Fixed column adsorption study can be operated in series or in parallel. There are two types of influent modes for fixed bed columns, down flow and up flow. The advantage of a down flow design is that the adsorption of organics and the filtration of suspended solids can be accomplished in a single step [1] . Although, up flow fixed bed reactors have been used, down flow beds are used more commonly to lessen the chance of accumulating particulate material on the bottom of the bed, where the particulate material would be difficult to remove by back washing. Small scale column tests can be employed to simulate the potential performance of the adsorbent and the results obtained extrapolated in the design of full-scale reactors [2] . Under continuous influent flow, the equilibrium adsorption zone moves downward through the bed. As the equilibrium zone approaches the bottom of the column bed, the concentration of adsorbate in the effluent increases, and finally equals the influent adsorbate concentration. From this, the concept of breakthrough can be defined as the amount of influent solution passing through the bed before a maximum effluent concentration is reached [3] [4] . Breakthrough and exhaustion are defined as the phenomena when the ratios of effluent-to-influent concentrations are 5% and 95% respectively [4] . Values of column breakthrough and exhaustion are often used to evaluate adsorption parameters in column adsorption systems. Packed column can be designed using two approaches, scale-up procedure and kinetic approach. In both approaches a breakthrough curve from the test column, either laboratory or pilot scale is required, and the column should be as large as possible to minimize side-wall effects. The scale-up procedure approach for the packed column design is as follows:

1) Use a pilot test column filled with the carbon (adsorbent) to be used in full scale application.

2) Apply a filtration rate and contact time (EBCT) which will be the same for full-scale application (to obtain similar mass transfer characteristics).

3) Obtain the breakthrough curve.

4) Work on the curve for scale-up.

The kinetic approach

This method utilizes the following kinetic equation:

where C = Effluent solute concentration, C_o = Influent solute concentration, K₁ = rate constant, q_o = maximum solid-phase concentration of the sorbed solute, e.g. g/g, M = mass of the adsorbent, e.g., g, V = throughput volume, e.g., litres, cm³ and Q = flow rate e.g., litres/hour, or m³/s. One advantage of the kinetic approach is that the breakthrough volume, V, may be selected in the design of a column. Assume the left hand side equals the right hand side of Equation (1), cross multiplying gives,

Rearranging and taking the natural logarithms of both sides yield the design equation.

A plot of against V will give a slope from which the design reaction constant, K₁ (L/s-kg)

can be calculated and the design maximum solid-phase concentration, q_o, (kg/kg) calculated from the intercept of Equation (3) [5] .

The amount of carbon (adsorbent) required for the design column, (kg) is estimated using Equation (3) by substituting the parameters calculated from the plot of against V.

One advantage of column adsorption study is the ability to distinguish the different shapes of the isotherm such as linear, convex, or concave. The use of packed column in analyzing non-linear adsorption model isotherms makes it to be more efficient compared to batch adsorption study.

The present work was carried out to evaluate the starch based material potential ability to adsorptively dehydrate ethanol-water mixtures in a fixed bed adsorption column and design a packed bed column from the breakthrough profile parameters generated. For the purpose of this packed column adsorption design, the scale-up approach was used.

Analytical grade of ethanol, de-ionized water, α-amylase, sodium azide, sodium phosphate, sodium chloride, and sodium hydroxide were purchased from accredited chemical dealers in Onitsha, Anambra State, Nigeria using a scale with an accuracy of 0.01 g.

The method of [6] was used for the enzyme modification of the corn starch. Ethanol-water mixture is prepared at the required mass concentrations of 90 wt% ethanol.

The fluid phase concentration was measured with the aid of an Abbérefracto meter with automatic calibration in the experimental range of concentration.

The effect of flow rate on the uptake of water on the enzyme modified corn starch adsorbent at flow rates of 6, 10, and 14 ml/min, an inlet concentration of 90 wt% and bed height of 90 mm has been studied. The effects of flow rate on the breakthrough curve obtained showed that the adsorptive dehydration efficiency decreased with increasing flow rate. The evaluated parameters from breakthrough curve were used to design a packed column using the scale-up approach. The volume of ethanol-water treated before breakthrough was 2039 cm³. The dehydration of ethanol with this enzyme modified corn starch required less energy compared to distillation that consumes up to 50% of the overall energy used in a typical grain ethanol plant [13] - [16] .