Used frying oil (UFO) is a byproduct of edible vegetable oil which is utilised as a medium to fry food. The disposal of UFO is a global and major environmental issue due to the straightforward dumping of the UFO into drains. Waste management issues are getting worse and endangering environmental preservation. Recycling UFOs could relieve disposal issues, but more importantly, it would improve the efficient usage of agricultural and food reserves. Most of the UFO's hazardous chemicals are oxidation products of free fatty acids (FFA), particularly polyunsaturated fatty acids. One of the main issues in the refinement of edible oil is the FFA concentration. It has also frequently been used to describe the oil's quality and suitability for food purposes. FFA is derived from triacylglycerol by cleavage of ester bonds due to the action of high temperature, oxygen and moisture. To reduce FFA, UFO is pre-treated by physical filtration, adsorption, heating, neutralisation, degumming, bleaching (whitening) and chemical treatment. In a base-catalysed system, it is preferable to have less than 1% of FFAs by weight of oil, or it will interact with the catalyst and produce soap. To enhance the quality of frying oil and UFO, numerous active filtering methods, or adsorption procedures have been researched. Bio-adsorption is economical, easily designable, environmentally friendly and is even an effective technique in the presence of competitive ions. Ions and molecules physically attach to or connect with surfaces during adsorption. The sorption capacity depends on the type of bio adsorbent and the nature of the oil. This review paper discusses the potential of four types of bio adsorbents which are coconut shell, palm kernel shell, rice husk, and bagasse in reducing FFA content in UFO. These materials possess a large surface area, which provides ample site for adsorption. The interaction and adsorption of FFAs are made easier by the presence of active sites such as hydroxyl (-OH) and carboxyl (-COOH) groups on the surface.