tons of bioethanol. CO₂ emissions from using only E0 (only gasoline), E5, and E10 are also shown in

Table 9. CO₂ emissions by various fuels [119].

Parameter	E0	E5	E10
Total gasoline (Kt)	2698.22	2563.31	2428.4
CO2 emission (Kt)	8904.1	8458.9	8013.7
Bioethanol (Kt)	0	202.36	404.73
CO2 emission of bioethanol (Kt)	0	386.51	773.03
Total CO2 emission (Kt)	8904.1	8845.41	8786.73
In percentage (%)	0	0.6	1.32

. It is seen from the table that using E5 can reduce 0.6% and 1.32% of CO₂ emissions in the transport sector in Algeria.

4.4. Comparison with Other Studies

The energy production potential from crop residues was established by Jingura et al. for Zimbabwe. Their study shows that crops, fruits, and forestry residues have an energy potential of 81.5, 4.9, and 44.3 PJ per year [93]. Another study based on Bangladesh found that out of 65.36 million tons of agricultural residues, 32 million tons of bioethanol can be produced [1]. A study estimated that Egypt could produce approximately 1.5 million tons of bioethanol annually from agricultural residues [120], while Spain has the capacity to produce about 0.8 million tons of bioethanol per year from crop residues [109]. Our study finds that only having 4% of cultivable land area, Algeria has a significant potential to harness bioenergy from almost 7 million tons of agricultural residues, and the amount of bioethanol generated is 1.65 million tons, which can reduce a significant amount of environmental pollution in the transport sector.

4.5. Limitations and Future Studies

As Algeria is trying to increase the renewable energy penetration, using sustainable fuels such as bioethanol can be a viable solution. Without any vehicle modification, E10 and E5 can be used in Algeria’s transport sector, greatly reducing pollution. Various studies also indicate that fossil fuels have a high emission rate, which is harmful not only for the environment but also for living beings [121,122,123]. Bioethanol produced from these waste residues will improve Algeria’s sustainability. However, logical constraints like feedstock collection, storage issues, seasonal availability, and economic constraints, like feedstock costs, market fluctuations, and capital investments, are the challenges remaining in this sector. Technological interventions such as automation in harvesting, advanced pretreatment method development, and storage technologies will help to overcome the remaining challenges. The feedstock quality, pretreatment efficiency, and energy consumption are the most significant contributors to uncertainty in both ethanol yields and economic feasibility. A 10% change in the feedstock cost or ethanol market price can alter the profitability of bioethanol production by 20–30% [124]. For future studies, a spatial analysis of the crop generation in various regions of Algeria could be explored, which would provide a better understanding of the availability of crop residues in different regions of Algeria in various seasons of the year and would also help to develop a long-term policy and establish bioethanol production facilities. Due to climate change, the world temperature is increasing day by day and hampering crop production, which directly hinders the crop residue. Due to the contingency upon various parameters, future studies could explore residues’ availability via forecasting and modeling. Also, policy interventions like subsidies, tax incentives, and waste to energy policy development will help to improve the feasibility of bioethanol production in the future.

5. Conclusions

This study explored agricultural residue production from various types of agricultural crop residues in Algeria. With the proper planning and development of an efficient framework, Algeria can utilize the waste agricultural crop residues. Utilizing these residues would help Algeria to meet a large portion of the energy demand and minimize its dependency on hydrocarbon resources. Our study reveals that in Algeria, considering the minimum amount of residues available from crops, 1.65 million tons of bioethanol can be generated. A total of 47.22% of the total bioethanol can be generated from cereal wastes, and 23.38% of the overall bioethanol can be generated from fruit waste. Wheat contributes to a significant portion of bioethanol production, but other plants and fruit residues can contribute to bioethanol production. This extensive study will be a valuable literature source for analyzing agricultural residues’ overall potential based on the current residue generation. This study also recommends that E10 and E5 in the transport sector of Algeria is a viable solution, contributing only 0.6% and 1.32% of CO₂ respectively. Also, there is no need for engine modifications; therefore, no additional investment is needed. However, for large-scale integration, policy development and a life cycle and techno-economic analysis of bioethanol production in different regions in Algeria could be another area of research. More research can lead to reducing emissions from the bioethanol process.