Attenuation of Phenol from Aqueous Solutions Using Fine-Grained Soils: Experimental Design Using a Statistical Approach

The disposal of toxic substances on land imposes adverse effects to the surrounding lithospheric environment. Suitable low cost and sustainable locally available materials are very much needed for attenuation of migratory pollutants through lithospheric media. Natural clay and fine-grained soils are widely used as primary liner material in containment and tailing pond structures because of their economic superiority, sustainability, and favorable removal capacity. An investigation was carried out to examine the potential capacity of two fine-grained soils (Type S1) and (Type S2) for attenuating phenolic migration through subsurface environment. Statistically designed experiments based on the central composite method (CCD) was used to describe the interacting effects of four independent variables such as initial phenol concentrations ($3–15\mathrm{mg}/\mathrm{L}$), soil mass amount ($4–20\mathrm{g}$), solution pH (4–10), and the nature of adsorbent (S1) and (S2) on the uptake of phenol. The CCD along with $\alpha$ (distance of each axial point) equal to 1.316 and six central points were used to develop the second-order mathematical model using the experimental results that were obtained through 40 batch test data. The significance of different independent variables and their influence on the phenol removal percentage was also identified by ANOVA. A desirability function was further introduced to optimize the process parameters. The results showed that soil type (S1) would be more suitable for removal of phenol (43.54%) and the optimum values of initial phenol concentrations, soil dose, and pH were $15\mathrm{mg}/\mathrm{L}$, $5.74\mathrm{g}/100\mathrm{mL}$, and 6.95, respectively, with a desirability value of 0.886.