Environmental Engineering Reference
In-Depth Information
Immobilized
catalyst
Inlet
Out
Pump
Sample
FIGURE 25.14
Schematic diagram of continuous reactor.
was studied. Large increases in turbidity reduced the eficiency since it decreases the opti-
cal penetration. The degradation rate was reduced slightly by the presence of bicarbonate
ions since it is changing the pH of the solution and it acts as a radical scavenger (Coleman
et al., 2005; Marugan et al., 2008). However, addition of dextrose did not show any change
in the eficiency of the system.
Comparison studies of SODIS and solar photocatalytic disinfection were conducted. The
bacterial solution was taken in polyethylene terephthalate (PET) bottles. The catalyst was
taken in suspended and immobilized form. All the PET bottles were kept under sunlight
for 6 h. There was 50% reduction of the bacteria after 15 min in the catalyst-suspended PET
bottles—100% inactivation was obtained after 1 h. It took 3 h for the immobilized catalyst
to completely inactivate the bacteria. In the SODIS method, complete inactivation occurred
after only 6 h (Figure 25.15).
Bacterial regrowth studies were done using SODIS-treated and photocatalytically treated
water samples. There was no regrowth in catalyst-treated water samples. However, bacte-
rial colonies appeared on plates containing SODIS-treated water samples after 24 h. This is
because the bacteria can repair the damage caused by the SODIS method if suficient time
is given. The change due to catalyst treatment is irreversible (Gelover et al., 2006).
1
Suspended
Immobilized
SODIS
0.8
0.6
0.4
0.2
0
0
1
2
3
4
5
6
7
Time (h)
FIGURE 25.15
Kinetics of bacterial kill by SODIS and photocatalysis methods.
