Biofuels an alternative to traditional fossil fuels: A comprehensive review

The 20th century witnessed the emergence of climate change as one of the most critical problems the world is currently facing. There is plenty of proof that human civilization is the primary cause of this climate change and that its effects are having an impact on global food and energy supply, economic and political stability, and migratory patterns [1]. The primary cause of this issue is the heavy reliance that has impact on fossil fuels, which account for nearly 80 % of all energy consumption worldwide [2]. Fossil fuels have traditionally been the main source of energy. However, the supply of fossil fuels will inevitably decline as fuel consumption rises. To combat the extraordinary rate of climate change brought on by the increase of greenhouse gases (GHGs) in the atmosphere, there is a clear need to shift energy dependency from fossil fuels to alternative energy sources. According to BBC 2022 reports, China is the leading producer of carbon emissions followed by the US, India, Russia, Japan, Iran, Germany, Saudi Arabia, South Korea and Indonesia [3]. To achieve the energy demand and economic goals the U.S. Department of Energy offers information that, the fleet and other transportation finds a way through alternative renewable fuels [4]. Renewable energy sources include solar, organic, wind and hydrothermal are quite important right now. The main elements driving the need to convert to an alternative solution are the reduced potential for pollution and the reduced impact on global warming. Most likely, to meet the world’s energy demands, interest is growing in biofuels that can be produced form organic material, diverse biomass feedstock both terrestrial plants and aquatic algae, have been found to provide sustainable fuels to replace fossil fuels [5]. Because they emit less carbon than other conventional fuels, biofuels are a more environmentally friendly substitute for traditional, non-renewable fossil fuels [6]. Fig. 1 compares the harmful effects of fossil fuels with the beneficial effects of biofuels.

One of the biofuels that are frequently produced is ethanol. In addition to bioethanol, other types of biofuels include biodiesel, bio-oil, biogas, and biohydrogen, which are frequently found in solid, liquid and gaseous forms [7]. The biofuels are categorized into first, second, third and fourth-generation biofuels which are based on the manufacturing process and feedstocks [8]. When it comes to the production of biofuels, the 1st, 2nd and 3rd generations contribute more. Fig. 2 shows the production of biofuels in various nations in the year 2022.

There are two types of production of bioenergy: “Traditional and Modern” [9]. The traditional use of biomass is primarily in households for cooking and heating but also within small-scale industries. While there is still a need for improvement in terms of traditional biomass sustainability, and effectiveness. But modern bioenergy contributes four times as much to the total amount of renewable energy like solar photovoltaic and wind combined by advance. It is anticipated to contribute 3 % to electricity output and about 4 % to the need for transportation energy [10].

Whereas in the production of solid waste agricultural feedstocks play a significant role in which crop residue, agro-industrial waste, livestock waste and algal matter and the organic fraction of municipal solid waste (OFMSW) are the examples of biomass that have ultimate biochemical and lignocellulosic analysis [11]. India alone makes 350 million tonnes of organic waste from agriculture. Agricultural waste contains lignocellulosic content, which can be used in biochemical and thermochemical conversion pathways to produce biofuels. The pellets, briquettes, and biochar are the solid biomass conversion product after densification and thermal process such as pelletizing [12], briquetting [13], pyrolysis [14], torrefaction [15], and hydrothermal carbonization (HTC)[16] which have less moisture content, higher calorific value and more stable in nature [17]. The biochemical approach uses enzymes and microbes to break down biomass into precursors (amino acids, sugar and fatty acids) that are transformed into liquid biofuels like biodiesel, and crude oil by transesterification of fatty acids, bioethanol by fermentation of starch, methanol, and butanol by distillation of dry woods and biogas by aerobic sludge through biological, biochemical, and thermochemical [18].

The USA and Brazil are two important bioethanol, biodiesel producers and consumers. The USA uses maize, while Brazil makes ethanol from sugar cane in order to create low-cost and high production using solid feedstock [19]. The OECD-FAO 2023 Agriculture Outlook 2015–2025 predicts a modern increase in worldwide ethanol production from 115.6 billion liters in 2015 to almost 128.4 billion by 2025. Currently, the USA is followed by the EU which succeeded Brazil in the production of bioethanol. On average America generated 86 billion liters of bioethanol in 2018. As a result, this country became the world’s greatest producer of bioethanol [20].

Hence, the Inflation Reduction Act, which includes benefits for renewable biodiesel, and sustainable aviation fuel as well as supports the infrastructure and production of biofuels was enacted by the US in 2022. Also supporting increased biofuel demands in the upcoming years are India- higher ethanol blending [21], Canada- clean fuel standards [22], Brazil-RenovaBio, U.S-California and Oregon low carbon fuel standards (LCFS) and other states considering LCFSs probably grow in coming decade in order substantial decline in overall energy demands [23].

This article provides a comprehensive overview of the management of crops and woody biomass waste in agriculture. Furthermore, it explores how these waste materials can be effectively utilized through strategic management to produce biofuels as an eco-friendly alternative to fossil fuels, thereby benefiting both the environment and human health. The discussion encompasses detailed insights into 1st, 2nd, and 3rd generation biofuels, including their production techniques, pretreatment approaches, and associated constraints. This review also focuses on cutting-edge methods for increasing the productivity of biofuel generation from non-food sources like algae and other waste products.