Prospects of Photocatalysis in the Management of Nitrate Contamination in Potable Water

Nitrate is one of the most widespread toxic inorganic compounds in groundwater due to its high water solubility. High levels of nitrate in potable water may pose serious risks to the environment and to human health. Heterogeneous photocatalysis has been widely used for water remediation and disinfection, however, less research studies, comparatively, have reported photocatalytic nitrate reduction because of the complexity of the mechanism of reaction. Mainly, nitrate photoreduction takes place directly via reaction with photo-generated electrons in the conduction band of the photocatalyst or by photo-produced reducing species under light irradiation. As a result, nitrate can be transformed into unpreferred by-products such as nitrite and ammonium, while the reduction into dinitrogen gas is much recommended due to its high importance. On the other hand, the issue of the re-oxidation of ammonium into nitrate has also been reported. The efficiency and selectivity of a photocatalytic system to reduce nitrate into dinitrogen depend on the operating parameters controlling the reaction, and more importantly, the selectivity strongly depends on the type of the photocatalytic nanomaterial. For this reason, a pool of studies have been performed in order to enhance the selectivity of nitrate reduction into dinitrogen by developing different kinds of nanomaterials. In this chapter, we examine: (i) the conventional technologies for nitrate removal/reduction, (ii) the effect of operating conditions on the photocatalytic nitrate reduction process, as well as (iii) the influence of the type of photoactive nanomaterial on the selectivity and the performance toward nitrate reduction.