Environmental Engineering Reference
In-Depth Information
25.11 TiO
2
for Disinfection
Studies on antimicrobial effects of titanium dioxide particles started 30 years ago.
Matsunaga et al. (1985) irst reported the antibacterial activity of titanium dioxide. They
used a metal halide lamp for excitation of TiO
2
and bacterial inactivation occurred in
60-120 min. Matsunaga et al. (1988) observed that 99% of
Escherichia coli
was removed
using immobilized TiO
2
in a continuous sterilization system. Other than
E. coli
, studies
have been conducted on other organisms like poliovirus (Watts et al., 1994), cyanotoxin
(Senogles et al., 2001),
Staphylococcus
(Chung et al., 2009), and cancer cells (Blake et al., 1999).
The combination of sunlight and photocatalyst can lead to a system that can degrade
pathogens and organic pollutants. Many studies have reported the effectiveness of solar
photocatalytic disinfection (Block et al., 1997; Blake et al., 1999; Salih, 2002; Rincón and
Pulgarin, 2003). Most of the studies used suspended forms of catalyst, which, in turn,
need a catalyst removal system. Less number of studies were conducted using an immo-
bilized form of catalyst (Dunlop et al., 2002; Salih, 2002; Rincón and Pulgarin, 2003). The
main concern in immobilization is regarding the stability of the catalyst. This can be
overcome by using a continuous reactor with catalyst-coated glass plates or using bottles
coated with catalyst on the inner wall. Better results can be obtained if relective coat-
ings are used (Sommer et al., 1997). This increases the intensity of solar radiation passing
into water. In the normal SODIS method, the treated water should be used within 24 h
because some bacteria are resistant to UV radiation and they are able to repair the dam-
age later. The main advantage of solar photocatalysis is that there is no regrowth after
treatment (Gelover et al., 2006). Since the damage to cells is irreversible, there is no chance
of regrowth. Thus, it has better residual effects.
Bekbolet and Araz (1996) conducted studies on
E. coli
using a suspended form of
Degussa P-25. They used cylindrical Pyrex glass vessels and a black light luorescent
lamp as the light source. Inactivation of 1000 colony-forming units (CFU)/mL
E. coli
was
achieved in 60 min using 1 g/L of TiO
2
. The reaction followed irst order. Ireland et al.
(1993) compared the action of Degussa on pure cultures of
E. coli
in dechlorinated tap
water and on surface water samples. They reported that if a signiicant amount of radi-
cal scavengers are not present, rapid cell death can be achieved even in a surface water
sample. They used a continuous reactor working under UV with TiO
2
coated on a iber-
glass mesh.
Another study was conducted on deactivation of
E. coli
using Degussa P-25, a hydro-
thermally prepared photocatalyst (HPC) and a magnetic photocatalyst (MPC) in a batch
spiral reactor (Coleman et al., 2005). They compared effectiveness of both suspended and
immobilized forms of catalyst. Degussa P-25 was eficient compared with HPC and MPC.
They studied the effect of buffer and catalyst loading. They reported that use of silver
nanoparticles along with TiO
2
increased the performance of the system. Optimum catalyst
loading was reported as 1 g/L.
Lonnen et al. (2005) conducted a study using the SODIS method and a solar photocata-
lytic method. The eficiency of both systems to degrade bacteria, fungi, and protozoa were
studied. Degussa P-25 powder was coated on acetate sheets. It was inserted into Duran
bottles. Simulated solar radiation was used for the studies. The bottles were irradiated for
8 h. The initial concentrations of microorganisms used were in the range of 10
4
-10
6
/mL .
