The effect of soil pH on photo-catalytic oxidation of polycyclic aromatic hydrocarbons (PAHs)

The environmental fate of polycyclic aromatic hydrocarbons (PAH) is a significant issue, raising interest in its clean up using remediation. However, the physical, chemical, and biological properties of soils can drastically influence degradation of pollutants. The effect of soil pH on degradation of PAHs with a view to modify soil pH to enhance the degradation of PAH's was studied. The degradation rate of key model PAHs was monitored in topsoil modified to a range of pH 4 to 9 at half pH intervals. Photo-oxidation of PAHs in presence of catalyst under UV light at two different wavelengths was studied. The degradation of PAHs during photo-oxidation was carried out at varying soil pH, whilst the degradation rate of individual PAH was monitored using HPLC. Photo-degradation of PAHs at 375 nm showed higher rate of degradation compared at 254 nm. Higher degradation was observed at pH 6.5, whilst in general, acidic soil had greater photo-degradation rates than basic pH of soil. pH 7.5 and pH 8 had slowest photo-degradation. Phenanthrene at both the wavelengths had highest degradation rate and pyrene had slowest degradation rate. Therefore, photo-catalysis can be used as alternative process to eliminate PAHs by manipulating soil pH to enhance remediation.