###### Abstract  
Bioremediation is a pollutant removal method that has had a great boom due to the diversity of agroindustrial waste that can be used for this purpose, and that has shown having great efficiency and profitability in the adsorption of heavy metals, such as Pb, Cu, and Co. Based on the above, the present work carried out kinetic and equilibrium studies of biosdorption of Cr (III) using orange peel (OP) as adsorbent, previously treated with methanol, water, and a water-methanol mixture at different pH (0.91, 1.78 and 2.72), and at 30 \({}^{\circ}\)C, finding that the adsorption capacity at equilibrium increases with increasing pH, having a maximum of 55 mg g\({}^{-1}\) at pH 2.72--under these conditions, lower adsorption energy was used to remove Cr (III). In addition, it was determined that there are no external mass transfer limitations. An isoelectric point analysis indicated that the adsorption is not carried out by electrostatic forces and a FTIR study of the functional groups of OP showed a decrease in the main functional groups (pectin, cellulose, and lignin, among others), which is directly related to the adsorption capacity of the biosdorbent. biodesorption; orange peel; removal; functional groups; mass transfer 2021 20  
treatment of effluents that contain large amounts of Cr. As such, it is necessary to find alternatives to be able to dump these wastes without the presence of this metal [1; 6]; there are currently some technologies that stand out in eliminating Cr (III) from wastewater, such as chemical precipitation, ion exchange, peroxidation, coagulation, membrane filtration, and photocatalytic degradation, among others. These methods, however, are characterized by their high operating costs and maintenance; in addition, some of them generate waste in the form of sludge, which implies a significant economic cost to its disposal [1; 3; 7; 8; 12]. On the other hand, bioadsorption is an ecological, versatile, simple, and economical method due to the use of peel residues from various fruits, vegetables, and plants, among others, which, if not handled properly, can also contaminate the environment where they are deposited; therefore, this alternative allows the reuse of waste by incorporating multiple advantages, such as their wide availability, simple treatments, biodegradable capacity, variety of sources, reduction of pollution, and waste management, as well as their high efficiency in the elimination of pollutants, such as heavy metals [1; 3; 10; 12]. Bioadsorbents are modified both physically and chemically to improve adsorption capacity, this can be done with milling operations, heat treatment, treatment with basic solvents, acids, and oxidizing agents, among others [3; 9; 10; 13; 14; 15]. Some agro-industrial wastes may be suitable candidates for the elimination of Cr (III), which represents a significant operating cost in industrial processes; as such, there is an economic interest in its recovery from wastewater [9; 11; 16; 17]. Among these candidates, the case of the orange peel stands out, which, due to its low cost and high content of organic compounds (pectin, cellulose, hemicellulose, among others) on its surface, along with a large amount of soluble compounds, requires a treatment that allows conditioning the biomaterial and obtaining an increase in its adsorption capacity [16; 17; 18; 19; 20; 21]. The orange peel that is discarded by the citrus-processing industry is characterized as having a high contaminating power, given its high content of moisture and fermentable sugars, low pH, and high content of organic matter, which gives it a high rate of fermentability, causing serious economic and environmental problems for its disposal. In addition, this residue can cause soil contamination in cases of direct disposal, water pollution due to the infiltration of putterfactive residues in the water table, and air pollution due to the uncontrolled production of greenhouse gases.