Statistical analysis and optimization of ammonia removal from aqueous solution by zeolite using factorial design and response surface methodology

The ability of zeolite as a low-cost adsorbent for ammonia removal from aqueous solution was studied through batch adsorption experiments. The results showed that zeolite was effective in eliminating ammonia from aqueous solution. Factorial design and response surface methodology were applied to evaluate and optimize the effects of pH, adsorbent dose, contact time, temperature and initial ammonia concentration. Low pH condition was preferred with the optimum pH found to be 6. High adsorbent dose generated high removal rate and low adsorption capacity. Results of factorial design and response surface methodology showed that temperature was not a significant parameter. The model prediction was in good agreement with observed data (R2 = 0.969). The optimum Qe was 22.90 mg/g achieved at pH 7 and initial TAN concentration of 3000 mg/L. The adsorption kinetics followed the Pseudo-second order kinetic model (R2 =  0.998). Equilibrium data were fitted to Langmuir and Freundlich isotherm models with Freundlich model (Kf = 2.24 L/mg, 1/n = 0.28) providing a slightly better predication (R2 = 0.992). The 1/n value of less than 1 indicated that the removal process was favorable.