*1.1. The Availability of Various Agricultural Waste*

Various types of agro-waste can be found in the environment, which depends upon the source and availability. They can be derived from many different sources such as municipal solid waste works, livestock excrements, lignocellulosic and agro-wastes, food crops, etc. Thus, such waste can be classified into four main generations based on their ability to produce different types of products [6]:

First-generation: This comprises various classes of food crops such as wheat, corn, rice, and sorghum. The direct utilization of these crops as a primary feedstock of interest is often associated with energy generation and the production of various products. However, one of the major challenges associated with this generation is the competition between its utilization in fuel and food production. Fuel production is viewed to be of a higher return on investment than food production.

Second-generation: This generation generally consists of lignocellulosic wastes like sugarcane bagasse, wood chips, crop residues, and organic waste that can be employed to generate bioenergy using different waste beneficiation techniques. This type of waste is associated with the overcoming of major limitations identified with the first-generation biomass.

Third generation: Microalgal biomass, which is used in engineered energy source production systems as a feedstock. Hence, its cultivation can easily be achieved in lagoons and open ponds using a high nitrogenous compound containing agro-waste containing wastewater.

Fourth generation: This type of biomass is from metabolically engineered species such as bacteria, including algae generated from cleaner disposal, or emissions control processes such as CO<sup>2</sup> capture systems. This increases the value of this generation as it can be used in high-value product production associated with higher polymeric hydrocarbon content requirements or any other bioenergy products.
