Characteristics Of PAHs Adsorption On Particles In Wastewater Treatment

Polycyclic aromatic hydrocarbons (PAHs) are a sort of important persistent organic pollutants (POPs). For their teratogenicity, carcinogenicity and mutagenicity, 16 kinds of PAHs have been put on the priority list to be detected by U.S. Environmental Protection Agency (U.S. EPA), they are, NapHthalene, AcenapHthylene, AcenapHthene, Fluorene, Pyrene, Benzo(a)pyrene, Dibenzo(a,h)anthracene, Benzo(b)fluoranthene, Benzo(k)fluoranthene, Benzo(g,h,i)perylene, Indeno(1,2,3-cd)pyrene. Domestic sewage and industrial waste water are major sources of the PAHs, so the municipal sewage treatment plant plays an important role in keeping down and blocking PAHs into natural water.Through a series of adsorption experiments using quartz sand, kaolin, and natural clay as inorganic adsorbents and laboratory-cultured activated sludge as organic adsorbent for adsorbing model polycyclic aromatic hydrocarbons (PAHs) of NAPT, PHEN and PYR, the characteristics of PAHs adsorption in wastewater treatment were studied. The result shows,1. As a result, the adsorption of PAHs by the inorganic adsorbents well followed the Langmuir isotherm while that by the activated sludge well followed the Freundlich isotherm;2. The inorganic adsorbents with higher surface area and more organic matters, their capacity adsorption of PAHs would be higher. The adsorption capacity of the activated sludge for PAHs was higher than that of the inorganic particles. The PAHs with higher octanol - water partition coefficient, the easier they could be adsorbed on adsorbents; 3. The adsorption experiments of kaolin and activated sludge for NAPT were conducted under different temperature (10oC, 25oC, 30oC), the result showed that the adsorption capacity of the kaolin for NAPT turned lower with higher temperature, showed a characteristic of exothermic reaction. On the contrary, the adsorption capacity of the activated sludge for PAHs turned higher, showed a characteristic of exothermic reaction, showed a characteristic of endothermic reaction;4. The adsorption experiments were conducted under different pH, the result showed that the effects of pH to the adsorption capacities of the kaolin and activated sludge for PAHs were not obvious;5. The research detected PAHs in the Third Municipal sewage treatment plant of Xi'an for one year. The secondary treatment could remove PAHs efficiently, with a removal rate of 79%, and the biological unit contributed most with a removal rate of 68%;6. The removal of PAHs in secondary treatment was the result of the adsorption from inorganic particles and the activated sludge, and the activated sludge played a more important role in the process.