Abstract

The main issue in our environment today is the rapid increase in greenhouse gases (GHGs), which is mainly caused by emissions from transportation and industries. Therefore, biomass-based biofuels are considered promising solutions for the reduction of GHGs owing to their carbon neutrality. This review presents an environmental impact analysis of different biofuels derived from different types of biomass. The characteristics of sustainable biodiesel are analyzed in this review. From the perspective of the existing cycle, it is important to evaluate and quantify the environmental effects of biofuel synthesis, such as biodiesel and bioethanol. The goal of this study was to foster a life cycle analysis information database for biofuels obtained from various types of biomass by utilizing the life cycle concept. The effect on climate was found to be the highest during the development stage compared to the other biomass life cycle stages. The variation in feedstock quality and contributions from various other components of life cycle assessment (LCA) cause a variation in GHG emissions, along with the use of different technologies for the conversion of biomass to biofuel. Biofuel technology development, enhanced energy efficiency and biomass agriculture management are significant measures that moderate the effects of existing biofuel patterns on the climate.

 

Introduction

The abrupt growth in energy demands and growing ecological concerns have evoked innovative and developing attitudes toward the utilization of fossil fuels and related products [1]. Rapid industrialization and population growth have led to estimates that energy requirements will double in the coming years’ [2]. It is noteworthy that currently global power generation in the transportation and industrials sectors are essentially dependent on fossil fuel products, such as oil (23 %), natural gas (22 %), and coal (27 %). Overall, 81 % of the essential energy utilized worldwide is generated mostly from non-sustainable resources, which are subject to exhaustion and price uncertainty. In addition, their utilization is accompanied by harmful ecological effects such as the emission of carbon dioxide (CO2), which is a widely recognized ozone-depleting substance [3]..

Concerns about exhaustion and climate issues have prompted people to swerve towards green and clean, sustainable energy sources. Efforts are being made by developing policies and implementing efficient measures to reduce greenhouse gas emissions [4]. Developed countries adopted the Kyoto Protocol to address climate change and global warming. Members of the protocol are obliged to consider different renewable energy sources to meet energy demands while maintaining low pollution levels and establishing a long-term sustainability project. Thus, a low-carbon society that supports both convenience and a blossoming populace has become an important driver of innovation. Biomass, a potential renewable fuel, has been extensively investigated as either biochar or biofuel. All types of performance assessments have been conducted for biomass related schemes, particularly for the retrofitting of existing coal power plants [5]. These investigations have prompted countries worldwide to include biomass as an accessory fraction in their national energy and climate change policies [6], [7].

In addition, owing to the advancement of modern technology, the hurdles to achieving a low-carbon society, high energy demands and economic concerns, can be effectively mitigated with the utilization of biomass [8]. Biomass is considered an efficient source of renewable energy. Gasification, which was earlier only used to supplement syngas, can now be extended to biofuel and electricity generation using different types of biomass [9], [10]. New alternatives to diesel and gasoline have been identified, mainly in the form of biofuels [11]. Biofuels derived from biomass have the advantages of extensive availability, accessibility, and sustainability. Recently, it has become widely known as the fourth most abundant energy resource after coal, oil, and gaseous petrol [12]. Given its growing importance, it is necessary to pay attention to the life cycle sustainability of designated biomass, specifically the agricultural practices and land areas required. Therefore, life cycle assessment (LCA) is used to evaluate the potential influence of biomass on the environment [13], [14].

The life cycle assessment is regarded as a highly useful tool for evaluating the impact of a fuel on the economy, society, and environment [15]. Investment in and commercial production of ethanol can be analyzed through life cycle assessment, which can guide modifications that will ultimately lead to sustainability. Investment in and commercial production of ethanol can be analyzed through life cycle assessment, which can lead to sustainability [16].

In the case of life cycle assessments (LCAs) of biomass-derived fuels, the main objective is to reduce hazardous elements that are a direct cause of climate change by adopting biomass resources. It allows quantitative estimation of the ecological impact throughout the life cycle of biofuels, which encompasses all stages from the growth of the raw material, the extraction, and its disposal [17], [18], [19]. These fuels include first-generation biofuels and second-generation bioethanol, with the latter expected to play a major role in the development of sustainable fuels in the future [20]. In addition, life cycle assessment is typically integrated with sensitivity analyses, making this combination an efficient methodology to decide the use of alternative fuels [21], [22]. A prominent example is the synthesis of bioethanol. The life cycle assessment was incorporated into the various processes involved in bioethanol synthesis to identify the impact of the respective phases on the environment, as reported by the National Renewable Energy Laboratory (NREL). During the harvest stage, the depletion of soil organic carbon increases carbon dioxide discharge. Similarly, there will be immediate and circuitous impacts as ranchers clear undisturbed environments for biomass plantations [23]. In addition, different cultivation practices have different impacts on the environment. Switching from a monoculture to a rotational system can have a significant ecological advantage from the perspective of land management [24]. Thus, life cycle assessments of biofuels have been used to evaluate the net impact on humans, ecosystems, weather, and other global conditions [25], [26]. However, it is very difficult to apply life cycle assessment to measure the environmental sustainability of various biofuels.

In this review, life cycle assessment applications for various biofuel sources, from lignocellulose to microalgae, are comparatively analyzed, and the environmental impacts of different biofuels are evaluated. More specifically, in contrast to previous life cycle assessment studies that focused on environmental effects, this review analyzes sustainable biodiesel characteristics and the natural effects of biofuel synthesis. The remainder of this paper is organized as follows. First, the methodology of life cycle assessments, including inventory analysis, impact assessment, and clarification, is presented. Then, the synthesis of biofuels is discussed. The main part of this review is divided into three sections: biodiesel, bioethanol, and biofuels from microalgae. Finally, prospects and challenges for the life cycle assessment of various biofuels are discussed.

 

Section snippets

Life cycle assessment methodology

The life cycle assessment has been widely applied to analyze environmental sustainability, and its goal may be the minimization of hazardous material emissions and the improvement of carbon neutrality. Technological interventions have contributed to improvements in functional units as specified in life cycle assessments. These efforts have supplemented the development of biomass-based synthetic fuels to displace fossil-based fuels, which have had a drastic impact on the environment.

The life

Biofuels synthesis

Over the past few decades, biofuel efficiency has become a major concern [78]. Biofuels derived from various biomasses [79] reduce reliance on petroleum derivatives and help improve climatic conditions (Table 1, Fig. 1). They effectively reduce global warming by consuming carbon dioxide during their cultivation Microalgae are well-known third-generation biofuels because of their high lipid content, simple methods of cultivation, and fast growth rates [80]. Microalgae can convert sequestered

Conclusion and future prospects

The life cycle assessment method is efficient for evaluating biofuels and their influence on the natural environment. The assessment shows that manufacturing, as well as the usage of biofuel is an efficient replacement for traditional petroleum, which has a positive impact on reducing global warming, ozone depletion, and other environmental threats. Biofuel production is dependent on the utilization of available carbon dioxide in solar energy used by plant vegetation or microalgae during

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

This work was supported by the Korea Institute of Energy Technology Evaluation and Planning(KETEP) grant funded by the Korea government(MOTIE) (20210310100020, Production of advanced biofuel from lignocellulosic biomass by a combination of fast pyrolysis and supercritical ethanol upgrading). Also this work was supported by National Research Foudnation of Korea (NRF-2020M1A2A2079801).