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Nitrogenous disinfection by-products (N-DBPs) in chlorinated drinking water are receiving increasing attention due to their elevated toxicities. An effective strategy to control N-DBP formation is to reduce their nitrogenous precursors (amino acids) before disinfection. This work was undertaken to study free amino acid l-tyrosine adsorption onto two activated carbons synthesized from date pits. The amino acid is plentiful in low-molecular weight algal organic matter, which helps the formation of nitrogenous and carbonaceous disinfection by-products during water treatment. The equilibrium adsorption of l-tyrosine was studied on well-characterized activated carbons prepared by KOH (ACK) and ZnCl2 (ACZ) activation, possessing textural properties evaluated by SEM analysis, N2 adsorption–desorption isotherms and FT-IR spectroscopy. Batch experiments were conducted to determine the activated carbons’ adsorption capacities. The effect of contact time, initial adsorbate concentration, solution pH, and temperature were studied. The Langmuir model gave the best fit for the experimental data of l-tyrosine with a maximum monolayer adsorption capacity of 178.57 and 102.04 mg·g−1 on ACK and ACZ, respectively. Thermodynamic parameters ΔG°, ΔH° and ΔS° were also estimated for the adsorption study. The adsorption was spontaneous and exothermic, and involved physisorption.