Biomass Waste Conversion Technologies for its Utilization and Energy Generation in India: A Perspective

The speedy reduction of fossil fuels and its analogous environmental issues make it necessary for attention to energy generation from alternative fuels. Biomass seems to be one of the likely sources of renewable energy and the computation of waste materials into an appropriate kind of energy, like fuel or electricity, can be completed in several multifarious feasible ways. Utilizing biomass for energy production offers several advantages, including cost-effectiveness, lower sulfur content, and reduced greenhouse gas emissions, contributing to improved environmental sustainability in energy generation processes. This paper takes stock of exploring various biomass conversion technologies for its utilization that can facilitate power generation from biomass waste. It is important to note that biomass utilization extends beyond traditional combustion methods. Latest conversion technologies, including thermal, chemical, and biological processes, have proven to be efficient methods that can replace fossil fuels for producing energy from high-grade sources.


Introduction
Growing concern over the attainability of the formation of CO2 (Carbon dioxide) emissions that occur due to the burning of fossil fuels has greatly influenced global change in climate which leads to the increase of attention towards renewable, sources of primary energy and alternative energy-producing technologies.From the available renewable energies, biomass seems to be one of the most significant energy sources in the coming future ranked third amongst primary energy sources as coal and oil continue leading sources of main energy globally [1].However, for the qualities and quantities, of energy requirements of the world, there seem to be no emerging technologies that can threaten to produce energy from biomass waste.As biomass is burned as a fuel, it absorbs the same amount of CO2 that results in a negligible global warming effect, and due to the absence of sulphur in biomass; their contribution to acid rain is also minimal.Because of wide spread obtainability of biomass and renewable and its potential is neutral about global warming [2].
According to the Ministry of New and Renewable Energy [MNRE] report, the availability of biomass is projected to be around 500 million metric tons/year which is currently present in India [3].Also, considering forestry and agricultural waste residues area, the predicted leftover biomass, which constitutes a probable of about 18000 MW energy, is approximately 120 to 150 million metric tons/annum [MNRE 2021 -22].Biomass can be measured, for the quality of energy generation, as a renewable source for producing energy.The potential of power generation from biomass is greatly higher in the world, as well as high in India.The estimated Potential of renewable power generation is mentioned in Table 1.
Biomass typically pertains to organic matter originating from living or recently deceased organisms, primarily encompassing plants or plant-derived substances, with a particular 1285 (2024) 012010 IOP Publishing doi:10.1088/1755-1315/1285/1/012010 2 focus on materials categorized as lignocellulosic biomass [4].By the conversion, biomass is categorized into two forms; Woody parts include forest-based and agro-industrial residues comprising low quantity of ash content and low moisture content having high bulk density and high calorific value, whereas nonwoody parts comprise crop residues and processing residues, containing high ash, high moisture and low bulk density and low calorific value.The biomass resources that can be used as a fuel are mentioned in Table 2. Agricultural residues can be used as fuel, but due to the presence of high volatile matter in large quantities and ash percentage present in agricultural residues and having low energy density as compared to wood fuels that results in the pre-treatment of agricultural residues [5].By 2007, the production of biogas was about 2 million cubic meters biogas production from 1000 digests and 6.8 million households resulting in 5 percent of China's overall gas energy [6].In 2002, the production of energy in Denmark was about 2.6 PJ of energy over 35 farm-scale plants and 20 centralized biogas plants [7].Presently, biomass contribution towards total renewable energy is about 70% for producing heat and electricity in Germany [8].[Grover et al. 2012] characterized the several renewable wastes that exist in Punjab (India) for power generation.[Vitali et al. 2013] studied the assessment of accessible crops for the production of Bioenergy in the European Union.[Rajak et al. 2022] employed blended diesel fuel with a combination of cooking oil that is available in waste form and biodiesel to perform the parametric examination of a diesel engine [46].[Dasore et al. 2022] predicted the alternate source of CI engines using blends of diesel and low-density ethanol.[47].The forest Remnants remain after logging activities and other discarded wooden waste from the forest.

Agricultural waste
Palm oil remains rice husks, sugarcane byproducts, coconut shells, coffee, and cocoa husks, along with cotton and maize residues, and more.

Wood waste
Packing material, wooden pallets, etc.
Organic waste Food processing, animal manure wastes Wastewater and landfills Landfill gas, Municipal sewage, etc.
The wood processing industry's waste Bark, sawdust, cut-offs and more.Throughout millions of years, Earth's natural processes have led to the creation of fossil fuels like oil, natural gas, and coal, which originate from the transformation of organic matter.In contrast, biomass fuels are derived from a diversity of various organic sources including trees, crops, and other living plant materials.Unlike other resources, utilizing biomass for energy production can be seen as a method of managing biomass waste, but this approach also carries potential environmental risks.Several challenges impede the advancement of biomass energy and the establishment of sustainable energy policies.Addressing these challenges is essential for the promotion and development of biomass energy.
Taking into account the biomass availability in India, three primary sources of abundant biomass are forests, agriculture, and waste materials as shown in

Highlights of the Power Sector in India
Presently, India is home to a comprehensive array of 288 undertakings dedicated to generating and co-generating biomass power, amounting to a collective capacity of 2,665 MW.In contrast, standalone biomass power plants independently contribute a capacity of 999 MW across 130 projects, whereas an additional 158 endeavors centered on bagasse co-generation enhance the overall capacity by aggregating 1,666 MW.As part of the nation's developmental initiatives, a cluster of 30 biomass power projects, capable of generating 350 MW collectively, has been established.Complementing these are 70 surplus-capacity co-generation projects, further bolstering the cumulative capacity to 800 MW.The concentration of bagasse cogeneration projects is notably pronounced in states such as Andhra Pradesh, Tamil Nadu, Maharashtra, Karnataka, and Uttar Pradesh.Conversely, the forefront of biomass power projects is occupied by states including Andhra Pradesh, Gujarat, Maharashtra, Chhattisgarh, Madhya Pradesh, and Tamil Nadu [11].For a visual depiction of the distribution of biomass cogeneration capacities across India, refer to Figure 1. Figure 2 shows the current portfolio of electricity generation in India from which renewable energies i.e.Biomass, wind, solar, and geothermal in a small percentage of shares.Currently, India's renewable portfolio is dominated by wind power which contributes about 60% of total installed capacity.Solar energy can be predicted to be the next big thing that can happen in India.As per Figure 2, Biomass acts as a source of power generation with Bagasse contributing about 65% of total biomass generation in India.India also added a small hydropower plant having a capacity of 250 MW [12].

Biomass conversion technologies and energy generation
For the utilization of biomass, a biomaterial is selected in the form of raw material by taking into account the demand, availability, and utilization purpose.Further raw material is converted into useful energy.Utilization of biomass waste is crucial to prevent engagement of Bioenergy utilization with food and feed.The main problem with biomass energy is its storage and transportation because of its degradation and bulkiness.Figure 4 represents the various processes for the conversion of biomass that can be used for optimum utilization of biomass from the resources using various supplies and systems by adopting various technologies.
Figure 4 Biomass conversion and utilization from biomass resources [16,18] Although direct combustion for biomass conversion into heat energy remains the utmost effective method, not all the power generated from the source is in the form of heat.Other diverse conversion processes illustrated in Figure 4 can also be harnessed to produce energy and materials, expanding the range of biomass applications.A plethora of solid fuels (in the form of charcoal), liquid fuels (like ethanol), as well as gaseous fuels (methane), can be derived from various biomass waste materials through the implementation of biomass conversion technologies.Broadly speaking, these conversion methods are defined into two main categories: bio-chemical and thermo-chemical.Additionally, an alternative technique for generating energy from biomass involves Mechanical Extraction (with esterification), exemplified by Rapeseed Methyl Ester, commonly referred to as RME [16][17][18].Among the biochemical processes, two primary approaches are Fermentation and Anaerobic Digestion.

Anaerobic digestion:
Through the process of anaerobic digestion, biomass materials like municipal waste and livestock manures are treated by naturally occurring microorganisms in the unavailability of oxygen.This procedure results in the production of biogas, containing mainly methane and CO2, as well as very small amounts of other gases like nitrogen and phosphorus."First-Generation Biogas-Reactors" encompass three primary biogas types: the static-design Chinese digester, the Indian Gobar-Gas Plant featuring a gas holder (floating type), and commercial-sized biogas digesters (rectangular type).In contrast, more modern technology, represented by high-rate bio-reactors tailored for low-strength liquid waste containing significant suspended solids, falls into the category of "Second Generation Biogas Digesters."The sequence of micro-organism stages within anaerobic digestion is illustrated in Figure 5. Bacteria play a pivotal part in the processing of biomass waste through anaerobic digestion, producing a gas with an energy percentage ranging from approximately 20 to 40 of the feedstock's having low heating value [19].Anaerobic Digestion represents a wellestablished commercial technique widely applicable for the treatment of organic wastes with high water percentages, typically ranging from 80% to 90%.The produced biogas can be employed as fuel in spark ignition (S.I.), gas engines, and gas turbines.Furthermore, it can be further promoted to produce better quality natural gas with the help of eliminating CO2, resulting in a total conversion effectiveness of 21% [20].

Fermentation:
A metabolic process that happens in the absence of oxygen that converts sugar into Ethyl alcohol.Strains of Saccharomyces cerevisiae are selected that change glucose into Ethyl alcohol as well as carbon dioxide.Fermentation is used commercially to produce ethanol on a huge scale from sugar crops.The nature of batch reactor and end product inhibition of yeast are two major causes for the high cost of ethanol formation.Figure 6 shows the fermentation process for producing ethanol.The grounded biomass produces starch converted by enzymes into sugar, with the help of yeast, then processes those sugars into ethanol production.The distillation process used for purifying ethanol is energy-intensive, requiring around 450 liters of ethanol formed from 1000 kg of corn (dry).The remaining residue in solid form, from this method can be utilized as feed for cattle.Additionally, the bagasse derived from sugar cane offers an alternative application, as it could be used in subsequent gasification processes or as fuel for boilers [21].

Thermochemical Conversion:
Under elevated temperatures, biomass waste can be readily transformed into a valuable energy resource.The process involves the complete oxidation of water and carbon dioxide through the combustion of fragmented particles, leading to simpler molecules.By carefully regulating factors like temperature, pressure, various catalysts, and the controlled availability of oxygen, it becomes feasible to extract useful fuels.This thermochemical conversion can be subdivided into three primary phases: the combustion process, pyrolysis, and the gasification process.
Figure 6: Flow process for producing ethanol by fermentation [44] 3.4 Combustion: The processing of biomass waste into mechanical power, electricity, and heat energy involves the combustion of the waste in the presence of air.This process employs different conversion methods and devices like furnaces, steam turbines, boilers, and stoves.The combustion process aims to change the chemical energy that is stored in biomass into these useful forms of energy.However, practical combustion is most effective for biomass with around 50% moisture content, unless and until the biomass is in pre-dried form.For biological conversion processes, biomass having a high moisture percentage is better suitable for the conversion process [22].When various types of biomasses are burned, they produce distinct ash compositions compared to coal ash.The inorganic components in biomass ash can lead to significant issues such as toxic emissions, fouling of economizers, and slagging.Biomass with a low heating value typically achieves electric efficiencies around or above 30%.Among biomass-based plants, those utilizing vibrating grates and circulating fluidized beds tend to exhibit the highest effectiveness.On the other hand, co-firing-where 4.5% of biomass is mixed with pulverized coal in a boiler-results in an efficiency of approximately 37% at a low heating value [23].In Figure 7, the process of combustion is illustrated, showcasing the various stages through which biomass is processed to generate electricity.
Figure 7: Combustion process for utilizing biomass to generate energy [23] 3.5 Gasification is the procedure of thermo-chemical reaction for the conversion of biomass waste into a low medium energy gas operating sub-stoichiometric quantities of oxidant [24].Figure 8 represents the gasification of biomass for various applications like Gas engines as well as gas turbines, which can run on gas, formed from biomass containing low energy density, and from the application point of view, the formed gas can be utilized as feedstock (i.e.syngas) for producing chemicals methanol [25].The producer gas produced from the gasification process can replace kerosene, diesel, and LPG in terms of fuels other than that biomass gasification can be used in high-fuel-consuming industries like ceramics industries running on fossil fuels.
Figure 8: Gasification of biomass [18] 3.6 Pyrolysis is a process of thermo-chemical decomposition at temperature (ranges from 300-500⁰ C), of organic waste in the unavailability of air or any halogen, that comprises the instantaneous change of physical phase and chemical composition.process flow stages of fuel production from the process of pyrolysis which is further used to generate power or heat.If flash pyrolysis is employed, then bio-fuel can be achieved for the conversion efficiency of about 80% by pyrolysis.The biofuels can be used as feedstock in refineries and to run gas engines and turbines but have issues regarding corrosion and thermal stability.Bio-oils can be upgraded after removing oxygen content and alkali by employing hydrogenation, yet catalytic cracking may require various applications [26].

Mechanical extraction:
A mechanical conversion process that involves extraction of oil from seeds of various crops of biomass like cotton, ground nuts, oilseed rape, etc.The mechanical extraction process also produces residual solid or "cake" other than the oil that is suitable as fodder for animals.About three hundred kilograms of rapeseed is necessary to produce rapeseed oil (per ton) which can be further managed to achieve bio-diesel utilizing a process termed esterification by reacting it with the alcohol [27].

Emerging Technologies
Innovative technologies aimed at converting biomass into biofuels are rapidly emerging.These advancements encompass a range of approaches, such as the cultivation of artificial yeast to enhance ethanol yields [28], the employment of novel microorganisms for ethanol formation [29], the application of pre-treatments to facilitate the digestion of cellulosic materials [30], the development of diverse fuel cells for directly processing sugars into electricity [31], and utilization of catalysts to improve the efficiency of biomass conversion into syngas [32].Considerable research has been conducted on microalgae, which are considered more proficient in photosynthesis compared to terrestrial plants and are, consequently, more effective at fixing CO2 [33].The carbon dioxide fixation ability of algae has been projected as a means to mitigate CO2 emissions from power plant flue gases, thereby contributing to reducing emissions (greenhouse gas  [34,35].A recent innovation known as "micro-diesel" involves the production of biodiesel in engineered bacterial cells, where ethanol is condensed with fatty acids [36].Nevertheless, the majority of these initiatives remain at the exploratory stage, with none having reached practical implementation. Figure 10: Flow sheet for the formation of methyl ester bio-diesel and glycerin [27] In Sub-tropical regions, the annual yield of harvested algal biomass, cultivated through specific methods, can potentially reach up to 40 tons per hour (dry matter) or even more when supplied with CO2.Additionally, simpler cultivation systems can achieve an output of around 100 grams per square meter per day of algal dry matter [37,38].Comparatively, it has been estimated that algae can produce nearly 100 times more oil per acre than soybeans [39].A noteworthy advantage of algae cultivation is that many prominent algae species can be cultured in either marine or freshwater environments, thereby avoiding the need for extensive land use.

Future aspects of Biomass in India
The global utilization of biomass is on the rise.Despite the various technological improvements in biomass energy, the predominant share of bioenergy consumption in India remains rooted in traditional applications.Modern approaches tend to process biomass into liquid fuels like methanol and ethanol, as well as synthetic gases and electricity [40].However, a significant hurdle in the adoption of modern technologies is the limited presence of biomass energy products in the market.As India gains more experience with modern technologies, it becomes evident that a combination of technology-driven policies and market-oriented strategies is necessary.The potential for modern biomass adoption spans four key sectors:  Utilization of charcoal and briquettes for cooking in commercial and domestic settings. Generation of electricity. Application of process heat in diverse industries that generate biomass waste.
 Incorporation of liquid fuels for the transportation sector. Reduction in Emission and improved Air quality.
The prospects of biomass lie in its effective integration with recent technologies to deliver reliable energy at competitive costs.Policy priorities should align biomass energy services with market dynamics, fostering fair competition by addressing externalities and optimizing energy sources.An economically viable approach involves leveraging waste materials.In India, agricultural residues and wood processing waste alone hold the potential to sustain energy generation at around 18,000 MW [11].However, given the escalating demand for biomass resources, additional strategies are necessary to ensure adequacy.Biomass offers a sustainable alternative for development, underpinned by social and environmental considerations.The Indian government should promote emerging energy technologies like wind power [41] and ethanol production from sugarcane [42].Key to this is the commitment of Indian policymakers to endorse renewable and clean energy resources, thereby driving energy transformation for sustainable development.Modern biomass technologies present a feasible pathway for such power transformation, paving the way toward a sustainable energy system in the coming years.

Summary and conclusion
When examined from the narrow perception of being a standard crop, having a carbon-neutral profile, and theoretically being replenishable as a fuel source, biomass emerges as an appealing avenue for renewable energy.While biomass indeed holds sustainability potential and has demonstrated its viability, its utilization remains constrained within certain limits.However, this perception begins to shift when we delve into the potential large-scale impacts of utilizing biomass waste for energy generation.
This article assesses various characteristics of biomass conversion processes as energy sources and categorizes the technological pathways currently available for their utilization.
Recognizing the potential of biomass can facilitate a smooth transition for developing countries, shifting from traditional, inefficient biomass energy use to a future marked by commercial, competitive, and efficient biomass energy utilization.Based on the presented data and information, the following findings are suggested:  Presently, the primary technologies for converting biomass waste into usable energy are Biochemical and Thermochemical. The choice of conversion technology hinges on the specific form of energy required. Technologies like Fermentation, Pyrolysis, and Mechanical extraction are adept at producing liquid fuels suitable for transportation purposes. Other conversion technologies yield energy in usable forms such as gas or hot air/steam, typically most effective at the point of manufacture.
Recognizing that Anaerobic Digestion, gasification, and pyrolysis stand out as the most cost-effective methods to produce fuels suitable for Gas Engine application suggests that, while other techniques possess technical capabilities to generate suitable fuels, it's likely that only gasification will exhibit commercial sustainability.These conclusions stem from evaluating the overall efficiency of gas production, the historical performance of gasifiers, and biomass feedstock considerations.

Figure 1 :
Figure 1: Installed biomass and cogeneration volume in various states/sectors of India [11].

Figure 2 :
Figure 2: India's current portfolio of electricity generation [12]Figure3shows the total electricity generation from all resources in India.The electricity generation goal for the 2023-24 fiscal year, which includes renewable energy, has been set at 1750 billion units (BU).This target represents a growth of approximately 7.2% compared to the actual generation of 1624.158BU in the preceding year, 2022-23.In 2022-23, the electricity generation amounted to 1624.158BU, showing an increase of about 8.87% from the 1491.859BU generated in 2021-22[12][13].

Table 3 .
Meanwhile, the various types of available biomasses in India are outlined in Table4.This study aims to demonstrate how energy can be generated from abundant biomass waste using different biomass conversion technologies.1285 (2024) 012010