Removal of polycyclic aromatic hydrocarbons (PAHs) from groundwater by heterogeneous photocatalysis under natural sunlight

Abstract

Abstract Polycyclic aromatic hydrocarbons (PAHs) are a class of persistent organic pollutants of special concern because they are carcinogenic and mutagenic compounds. In this paper, photodegradation of a mixture of six PAHs in groundwater at pilot plant scale is reported. Semiconductor materials (ZnO and TiO 2 ) as photocatalysts in tandem with Na 2 S 2 O 8 as oxidant under natural sunlight were used. The PAHs were benzo[ a ]pyrene, benzo[ b ]fluoranthene, benzo[ ghi ]perylene, benzo[ k ]fluoranthene, fluoranthene, and indene[1,2,3- cd ]pyrene. As expected, the influence of both semiconductors on the degradation of PAHs was very significant in all cases. Photocatalytic experiments show that the addition of photocatalyst, especially for ZnO/Na 2 S 2 O 8 system, strongly improves the elimination of PAHs in comparison with photolytic tests; significantly increasing the reaction rates. The first-order equation (monophasic model) satisfactorily explained the disappearance process although it ignores small residues remaining late in the process. These residues are important from an environmental point of view and the Hoerl function (biphasic model) better predict the results obtained. In our conditions, the time required for 90% degradation was in the range 7–15 min and 18–76 min for ZnO and TiO 2 systems, respectively. Thus, the use of the tandem ZnO/Na 2 S 2 O 8 makes possible the economical decontamination of groundwater containing non-biodegradable pollutants like PAHs.