"Semiconductor heterogeneous photocatalysis... is a versatile, low-cost and environmentally benign treatment technology for a host of pollutants. ...photocatalysis demands that the pollutant, the catalyst and source of illumination are in close proximity or contact ...The ability of advanced oxidation technology to remove low levels of persistent organic pollutants as well as microorganisms in water has been widely demonstrated and... the technology is now being commercialized... This review considers recent developments... for the treatment of low-level concentrations of pollutants in water and air using titanium dioxide as a "model" semiconductor."