Catalytic and photocatalytic processes for the abatement of N-containing pollutants from wastewater. Part 2: Organic pollutants

Several N-containing organic compounds of anthropic origin, namely dyes, pesticides/herbicides and pharmaceuticals, are responsible of water pollution, due to their high solubility in water and low adsorption in soil, leading to a high mobility in the aquifer. Besides pesticides and dyes, widely recognized as water pollutants, environmental contamination by pharmaceuticals is an emerging issue, since both drugs and their metabolites may act as water pollutants, and most of water potabilization plants do not treat them. Removal of such species by physico-chemical methods (adsorption and coagulation; sedimentation; filtration; use of membranes and chlorination) suffers from several drawbacks, including high operating costs, and formation of secondary pollutants that are then released in the environment. Nonetheless, currently employed biological methods do not allow removing non-biodegradable pollutants. Advanced oxidation processes (AOPs), which imply the in situ production of highly reactive species (i.e., H2O2, OH•, O2•-2, O3) under relatively mild experimental conditions, allow the degradation (and eventual mineralization to CO2 and H2O) of refractory organics into readily biodegradable compounds and may be used either before or after biological treatments. This review addresses the most common catalytic and photocatalytic AOPs that can be adopted for the removal of some N-containing compounds of different origin and nature.