1 Introduction

The total global energy consumption has been rising due to the population growth, industrialization and increase of the living standards level. In 2017, the world total energy consumption was 609.5 quadrillion Btu and it is expected to reach 910.7 quadrillion Btu in 2050 with 49% growth rate [1]; More than 80% of the world energy demands are supplied by non-renewable fossil fuels (natural gas, crude oil and coal) [2]. This increasing trend, not only causes a serious crisis in energy supply, but also leads to numerous environmental issues such as climate change and global warming, caused by greenhouse gases emissions [3]. Renewable and non-fossil fuels could be a great alternative to solve this problem. In 2017, 14.6% of total world energy consumption was supplied by renewable energies [4]. The use of biofuels is growing as an option in developed countries. In 2017, 1.0% of the total global energy consumption was provided by biofuels which is equivalent to 6.8% of total renewable energies [4].

Iran is a developing country located in the Middle East, with a population of about 80 million and highly dependent on low-price fossil fuels [3, 5]. In 2017, the total primary energy consumption was 285.7 Mtoe (million tonnes of oil equivalent, 1 Mtoe = 41,868,000 GJ), more than 90% of which was supplied by crude oil and natural gas resources as indicated in the Fig. 1 [6]. In this year, 217 million liters/day of various types of petroleum products were consumed in Iran, 38% of which (equals to 30,277 million liters/year) was diesel. This presents 90% of total diesel production in Iran, about 2394 million liters of which has been exported this year (Fig. 1); However, compared to the previous year, diesel consumption has been reduced in all sectors while is increased in the transport sector (the second largest part in energy consumption and the largest diesel consumer in Iran) with a growth rate of 2.6% [7]. In 2017, 72% of suspended particulate matter (SPM), 34% of Nitrogen oxides (NOx) and 58% of Sulphur oxides (SOx) emissions, were released due to diesel consumption in the energy sector of Iran [7]. In other words, 8.2, 16.9 and 10.6 tonnes of SPM, NOx and SOx are produced per million liters of diesel consumption, respectively. These contaminants are the basic factors to corrosion, acid rain, and damages to trees and plants. In addition, diesel combustion and its greenhouse gases emissions cause reduction in visibility and ground-level ozone. Furthermore, organic compounds coming out of diesel engines exhaust contain carcinogens like nitro- polyaromatic hydrocarbons [8]. Therefore, the consumption of this petroleum product is the main cause of the most dangerous pollutants emissions in Iran which should be replaced by non-carbon biofuels such as biodiesel. Studying biodiesel production methods, as a carbon–neutral fuel can be certainly an important stride in substituting this clean energy with diesel. The potential assessment can support planning for the sustainable development of the bioenergy system.

Fig. 1
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Primary energy consumption of Iran by carriers and sectors, 2017 [6, 7]

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The first purpose of this paper is to evaluate the various feedstocks as well as explain a brief overview of the technologies currently used for biodiesel production. The second purpose is to assess the potential of biodiesel production and consumption from chicken fat as feedstock and its cost in Iran, which research methodology is described in Sect. 3. According to the results and discussion, Sect. 4 concluded weather biodiesel is an acceptable and sustainable alternative for diesel in Iran or not?

2 Biodiesel: feedstocks and production methods

The mono-alkyl ester of long chain fatty acid is called biodiesel. It is a renewable alternative for the petroleum-derived diesel which has non-renewable nature [9, 10]. The impressive features of biodiesel made it acceptable in the energy market. However, it is worth noting that these biofuels have some disadvantages too. The pros and cons of biodiesel is tabulated in Table 1 [8,9,10,11,12,13,14].

Table 1 Advantages and disadvantages of biodiesel in contrast with diesel
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Figure 2 shows the world’s largest producing countries in 2017. In this year, U.S. was the largest biodiesel producer in the world, generating 6 billion liters; To produce this amount of biodiesel, in U.S. during 2017, various feedstocks were used, including soybean oil (52%), recycled feeds (13%), corn oil (13%), canola oil (12%) and animal fats (10%) [15].

Fig. 2
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Biodiesel production in different countries, 2017 [4]

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One of the major challenges in biodiesel production is the supply of raw materials, because more than 70% of the total cost of biodiesel production depends on it. Another challenge is the availability of feedstock which depends on various factors, including the geographical conditions of the region and the nature of the oil resources. In general, biodiesel is divided into five types based on feedstock that are introduced and discussed in Table 2 [8,9,10, 16,17,18,19,20]. Currently, more than 95% of biodiesel production in the world is based on 1st generation feedstocks that are commonly used in rich countries in terms of agricultural land and water resources. However, producing this type of biodiesel results in increasing land use change (LUC) and reducing land allocation for cultivation of food crops, leading to food shortages and price increase [21,22,23]. The 2nd generation of biodiesel production does not compete with food production plans but affects LUC criterion. In addition, the use of chemical fertilizers, irrigation and harvesting is inevitable in order to achieve the maximum yield of 2nd generation feedstocks. The approach of using waste sources (waste oil produced from the consumption of edible oil and animal waste) for biodiesel production not only avoids the extra cost and environmental problems but also eliminates competition for food, water and land. In addition, it ensures the supply of feedstocks for biodiesel production thanks to their variety and plenitude [24]. Extensive research directed on biodiesel production from 4th and 5th generation feedstocks that showed production cost is high compared to petroleum-derived diesel. Therefore, only 3rd generation biodiesel production is possible in viewpoint of cost and feedstock sustainability.

Table 2 Biodiesel feedstock classification based on the sustainability issue
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However, the direct use of pure oil from these types of feedstocks are not satisfactory and practical in diesel engines as it results in polymerization during storage and combustion and, subsequently, gum formation, carbon deposit and incomplete combustion, due to its high viscosity, acid composition and free fatty acid content. To resolve this problem, either pure oil needs to be diluted or its hydrocarbon chains have to be broken down into simpler components. It can be performed in several methods: physical methods, including direct use and blending (dilution) and microemulsion; and chemical methods, including pyrolysis (thermal cracking) and transesterification (alcoholysis). Today, transesterification is the most common method used in industry [25,26,27,28]. The comparison of these four main techniques is shown in Table 3 [12, 17, 19, 29,30,31,32,33,34,35,36,37,38,39,40].

Table 3 Comparison of four main methods for biodiesel production
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3 Materials and methods

3.1 Feedstock

Chicken slaughterhouse wastewater is often discharged directly (untreated) to municipal wastewater or in most cases to surface water sources and their solid waste is also usually burned or buried. These disposal methods will result in environmental pollution as outflows in the slaughterhouse industry have a lot of BOD (Biochemical Oxygen Demand) and COD (Chemical Oxygen Demand). In addition, the presence of pathogenic microorganisms in this waste type results in its decomposition into the environment and odor production and uncontrolled greenhouse gas emissions to the atmosphere; Consequently, it threatens the health of residents near disposal sites.

It is proved that chicken fat is a promising feedstock for biodiesel production [14, 41, 42]; Although slaughter waste requires pre-processing, compared to low fatty acid sources. It is considered as one of the cheapest industrial products to produce biodiesel [43,44,45]. Furthermore, the amount of non-edible oil produced from chicken fat extraction is by far more than the related counterpart for vegetable oil; Rendering it is more cost-effective compared to the other feedstock. Chicken oil contains high energy content (Its calorific value is 39.4 MJ/kg [46], which is just a bit lesser than that of petroleum fuel). In biodiesel production, The highest yield has been acquired from chicken fat (approximately 99.1% [42]) in comparison with other types of biodiesel feedstock and it can be used as a solvent to improve alcohol and diesel properties (since it is more lubricant than petroleum diesel) [11, 47,48,49]. In this paper, the potential and cost of biodiesel production from chicken fat is investigated in Iran.

3.2 Calculation of biodiesel production potential from chicken fat

In Iran, there is no accurate data on the amount of produced waste in poultry slaughterhouses. Only, there are some statistics on the number of chickens and live chicken weight. The 2017 statistics, separated by province, are presented in Table 4 [50].

Table 4 Amount of live broiler chicken produced in each province in Iran according to the data in 2017 [50]
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The amount of slaughter waste production in each region varies based on feeding conditions, the number and type of slaughter as well as the percentage of waste from each animal; However, at least 28% of the weight of a live broiler chicken constitutes solid waste [51, 52] (Table 5). 35% of the waste is converted to high protein meal and 1.09 kg of Chicken fat oil (with density equal to 0.87 kg/l) can be extracted by rendering 7.5 kg waste [53]. Efficiency of converting chicken fat oil to biodiesel is 88.1% by transesterification process in the presence of homogeneous alkaline catalyst KOH. Finally, according to all these, the potential of biodiesel production is calculated for broiler slaughter waste [42, 54].

Table 5 Poultry slaughter wastes and their potential uses [51, 52]
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3.3 Estimation of the cost of biodiesel production from chicken fat

Chicken fat is a by-product in the rendering process of chicken slaughter waste for meal preparation (Fig. 3). So, it is free and only the cost of collection and transportation is considered.

Fig. 3
figure 3

Rendering process of poultry wastes [42], with permission from “Elsevier” Copyright© 2020

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In this paper, the transesterification process with methanol as alcohol (due to its low cost, better physical and chemical properties and easy removal from glycerin) and KOH as catalyst (due to its low cost, high catalytic activity and mild operating conditions) were considered to estimate the cost of biodiesel production from chicken fat [41, 54, 55]; The most important parameters of this process are: reaction temperature, alcohol to oil ratio, type and amount of catalyst, mixing intensity and type of raw oil. The various stages of the process are shown in Fig. 4 [54]. Chicken fat is slowly melted and then filtered. 1000 ml of chicken fat oil is poured into a volumetric flask; volumetric flask is manually shaked and simultaneously heated. When the raw oil temperature reaches 60 °C, methanol (200 ml) and KOH solution (7.5 g) are added separately to the oil and the volumetric flask door is closed. Then, the solution is stirred at high speeds. The temperature should not exceed 60° C as methanol evaporates, if temperature passes 60 °C. This solution is stirred for an hour and transferred to a separating glass conical flask. Upon separation, biodiesel accumulated at the top and glycerin at the bottom. By opening the valve, the conical flask is cleared from the glycerin. At this time, the biodiesel is repeatedly washed with distilled water at 50 °C to clean the soap thoroughly. Finally, it is heated to temperature above 100 °C to evaporate the water. The result is ready-to-use chicken fat biodiesel. The data and assumptions needed to estimate the net cost of biodiesel production are presented in Table 6.

Fig. 4
figure 4

Various stages of chicken fat biodiesel production by transesterification process [54]

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Table 6 Data and assumptions for net cost estimation of biodiesel production from chicken fat
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4 Results and discussion

In 2017, 2,539,761 tonne live chickens were bred per 1,104,918,000 chickens in Iran (2.30 kg per chicken). The amount of poultry slaughter waste was estimated at 7.632 × 105 tonne. Figure 5 shows the amount of waste generated based on its type. 2.671 × 105 tonne of high protein meals and 110.918 × 103 tonne of chicken fat oil can be obtained from this produced waste.

Fig. 5
figure 5

Estimated average quantities of produced waste from poultry slaughter in Iran, 2017

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The potential of biodiesel production is given for each province in Table 7. Based on these results, 127.492 million liters of chicken fat oil can be produced with the potential of producing 112.321 million liters of biodiesel in Iran. The highest contributions are determined for the provinces of Mazandaran (12.49%), Golestan (9.08%), Razavi Khorasan (7.88%), Gilan (7.51%), Isfahan (6.49%), and Fars (6.58%). In other words, these Six provinces can produce approximately half of the total biodiesel production potential from slaughter wastes in Iran. This amount of biodiesel production potential is equal to 0.6% of consumed diesel in the transportation sector in 2017. By managing that, 561.602 million liters of B20 (80% diesel and 20% biodiesel) can be replaced with required diesel for transportation, which is approximately equivalent to increasing diesel consumption in this sector compared to 2016; Or supplying 30% of diesel consumption in the transportation sector as B2 (98% diesel and 2% biodiesel). This will be efficient for reducing the emission of pollutants, especially SPM and SOx. Although the potential of biodiesel production from edible oilseeds is estimated at 721 million liters [56], oilseeds are consumed only in the food sector in Iran. Also, using poultry slaughter waste to produce biodiesel can solve the problem of disposal.

Table 7 Amount of produced waste from broiler chicken slaughter and its biodiesel potential in each province of Iran according to the data in 2017
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The annual cost was estimated to produce biodiesel from 1000 L/day of chicken fat (as feedstock consumption); The results of cost evaluation are presented in Table 8. Despite the use of free feedstock (chicken fat), these results show that 90% of the biodiesel production cost is related to raw materials (collection and transportation and melting chicken fat, Methanol and KOH), 51% of which is related to chemicals. Income comes around 270 million rial/year from producing glycerin, which can cover 6% of biodiesel production cost. Therefore, the net cost of biodiesel production is 4590.889 million rial/year equals 14,277 rial/lite from chicken fat. According to the declaration of the National Iranian Oil Refining and Distribution Company (NIORDC), the price of diesel is 3000 rials [57] per liter and the subsidy is paid more than 65,500 rials per liter of diesel. The use of biodiesel can reduce subsidies. Also, consuming biodiesel instead of diesel can reduce external cost.

Table 8 Cost of biodiesel production from chicken fat
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5 Conclusion

The growing need for new sources of energy has become a major problem in recent years. This energy crisis has led to widespread use of exhaustible and non-renewable fossil fuel resources and severe environmental problems. Therefore, replacing fossil fuel sources with renewable biofuels is essential for achieving sustainable development, environmental protection and controlling greenhouse gas emissions. Biodiesel is known as an alternative fuel for diesel. In addition to reviewing feedstock types and biodiesel production methods, this paper evaluated the potential of biodiesel production from slaughter wastes of broiler chicken. According to the results, in 2017, 763 kilotonnes of poultry slaughter waste was produced in Iran; The biodiesel production potential was estimated at 112 million liters from this source that Mazandaran province has the highest potential for producing biodiesel with 14 million liters per year. The results of this study show that we can supply 30% of the diesel demand in the transportation sector by B2 by this amount of biodiesel production. The cost of biodiesel production was estimated to be less than 15,000 rial/liter from chicken fat by transesterification process with methanol and KOH; This cost will even become minimal if socio-economic benefits like reducing pollution and employment generation are considered. In the following, it is suggested to evaluate the potential of biodiesel production from various types of animal fat waste in Iran and to identify the provinces with the highest potential. This knowledge helps to better plan for sustainable development of the bioenergy system.