Bio-refineries play a significant role in promoting the circular economy by converting biological resources and organic waste into valuable products such as biofuels, bio-based chemicals, power, and heat. Unlike traditional linear production systems that follow a “take, make, and dispose” model, bio-refineries are designed to utilize renewable biomass efficiently and ensure that waste generated in one process becomes a resource for another. This approach helps reduce environmental pollution, conserve natural resources, and improve overall resource efficiency. A bio-refinery operates in a manner similar to a petroleum refinery but uses biomass such as agricultural residues, forestry waste, animal manure, municipal organic waste, and energy crops as feedstock. Through various biological, chemical, and thermochemical processes, these materials are converted into multiple products including bioethanol, biodiesel, biogas, biohydrogen, and other value-added compounds. By integrating different conversion technologies within a single facility, bio-refineries maximize the use of raw materials and minimize the generation of waste. One of the major contributions of bio-refineries to the circular economy is the efficient utilization