**1. Introduction**

In organic biomass, particularly in the plant biomass, lignin is one of the rich carbon matter. Lignin is part of plant cell wall, which provides a mechanical muscle to keep herbs, plants and large tree standing. The process of synthesis of lignin inside plant biomass is known as lignification. The lignin is a long amorphous polymer containing three major synapyl, *p*coumaryl alcohols and conniferyl phenylpropanoid monomers. Due to this aromatic polymeric nature, lignin supports the other carbohydrates components like cellulose and hemicellulose in lignocellulosic plant biomass. So its acts like a binder for the carbohydrates of plant biomass to make a strong cross link and bond between hemicellulose and cellulose [1].

An estimated quantity of 5 to 36 × 108 tons of lignin is reported annually in natural organic biomass [2]. The uppermost 26–45% of dry matter lignin part is naturally observed in softwood whereas 15–25% a lower amount of lignin in hardwoods biomass [3]. The value of lignin in grasses and straw is relatively low from the softwood range between 15 and 27%, and a small percentage in algae and mosses. As an evolutionary perception, the development of aromatic lignin structure in plant cell wall, is for fast water transportation inside the tracheid plant cell structure [2]. This is an important material of organic carbon polymer incorporation in plant biomass for possible growth in dry land. The lignin makes the biomass rigid and hard, possiblily can decrease the water loss in dry and drought condition.

#### **1.1 Significance of biomasses**

The word biomass means organic substance made of plants materials. This could be a forest wood, cereal crops, seaweed and leftover substrates from agriculture biomass. Other sources of biomass are human, animals, household and industrials waste. These biomasses contain chemical energy trapped directly from sun through photosynthesis. Photosynthesis converts carbon dioxide and water with the help of sun energy in to sugars units, that's make different carbohydrates in fruits, vegetables, and other crops plants. Biomasses for example straw, food like potato, cassava, corn starch, sorghum, wastewaters and other agro-industrial residues are a good source of sugars (glucose, xylose, arabinose, starch, sucrose, cellulosic, and reducing sugars) that can be recycle for multiple products at commercial level. Biomasses (softwood, hardwood, herbs, straw and grasess) are also a good source of organic carbohydrates materials. On the basis of high organic contents, these biomass are favourit food for most of the living species on the globe. Beside, food purpose, the left over residue and waste biomass can also contribute about 7–10% to the global energy stream. These agriculture biomasses, softwood, hardwood, herbs, straw and grasess contained high carbon and water content, thus considered a significant input carbon for production of renewable energy like biodiesel, bioethanol, biogas, biohydrogen. Currently, 8–15% of the overall energy stream is reported in industrials zones of developed countries, while a low amount in developing countries as well [4, 5]. Beside, renewable energy, most of the countries practiced to burn these biomass either in the field or for cooking in stoves, thus a massive amounts of carbohydrates biomass containing useful carbon (lignin, cellulose and hemicellulose) is destroyed on low price [6]. Food waste and waste lignocellulosic biomass are of potential interest, which includes utilization for bio-methane, ethanol, butanol, biomaterials, and biobased products [7, 8]. Food waste is easily digestible in fermentation process for biofuel production [9], however, lignocellulosic biomass like grasses, waste paper, wood residues, and crop residues are diffficult to convert direct into fuel. Because the lignocellulosic biomass is comprised of mainly three basic molecules, 20–40% lignin, and 60–70% hemicellulose, cellulose and other extractives in collectlivelly [10]. The composition of carbohydrates varies depending on the growth and nature of the biomass. There is a big barrier in utlization of lignocellulosic biomass containing high lignin content, due to strong crosslinking of ether and ester bonds around polysaccharides (cellulose and hemicellulose) which confers hydrolytic stability, resist degradation and structural recalcitrance [5]. Therefore, to utilize these lignin containing biomasses, pretreatment process are necessory to make them digestible in the fermentation process and synthesis of value added materials.

Energy is the eventual source need for each operation through the globe. More than 25% of the World population is suffering the lack of energy for cooking, lighting, power generation and transportation fuel. The consumption of the energy is higher than the production percentage [11]. The demand for extra energy production builds an energy crisis throughout the world. The details reports released by the European Environment Agency and International Energy Agency (IEA), Energy Information Administration (EIA), oil usage and cost is mounting constantly. The published reports indicated some problems and hurdles in future for energy production and emphasized on potential alternate resolutions. The estimated amount of energy used for heat and power from oil 31.0%, natural gas 21.5%, nuclear 5%, coal 29.0%, hydro 3%, biofuels and waste 10.0%, and 'other' 4%. The electricity generation estimated data was natural gas 22%, oil 31.1%, coal 28.9%, nuclear 12%, hydro 13%, biofuels and waste 10.2%, and 'other' 6% as shown in the (**Figure 1**). These values specify that

#### **Figure 1.**

*The results shown here is replecting the energy production percentage around the globe with less ttention for biofuels from waste biomass.*

generation of energy from alterantive sources like biofuels and bioenergy are receiving more attention instead of fossil fuels [12, 13]. Consumption of waste biomasses (agribiobiomass and municipal solid waste) for biofuels could meet a rational demand of energy percentage in the future.

To solve the problems of energy crises, production of renewable energy from waste biomass sources is getting more interest instead of fuel generation from fossil sources. Waste biomass especially lignocellulosic biomass residue along other biomassess is a good waste reserve that could be reuse for important products [14]. So, utilizing the waste biomass can produce clean bioenergy and has a benefit of to efficiently manage solid waste to reduce environmental pollution. The agriculture waste and waste residue which is about 60–70% around the world can be a cheap carbon material for biofuel and bioenergy production. The cellulose and hemicellulose are carbon source which can be transformed in to verities of fuels, which includes ethanol, butanol, bio-methane and biohydrogen [1, 15]. However, lignin is an aromatic component, cross link both cellulose and hemicellulose of the lignocellulosic biomass which makes it recalcitrant and harder, so decrease the yield of energy production [16]. Therefore, pretreatment process are carried out to remove the lignin, cellulose and hemicellulsoe for the biofuel production. The separated lignin is also a good source of fine chemicals and industrially relevant materials discussed in details below.

For the improvement of effective anaerobic fermentation processs, the choice of waste biomass, nature and chemistry of biomass is mainly essential factors. The lignin percentage and quantity of water are the next important properties in picking substrates for the fermentation reaction. While the total organic carbon TOC is the most critical concern factor in the conversion of the waste carbon biomass [17, 18]. The efficiency of the microbial hydrolysis of the biomass in anaerobic fermentation reaction is linked to the biodegradability of biomass [19, 20].
