Removal of ammonium from fish farms by biochar obtained from rice straw: Isotherm and kinetic studies for ammonium adsorption

Ammonium is a water pollutant that harms the environment, particularly fisheries. Rice straw is also an economic waste of rice, with millions of tons produced per year around the world. In this paper, physical and chemical procedures for the modification of rice straw were studied. The kinetic and isothermal adsorption trends were investigated, including the ammonium removal efficiency, the contact time of the adsorbent, the amount of adsorbent, and the initial concentration of NH4+. The effect of temperature and pH on the adsorption process was discussed. The removal efficiency of NH4+ recorded 43, 53.7, and 69.5%, with maximum adsorption values of 2.9, 3.5, and 4.5 mg/g at temperatures of 25 ± 5, 35 ± 5, and 45 ± 5°C, respectively, at pH 7.5. The biochar obtained from rice follows the pseudo-second-order equation for ammonium adsorption kinetics (R2 = 0.98). The adsorption isotherm follows Freundlich’s model (R2 = 0.99) and Langmuir’s model (R2 = 0.98).