299
Water Quality
In a full-scale plant for water treatment, a number of technical issues have to be
sorted out. Water quality of the influents in the treatment plant can vary with time.
In this section, the implication of TiO 2 photocatalytic processes for treatment of
water sources of different qualities is discussed. This enables a fuller understanding
of the effects of various key water quality parameters on the suitability of applying
such advanced TiO 2 photocatalytic processes.
Turbidity
Turbidity often refers to the insoluble particulates that are present in the targeted
water [314]. The presence of such insoluble particulate matters is highly detrimental
to the TiO 2 photocatalysis-based process, as they can affect the optical properties
and further impede the penetration of UV light by strong scattering and absorption
of the rays [47, 301]. This will cause a variation in the predicted use of TiO 2 loading,
UV penetration path, and light intensity. Also, excessive levels of turbidity can
reduce both the photomineralization and photo-disinfection efficiency of the pollutants that are present in water owing to the shielding effects that attenuate the light
penetration causing those pollutants to flee from the treatment [47, 276, 301].
Suspended solids will also shield target pollutants from oxidation reactions. In this
instance, the suspended solids refer to the nonfilterable residue that is retained on
the filter medium after filtration. All these factors ultimately decrease the overall
photocatalytic efficiency for water treatment. To ensure rapid photocatalytic reaction rate, the turbidity of the targeted water should be kept below 5 nephelometric
turbidity units (NTU) for optimal UV light utilization and photocatalytic reaction
[91, 105]. Rincón and Pulgarin [274] observed that the water turbidity higher than
30 NTU will negatively affect the rate of photocatalytic disinfection. The limit of 5
NTU is arbitrary and depends on the receiving water bodies and the treatment levels
required. Since TiO 2 photocatalytic processes are retrofitted to advanced water
treatment stage, prior reduction in turbidity could be achieved via conventional
treatment processes such as screening, filtration, sedimentation, coagulation, and
flocculation. The standard for 1 NTU is a 1.0 mg/L of specified size of silica suspension and can be prepared for laboratory investigation. The turbidity standard can be
calibrated with a photoelectric detector or nephelometry for the intensity of scattered light.
Inorganic Ions
The presence of inorganic ions in the targeted water for TiO 2 photocatalytic treatment is expected. To functionalize a TiO 2 water treatment process, the basic understanding of the role of these inorganic ions on the photocatalytic performance is
essential. Crittenden et al. [68] reported that when a photocatalyst is utilized in
Recent Developments in Photocatalytic Water Treatment Technology
Water Quality
In a full-scale plant for water treatment, a number of technical issues have to be
sorted out. Water quality of the influents in the treatment plant can vary with time.
In this section, the implication of TiO 2 photocatalytic processes for treatment of
water sources of different qualities is discussed. This enables a fuller understanding
of the effects of various key water quality parameters on the suitability of applying
such advanced TiO 2 photocatalytic processes.
Turbidity
Turbidity often refers to the insoluble particulates that are present in the targeted
water [314]. The presence of such insoluble particulate matters is highly detrimental
to the TiO 2 photocatalysis-based process, as they can affect the optical properties
and further impede the penetration of UV light by strong scattering and absorption
of the rays [47, 301]. This will cause a variation in the predicted use of TiO 2 loading,
UV penetration path, and light intensity. Also, excessive levels of turbidity can
reduce both the photomineralization and photo-disinfection efficiency of the pollutants that are present in water owing to the shielding effects that attenuate the light
penetration causing those pollutants to flee from the treatment [47, 276, 301].
Suspended solids will also shield target pollutants from oxidation reactions. In this
instance, the suspended solids refer to the nonfilterable residue that is retained on
the filter medium after filtration. All these factors ultimately decrease the overall
photocatalytic efficiency for water treatment. To ensure rapid photocatalytic reaction rate, the turbidity of the targeted water should be kept below 5 nephelometric
turbidity units (NTU) for optimal UV light utilization and photocatalytic reaction
[91, 105]. Rincón and Pulgarin [274] observed that the water turbidity higher than
30 NTU will negatively affect the rate of photocatalytic disinfection. The limit of 5
NTU is arbitrary and depends on the receiving water bodies and the treatment levels
required. Since TiO 2 photocatalytic processes are retrofitted to advanced water
treatment stage, prior reduction in turbidity could be achieved via conventional
treatment processes such as screening, filtration, sedimentation, coagulation, and
flocculation. The standard for 1 NTU is a 1.0 mg/L of specified size of silica suspension and can be prepared for laboratory investigation. The turbidity standard can be
calibrated with a photoelectric detector or nephelometry for the intensity of scattered light.
Inorganic Ions
The presence of inorganic ions in the targeted water for TiO 2 photocatalytic treatment is expected. To functionalize a TiO 2 water treatment process, the basic understanding of the role of these inorganic ions on the photocatalytic performance is
essential. Crittenden et al. [68] reported that when a photocatalyst is utilized in
Recent Developments in Photocatalytic Water Treatment Technology