Agricultural waste + Microorganisms → Biogas + Digestate (1)

In the fermentation process, which also works in the absence of oxygen, the production of valuable products such as alcohol, organic acids, and a mixture of gases due to microorganisms' action is observed. It is believed that the fermentation of agro-waste is difficult and time-consuming due to the presence of long-chain polymeric molecules and requires acid or enzymatic hydrolysis before fermentation to produce valuable endproducts. For instance, bio-butanol production can be achieved with the help of a bacteria called *Clostridium* spp., coupled with sugar production from various types of agro-waste. The process comprises two main steps, i.e., acidogenesis and solventogenesis, which is

referred to as acetone, butanol, and ethanol (ABE) fermentation. Hence, it is a promising technology, but it is costlier and time-consuming.
