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Biomass is finding increased attention in industry and academia as one of the preferred choices of eco-friendly and sustainable energy sources. The need for biomass has multiplied in recent years because of government support in many countries and sharp cost reductions for power generation fuel and heat generation in industry and as a fuel used in transport. Biomass has so far been the renewable energy source most resilient to Covid-19 lockdown measures. The share of renewables in the global electricity supply reached nearly 28% in the first quarter of 2020, up from 26% during the same period in 2019 [1].

Bioenergy must be produced in ways that are environmentally, socially and economically sustainable. The potential is enormous to produce bioenergy cost-effectively and sustainably on existing farmlands and grasslands and to use residues from existing forests without encroaching upon rainforests.

Biomass is mainly classified into two categories: modern and traditional. In recent years, biomass has become a very popular source of renewable energy; its supply to final energy demand across all sectors is five times higher than wind and solar PV combined, even when the traditional use of biomass is excluded [1, 2]. Many countries are interested in developing biomass energy generation. The most responsible player for bioenergy market contraction is the US [3]. The cumulative capacity of biomass power worldwide from 2009 to 2019 is illustrated in Figure 1.1 [4].

Bioenergy technologies utilize plant or animal waste, and it also involves material after their natural and artificial transformation and can be used for energy production [5–9] or, in other words, the resources of bioenergy are made of carbon, hydrogen, nitrogen and oxygen [10, 11]. Examples of bioenergy resources are bagasse, sawdust, household waste, and wastewater, pelletized agricultural waste, etc. [12–15].

The energy obtained from biomass will help in the reduction of dependency on fossil fuels [16–18]. In 2017, modern bioenergy contributed an estimated 5.0% to total final energy consumption, as shown in Figure 1.2 [19]. Biomass is regarded as one of the major energy sources for several developing countries, and its use could be as high as 20-33%, but if one compares it with an industrialized nation, the total share could be as low as 9-14% of the total consumption of resources and the trend is gradually increasing [20]. It has traditionally been used since time immemorial, and its sustainable use is increasing rapidly because of its economic potential in terms of agricultural waste, sewage and household waste. This source of energy is carbon neutral since, at the time of growth of biomass, it absorbs CO₂ from the atmosphere, which is added due to its combustion. Thus, it provides a net zero balance of total CO₂ produced by it [21, 22]. Although the main focus of the current society is the use of fossil fuels but in order to fight climate change, biomass will definitely be beneficial at large [23]. Urban society is contributing 70% of the total CO₂ addition to the environment and is contributing the most to climate change, and its after-effects are already beginning to show in several cities across the globe [24, 25]. With the help of available processes like physical, chemical and biological, biomass can be converted into gaseous, liquid and solid combustible substances [26, 27].

The biomass obtained from peanut shell, mango stone and the seed of sunflower is found to have a Higher Heating Value (HHV) very close to other commercially available biofuels [28–31]. Several research works are going on for the constant development of decentralized biomass boilers for energy production [32, 33]. Cogeneration means the use of low-grade fuels with high-grade fuels for the production of electrical energy [34]. In 2017, electricity from biomass-based sources was the third-largest renewable electricity source after hydropower and wind with 596 TWh of biopower generated and is shown in Figure 1.3 [35]. China is the world leader in bioenergy-based electric power generation.

Figure 1.1 Global cumulative bioenergy power capacity from 2009 to 2019 [4].

Figure 1.2 Bioenergy estimated share in total final energy consumption, 2017 [19].

Now there is a sharp rise in the use of biomass as an alternate source of energy as it mainly comprises a green source [36, 37]. Biomass is evenly distributed throughout the globe as it can also be obtained as a by-product of agricultural and industrial waste, thus having a high growth potential [38, 39]. The greatest benefits are the use of forest area for the collection of twigs and woods, which will ultimately prevent forest fires, and at the same time, it offers new employment. 9.8 million people worldwide got their livelihood through renewable source in 2016, an increase of 1.1% over 2015. A detailed description is given in Table 1.1 [29]. The main focus is to obtain eco-friendly energy from biomass for sustainable growth and also to gradually replace conventional fossil fuels [40]. It has a huge amount of potential for the large-scale generation of biofuels which can be utilized for electricity, heat (shown in Table 1.2) [35] and also for transportation [41].

The US Department of Energy and the European Commission have worked on an “Action plan for Biomass” in which they have made a clear-cut emphasis on bioenergy [42]. This is relevant for the major issue of climate change, as covered by the International Panel on Climate Change (IPCC), which monitors greenhouse gas emissions in the atmosphere [42, 43]. The biomass produces net zero carbon in its cycle as the CO₂ liberated by the biomass is again reused by plants [43–45]. Each and every material or substance being derived from photosynthesis indirectly or directly is termed as biomass [46]. The total biomass on our planet earth has the potential to provide eighty times more energy as compared to the total requirement of the entire globe [47]. The biggest challenge today is energy-saving and, at the same time, the reduction of harmful emission [48, 49]. The advantages and limitations of bioenergy are shown in Table 1.3.

Figure 1.3 Electricity generation from biomass [35].

Table 1.1 Estimated direct and indirect jobs in bioenergy, by country/region and technology, 2017-2018 [29].

	World	China	Brazil	United States	India	European Union
Thousand jobs
Liquid biofuels	2,063	51	832	311	35	208
Solid biomass a, b	787	186		79	58	387
Biogas	334	145		7	85	67

^a Power and heat applications.

^b Traditional biomass is not included.

Table 1.2 Heat production from biomass in EJ [35].

Years	Total	Biomass
2016	1.10	1.05
2017	1.12	1.08

Table 1.3 Bioenergy technologies [4–49].

Characteristics	Advantages	Disadvantages
Bioenergy conversion schemesa. Bioenergy share is 13-14% of the world’s total energy consumptionb. Traditionally biomass energy is mainly utilized forc. Heating and cooking, which accounts for about 8%.d. Modern bioenergy is utilized for running plant and transport.e. USA is largest producer of biodiesel and ethanol.	i) A suitable source of energyii) They are used in transportation fuel generation, i.e., bio-diesel etc.	Carbon emissions from burning Wastes Resource availability risk