**3.1 Biodegradation of agricultural waste by fungi**

Tons of agricultural residue generated each year from the cropland and some of these residues are used as animal feed and others for industrial use but the majority of the residue is burned in the crop field causing environmental pollution, but using fungal species these are converted into compost or either used for the production of the edible mushroom. Since fungi possess a proficient hydrolytic system that is capable to convert lignocellulosic material to essential metabolites in the form of mushrooms. Usually, fungi (micro and macrofungi) secrete enzymes, including cellulases (cellobiohydrolases, endoglucanases), hemicellulases (xylanases), and β-glycosidases [21, 22]. The recent developments in our understanding of the genetics, physiology, and biochemistry of fungi, has led to the exploitation of fungi for the preparation of different agriculture and industrial products of economic importance [4], therefore the agric residue which is rich in lignocellulose consists of lignin, hemicellulose, and cellulose [11, 23] can potentially be converted into different value-added products as depicted in (**Figure 1**) including biofuels, chemicals, animal feed, textile and laundry, pulp and paper. Production of ethanol and other alternative fuels from lignocellulosic biomass can reduce urban air pollution, decrease the release of carbon dioxide into the atmosphere, and provide new markets for agricultural wastes [21].

As the lignocellulosic biomass is made up of complex carbohydrates, which is a source of the sugars that can be processed to obtain ethanol, but due to the recalcitrant nature of the lignocellulose biomass it is very difficult to produce ethanol out of this biomass, production of ethanol from these biomass involves series of step to convert complex cellulose to simple sugars one of the major steps in the production step of ethanol is pretreatment of the recalcitrants biomass, which raise the cost of production of ethanol. The three methods physical,

#### **Figure 1.** *Different value-added products from agric residues.*

chemical, and biological methods are used in the pretreatment of the biomass. Pretreatment is done to digest the lignocellulose to produce simpler sugars that are further converted into bioethanol [24]. The biological methods of treatment using microbes are eco-friendly and produce clean fuel, among all microbes fungi have great potential to convert recalcitrants into simpler sugars through enzymatic and hydrolytic methods [25]. The existence of the enzymatic system in the fungi serves as the treasure of the Novo enzyme source for the finding of candidates of the enzyme to digest lignocelluloses, enzymes like catalases, laccase, hemicellulases, ligninases, pectinases play a crucial in the digestion of the recalcitrants biomass [26]. The effectiveness of a biological pretreatment is determined by several factors like composition of biomass, inoculum concentration, aeration rate, moisture content, incubation time, incubation temperature, pH, and the fungi species involved [27]. The most common mechanism of pretreatment is illustrated in **Figure 2**.

**Figure 2.** *Schematic diagram for biological treatment by fungi of lignocellulosic biomass.*
