Mathematical Models for Adsorption Capacity and Percent Removal of Heavy Metals from Water Using Stat-Ease 360

Heavy metal removal using adsorbent materials like watermelon rind, as investigated herein, will ensure a safe drinking water for consumption. For the first time, mathematical models taking A = adsorbent dosage, B = contact time and C = initial concentration as input variables were developed using Stat-Ease 360 design of experiment (DOE) tool for adsorption capacity (R1) and percent removal of heavy metals including, arsenic, cadmium, chromium, copper and lead (R2) in water, as two sole output variables. The models generated based on existing experimental observations (A, B, C) can be used to predict the responses or outputs of the adsorption process, especially looking at their respective satisfactory statistical performance parameters obtained. Several 3D surface and contour plots reveal the optimal factor combination for peak response performance for a particular metallic contaminant in the water. Optimal values for arsenic removal are 0.1g A, 120 min B, 3.12 mg/g R1 and 100% R2. Those of other metals present are as follows: 0.1g A, 60 min B, 0.17 mg/L C, 144.75 mg/g R1 and 85.78% R2 for cadmium; 0.1-1.2g A, 0<B≤120 min, 0.028 mg/L C, 215 mg/g R1 and 85.53% R2 for chromium; 0.1-1.2g A, 0<B≤120 min, 0.041 mg/L C, 275 mg/g R1 and 80% R2 for copper and; 0.1-1.2g A, 0<B≤120 min, 0.029 mg/L C, 205 mg/g R1 and 83.42% R2 for lead. This study falls short of many heavy metals such as zinc, nickel, cobalt, antimony, iron and mercury removal used to test the effect of other factors like pH, presence of co-existing ions, temperature and sorbent particle size for their adsorption performance.