3. Fixed bed studies

## 3.1 Effect of initial phenol concentration

The sorption breakthrough curves obtained at inlet phenol concentrations of 200, 400 and 600 mg/L at 0.106 L/h flow rate are given in Figure 4.

A decreasing inlet concentration gave a later breakthrough curve as displayed in Figure 4. The treated volume was greatest at the lowest inlet concentration due to a lower concentration gradient caused a slower transport and the decreasing in diffusion coefficient or decreasing in mass transfer coefficient. The breakpoint time decreased with increasing inlet phenol concentration as the binding sites became more quickly saturated in the system. The breakthrough concentration (Ct/ Co = 0.03) occurred after 30 hours (3000 mL of effluent) i.e. 200 mg/L phenol inlet concentration. It appeared after 17 hours and 15,5 hours corresponding to 1700 mL and 1550 mL of inlet concentration of phenol 400 and 600 mg/L, respectively.

#### 3.2 Effect of the flow rate

The effect on flow rate for the adsorption of phenol at flow rates 0.8; 2.0 and 4.0 mL/min at an influent concentration of 600 mg/L and bed height 19.5 cm displayed in Figure 5. It was clearly observed that a rapid uptake was noticed in the initial stages of adsorption and decreases thereafter and finally reaches saturation. The increase in flow rate, the breakthrough curves become steeper and reach the breakpoint quickly. This probe displayed a well-defined of the residence time of the solute in the column, which was not long enough for adsorption equilibrium to be reached at a high flow rate. So at the high flow rate, the phenol solution left the column before equilibrium occurs. Furthermore, a fixed saturation capacity of bed based on the same driving force gave rise to a shorter time for saturation at a higher flow rate [8, 34, 35].

#### 3.3 Effect of bed height

The breakthrough curves for the adsorption of phenol on macro-aromatic resin FPX66 at various bed heights by fixing the influent concentration at 600 mg/L and flow rate at 2 mL/min are given in Figure 5. The results indicated that the throughput volume of phenol solution increased with increasing bed height, due to the

availability of more sorption sites due to the increase in the total surface for adsorption [34]. The equilibrium capacity decreases with the increase of the bed height. In a fixed bed method the probability of contact between the adsorbate and the adsorbent is less when compared to the batch mode, which results in lesser equilibrium sorption capacity in column mode.
