use a slurry system in preliminary testing to establish the feasibility of pollutant

mineralization or microbe inactivation. For these systems, an optimum weight of TiO2

per volume of solution (wt/vol) was found that yielded the most degradation for specific

types of compounds at a specific light intensity. For instance, Goswami et al. (1993)

found 0.1% (wt/vol) TiO2 to be the optimum loading for most hydrocarbons and Block

and Goswami (1995) found 0.01% (wt/vol) as the best for microbial destruction.

 Although slurry systems are considered to be the most photocatalytically efficient,

there is a dilemma to be addressed in the design of the reactor. Due to the extremely

small size of the particles (between 0.1 30 nm, depending on the manufacturing

source), there is a difficulty in recovering the catalyst from the purified water. This

problem has directed research to investigate the use of catalyst supports.

 There are many research groups that have examined the immobilization of

photocatalysts on nonporous glass surfaces as a way of providing a backbone of support

for the particles, while also allowing the penetration of light to activate the catalyst

surface. Successful immobilization has been done on glass beads (Jackson et al., 1991;

Serpone et al., 1986; Zhang et al., 1994) and on the inside surface of glass tubes (Al-

Ekabi and Serpone, 1988; Matthews, 1988). The oxidation rates were usually lower with

the immobilized catalysts than with free suspensions. The determinate factor was

assumed to be the result of mass transfer limitations, for it was observed that as the flow

rate increased, resulting in more efficient mixing, the oxidation rate likewise increased.

 While these designs may have certain advantages, it is hypothesized that an

efficient support for a catalyst would be a material with adsorption capability that would

bring the contaminants into close contact with the catalyst surface (see Figure 2-4) where