Performance of granular ferric hydroxide process for removal of humic acid substances from aqueous solution based on experimental design and response surface methodology.

Response surface methodology has been used to design experiments and to optimize the effect of independent variables responsible for higher adsorption of humic acid (HA) by granular ferric hydroxide (GFH) from aqueous solutions. The variables of pH (3-11), contact time (15-120 min), adsorbent dose (1-5 g/L) and initial concentration of humic acid (5-20 mg/L) were examined. The adsorption isotherms and kinetics of humic acid substances on granular ferric hydroxide (GFH) were studied. Also the design of the experiments was performed using R software by the CCD (central composite design) method. Variance analysis (ANOVA) was used as the statistical response analysis method. Result of this study proved the optimal values of the independent variables of the adsorbent dose, contact time, initial concentration of humic acid and pH were 4 g/L, 93.75 min, 16.25 mg/L, and 5, respectively. The experimental data followed the Langmuir isotherm and pseudo-second kinetic model. Based on the response surface methodology, higher HA removal efficiencies were obtained with acidic condition, longer reaction time, and appropriated loading amount of GFH.