**2.5 Fixed bed column**

For each column study, the fixed-bed column was set-up using a glass column with a 15 mm internal diameter and 750 mm bed height and a peristaltic pump with medium flow range (1 mL/min). The schematic diagram of the fixed-bed column system is illustrated in **Figure 1**. For each column study, the column was packed by 2–4 mm diameter CFA beads, one type at a time. The mass of the CFA beads typically varied in a range of 50–75 g with a varied height of the bed of CFA beads in a range of 505–655 mm, which is dependent on the size distribution of the CFA beads produced from the above immobilization process. A layer of washed sand with a height of 25 mm was placed at the bottom of the CFA beads to protect any loss of beads as well as give mechanical support in the fix-bed column system. The top of the bed of CFA beads was submerged at least 50 mm below the water surface of the PME sample in the column by maintaining a high position of the outlet in treated effluent tubing (inverse "U" shape) shown in **Figure 1**.

All of these column studies were performed at room temperature (20 � 1°C) at the WERL at GSU and the treated PME samples were collected at different intervals: every 1 h from the 1st hour to 12th hour, every 2 hours from the 13th hour to 24th hour until the column of the CFA beads was exhausted. These samples were analyzed for color. Meanwhile, all the treated PME samples were collected in the treated PME container as an accumulated sample and its color was tested in the end of a column study. The treated PME sample was separated by vacuum-filtering the mixture through a Supor-450 47 mm 0.45 μm membrane paper. Immediately after filtration, the filtrated samples were collected to test color. Duplicate flasks with identical CFA and effluent mixtures were used to represent each sample. The average reading of color and pH measurements between the two duplicate samples were documented. The color of PME samples was measured using HACH DR 5000 Spectrophotometer and HACH Method 8025.

Color removal efficiency of CFA can be calculated using following equation:

$$\text{Removal Efficiency} \left( \% \right) = \frac{\left( \text{C}\_i - \text{C}\_t \right) \* \mathbf{100}}{\text{C}\_i} \tag{1}$$

where *E* = Removal Efficiency (%), *Ci* is the initial color concentration (mg/L), *Ct* is the color concentration at time *t* (mg/L).

**Figure 1.** *A schematic diagram of column.*

*Immobilization of Powdered Coal Fly Ashes (CFAs) into CFA Beads and Column Studies… DOI: http://dx.doi.org/10.5772/intechopen.94293*

The effluent volume (*Veff*) can be expressed as:

$$\mathbf{V}\_{\rm eff} = \mathbf{Q} \times \mathbf{t}\_{\rm total} \tag{2}$$

Where, *Q* stands for volumetric flow rate (mL/min) and *ttotal* stands for the time of exhaustion (min).

The area under the breakthrough curve (*A*) can be determined by integrating color adsorbed concentration (*CAd*) vs. time (*t*). For a given volumetric flow rate (*Q*) and initial color concentration (*C*0) of PMEs, the total amount of color adsorbed (*qtotal*) can be calculated by the following equation:

$$q\_{total} = \frac{Q}{\mathbf{1000}} \int\_{t=0}^{t\_{total}} \mathbf{C}\_{Ad} dt \tag{3}$$

Total amount of color, *Mtotal* (mg) passed through the fixed-bed column system is determined by following equation:

$$M\_{\text{total}} = \frac{\mathbf{C}\_0 \times \mathbf{Q} \times t}{1000} \tag{4}$$

Where, *C*<sup>0</sup> is denoted as initial color concentration (mg/L) of PME, *Q* is the volumetric flow rate (mL/min) of PMEs.

The fixed-bed column system color removal efficiency with respect to the flow volume can be calculated by following equation:

$$\text{Removal Efficiency} = \frac{q\_{\text{total}}}{\text{M}\_{\text{total}}} \times \mathbf{100} \tag{5}$$

#### **3. Results and discussions**

#### **3.1 Immobilization of powder CFAs**

In each batch trial during the immobilization process, CFA beads were produced with small spherical shape and maintained CFA grayish original color. It was observed that the RPM and inclined vertical angle of the pan of pellitizer, and water mixing ratio with CFAs were important factors that affected beads size distribution. In the immobilization process, at high RPM of the pan reduced the size of CFA beads while at low RPM beads diameters were increased. The optimal rotational speed of pelletizer and vertical angle of the pan were found to be 32 RPM and 45 degree, respectively, and were maintained the same during the whole immobilization process. It is also found out that CFA1 (Class "C") or hydrated lime can be used as binder to produce CFA beads. The combination of hydrated lime and CFAs required more water while the combination of CFA1 with CFA2or CFA3 required less.

For each batch of immobilization process, cost effective blinders were used to produced relatively uniform and consistent size and shape. The newly produced beads were put into large foil tray with thin layer and covered with a soaked wet cloth at room temperature of 20 � 1°*C* for two weeks. The cloth was kept wet during these two weeks and then was removed. The beads were continually exposed to the atmosphere for air dry at room temperature of 20 � 1°*C* for one week. In this study only the amount of water used for immobilization was documented while the water used during 2-week "wet" curing period was not documented. It was observed that about 10–20% of water contents could produce the CFA beads with a

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high strength. In general, it was observed that the strength of the beads increased with in increased weight percentage of hydrated lime, adsorbed more water during curing period, and much more pores formed. It was observed that about 10–20% of water content could produce the beads with a high strength. In this study, it was particularly important for the CFA beads to hold their shape in PMEs. Those CFA beads, which could hold their shape in PMEs at least 24 h, were considered to be beads with a high strength. A summary table for total five (5) types of CFA beads is shown in **Table 3**.

The five (5) types of CFA beads produced from the three (3) CFA samples are shown in **Figure 2**.
