ABSTRACT The present study investigates the reduction of free residual chlorine (FC) from aqueous solution using non- modified biochar (NM-B) and chemically modified biochar (M-B) derived from date palms. The role of biochar dose, biochar particle size, reaction time, solution pH, and initial concentration of FC on adsorption efficiency were assessed. The optimum contact time for higher FC uptake was reached after 20 min using NM-B and 8 min using M-B, with a biochar dose of 10 g/L. The optimum pH values and biochar size for higher FC adsorption was 4 and 0.6 mm, respectively. Higher removal was reached to 88% using NM-B and 96% using M-B. The pseudo-second order model matched well with the kinetic outcomes. Langmuir isotherm was fitted well with the equilibrium results of FC uptake on NM-B and M-B, with regression coefficient (R2) values of 0.98 and 0.998, in that order. The separation parameter was within the limits of favorable adsorption of FC by both biochars. The higher uptake capacity (0.215 mg/g) was linked with the M-B, indicating that chemical modification of biochar was successful for increasing FC uptake from aqueous solutions. This study confirmed that utilizing of biochar derived from date palms for FC removal is very beneficial and cost-effective solution, especially in the countries that considered as a largest date producer in the world.