The effectiveness of alkali-acid modification in enhancement the adsorption capacity of rice straw (RS) for removing a basic dye was studied. The obtained adsorbents were characterized by slurry pH, pHPZC, iodine number, methylene blue number, FTIR, and SEM analyses. Adsorption of methylene blue (MB) was described by the Langmuir, Freundlich, Tempkin, and Redlich-Peterson isotherm models. Effects of contact time, initial concentration of MB dye, pH of solution, adsorbent dose, salt concentration of NaCl, and desorbing agents on the removal of MB were reported. Kinetic studies were analyzed using the pseudo-first-order, pseudo-second-order, and the intraparticle diffusion models and were found to follow closely the pseudo-second-order model. Equilibrium data were best represented by the Langmuir and Redlich-Peterson isotherms. The adsorption capacities were varied between 32.6 and 131.5？mg/g for untreated and treated RS samples with NaOH-1M citric acid (ARS-1C), respectively. Adsorption behavior of the ARS-1C sample was experimented in a binary mixture containing methylene blue (basic) and reactive blue 19 (acidic) dyes which showed its ability to remove MB higher than RB19. Overall, the results indicate that the alkali-acid treatment proved to be potential modification for producing effective low-cost adsorbents for the removal of the basic dyes from wastewater. 1. Introduction Nowadays, industrial societies suffer from two main problems with respect to disposal of colored pollutants in wastewater and agroresidues in environment. Thus, with compliance to the decrease in natural water resources and the increase in water pollution, researchers have urged to find appropriate and environmentally friendly treatment techniques. The main sources of wastewater can be attributed to discharge of toxic industrial wastes, dumping of industrial effluents, and runoff from agriculture fields. It is well known that 70%–80% of all illnesses in developing countries are related to water contamination particularly susceptible for women and children [1]. For instance, wastewater contaminated with dyes comes from a wide range of industries such as textile, paper, tannery, food, chemical, pharmaceutical, and many others. Consequently, environmental regulations demand the removal of dyes before discharging industrial effluents into water bodies due to their mutagenic and carcinogenic impacts to aquatic living organisms, and its presence of even very small amounts in water (less than 1？ppm) is highly visible and undesirable [2–6]. Methylene blue (MB) is the most commonly used
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