Bioconversion of Lignocellulosic Biomass to Biogas

Doctoral Thesis / Dissertation , 2020 , 154 Pages

Chemistry - Bio-chemistry

The aim of the present study is to investigate the optimum pretreatment method and performance characteristics of anaerobic digestion of lignocellulosic biomass for biogas production in batch mode. To assess the potentiality towards biogas production, three different types of biomasses were collected and characterized. Based on the results obtained from the characterization, three different lignocellulosic biomasses viz sugarcane bagasse, wheat straw and rice husk were selected, upon which small scale anaerobic digestion was performed. In this research, therefore, an optimal achievement of the lignocellulosic plant has been evaluated in the pretreatment impact (physical, chemical and biological) and multiple biogas manufacturing parameters. The pretreatment method focused on removal of lignin content by applying different alkaline and acid condition and then anaerobic digestion of pretreated biomass (WS, RH, and SB).

CONTENTS

- Declaration

- Certificate by Supervisor

- Abstract

- Acknowledgement

- List of Content

- List of Tables

- List of Figures

- List of Appendices

- Abbreviations

CHAPTER-1 INTRODUCTION
1.1 BACKGROUND
1.2 COMPOSITION AND PROPERTIES OF BIOGAS
1.3 APPLICATIONS OF BIOGAS
1.4 ANAEROBIC DIGESTION PROCESS
1.5 TYPES OF BIOMETHANATION PROCESS
1.6 COMMONLY USED FEED MATERIALS FOR BIOGAS 7 PRODUCTION
1.7 PRETREATMENT OF BIOMASS
1.7.1 LIGNOCELLULOSE
1.7.2 PRETREATMENT OF LIGNOCELLULOSIC BIOMASS
1.7.3 UTILIZE OF LIGNOCELLULOSIC BIOMASS FOR IMPORTANCE-ADDITIONAL PRODUCTS
1.8 MANURES
1.9 OBJECTIVES OF THE PRESENT WORK
1.10 ORGANIZATION OF THESIS

CHAPTER -2 REVIEW OF LITERATURE
2.0 INTRODUCTION
2.1 STRUCTURE AND PROPERTIES OF LIGNOCELLULOSES BIOMASS
2.1.1 CELLULOSE
2.1.2 LIGNIN
2.1.3 HEMICELLULOSE
2.1.4 PRETREATMENT TECHNOLOGIES
2.1.4.1 PHYSICAL PRETREATMENT
2.1.4.2 PHYSICOCHEMICAL PRETREATMENT
2.1.4.3 CHEMICAL PRETREATMENT
2.1.4.3.1 ALKALINE PRETREATMENT
2.1.4.3.2 ACID PRETREATMENT
2.1.4.4 BIOLOGICAL PRETREATMENT
2.2 FACTORS AFFECTING BIO-METHANATION PROCESSES
2.2.1 EFFECT OF TEMPERATURE ON BIOGAS PRODUCTION
2.2.2 EFFECT OF FEED MATERIAL ON BIOGAS PRODUCTION
2.2.3 EFFECT OF CO-DIGESTION OF BIOMASS ON BIOGAS PRODUCTION
2.2.4 EFFECT OF CARBON AND NITROGEN RATIO ON BIOGAS YIELD
2.2.5 EFFECT OF LOADING RATE (LR) ON BIOGAS PRODUCTION
2.2.6 ROLE OF PH ON BIOGAS PRODUCTION
2.2.7 EFFECT OF HYDRAULIC RETENTION TIME (HRT)
2.2.8 EFFECT OF MECHANICAL STIRRING AND AGITATION ON BIOGAS YIELD
2.2.9 EFFECT OF ADDITIVES ON BIOGAS PRODUCTION
2.2.10 EFFECT OF TOXICITY ON BIOGAS PRODUCTION
2.2.11 INFLUENCE OF TOTAL SOLID (TS) ON BIOGAS PRODUCTION
2.2.12 BIOSLURRY AS MANURES
2.3 SUMMARY

CHAPTER - 3 CHARACTERIZATION OF BIOMASS
3.0 INTRODUCTION
3.1 SAMPLE PREPARATION
3.2 CHARACTERIZATION OF BIOMASS FEEDSTOCK
3.2.1 PROXIMATE ANALYSIS
3.2.1.1 MOISTURE CONTENT
3.2.1.2 VOLATILE MATTER CONTENT
3.2.1.3 ASH CONTENT
3.2.1.4 FIXED CARBON CONTENT
3.2.1.5 TOTAL SOLID (TS) CONTENT
3.2.1.6 ULTIMATE ANALYSIS
3.2.1.7 CALORIFIC VALUE OF FEED MATERIALS
3.2.1.8 FIBRE ANALYSES OF BIOMASS
3.3 PROXIMATE ANALYSIS
3.4 ULTIMATE ANALYSIS (UA)
3.4.1 CALORIFIC VALUE OF BIOMASS
3.4.2 FIBRE ANALYSIS
3.5 SELECTION OF LIGNOCELLULOSIC BIOMASS FOR PRESENT STUDY
3.6 SUMMARY

CHAPTER - 4 RESEARCH METHODOLOGY
4.0 INTRODUCTION
4.1 MATERIAL & METHODOLOGY
4.1.1 GLASSWARE
4.1.2 EQUIPMENT
4.1.3 CHEMICALS
4.1.4 INOCULUM
4.1.5 BIOMASS (RICE HUSK, SUGARCANE BAGASSE, WHEAT STRAW)
4.1.6 DESIGNING LAB SCALE REACTOR FOR BIO­PROCESSING
4.2 EXPERIMENTAL PROCEDURES & METHODOLOGY
4.2.1 BIOGAS PRODUCTION POTENTIAL FROM BIOMASS (WS, RH, SB)
4.2.2 PRETREATMENT OF BIOMASS
4.2.3 BIO-DIGESTION OF PRETREATED BIOMASS
4.2.4 ANALYSIS OF MANURE
4.2.5 PRETREATMENT OF BIOMASS
4.2.5.1 PREPARATION OF STANDARD LIGNIN SOLUTION
4.2.5.2 PHYSICAL PRE-TREATMENT
4.2.5.3 ACID TREATMENT OF BIOMASS
4.2.5.4 THERMAL HYDROLYSIS
4.2.5.5 ALKALINE HYDROLYSIS
4.2.6 PRODUCTION OF BIOGAS
4.2.7 YIELD OF BIOGAS
4.2.8 PRETREATMENT OF WHEAT STRAW, RICE HUSK AND SUGARCANE BAGASSE
4.2.9 BIO-METHANATION
4.2.9.1 EFFECT OF TOTAL SOLID CONCENTRATION ON METHANE CONTENT (ML) OF BIOMASS
4.2.9.2 EFFECT OF NITROGENOUS SUBSTANCE ON BIOGAS YIELD
4.2.9.3 EFFECT OF pH ON BIOMETHANATION OF BIOMASS
4.2.9.4 EFFECT OF TEMPERATURE ON BIOMETHANATION OF BIOMASS
4.2.10 BIOSLURRY AS MANURE
4.3 SUMMARY

CHAPTER - 5 RESULT AND CONCLUSION
5.0 CONTRIBUTION OF THE PRESENT WORK
5.1 IMPROVED CHARACTERISTICS OF BIOMASS
5.2 COMPARATIVE PRETREATMENT FOR BIOMASS (WS, RH, SB)
5.3 OPTIMIZED ANAEROBIC CONDITION FOR BIOGAS PRODUCTION
5.4 END PRODUCT OF THE PRE-TREATMENT AND DIGESTER: MANURES
5.5 FUTURE STUDIES

REFERENCES

APPENDIX

PUBLICATIONS

ABSTRACT

Consumption of petroleum derivative and increment in ecological contamination at a disturbing rate has persuaded the analysts to search for the naturally benevolent just as financially savvy elective wellsprings of vitality. Biomass is a sustainable power source created from living or as of late living plant and creature materials, which can be utilized as fuel. The primary segments present in biomass are polymers, for example, sugar, protein, cellulose, lignin and fat. Biogas is delivered when the biomass is anaerobically corrupted by microorganisms. The procedure of anaerobic assimilation (AD) happens in four stages: hydrolysis, acidogenesis, acetogenesis, and methanogens. Biogas creation from biomass is getting a ton of consideration because of its simple accessibility and moderately basic biomass to vitality change innovation. Co-processing of biomass with dairy cattle waste is another promising technique for changing over biomass to vitality through anaerobic assimilation.

In most developing countries like India, China etc. The principal occupation of the people is crop production and the crop residues remaining after harvesting is a major challenge to deal with. These biomasses are lignocellulosic in nature as they contain cellulose, hemicellulose and lignin. They are not economically used; rather they are arranged off in the open condition or consumed, causing genuine medical issues and ecological contamination. Lignocellulosic biomasses are evaluated for the utilization of anaerobic processing with the goal of creating biogas from it and performing motor examination on the delivered biogas. The point of the current examination is to research the ideal pretreatment technique and execution attributes of anaerobic processing of lignocellulosic biomass for biogas creation in clump mode.

To evaluate the probability towards biogas creation, three unique sorts of biomasses were collected and characterized. Based on the results obtained from the characterization, three different lignocellulosic biomasses viz. sugarcane bagasse, wheat straw and rice husk were selected, upon which small scale anaerobic digestion was performed. In this research, therefore, an optimal achievement of the lignocelluloses plant has been evaluated in the pretreatment impact (physical, chemical and biological) and multiple biogas manufacturing parameters. The pretreatment method focused on removal of lignin content by applying different alkaline and acid condition and then anaerobic digestion of pretreated biomass (WS, RH, and SB). The parameters considered for the analysis TS of biomass, temperature of substrate, C:N ratio and pH.

Biologically, Lignocellulose biomass gave maximum biogas yield followed by acid and alkaline treatment. Among thermal treatments, best results in the increase of methane formation were observed with the treatment of wheat straw followed by sugar cane bagasse and rice husk at 121°C & 120 minutes (19,8%,18%, and 13%, respectively). Acid pretreatment at optimized condition (30%, (60 minutes) and % increase in methane content is found maximum with anaerobic digestion of wheat straw (25%), sugarcane bagasse (20%) followed by rice husk (17%). Acid pretreatment has maximum impact on biomethanation of wheat straw biomass at optimized condition. Biological pretreatments performed with a fungal strain, improves methane production. The percentage increase in methane content after pretreatment with fungal strain is found maximum for wheat straw (34%), followed by sugarcane bagasse (30.2%) and rice husk (27.7%) respectively.

Discoveries additionally show that these biomasses have high unstable issue content (above 60%) and high fixed carbon content (above 10%) which make them intense for biogas creation. Impact of absolute strong and molecule size of biomass on biogas creation was considered and it was discovered that with 8-9% of all out strong and 0.355 mm of molecule size, most extreme measure of biogas can be delivered. Impact of temperature on biogas creation from lignocellulosic biomass was additionally learned at five distinct temperatures from 35°C to 55°C at a stage of 5°C and it was discovered that with increment in temperature of the digestate from 40°C to 55°C, biogas creation from substrates can be expanded. It is additionally seen that in mesophilic condition, biogas age is the most noteworthy at 35°C followed by 40°C.

Alongside the biogas delivered, AD additionally changes the additional feedstock into digestate that can be utilized as a compost which is high in nitrogen, potassium and phosphorus substance. The N (%) from spent slurry from anaerobic assimilation of biomass (WS, RH, SB) was in the scope of 0.93 to 0.98, most noteworthy P(%) and K(%) found from slurry of anaerobic processing of rice husk.

ACKNOWLEDGEMENT

This research would have not reached its closure without the constant encouragement and guidance of people at various milestones of my journey, in the last seven years. I take this opportunity to express my sincere gratitude to all the people who have been contributory in the successful completion of this thesis.

Most importantly, I might want to communicate my heartful thankfulness and gratitude to my manager Dr. Shailey Singhal, Professor, Department of Chemistry, University of Petroleum and Energy Studies, Dehradun, for her enormous assistance, significant direction and inclusion at each progression of this exploration.

Her passion in scientific research and tireless mentorship are the key motivating factors behind my successful completion of this thesis. I am sincerely grateful to his invaluable patience and advice in research as well as my life. Here, I appreciate her help and guidance during these challenging but wonderful years.

I would like to express a special appreciation to Chancellor Dr. S. J. Chopra, Vice-Chancellor Dr. Deependra Kumar Jha, University of Petroleum and Energy Studies for their constant consolation and backing.

I want to offer my thanks to Mr. G Sanjay Kumar, General Manager, Chemplast Sanmar Ltd. Tamil Nadu, India for his valuable suggestions and advice in my research, which helped me to improve the quality of my research work. I want to thank with my heart, Dr. Rohit Sharma my friend, for his support in analysis and report writing.

I also want to acknowledge Dr Naveen Singhal, Professor, DIT University, Dehradun and Dr. Amit Kumar, Dept. of Chemistry, UPES for their continuous support in completing my work. This study would have not been complete without the support of MNRE for the project“Integrated Research, Development and Demonstration of Biogas Generation from Leaves Fruit Hull and De-oiled cake of Jatropha using CSTR Digested”(Sanction Order No: 19- 1/2011-BE/R&D), at UPES, Dehradun, for allowing me the space and opportunity to use its facility. Last but not least, I would like to thank my parents, my wife and all my other family members for their unconditional support, patience, understanding and love not only for this thesis but also for my life at every move. Thanks for all this.

Rajan Sharma

LIST OF TABLES

Table 1.1 GENERAL COMPOSITION OF BIOGAS

Table 1.2 GENERAL PROPERTIES OF BIOGAS

Table 1.3 VARIOUS KIND OF FEED MATERIAL USED FOR BIO- METHANATION PROCESSES

Table 2.1 ADVANTAGES AND DISADVANTAGES OF SELECTED GREEN CHEMISTRY PRETREATMENT METHODS

Table 2.2 KEY FACTORS FOR AN EFFECTIVE PRETREATMENT METHOD FOR LIGNOCELLULOSIC BIOMASS

Table 2.3 LITERATURE ON VARIOUS FEED MATERIAL AND THEIR RESULTS

Table 2.4 LITERATURE ON EFFECT OF CO-DIGESTION OF BIOMASS ON BIOGAS PRODUCTION

Table 2.5 C:N RATIOS IN VARIOUS ORGANIC WASTES

Table 3.1 COMPARISON OF RESULTS OF PROXIMATE ANALYSIS OF THE FEED MATERIAL AND LITERATURE

Table 3.2 COMPARISON OF RESULTS OF ULTIMATE ANALYSIS OF THE FEED MATERIAL AND LITERATURE

Table 4.1 INVENTORY OF EQUIPMENT

Table 4.2 LIST OF CHEMICAL

Table 4.3 PRETREATMENT VARIABLES FOR BIOMASS

Table 4.4 DELIGNIFICATION OF WHEAT STRAW UNDER CHEMICAL TREATMENT

Table 4.5 DELIGNIFICATION OF WHEAT STRAW UNDER BIOLOGICAL TREATMENT

Table 4.6 DELIGNIFICATION OF RICE HUSK UNDER CHEMICAL TREATMENT

Table 4.7 DELIGNIFICATION OF RICE HUSK UNDER BIOLOGICAL TREATMENT ON RICE HUSK

Table 4.8 DELIGNIFICATION OF SUGARCANE BAGASSE UNDER CHEMICAL TREATMENT

Table 4.9 DELIGNIFICATION OF SUGARCANE BAGASSE BELOW BIOLOGICAL TREATMENT

Table 4.10 METHANE CONTENT IN BIOGAS AFTER CHEMICAL TREATMENT OF WS

Table 4.11 METHANE CONTENT IN BIOGAS AFTER BIOLOGICAL TREATMENT OF WS

Table 4.12 METHANE CONTENT IN BIOGAS AFTER CHEMICAL

Table 4.13 METHANE CONTENT IN BIOGAS AFTER BIOLOGICAL TREATMENT OF RH

Table 4.14 METHANE CONTENT IN BIOGAS AFTER CHEMICAL TREATMENT OF SB

Table 4.15 METHANE CONTENT IN BIOGAS AFTER BIOLOGICAL TREATMENT OF SB

Table 4.16 EFFECT OF TOTAL SOLID CONC ON METHANE

Table 4.17 IMPACT OF C:N RATIO ON BIOGAS YIELD

Table 4.18 EFFECT OF pH ON BIOMETHANATION OF BIOMASS

Table 4.19 EFFECT OF TEMP ON BIOMETHANATION OF BIOMASS

Table 4.20 ANALYSIS OF NPK VALUE OF SLURRY FROM DIGESTOR

Table 4.21 OPTIMIZED PRETREATMENT CONDITION (WS, RH &SB)

Table 5.1 A SUMMARY OF TECHNIQUES INVESTIGATED FOR ENHANCING BIOGAS PRODUCTION FROM LIGNOCELLULOSIC MATERIALS

LIST OF FIGURES

Fig. 1.1 STAGES OF AN ANAEROBIC DIGESTION

Fig. 1.2 COURSE OF ACTION OF CELLULOSIC MICROFIBRILS IN PLANT CELL DIVIDERS (MURPHY AND MCCARTHY, 2005)

Fig. 1.3 BUILDING BLOCKS OF LIGNIN

Fig. 1.4 RESULT OF PRETREATMENT ON LIGNOCELLULOSIC BIOMASS

Fig. 1.5 EFFECT OF HYDROLYSIS OF LIGNOCELLULOSIC BIOMASS

Fig. 1.6 DIFFERENT VALUE ADDED PRODUCTS FROM LIGNOCELLULOSIC BIOMASS

Fig. 2.1 CONSTITUTION OF CELLULOSE

Fig. 2.2 MODEL STRUCTURE OF SPRUCE LIGNIN

Fig. 2.3 SCHEMATIC PORTRAYAL OF THE HEMICELLULOSE SPINE OF ABSORESCENT PLANTS

Fig. 2.4 A RUNDOWN OF DIFFERENT STRATEGIES UTILIZED IN THE PRETREATMENT OF LIGNOCELLULOSIC SQUANDERS

Fig. 2.5 GROWTH PRICE OF METHANOGENS UNDER PSYCHROPHILIC, MESOPHILIC AND THERMOPHILIC CONDITIONS

Fig. 2.6 MAXIMUM SPECIFIC GROWTH RATE FOR DIFFERENT PH VALUES

Fig. 2.7 PRESENT THE BIOGAS PRODUCTION WITH HRT FOR 39 DIFFERENT KINETIC CONSTANT

Fig. 3.1 FIBER CONSTITUENTS IN BIOMASS

Fig. 3.2 MOISTURE CONTENT OF BIOMASS

Fig. 3.3 VOLATILE MATTER CONTENT OF BIOMASS

Fig. 3.4 ASH CONTENT OF BIOMASS

Fig. 3.5 FIXED CARBON CONTENT OF BIOMASS

Fig. 3.6 TOTAL SOLID CONTENT OF BIOMASS

Fig. 3.7 CALORIFIC VALUE OF BIOMASS

Fig. 3.8 CELLULOSE CONTENT (%) OF BIOMASS

Fig. 3.9 HEMICELLULOSE CONTENT (%) OF BIOMASS

Fig. 3.10 LIGNIN CONTENT (%) OF BIOMASS

Fig. 3.11 LIGNIN TO CELLULOSE RATIO (%) OF BIOMASS

Fig. 4.1 REACTOR DESIGN

Fig. 4.2 BATCH STIRRED TANK REACTOR WITH WATER DISPLACEMENT

Fig. 4.3 EFFECT OF CHEMICAL TREATMENT

Fig. 4.4 EFFECT OF TOTAL SOLID ON BIO GAS PRODUCTION FORM PRETREATED AND UNTREATED

Fig. 4.5 BIO GAS YIELD ON FEED TO WATER DILUTION RATION

Fig. 4.6 NITROGEN CONTENT IN BIO GAS YIELD

Fig. 4.7 EFFECT OF TEMPERATURE ON BIO GAS PRODUCTION

Fig. 4.8 EFFECT OF BIOLOGICAL TREATMENT

Fig. 4.9 COMPARATIVE BIOMETHANE CONTENT OF WHEAT STRAW

Fig. 4.10 COMPARATIVE BIOMETHANE CONTENT OF RICE HUSK

Fig. 4.11 BIO METHANE CONTENT OF SUGARCANE BAGGASE

Fig. 4.12 COMPARATIVE BIOMETHANE CONTENT OF BIO MASS (SB, RH & WS)

Fig. 4.13 EFFECT OF PRETREATMENT ON PERCENTAGE INCREASE IN METHANE CONTENT OF BIO MASS (SB, RH & WS)

Fig. 4.14 EFFECT OF PRETREATMENT ON YIELD OF BIOGAS(ML/gVS) CONTENT OF BIOMASS(WS,RH &SB)

LIST OF APPENDIX

APPENDIX I Characterization of Biomass

APPENDIX II Control of C:N ratio and TS of substrates

APPENDIX III List of equipment/instrument used

APPENDIX IV Accessoried Used in the Experimental Set-Up

APPENDIX V GC Gas Analysis

ABBREVIATIONS

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CHAPTER - 1 INTRODUCTION

1.1 BACKGROUND

Energy is a crucial contribution to economic growth , social development and human development. Global demand for energy has risen rapidly in recent years of rising global populations and improving affluence, industrialization and quality of life (Surendra et al., 2014; Perin et al., 2019). In 2010, global vitality consumption surpassed 524 QBtu and is projected to reach 800 QBtu by 2040 compared to a conventional growth rate of 1.5 percent per year (EIA, 2013). Fundamentally, an enormous part of the world's all out vitality requests (over 84%) is bolstered by non- sustainable fossil assets, for example, coal, oil, and petroleum gas. These assets are restricted in flexibly as well as effetely affect the earth because of the discharge of ozone harming substances (GHGs) into the climate (EIA, 2013). Petroleum products are the predominant wellspring of essential vitality due to their simple accessibility. Aside from their indigenous creation, most of creating nations import raw petroleum to adapt up to their expanding vitality request. Along these lines, a critical bit of their well- deserved fare profit is spent on the acquisition of oil based commodities. India is additionally a net vitality shipper and around 80% of the nation's fare profit are legitimately spent on the acquisition of oil based commodities (Correa et al., 2019). There has been a sharp increment in the utilization example of oil based commodities in India. The constrained save of non-renewable energy source has involved worldwide worry as these are under danger of misfortune because of overexploitation. According to the World Energy Forum prediction, reserves of fossil fuels will exhaust in less than another ten decades.

The constrained hold of petroleum derivative has involved worldwide worry as these are under danger of exhaustion because of overexploitation. Coal and gaseous petrol are the two essential wellsprings of intensity age. Exacerbating ecological conditions have become an issue of ever-expanding overall open worry in present occasions. At present, the burning of petroleum products is a critical wellspring of discharge of Carbon Dioxide (CO2). There are endeavours all around the world to shield the natural condition from further disintegration. Therefore, it is a need of today's world to concentrate on the renewable energy source to satisfy the demand, conserve our finite natural resources for the generations to come.

In India, there are various sources of renewable energy but the practice of traditional biomass is decades old (Patinvoh et al., 2017). Notwithstanding, conventional biomass is utilized predominantly for cooking and warming and is portrayed by the low proficiency of utilization. The unreasonable extraction and utilization of conventional biomass vitality lead to debasement of the nearby condition and timberlands, deforestation, and the subsequent loss of woodland items, soil disintegration and loss of biodiversity, residential air contamination influencing human wellbeing, and so forth. Yet, the cutting edge types of biomass vitality give various natural advantages. Of all the sustainable power sources, biomass (lignocellulose, herbaceous yields, farming and city squanders) is the biggest, generally different and most promptly exploitable asset. Bio-vitality advancements give chances to the transformation of biomass into fluid and vaporous powers just as power. Use of biodegradable resources to produce biogas and thereafter use of that biogas for generating power and thermal applications has multiple benefits on environmental, social, economic aspects, etc.

Biomass energy could assist with lessening the world's reliance on oil and fossil fuels.Bioenergy can play a noteworthy role in mitigating global warming. This is because CO2 released during combustion is used by the plant for photosynthesis and accordingly doesn't expand the net CO2 in the air. In this way, the utilization of inexhaustible biomass (counting vitality yields and organic wastes.) as an energy resource is not the only greener concerning most pollutants, but its use represents a closing balance of carbon cycle with respect to atmospheric carbon dioxide.

Considering the importance of renewable energy, the Indian government has put Biogas as a sustainable power source, under the subject of The Ministry of New and Renewable Energy. It has executed National Biogas Programs for the scattering and organization of family/little biogas plants in the far off, provincial, semi-urban zones of the nation. It helps in many ways by converting the biomass wastes into useful gains to the beneficiaries by providing clean power for various applications, thermal and cooking fuel, reductions in health hazards and mitigating emissions of Green House Gases (GHGs), combating climate change and simultaneously producing biogas slurry as nutrient- enriched organic fertilizer/manure as a by-product of the biogas generation/ production. The organic bio- manure/ fertilizer when applied in farming, contributes to higher crop production and yield and help in conserving the soil health and water. The Chhattisgarh government has decided to set up at least six biofuel plants to produce ethanol in the state. It will be the first state in India to use rice and paddy husk to produce the biofuel (Sharma, 2019).

Several possible advancements in the territory of sun powered, wind and biomass have been found and popularized. Despite the fact that most of sustainable power source innovations are better eco-accommodating when contrasted with ordinary vitality alternatives, their selection is exceptionally moderate as a result of different reasons, for example, monetary imperatives, absence of gracefully and not easy to use's procedures and so on. Further, the employments of these innovations are as yet restricted to most of the steady activities primarily because of mechanical impediments and helpless financial matters.

Additionally, biofuels creation alongside side-effects, can give new salary as well as business open doors in provincial regions. In this way 21st Century is searching for a move to interchange modern feedstock and green procedures to create these synthetic substances from inexhaustible biomass assets. Lignocellulosic biomass transformation is the best option for bioenergy fuel. Lignocellulosic biomass is one of the biggest sustainable power resource (Azevedo et al., 2019) It is an essential component of the primary food crops; it is the non-palatable segment of the plant, which is undertow and can be utilized for biogas production Transformation of these lignocellulosic residues into renewable fuel offers a prominent possibility in decreasing the use of nonrenewable fossil sources (oil, coal, and flammable gas) (Zhe et al., 2017). Biogas generated from waste substances is a promising sustainable power source utilized for generating electricity and heat. It is also used as vehicle fuel in numerous countries. In short, lignocellulosic biomass holds the way to supplying society's essential liquid transportation fuel without affecting the country's food supply. It is the best solution for cooking gas, bio CNG for the transportation sector, and power generation. Its practice will demotivate the utilization of fossil fuels and reduce the dependence of imported crude oil that will ultimately check the rapid exhaustion of fossil fuels and also will protect the environment save the cost of importing the petroleum product.

Lignocellulosic biomass consists of cellulose , hemicellulose and lignin and can be used as the primary agent for the processing of biogas (Hayn et al. 1993).. A reasonable pretreatment technique is needed to strengthen the biodegradability of lignocelluloses materials. The pretreatment aims is to build up enzyme accessibility by improving the digestibility of cellulose (Surendra et al., 2018). The lignocellulosic raw materials available in India include cellulose-containing waste, Like husked wheat, , rice husk , rice straw, sugarcane bagasse, vegetable waste as well as municipal waste. The major deposits amount to around 39.0 million metric tons or roughly 18-20 million metric loads of biodegradable cellulose (Paudel et al., 2017).Fuels acquired from cellulosic biomass for example the woody, and normally unpalatable pieces of plant give an option in contrast to conventional power sources that support national economic development and environmental goals (Petersson et al., 2007). Besides, biogas from lignocelluloses may provide new job opportunities for local people in rural territories, which can make a great socio-economic impact (Wyman, 2005). Biomass sources utilized for power generation include rural and forest waste, municipal waste, and aquatic waste utilized for energy purposes (Surendra et al., 2018). Reasons behind the generation of power from crop as well as agro-unused is because bioenergy is renewable type of energy form, which can be produced from lignocellulose upon need. This energy can be seen as more effectively accessible than fuel sources and may be produced using significantly involving low capital cost. In various cases, usage of biomass can add to handle environmental issues, for example, use of biomass produced due to eutroplication as raw material for producing biogas. Its use lead to the decrease of dependence upon petroleum- based energy sources.

1.2 COMPOSITION AND PROPERTIES OF BIOGAS

Biogas is manufactured by anaerobic absorption of waste in anaerobic reactor. The most important fundamentals of biogas is methane and carbon dioxide. Apart from that, a
trace quantity of hydrogen sulfide, nitrogen, and hydrogen are there depending upon the variety of substrates used for producing the biogas. Table 1.1 suggest a general component of biogas.

Table 1.1 General composition of biogas (Deublein and Steinhauser, 2008)

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The most important part of the energy of biogas is the calorific value of its CH4 content. This property of biogas makes it fit to be used as fuel for industry and domestic purposes.

Table 1.2 indicates the general propertied of biogas.

Table 1.2 General properties of biogas (Deublein and Steinhauser, 2008)

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1.3 APPLICATIONS OF BIOGAS

Utmost constituents of biogas are methane with carbon dioxide. Methane is a prime constituent of natural gas. So, if somehow carbon dioxide can be take out from the biogas, Like wheat huskit, it will be a source of immense energy, which can be used effectively for different purposes like cooking, lighting, vehicle fuel and generation of electricity (Jeoh et al., 2017). After scrubbing the biogas it can be compressed and used as vehicle fuel like CNG and also it can be stored in cylinders and transported to other places.

1.4 ANAEROBIC DIGESTION PROCESS

The method of anaerobic breakdown of organic matter such as biomass, manure, agricultural residue, etc. can be used to synthesize biogas. Anaerobic processing is a strategy where micro-organisms in the truancy of oxygen to produce biogas decompose the biodegradable mass of the organic matter (Curto and Martin, 2019).The biomass breaks down to simpler substances during hydrolysis which is then acted by acidogenic bacteria, acetogenic bacteria followed by methanogenic bacteria. The reaction takes place through a significant number of steps with the help of the methanogens (Mahanta et al., 2004). The entire method of anaerobic digestion is partitioned into four noteworthy steps to perceive the framework appropriately. They are recognized as

- Lignocellulosic biomass hydrolysis to soluble compound
- Soluble compound acidization & degradation to volatile fatty acids.
- Acetogenesis producing derivatives of hydrogen , carbon dioxide and acetic acid
- Biogas creating methanogenesis

As shown in Figure. 1.1, the digestion procedure begins with the breakdown of the biomass taken as input and breaks them down to insoluble simpler substances, which can be digested by bacteria. The acidic bacteria convert Sugars and amino acids of carbon dioxide, hydrogen , nitrogen, and fatty acids. These organic acids, along with additional ammonia, hydrogen and carbon dioxide, are then converted by acetogenic bacteria into acetic acid. Methanogenic bacteria ultimately transform these materials into methane and carbon dioxide. Anaerobic absorption generates biogas and prevent the production of foul smell and additionally produces manures with high nitrogen content (Mittal, 1996). The response that occur in the procedure of methanogenesis is conveyed in Figure 1.1 (Mata-alvarez et al., 2000).

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Fig. 1.1Stages of an anaerobic digestion (Mata-alvarez et al., 2000)

1.5 TYPES OF BIOMETHANATION PROCESS

Anaerobic digestion can be executed as a batch system or a continuous system. In a batch reactor biomass is added to the digestor at the beginning of the procedure. The reactor is then sealed for a period of the process. Since batch processing is not complicated and requires fewer devices and lower rates of plan work, absorption is typically more economical than persistent digesters. In persistent absorption the biomass slurry input is added at regular intervals of time with the continuous removal of waste from the other side. The continuous digestion is better for production of biogas.

1.6 COMMONLY USED FEED MATERIALS FOR BIOGAS PRODUCTION

Biogas producing from all different feed material is never equivalent. It shifts from substrate to substrate. Aside from that, there are numerous different parameter which affects the production of biogas. Some of them are C:N of substrate utilized, temp., pH interest, loading rate of input, hydraulic retention time, the toxicity of slurry, dilution and consistency of input feed and so on. The impact of agitation and added substances on biogas assembling is furthermore quite critical. Diverse types of material utilized as
feed for bio-methanation can be classified as animal waste, plant waste and domestic waste in Table 1.3.

Table 1.3 Various kind of feed material used for bio-methanation processes

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1.7 PRETREATMENT OF BIOMASS

1.7.1 Lignocellulose

Lignocellulose biomass comprises cellulose; hemicellulose and lignin (Jiang et al, 2018). The plant outermost structure is made up of cellulose which provides toughness and elasticity. The protective coat present outside the cell wall is lignin. A strengthening material which is available among cellulose and lignin is alluded to as hemicellulose. The diagram structure of cellulose is exhibited in Figure 1.2 however building block of
lignin is showed up in Figure 1.3. In this Figure (1.2), straight bundles appeared associated with lignin. The structure of lignin is then bound by particular hemicelluloses like xyloglucan, gelatin. Agricultural items, paper mash or tree industries alongside various agro essentially based exercises are sources of lignocellulosic biomass.

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Fig. 1.2 Course of action of cellulosic microfibrils in plant cell dividers (Murphy and McCarthy, 2005)

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1.7.2 Pretreatment of lignocellulosic biomass

Lignocellulosic biomass has more opposition to hydrolysis (Rajendran et al., 2018). This is because of its remarkably well-ordered structure. This is the significant reason for its applications for the generation of various value presented stock i.e., ethanol, lactic acid, bio-oil, biogas are limited to some extent. In lignocellulose, sugar polymers are bounded with lignin with the help of hydrogen and covalent holding, which transforms into an unmanageable structure for hydrolysis and generation of value- added products such as biogas, etc (Kumari and Singh, 2018). In this manner, this structure of lignocellulosic biomass contains cellulose; hemicellulose and gelatin polymers join together and produce tough three- dimensional structure because of which hydrolysis is difficult (Perin et al., 2019). Figure 1.4 reveals the impact of pretreatment on the lignocellulosic biomass.

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Fig. 1.4 Result of pretreatment on lignocellulosic biomass (Fernandes et al., 2007)

1.7.3 Utilization of lignocellulosic biomass for importance-additional products

Lignocellulosic biomass is an inexhaustible valuable asset which is present in plant cell and can be utilized for energy production, to be utilized for various purposes (Veluchamy and Kalamdhad, 2017). The effect of breakdown of lignocellulosic biomass is shown in Figure 1.5

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Fig. 1.5 Effect of hydrolysis of lignocellulosic biomass (Das et al., 2010)

But, it is essential to break the three- dimensional structure of polymer which is available in biomass into the less difficult composites for producing different types of significant items. The various types of significant worth included items from lignocellulosic biomass are showed in Figure 1.6.

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Fig. 1.6 Different value added products from lignocellulosic biomass (Huang et al., 2008

Anaerobic processing is well- developed technology and is used worldwide for the production of bioenergy from different feedstock. These different sorts of substrate have high organic material of biodegradable nature which makes them a perfect biomass for anaerobic digestion process. Huge waste in farming and industrial level, can be used for producing biogas and manures.

1.8 MANURES

Bioslurry is a good fertilizer for crops and improves the soil fertility, soil structure and yields of crops. It is better than ordinary Farmyard manure (FYM) and may likewise lessen the utilization of chemical fertilizers. Bio slurry can be utilized to manufacture solid prolific soils for yield generation. Surely, bioslurry structure and substance settle with two- fold nitrogen content, which is not the same as Farmyard Manure (FYM). Likewise, the amount of the bio- slurry is additionally higher than normal FYM. Bioslurry contains helpful plant nutrients and more prominent measures of supplements, micronutrients than FYM. The results of bioslurry utility are similar to the results of the product of chemical fertilizers. In that capacity, bioslurry can be a genuine option in contrast to chemical fertilizers.

1.9 OBJECTIVES OF THE PRESENT STUDY

The wide objective of the proposed work is the transformation of lignocellulosic biomass to biogas and its upgraded outcomes as an exercise to protect the environment. As per the literature survey, it was found that three lignocellulosic biomass named wheat straw, rice husk and sugarcane bagasse are in abundance in our country and can be a profitable step to increase energy generation in a developing country. The utilization of biomass for energy also decreases the gap generated due to energy demand and supply. The specific targets of the study are:

- Optimizing the pretreatment prerequisites of agricultural biomass (wheat straw, rice husk and sugarcane bagasse) to cause delignification.
- To study the impact of reaction conditions (temp, pH, concentration, Nitrogenous substance) on biogas generation.
- Analysis of outlet slurry for fertilizer value.

1.10 ORGANIZATION OF THESIS

Chapter 1 discusses the brief introduction about the biogas production and the feedstocks for biogas production. Chapter 2 discusses the various techniques for pretreatment of lignocellulose waste, selection of suitable pretreatment methods to our research and Anaerobic digestion of treated waste to biogas. Chapter 3 addresses the material and methodology to achieve the research objectives, namely designing conditions for our experiments. This involves culturing of Pretreatment of lignocellulose waste and the effect of different factors on biomethanation. The achieved targets are discussed in Chapter 4 wherein it will be explained how the researcher has implemented conditions in the pretreated biomass for bio methane production and manure production. The results will also be discussed the optimum for different levels of pretreated biomass which were studied and then will finalize the best optimum condition for specific biomass. Chapter 5, includes the summary of the final conclusion and findings for the research questions and problem statement, as well as give recommendations for future research.

CHAPTER-2 REVIEW OF LITERATURE

2.0 Introduction

Many fuels are obtained from fossilized biomass, but financial and natural considerations are pushing for an growing commitment to ongoing biomass capable to closing the CO2 obsession / outflow circle within environmental cycles. The capability of biomass is practically tremendous. It is a direct result of this explanation that the earthly net essential creation compares roughly to 2000 EJ Y-1 (Krausmann et al., 2013). Be that as it may, the viable capability of bioenergy isn't effectively quantifiable. It is subject to numerous vital suppositions, for example, the level of supportability, land accessibility, dietary propensities that clarify the wide range (Slade et al., 2014). The lively store created by plants as a net productivity is used to help the increased trophic degrees of biological systems, in this manner occupying some portion of this vitality stream out into human uses and profoundly affects the earth and the dissemination of assets (the evaluated human assignment is one-fourth of the hypothetical net essential efficiency). To dodge or limit the opposition with different goals, the creation of bioenergy from squanders and buildup is energized thinking about that its latent capacity is regarded to be noteworthy. Anaerobic processing (AD) is currently one of the main advances equipped to convert biodegradable substrates into a fuel, methane that is framed in biogas alongside carbon dioxide (a blend of around 60­65 per cent CH4 and 35-40 per cent CO2) through a network of prokaryotic creatures. The multifaceted nature of the metabolic pathways prompting biogas from biopolymers is traditionally separated into four successive advances: debasement of biopolymers into littler atoms like monomers (hydrolysis), which are aged chiefly into unpredictable unsaturated fats VFAs (acidogenesis), further processed into CH3COOH, CO2 and H2 (acetogenesis) which are ultimately changed over in a definitive items CH4 and CO2 (methanogenesis) (Fabbri and Torri,2016).

The hydrolysis step is rate-restricting because of the nearness of complex polymers in biomass. Pretreatment is a procedure wherein the biomass is prepared for microbial assault. This pretreatment can be physical tasks, for example, mechanical commmunition, light and so forth.; synthetic treatment with soluble base, acids, wet oxidation and so forth.; natural pretreatment, by parasites or catalysts; or a blend of these procedures (Karuppiah & Azariah, 2019).

Micro-anaerobic pretreatment is a proficient and financially savvy pretreatment technique to meet the requirements for the industrial applications. Amin et al, (2017) concluded that the development of cellulosic fibre for enzyme attack, prevention of the emergence of fermenting microorganism inhibitors and hydrolytic enzymes, lessen power call which finally decrease the price of the feedstock. An ongoing update concerning advancements in the field of pretreatment was created. The improvement of the productivity and cost impediments by consolidating both substance and physical strategies was found to be more beneficial as compared to both methods in individuals. Furthermore, the substance pretreatment can give numerous drawbacks identified with the broad waste creation and consumption of the reactors (Marcin et al., 2019).

Considering different bioenergy resources, lignocellulosic has been recognized as the chief source of biofuels and many upgraded products (Kumar et al., 2008) . This biomass is an excess of organic material that can be used in the sustainable development of bioenergy and biofuels like biogas (Zheng et al, 2014). Lignocellulosic wastes acquired from power crops, woodlands and agri-food leftover constitute the significant sources of renewable biomass (Lin and Tanaka 2006; Kumar et al., 2008). It has been found that the plant photosynthesis accumulated around one hundred fifty billion stores of dry fabric every year with which about half is cellulose (Persson et al., 1991).The lignocellulosic biomass from plants and leftover wastes of agricultural activities amounts to the biggest inexhaustible supply of fermentable sugars on earth, which is otherwise considered as agricultural waste (Azevedo et al., 2019). Because of their easy availability, huge amount and sustainability, there has been an rising enthusiasm of mainstream researchers in utilizing lignocellulosic wastes for the rebuilding of a lot of valuable stock and biomaterials (Pandey et al., 2000; Howard et al., 2003; Das et al., 2010; Saha et al.,2005; Foyle et al., 2006; Tomas-Pejo et al., 2011; Mtui, 2008; Huang et al., 2008).

For example , agricultural squanders such as straws, nutshells, shells of organic products, seeds of natural products, stoves of plants, green leaves, and molasses are potential assets of sustainable power sources. Many creating nations have an abundant assortment of agrarian deposits. However, massive amounts of horticultural plant deposits are created worldwide annually but are incomprehensibly underused (Demirbaç., 2001). Rice straw is an agrarian buildup that is bountiful and in large measure unused. In the creating nations of East and Southeast Asia, rice straw is used as a basic food for ruminants, accounting for 90 % of world rice production (Zhong et al., 2011). It produces about 731 million tons of rice straw. This sort of removal strategy has caused across the board ecological worries as it adds to air contamination (As in the case of Punjab, Haryana, UP, etc). It can't be denied that one of the reasons for the air pollution in Delhi since mid-October is the stubble burning of crops in Punjab and Haryana (Nirmal., 2019).

Dumping agrarian deposits in the field once again can reduce crop production, increase foliar diseases as well as degrade agronomic parameters (Siddique et al., 2017). Thereafter, financially savvy advances for removal of different biomasses.

Anaerobic degradation of organic residue and deposits consolidates practical treatment as well as sustainable power source creation. Biomass, are impervious to anaerobic processing and can be changed over into biogas, albeit just to low degrees. Anaerobic assimilation of industrial waste and waste deposits consolidates both effective treatment and the production of renewable energy sources. Lignocellulosic materials are unaffected by anaerobic processing and can be converted into biogas, but only to low degrees. Such materials' low susceptibility to turn to biogas is due to their piece and structure. Lignocellulose is the mind boggling and unbending lattice of plant cells; as a result of the strong association between lignin, cellulose , and hemicellulose it is impervious to enzymatic attack. This can corrupt cellulose and hemicellulose in the form of biogas. Be that as it might, under anaerobic conditions, lignin can not be corrupted. Thusly, pretreatments, including the dissolution and decomposition of the hemicellulosic and lignin parts of the stratum, are important to encourage biogas creation by conquering breakdown restrictions (Nizami et al, 2009). Medicines 16

encouraging the availability of hemicellulose are important to expand the biogas capability of filaments, for example, corn stalks and wheat straw. Numerous medicines for expanding the biodegradability of lignocellulosic material have been accounted for. One of the targets of this examination likewise centers around this. (Sawatdeenarunat et al,2015).

The utilization of chose developing innovations like high and low energy radiation; beat force field; ultrasound and high weight; as a instrument in the debasement of lignocellulosic biomass was considered and talked about in beneath table (Shady et al., 2018).

Table 2.1: Advantages and disadvantages of selected green chemistry pretreatment methods (Shady et al., 2018)

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Bioenergy, especially biogas supplied through anaerobic processing (AD) of sustainable feedstocks, is viewed as one of the exceptionally encouraging options as compared to fossil-determined vitality due to a few natural and notable benefits (Kaparaju et al., 2009). Because of its potential benefits over regular fossil-inferred assets, AD has been embraced and coordinated throughout the only remaining century in society, with a large number of full-scale plants currently operating around the world. Advertising is ideal for turning into vitality-rich biogas over unclean, special, complex feedstocks.

Numerous biodegradable feedstocks, for example, mechanical wastewater, food squanders, creature excrement, agricultural-squanders, sewage slop, natural part of city strong waste was used as substrates for the manufacture of biogas for industries, among others. Such offices outline the specific opportunities for treatment and residue balance with the simultaneous development of bioenergy. Moreover, lignocellulosic biomass, particularly agricultural deposits as well as vitality batch, has increased considerably as up-and-coming feedstocks for bioenergy delivery and biobased products. Different from conventional bio-inexhaustible content lignocellulosic biomass does not compete directly with the production of food or feed. In addition , high biomass yields significantly under low vitality, soil, composts and energy creation.

As of now talked about, the hydrolysis of lignocellulose frequently turns into the rate­constraining advance during customary AD. A few examinations have concentrated on improving the absorbability of lignocellulosic biomass through mechanical, manufactured, natural as well as hybrid pretreatment in liquid fill development (essentially ethanol) through biochemical pathway methods (Fitz Patrick et al., 2010; Takara and Khanal, 2011). Physical preparing, vapour blast , high temp water washing, destructive and salt pretreatments and smelling salts fibre advancement, among others, have been used as ascending unit exercises to upset the unpredictable structure of biomass, in this manner extending its permeability, emptying lignin and also hemicellulose, and decreasing the absolute biomass structural crystallinity to enable the natural transformation of biomass into bioenergy and biobased materials (Monlau et al., 2013; Agbor et al., 2011). A good amount of such pre-treatments, be that as it may, are monetarily and ecologically negative because of the significant expense of proteins and the creation of strong/fluid waste streams (Monlau et al., 2013). Advertisement is the normally happening, natural pretreatment of natural substrates completed by strong, blended culture microbial networks without oxygen (Petersson et al, 2007). The association of microorganisms tasks collaboratively to explicate unmanageable biomass structures (like lignocellulose) into their separate crucial segments. In ordinary bioprocessing methodologies, the entire lignocellulosic feedstock is ground and taken care of into an anaerobic digester to change over compound starches as well as natural issue into vitality abundant biogas (Kratky and Jirout, 2011). In spite of the fact that compelling, this methodology is time - devouring and vitality concentrated, therefore constraining its application for huge scope bioenergy creation from devoted vitality crops. An astute examination directed by Yuan et al. (2016) proposed that specific microorganisms present in the AD slurry may incline toward explicit biomass integral over others (Sawatdeenarunat et al., 2015).

Biomass is a natural material made out of polymers which have enormous bonds of carbon molecules connected to different macromolecules. The polymer backbone comprises of bonds connecting carbon with carbon or carbon with oxygen or once in a while with various components, for example, nitrogen or sulfur. It tends to be seen as congregations of some enormous atomic units. Lignocellulosic material comprises of the fundamental three abundant polymers in particular cellulose (40-half), hemicellulose (25-35%) and lignin (15-20%) which are interrelated. Because of cellulose, the reiters device is the glucan head, the machine is a 5-carbon sugar xylose, a little glucose utilizing one molecule of water. Hemicellulose polymers are, however, not simple chains like the polymers of cellulose. Some units are expanded and others provide a chain of views of very specific acetyl sections. The lignin polymers are made out of phenyl propane subunits, a complex made up of different monomer through C-C and C­O bonds with the methoxy groups(Kumar et al., 2018). These bonds and complexes can be biotransformed by whole microbes or their enzymes by selectively degrading either of cellulose, hemicellulose or lignin. These three biopolymers are the main overall plant assets that can be successfully changed over to animal feed, bio stocks, biofuels, biochemicals, biomaterials, and biopower (Fernandes et al., 2007; Kaparaju and Felby, 2010; Cherubini and Stromman, 2011).

2.1 STRUCTURE AND PROPERTIES OF LIGNOCELLULOSES BIOMASS:

2.1.1 CELLULOSE

Cellulose is the ß-1,4-polyacetal of cellobiose (4-O-ß-D-glucopyranosyl-D-glucose) (Jiang et al., 2018). However, cellulose is normally considered as a polymer of glucose since cellobiose comprises of two molecules of glucose (Figure 2.1)

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Fig. 2.1 Constitution of cellulose (Rocha et al 2009).

The cellulose obtained from the wood has around 11,000 glycosyl units in chains that form the structure of fibrils, broad bundles of monomer, which are stabilized with the help of several strong intermolecular hydrogen bonds between hydroxyl molecules of bonded particles (Bon and Ferrara, 2008). Due to β-1,4 linkage, cellulose is especially lucid and quite resistant to degradation by microbes and/or their enzymes (Wyman, 2003; Gray et al., 2006). Cellulose is a remarkably absorptive material connecting with 8-14% water underneath regular aeroscopic conditions (25°C, 65% relative wetness). Further, cellulose is insoluble in different solvents (including water) at lower temperatures. The dissolvability of the polymer is directly associated to the extent of breakdown accomplished. At higher temperatures, it will dissolve, as the bond dissociation energy is sufficient to dissociate the hydrogen bonds that protected the crystalline structure of the atom. Cellulose, also, is dissolvable in mineral acids, accompanied by hydrolysis (Yuan et al., 2016). Higher cellulose degradation is achieved when this polymer swells due to the deterioration of the low atomic mass subunits (Krassig and Schurz, 2002). Moreover, watery salt solution, for example, zinc chloride, degrades the structure of cellulose (Kirk-Otmer, 2001). Cellulose ° does not separate with temperature, yet its decomposition begins at 180 C.

2.1.2 LIGNIN

The lignin biopolymer is an amorphous, cross-connected and amazingly complex 3-D polymer of various phenylpropanoid subunits, polymerized with the help of the carbon- carbon(C-C) and carbon-oxygen (C-O) bonds (Figure 2.3). Lignin present between the external sheets of the strands, resulting in the structural rigidity and possessing the filaments of polysaccharides in conjuction (Davin and Lewis, 2005). Lignin is connected to hemicelluloses and cellulose, thus always resisting enzymatic attack of different fungi (Wood rotting white-root and brown-rot) and bacteria (Thomas et al., 2019). Generally, softwoods fuse additional lignin as compared to that of hardwoods(Ahring et al., 2015). Even though that the fundamental basic factors in lignin have been for the most part explained, numerous variables of their science still remain to be discovered.

Lignin building subunits includep-coumaryl liquor, coniferyl liquor and sinapyl liquor (Howard et al., 2003; O'Connor et al., 2007; Tomas-Pejo et al., 2008; Sanchez, 2009). Softwood lignin is made of coniferyl liquor units, while hardwood lignin is of coniferyl and sinapyl alcohol units (Pu et al., 2007). The main function of the lignin is to offer the plant basic help, impermeableness, and opposition towards microbial attack and oxidative assistance (Fengel and Wegener, 1984; Hendriks and Zeeman, 2009). In lignocellulosic biomass, lignin is bonded to hemicellulose and cellulose and this strong affiliation impacts enzymatic degradation (Tomas-Pejo et al., 2008; Hendriks and Zeeman, 2009).

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2.1.3 HEMICELLULOSE

Hemicellulose is a not well depicted and heterogeneous get-together of polysaccharides (copolymer of any of the monomers of glucose, galactose, mannose, xylose, arabinose and glucuronic hurting) (Figure 2.3). Hemicellulose combines the cellulose strands and is a hyperlink among cellulose and lignin (Siddique et al., 2017). Hemicelluloses are heterogeneous polymers of pentoses (xylose and arabinose), hexoses (for example mannose, glucose and galactose) and sugar acids (Hendriks and Zeeman, 2009; Girio et al., 2010). Divergent cellulose, hemicelluloses are before long not misleadingly homogeneous. The level of fanning and nature of the monomeric sugars in hemicellulose depend on plant type (Laine, 2005; Gray et al., 2006; Albertsson et al., 2010). Dependent upon sugar type, the hemicelluloses are proposed as mannans, xylans or galactans. The C5 and C6 sugars, related by techniques for 1-3, 1-6, and 1-4 glycosidic bonds and in different events acetylated, structure a free, particularly hydrophilic structure that goes about as glue among cellulose and lignin (Bon and Ferrara, 2008). Hemicellulose change from cellulose by different sugar units, by closeness of shorter chains and by growing the essential chain which made structure less easier to hydrolyzein connection with cellulose (Tomas-Pejo et al., 2008). The breakage results in their monomeric parts containing mannose, glucose, galactose, xylose, arabinose and little degrees of rhamnose, hazardous, methylglucuroni harming and galacturonic subordinate .

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Fig. 2.3 Schematic portrayal of the hemicellulose back bone of arborescent plants (Bon and Ferrara, 2008)

Hardwood hemicelluloses commonly includes xylans notwithstanding, softwood hemicelluloses contain glucomannans (Cara et al., 2008). Xylans are the most plenteous or plentiful hemicelluloses. Xylans of man plant materials are heteropolysaccharides with homopolymeric back chain of 1, 4-related β-D-xylopyranose units. Xylans can be gotten from various plant sources, for example, grasses, grains, softwood and, hardwood. The level of polymerization of hardwood xylans (150-200) is higher than that of softwoods (Dahlman et al., 2003; Tomas-Pejo et al., 2008; Alonso et al., 2009; Scheller and Ulvskov, 2010). Further, of all the three segments: (Figure 2.6) cellulose, lignin and hemicellulose, the hemicelluloses are the most thermo-artificially delicate (Sweet and Winandy, 1999; Hendriks and Zeeman, 2009).

2.1.4 PRETREATMENT TECHNOLOGIES

Pretreatment refers to the disruption of outer protective lignin covering to fasten the cellulose hydrolysis by enzymes. The most important step in the biofuel formation is pretreatment of the lignocellulosic biomass (Li et al., 2018). Pretreatment indicates the solubilization of cellulosic biomass. It assembles the treated solid biomass extra available for physical, chemical and biological treatment (Mosier et al., 2005; Wyman et al., 2003; Demirbas A., 2001; Gray et al., 2006). The lignocellulosic complex is comprised lignin and cellulose connected through chains of hemicellulose . Upgrades in pretreatment productivity and advancement of new enzymes require better comprehension of the components that decide the rate of enzymatic hydrolysis. Variables that are generally demonstrated to affect the enzymatic hydrolysis are cellulose crystallinity and level of polymerization.

The pretreatment is applied to crush the lattice so as to diminish the confirmation of crystallinity of the cellulose and to expand the content of formless cellulose, for enzymatic attack (Sanchez,2007). Objectives of a magnificent pretreatment system are:

(I) Formation of sugars immediately through breakdown.

(II) Prevent the disintegration of sugars devised.

(III) To restrict development of forbid items.

(IV) To limit power demand as well as prices.

Physical, concoction, Physico-compound and natural are the four essential kinds of pretreatment systems used. Mix of these techniques are utilized in the pretreatment step. Pretreatment additionally influences the expense of the unique operational advances that
is downstream expense, enzymatic hydrolysis rate and fermentation process variables factors (Carvalheiro et al., 2008; Taherzadeh and Karimi, 2008; Yang and Wyman, 2008; Hendriks and Zeeman, 2009 ;Alvira et al., 2010; Girio et al., 2010)

Table 2.2 Key factors for an effective pretreatment method for lignocellulosic biomass.

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During the most recent decade, countless assorted pretreatment innovations have been proposed, typically characterized into natural, physical, chemical, and Physico­chemical.

2.1.4.1 PHYSICAL PRETREATMENT

Mechanical pretreatment is utilized to lessen the atom crystallinity and size of lignocellulose to extend the surface domain aa well as reduction the insistence of polymerization (Palmowski and Muller, 1999 and Hendriks and Zeeman, 2009). Physical pretreatment degrees of progress upgrades the absorbability of hemicellulose and cellulose in the lignocellulosic biomass. Decrease of biomass underneath 20mm size demonstrates the magnificent mechanical exhibition (Sousa et al., 2004; Mtui, 2009). Physical treatment result in an expanded ethanol yield, low hydrolysis cost and no inhibitors were created (Hendriks and Zeeman, 2009; Hideno et al., 2009).

Mechanical pretreatments (chipping, crushing and processing) decrease cellulose crystallinity anyway require extreme energy and capital charges (Sun and Cheng, 2002; Sanchez, 2007; Tomas-Pejo et al., 2008). Considering the high power necessities of processing and the constant ascent of the power costs, it is plausible that processing is by the by not financially achievable (Hendriks and Zeeman, 2009).

Mechanical pretreatment decreases cellulose transparency as well as upgrade the practicality of latter handling. Wet taking care of, vibratory ball planning together with weight taking care of are normally done. The quality duty for mechanical treatment of agrarian waste contingent on the starter and remaining molecule sizes, dampness content material and on squander (hardwood, softwood, wiry, and so on) being directed. Size decrease may correspondingly gracefully higher results however some time it might affect issue to pretreatment and enzymatic hydrolysis. Size decrease is important employable procedure for expanding the enzymes availability to lignocellulose. Be that as it may, a large number of the physical strategies for size decrease (processing, granulating, and so on.) are not financially attainable in light of the fact that a high- vitality input is required.

2.1.4.2 PHYSICOCHEMICAL PRETREATMENT

Combined Physical and chemical treatment structures are of significance in breakdown of hemicellulose and modify of lignin formation, presenting a comprehensive availability of the cellulose for hydrolytic enzymes (Kumari and Singh, 2018). The most advantageous physiochemical pretreatments join thermochemical prescriptions, for instance, steam impact, liquid warm water (lhw), smelling salts fiber impact (afex) and CO2 impact. In these techniques, chipped biomass is made do with high pressure splashed steam, liquid smelling salts or CO2r4 and a short time later the strain is all of a sudden decreased, making the biomass to undergo decompression (Hendriks and Zeeman, 2009; Mtui, 2009).

Condensation impact is very broadly utilized physico-chemical pretreatment for biomass. During the time spent vapour pretreatment, the biomass is placed in vessel and condensed at a high temperature (upto 240°C) for a few minutes. After a set time, the steam is and the biomass is rapidly chilled off (Hendriks and Zeeman, 2009).The structure causes hemicellulose breakdown or division and lignin change because of high temperature causing conceivable of cellulose hydrolysis (Mtui, 2009). Steam sway rather than different pretreatments, presents potential for lessening capital potential, through and through lower ecological effect, progressively workable for vitality proficiency, less arrangement of inhibitor and complete sugar recuperation (Avellar and Glasser, 1998; Sun and Cheng, 2002; Tomas-Pejo et al., 2008). Steam blast is a physicochemical pretreatment for deconstructing biomass (Hamelinck et al., 2005). These days, it is a best among pretreatment technique for creation of biogas.

The mechanical effects are incited in light of the fact that the strain is simultaneously decreased and strands are disconnected since of the precarious decompression. In total along the midway hemicelluloses breaking and dissolution , the lignin is reallocated as well as fairly arranged of from the fibre. Hemicellulose end will

assemble compound receptiveness to the cellulose microfibrils by using revealing the cellulose outside. Fume impact fragmentates the biomass in two divisions:

(i) A fluid segment rich in monomeric and oligomeric sugars consistently from hemicellulose dissolution.

(ii) A strong component of absorbable cellulose and lignin. Steam impact mechanical capacity has been precisely attested for biogas creating from an immense extent of uncooked materials.

Its fundamental disadvantages are strategy gear necessities (Oloffson et al., 2008), incomplete hemicellulose debasement and age of some harmful mixes got from sugar corruption over the span of pretreatment that might need to affect following hydrolysis and aging advances (Zaldivar et al., 2001; Oliva et al., 2003). The fundamental terminators are furan subordinates, phenolic acids and vulnerable acids. The real furan subsidiaries are hmf got from debasement of pentoses and hexoses separately. Frail acids created for the term of pretreatment are generally acidic corrosive shaped from the acidic organizations existing in the hemicellulosic division and levulinic and formic acids . Wide scope of phenolic mixes are produced because of the lignin breakdown shifting broadly between select crude materials.

Other physic-synthetic pretreatment methodologies incorporate fluid high temp water pretreatment (Sun and Cheng, 2002; Mtui, 2009), smelling salts fiber/solidify blast (Holtzapple et. al., 1991, Dale and Moreira., 1982; and Olofsson et al., 2008), ultrasound pretreatment (Mielenz, 2001; Nikolic et al., 2010), microwave pretreatment (Keshwani and Cheng, 2010), wet oxidation (Olsson and Maria, 2005; Kaparaju and Felby, 2010), and the utilization of supercritical liquids (Gray et al., 2006; Luterbacher et al., 2012).

2.1.4.3 CHEMICAL PRETREATMENT

Synthetic compounds going from oxidizing specialists, soluble base, salts and acids can be utilized to debase lignin, hemicellulose and cellulose from lignocellulosic structure (Mtui, 2009). Ground- breaking oxidizing venders, for example, ozone and hydrogen peroxide viably expel lignin and the reaction is done at room temperature (Sun and Cheng, 2002 and Mtui, 2009).

2.1.4.3.1 ALKALINE PRETREATMENT

Liquid lime or NaOH pretreatment is highly effective for sugarcane bagasse with lower temperatures than destructive pretreatments, regardless, in such cases the treatment

times are hours long. For instance Chang et al., used lime with at 85°C for 3 h (Pu et al., 2008). The solvent frameworks will by and large have increasingly unmistakable of degrading lignin and leaving hemicellulose and cellulose intact (Kim and Holtzapple, 2005; Alizadeh et al., 2005; Gray et al.,2006 and Carvalheiro et al., 2008). The exchange of hemicellulose remarkably impacts the degradability of cellulose. It is delineated to reason low sugar pollution than ruinous pretreatment and it was demonstrated to be high basic beguiling on rural stores than on woody substances (Kumar et al., 2009). The conceivable loss of dissolvable sugars and some storing up of inhibitory mixes should be taken as a plan to improve the pretreatment conditions. NaOH, KOH, Ca(OH)2, and NH4OH are the best added substances for dissolvable pretreatments. NaOH causes expanding, broadening within cellulose surface and lowering the component of polymerization and crystallinity, which likewise prompts lignin shape disrupting impact (Taherzadeh and Karimi, 2008). NaOH has been proposed to make more vital hardwood absorbability from 14% to 55% by utilizing diminishing lignin content from 24-55% to 20% (Kumar et al., 2009). Additionally, pretreated switch grass uncovered a strategy of pore progression in the NaOH pretreatment developing the open floor a region to the proteins likewise as chopping down lignin content material (Nlewem and Thrash, 2010). Expansion of an oxidant overseer (oxygen/H2O2) to corrosive neutralizer pretreatment (NaOH/Ca(OH)2) can improve the show by systems for preferring lignin end (Carvalheiro et al., 2008). Overhauls for enzymatic hydrolysis have been in like way reflected in extraordinary biogas conveying from pretreated with corrosive pretreatment technique (Kumari et al, 2018).

2.1.4.3.2 ACID PRETREATMENT

The acid treatment process is one of the most prepared, least complex and most condition heartfelt strategies of delivering biogas from biomass. The weaken corrosive is used to hydrolyze the biomass to sugars. The Liquid hydrolyzates are then killed and poisonous inhibitor for assimilation are evacuated before anaerobic absorption of corrosive treated biomass to biogas (Brennan et al., 1986).The hydrolysis is done with debilitate or energetic acids. The goal is to solubilize the hemicellulose, and accordingly making cellulose higher open (Lin et al., 2010; Hendriks and Zeeman , 2009). It will 28 hydrolyze the hemicellulose part while leaving the cellulose and lignin faultless in the additional solids. The most notable procedures use sulfuric destructive, yet other ground-breaking acids have additionally been endeavored (Lloyd and Wyman, 2005; Mosier et al., 2005; Gray et al., 2006). Debilitate destructive hydrolysis generally uses 0.4-2% H2SO4 at a temperature of 160-220°C to put off hemicelluloses and improve cellulase absorption of cellulose (Willfor et al., 2005; Pu et al., 2007). Among all, debilitate destructive hydrolysis has been capably made, redesigning famously the subsequent plan of enzymatic hydrolysis (Esteghlalian et al., 1997; Tomas-Pejo et al., 2008; Hsu et al., 2010; Parawira and Tekere, 2011; Kasthuri et al., 2012; Meinita et al., 2012) as a result of the truth of their sufficiency and sensibility. These methods have been associated in pilot pants and hence are close to commercialization (Ropars et al., 1992; Schell and Duff, 1996; Olofsson et al., 2008). Distinctive exploration take a shot at corrosive pretreatment (Campo et al., 2006 ; Karimi et al., 2006) has discovered that 0.5% H2SO4 is generally trustworthy for the rebuilding of squanders from vegetation and rice straw(Mtui, 2009).

The expansion of corrosive hydrolysis is the solubilization of hemicellulose and by means of this, making the cellulose more accessible for breakdown by proteins in the assimilation procedure. There is, on the diverse hand a risk on the relationship of shaky defilement item where this carbon is lost for the change to ethanol. The development and precipitation of solubilized lignin is an unfortunate reaction, as it decreases absorbability (Cara et al., 2008; Hendriks and Zeeman, 2009; Rocha et al., 2009; Ferreira et al., 2010). Solid corrosive hydrolysis for biogas creation is by and by not charming, since there is likelihood of the improvement of inhibitory items. Debilitate destructive hydrolysis, at any rate is viewed as one of the promising pretreatment procedures; for the explanation that assistant reactions all by means of the pretreatment can be refused in debilitate destructive pretreatment (Hendriks and Zeeman, 2009; Alvira et al., 2010).

Characteristic acids, for instance, maleic, fumaric or even acidic destructive have been endorsed as judgments to inorganic acids. Regular acids don't expand degradation reactions that have been delineated in destructive hydrolysis, realizing lower gathering of unsafe blends. Both maleic and fumaric acids have been differentiated and H2SO4 in 29

enzymatic hydrolysis yields from wheat straw. Results insisted that natural acids can hydrolyze with over the top yields notwithstanding the way that fumaric destructive used to be when less high gauge than maleic destructive. In addition, quite less proportion of furfural used to be once framed in the maleic and fumaric destructive pre­treatment than H2SO4 in hydrolysis (Kootstra et al.,2009).

Organosolv pretreatment (Park et al., 2010; Obama et al., 2012), ozonolysis (Silverstein et al., 2007; Shatalov and Pereira, 2008 and Kumar et al., 2009), Ionic rewards (as natural solvents) (Olivier-Bourbigou et al., 2010; Fu and Mazza, 2011), and sulfite pretreatment (Zhu et al., 2009) are an assortment of methods used for engineered pretreatment of lignocellulosic squander.

2.1.4.4 BIOLOGICAL PRETREATMENT

The natural lignocellulose treatment includes organisms or their microbial proteins in the pretreatment of lignocellulosic/farming squanders (Li et al., 2018). The two microbes and various types of parasite are used for biotreatment of lignocellulosic waste (Bremond et al., 2018). Normal pretreatments use microorganisms a great part of the time dim shaded, white and sensitive rot growth which spoil lignin and hemicelluloses and close to no of cellulose, extra safe than the different strategies (Sanchez., 2007). Contagious pretreatment of farming biomass is another system for the improvement of biomethane substance of biomass (Singhania et al., 2006). White, dull hued parasite have been use to break lignin and hemicellulose in squander matter. The diverse white­decay growths can be utilized to debase lignin specifically (Siddique and Wahid, 2018). Such particular lignin-debasing parasites can be strongly utilized in microbial pretreatments. A couple of white-decay organisms, for instance, Ceriporia lacerata, Cyathuss tercolerus, Ceriporiopsis subvermispora, Pycnoporus cinnarbarius and Pleurotus ostreatus have been read for their extraordinary high delignification adequacy of various agro deposits (Sun and Cheng, 2002; Keller et al., 2003; Arora et al., 2005; Kumar et al., 2009; Mtui, 2009; Wan and Li, 2012).

Earthy coloured decay growths as frequently as conceivable corrupt cellulose while white and sensitive decay strike cellulose as well as lignin (Rudakiya and Gupte, 2017). Dim hued infectious pretreatment has been starting at now raised as a definite procedure
for improvement of the enzymatic hydrolysis yields of P. emanate and Pinus sylvestris achieving saccharification yields around 70% (Roy et al., 2010). For this circumstance, it was recommended that some common acids released by method of capability of the used developmented Caniophora puteana reduced the pH and depolymerized it somewhat. When all is said in done, such strategies give points of interest, for instance, low capital cost, low imperativeness, no fake substances essential, slight biological specifications, and no inhibitory compound blends (Hosseini et al, 2019). The huge disadvantage to upgrade common methodologies is the low synthetic based hydrolysis cost by natural corrosive and bases (Tomas-Pejo et al., 2008; Dashtban et al., 2009).

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Fig. 2.4 A rundown of different strategies utilized in the pretreatment of

Bacterial pretreatment of lignocellulosic squander includes anaerobic and high-impact smaller scale life form (Kong et al, 2018). Anaerobic corruption utilizes recognizable mesophillic, rumen inferred microorganism (Han and Shin, 2002; Hu and Yu, 2005; Neves et al., 2006; Hu et al., 2008 and Mtui, 2009). In oxygen consuming structure, Actino mycetes to be specific, Streptomyces griseus is the best-read for the creation of extracellular hydrolytic proteins that debase lignocellulose (Arora et al., 2005 and Mtui, 2009, Peterson and Ingram.,2009). To proceed, for cost-forceful common pretreatment of lignocellulose to improve the hydrolysis, and, at long last, improve biogas produce, it is crucial to continue to scrutinize and taking a gander at extra developments for their capacity to remove lignin from the plant texture rapidly and viably (Figure 2.4).

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• College: University of Petroleum and Energy Studies
• Author: Dr. Rajan Sharma (Author)
• Publication Year: 2020
• Pages: 154
• Catalog Number: V1372897
• ISBN (PDF): 9783346909374
• ISBN (Book): 9783346909381
• Language: English
• Tags: bioconversion, lignocellulosic, biomass, biogas