repelling RR. As the pH approaches 3, the silica has less of a negative charge and would

allow the penetration of RR into the pores. Hence, acidic conditions would increase the

ability of RR to get within the vicinity of the titania.



 Destruction U Adsorption
 100 100
 90 90
 80 80
 70 70 c
 0 60 60
 E
 0 50 50 C.
 S 40 40 0
 -%
 30 30 "
 S20 20
 10 10
 0 0
 0 1 2 3 H 4 5 6 7 8
 pH

Figure 4-8. Destruction of RR (10 mg/L) after 1 hour UV with TiO2 slurry at various
 pHs.

 Grey water contains many sulfates, phosphates, and salts that may inhibit the

destruction of unwanted compounds (Chen et al., 1997). The addition of sodium

bicarbonate allows one to see the performance of the silica-titania composites in a

realistic feed stream. In Figure 4-7, it is also interesting to notice the affect of bicarbonate

on the destruction efficiency. There is little increase in destruction (with no bicarbonate)

at a pH of 7.6 within a range of 0.77% to 6% TiO2. At a larger TiO2 percentage, the

difference becomes very noticeable. However, Figure 4-9 shows that the increase in

destruction without bicarbonate present is only seen within a certain range of TiO2

loading (8% to 12%).