12
ENVIRONMENT ASPECTS
"PHOTOCATALYTIC DEGRADATION FOR ENVIRONMENTAL
APPLICATIONS A REVIEW"
Prepared by:Lee Siang Hua (HT033441Y)
Prepared for: Assoc. Prof. Marc Garland
Date of submission: 30 March 2005
Dept. of Chemical & Biomolecular Engineering,
National University of Singapore,
10, Kent Ridge Crescent, Singapore 119260
Email: g0302120@nus.edu.sg
BACKGROUND
All of the pharmaceutical compounds are complicated in structures. The difficulties of synthesis are well-
known, and thus implied on their high price in the market. The opposite sides of this, these compounds
are similarly difficult to decompose or degrade. Studies shown residues of pharmaceutical and diagnostic
compounds have been detected in effluents of sewage treatment plants, surface, ground and drinking
waters. Ternes & Hirsch (2000) reported the occurrence of iodinated X-ray contrast media derive from
radiological examinations (diatrizoate, iopamidol, iopromide and iomeprol) in sewage treatment plant
effluent. Similar study on 1997, Ternes, T.A. reported the occurrence of 32 drugs residues in German
municipal sewage treatment plant discharge, river and stream waters. When applying pharmaceuticals
and diagnostic agents to humans, a good part of the substances reach the municipal sewage system
unchanged or as metabolites.
Ternes, T.A. et al (2002) has shown that drugs and diagnostic agents are not removed quantitatively
during waste water treatment by current techniques. From the report, the residues (bezafibrate, clofibric
acid, carbamazepine, diclofenac) are un-removable with flocculation and sand filtration only, with
ozanation, we can achieve 90% removal of diclofenac and carbamazeipine, 50% removal of bezafibrate,
clofibric un-removable, with granular activated carbon followed by ozonation, all residues are effective
removal except clofibric acid. Hence, it is necessary to develop and evaluate water treatment processes
with regard to their potential for eliminating pharmaceuticals and diagnostic agents.
Photocatalysed degradation techniques with titanium dioxide have developed to be one of the most
remarkable ways for the treatment of water (wastewater or drinking water) containing organic
contaminants. The surface of TiO
2
has a very high oxidation potential (3.0eV) compared to conventional
oxidizing agents such as chlorine (1.36eV) and ozone (2.07eV), make it capable of breaking down many
organic substance (Fujishima A. et. al.: 1997). The strong oxidizing power of the photogenerated holes,
together with the chemical inertness and non-toxicity of TiO
2
, has made it an attractive photocatalyst.
SUMMARY OF SELECTED PAPER
DS Bhatkhande, et al (2001) gave a thorough review of the photocatalytic degradation process in tertiary
wastewater treatment. . The review covered the mechanism of the process, a summary of different
compounds degradable using the process, the control factors on the process such as light source,
adsorption, pH, anions, cations, temperature and surface area. In additions, the catalyst reusability and
degradation rates for different compounds had been discussed.
Mechanism
Photons of a certain wavelength incident upon the photocatalyst surface, electrons are promoted from the
valence band to the conductance band. This leave positive holes on the valence band, which react with
the hydroxylated surface to produce OH* radicals which are the most potent oxidizing agent. If a suitable
