**Abstract**

Lignocellulosic biomass has gained increasing recognition in the past decades for the production of value-added products (VAPs). Biomass feedstocks obtained from various sources, their composition, and pretreatment techniques employed for delignification into bioenergy production are discussed. The conversion processes of biomass into VAPs involve various methods. Notable among them are biochemical conversions; namely, anaerobic digestion and ethanol fermentation, and thermo-chemical conversions; namely, pyrolysis and gasification which are considered in this chapter. Microalgae can adapt to changes in the environment, producing biomass that serves as a precursor for a variety of biomolecules, such as proteins, which find their application in pharmaceutical, cosmetic, and biofuel industries. Suitable strains of freshwater microalgae biomass contain high levels of lipid which can be harnessed for bioenergy production. Hence, the advancement in the conversion of biomass into VAPs could help scientists and environmentalists for sustainable use of biomass in future developments.

**Keywords:** biomass, freshwater microalgae, lignocellulose, microalgae, value-added products

#### **1. Introduction**

Biomass resources are readily available globally as residual wastes derived from agricultural and industrial sources. Crop residues such as corn straw, wheat straw, and rice straw are classified as important and relatively abundant renewable biomass resources [1, 2]. With regards to the abundance of biomass resources, China still leads as one of the largest agricultural-based economies in the world, producing approximately about 216 million metric tons of corn straw per annum. For the aforementioned, more than half of that reported from China remain unutilized [3]. Lignocellulose arises from corn straw containing non-edible plant material, composed largely of cellulose, hemicellulose, and lignin. These three components comprise covalent cross-linkages between the polysaccharides (cellulose and hemicellulose) and lignin, making biomass a composite material [4]. The sources and compositions of lignocellulose play a very important role in predicting its potential as value added-products. The hemicellulose is present as the matrix that surrounds the cellulose skeleton, while lignin is present as an encrusting material and serves as a protective layer. However, biomass pretreatment is an essential tool for cellulose conversion processes as it changes the structure of cellulosic biomass to make cellulose more available to the enzymes that convert the carbohydrate polymers into fermentable sugars [5]. Other studies have reported that pretreatment of lignocellulosic biomass (LB) aids to overcome recalcitrance through the combination of chemical and structural changes to the lignin and carbohydrates. Some of the different methods of pretreatment include physical; namely, mechanical pretreatment, physicochemical; namely, steam explosion, chemical; namely, alkali and acidic pretreatment, and biological; namely, manure addition or mixed microorganisms [6, 7]. Nonetheless, these traditional methods of pretreatment are cost-intensive, as additional chemicals or energy are required [8]. Also, useful information for policymakers and researchers on lignin biorefinery is presented in this chapter.
