**3. Economic and environmental implications, limitations and prospects**

### **3.1 Economic feasibility of biofuel compared to fossil fuel**

The rise of international bioenergy markets is critical to maximizing the utilization of global biomass resources and market potential [63]. The global biomass and biofuel markets, on the other hand, are still expanding and are subject to tariffs and non-tariff trade restrictions, resulting in substantial and often unexpected changes in the international trade flows [64, 65]. In contrast to fossil fuel markets, bioenergy markets have limited trade flows, which exacerbates these problems. Additionally, feedstock supply (easily accessible), offtake (easily secured contracts), capacity utilization (75%) and sustainability compliance are key factors required for bioenergy plant establishment [63, 65, 66]. According to Bloomberg New Energy Finance [65] the annual value of renewable energy capacity can rise from 395 USD billion in 2020 to 460 USD billion in 2030. This can result in bioenergy market been expanded by 7 USD trillion for the next two decades. The use of biofuel can be economically and environmentally advantageous to both developed and undeveloped countries [63, 65, 66]. Consequentially, biofuels have the potential to be a sustainable, renewable, and viable energy source, especially in the transportation sector. This makes the biofuels industry to have many potentials with ecological and economic benefits [67, 68].

However, when compared to the gasoline cost of production (from fossil fuel), which is about 0.3 USD – 0.4 USD/LGE (liter per gasoline equivalent) in 2020, sugarcane and corn ethanol production cost is approximately 0.40–0.50 USD/LGE, making ethanol less competitive commercially [69]. Likewise, sugar beet, maize, or wheat ethanol cost between 0.6 USD and 0.8 USD/LGE. The comparatively higher

price and energy content of ethanol are significant drawback to its utilization as a viable sustainable biofuel and as a gasoline additive. The energy content of a gallon of ethanol is approximately one-third that of a gallon of gasoline. Consequently, ethanol has not been economically viable when likened to gasoline; however, with government incentives, the cost of producing ethanol will be significantly reduced [70]. In actual fact, when compared to fossil fuels, the use of biofuels will minimize the net cost of fuel through biofuel regulations which may reduce fossil fuel use by less than 2.5% at a cost of 67 USD billion plus a 6 USD billion gas tax [63, 65, 66]. The primary concern is that, in the near future, more biofuels will make overall fuel costs more expensive than fossil fuels. Notwithstanding, the long-term savings in fuel prices may offset the initial expenditures [71].

#### **3.2 Environmental impacts and benefit**

Replacing fossil fuels with biofuels (fuels made from renewable organic material) is possible to reduce conventional and greenhouse pollutant emissions. Additionally, producing energy from biomass has substantial distinctive environmental benefits. The abatement of acid rain, soil erosion, water pollution, and landfill pressure, while also providing habitat for wildlife and improving forest reserves through proper management are among some of the advantages [72, 73]. Although there are certain uncertainties about employing biomass indirect combustion, gasification, or pyrolysis processes can provide still significant environmental benefits. For instance, the production of SO2, CO2, and ash is often much lower in biomass power systems than in coal combustion and conversion systems [68, 72, 74]. The sources and side effects of coal combustion which makes biomass combustion more advantageous include reduce emission Hazardous air pollutants (HAP) and SO2 of the following [75]. Hence, sulfur and nitrogen content of biomass combustion are so low to be neglected.

Biomass, on the surface, appears to be an appealing renewable fuel for boilers, even though its composition is liable to change. For example, the ash composition of biomass differs significantly from the ash composition of coal. Also, many undesired processes in combustion furnaces and power boilers are caused by metals in ash when combined with other fuel constituents such as silica, sulfur, and chlorine [72, 73, 75, 77]. Conversely, in biomass combustors, elements such as Si, K, Na, S, Cl, P, Ca, Mg, and Fe are engaged in processes that can contribute to ash fouling and slagging [76, 77]. The effects of biomass content on combustion are non-hazardous and provide great environmental safety. The principal benefit of using biomass energy is the reduction of greenhouse gas pollution. Furthermore, reburning of biomass fly ash as a fuel-flexible material can provide well-burnt ashes for common fuels. Additionally, eliminating ash stabilization (chemical hardness) can significantly enhance ash potential. This can reduce NOX emissions by 20% while slightly increasing CO emissions. However, the rise of CO level is usually around 100–140 ppm, which are within the permissible average limit of 150 ppm CO [67, 75, 77]. Also, the ash produced can be returned into the forest, replenishing the nutrients loss by the soil. Therefore, the nutrient compounds in the ash can be recycled or repurposed as fertilizers for good sustainable energy practices based on biomass.

#### **3.3 Limitations of bioenergy production**

Improper burning of biomass releases CO2, N2O, CH4, and other hydrocarbons, all of which are detrimental to health. Human activity contributes 60% to global

climate change [67, 73]. Activities such as using chemicals like chlorofluorocarbons (15%), agricultural biomass (12%), land-use alterations (9%) and other human activities (4%) also contribute to high levels of greenhouse gases in the atmosphere [68, 75]. Currently, global greenhouse gas emissions are increasing year on year. CO2 has been increasingly linked to global warming [78, 79]. The greenhouse effect caused by gases (with three or more atoms) with higher heat capacity than O2 and N2. The primary human-caused greenhouse gas is CO2 (CO2). CO2 emissions from fossil and biomass fuel combustion significantly contribute to the greenhouse effect and global warming. The reactivity of ash in biomass combustion can be detrimental. In the diverse activities of this sustainable feedstock, trace elements found in biomass play a significant role. Trace elements (usually metals) are biochemically important, as well as nutritionally and environmentally [76–78]. The amounts of trace element levels are related to biomass species, sample growing site, plant age, and distance from the pollution source. Metals such as Cd, and Hg ions are potentially detrimental to plants. As boilers flue gas undergoes chemical processes, phase transitions, and precipitation because of a wide temperature differential, high element concentrations in both biomass and boiler fly ash are essential [9, 13, 14, 75–77].

#### **3.4 Potentials and future work considerations for effective bioenergy production**

Since fossil fuels have caused havoc on the ecosystem, it is critical to explore solutions. Biofuels can provide energy requirements while limiting environmental impact by exploiting readily available biomass as feedstocks. According to life-cycle analyses, advanced biofuels and cellulosic biofuels have the potential to achieve baseline GHG reduction targets of 50% and 60%, respectively (including indirect land-use change). Although transportation currently contributes around 23% of all CO2 emissions caused by energy use. To achieve a 50% decrease in energy-related CO2 emissions by 2050, sustainably produced biofuels could account for 27% of total transportation fuel consumption [63, 66, 80]. In essence, biofuels derived from waste biomass could be the most sustainable energy alternative to fossil fuels in the transportation industry [81–83]. Nevertheless, concerns about the biomass supply chain, energy efficiency, and product yield persist. Different processing improvement techniques, either alone or in combination with nanomaterials, may be used to tackle these problems. Advancing biomass combustion technology can result in increased conversion efficiency at a low cost. Additionally, several research have reported on the use of nanomaterials in conjunction with microwave, mechanical vibration, pulsation, and ultrasonication to enhance biofuel production [19, 20]. Compared to other nanocatalysts, ferrofluids are easy to separate and move in oscillating magnetic fields [76, 77]. Therefore, they could be used with some of the technologies to improve the biomass-based energy economy.

Continuous biofuel synthesis using microchemical and Coiled Flow Inverters (CFI) are also possible. Heat transfer fluids (HTF) and ionic liquids (IL) could also be employed in biofuel production to save energy. In the future, the use of biomass in biofuel synthesis and utilization is very promising to be explored to further improve the overall process economy. According to the EU's Renewable Energy Directive (RED), biofuels must meet certain sustainability standards before they may contribute to the binding national targets each member state [63, 65]. Several attempts to develop sustainability criteria and standards for biofuels are underway in this section. Other international initiatives include the Global Bioenergy Partnership, the Roundtable on Sustainable Biofuels (RSB), and ISO (International Organization for

Standardization) standards aimed at increasing bioenergy production's efficiency and lowering emissions [63, 64].
