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The objective of this work is to examine the effectiveness of low cost material as adsorbent for the removal of free amino acid l-tryptophan from aqueous solutions in order to avoid the formation of undesirable disinfection by-products, trihalomethanes and iodinated trihalomethanes, during the water chlorination. The adsorbent was prepared from date pits and activated with H 3 PO 4 (DPH). The textural properties of DPH were characterized by FT-IR spectroscopy, SEM analysis and N 2 adsorption-desorption isotherms. DPH possesses a large specific surface area (1040 m2 g−1) and a high total pore volume (1.089 cm3 g−1). Batch adsorption experiments were investigated to examine the effects of contact time, initial concentration, temperature, ionic strength and pH on the l-tryptophan adsorption. Among three isotherm models, the Langmuir model gave a perfect fit for the experimental data of l-tryptophan with a maximum monolayer adsorption capacity of 144.93 mg g−1 on DPH. The functional groups on the DPH surface can attract the l-tryptophan via π–π hydrophobic interactions, dipole-dipole hydrogen bonding and n–π interactions. The thermodynamic parameters suggested that the l-tryptophan adsorption is spontaneous and exothermic with a physisorption process. After four cycles, the regeneration efficiency of the used DPH was about 59.9%. Image 1 • Low cost activated carbon from date pits for the adsorption of l-tryptophan. • The initial pH has a greater effect on the removal of free amino acid l-tryptophan. • The maximum adsorption capacity was achieved 144.93 mg g−1 over DPH. • The thermodynamic analysis of l-tryptophan adsorption exhibits a physisorption. [ABSTRACT FROM AUTHOR]