sizes larger than 200 A. The duplicated column exhaustion curves for each pore size are

shown in Figures 4-18 and 4-19. The duplicated runs were done with pellets made from a

separate batch.

 Table 4-2 summarizes the exhaustion results and shows a longer time to

breakthrough of the initial concentration for the column of 30 A gels. Yet, after the 30 A

pellets reached exhaustion and the system was regenerated by photocatalysis, its level of

adsorption ability decreased after each cycle. This was also visually observed. After one

hour of UV exposure the 30 A pellets were still slightly purple, while the 140 A

pellets had regenerated and returned to its initial white state.


 -- Run 1 ---*--- Run 2

 0.9
 0.8
 0.7----
 0.6
 0
 0.5---
 00.4.
 0.3 -
 0.2
 0.1 ,
 0 $- ------__, -.----

 0 50 100 150 200 250 300 350 400 451
 Time (minutes)

Figure 4-18. Column exhaustion curve for 140 A pellet (12% TiO2).