The treatment of colored effluents containing Procion Red dye (PR) was investigated using HSO and HNO modified avocado shells (Persea americana) as adsorbents. The adsorbent materials (AS-HSO and AS-HNO) were properly characterized. The adsorption study was carried out considering the effects of adsorbent dosage and pH. Kinetic, equilibrium, and thermodynamic aspects were also evaluated. Finally, the adsorbents were tested to treat simulated dye house effluents. For both materials, the adsorption was favored using 0.300 g L of adsorbent at pH 6.5, where, more than 90% of PR was removed from the solution. General order model was able to explain the adsorption kinetics for both adsorbents. The Sips model was adequate to represent the isotherm data, being the maximum adsorption capacities of 167.0 and 212.6 mg g for AS-HSO and AS-HNO, respectively. The adsorption processes were thermodynamically spontaneous, favorable (- 17.0 < ΔG  < - 13.2 kJ mol), and exothermic (ΔH values of - 29 and - 55 kJ mol). AS-HSO and AS-HNO were adequate to treat dye house effluents, attaining color removal percentages of 82 and 75%. Avocado shells, after a simple acid treatment, can be a low-cost option to treat colored effluents.