Distribution Of Polycyclic Aromatic Hydrocarbons And Their Derivatives In Beijing Rivers And The Study Of Photocatalysis

Polycyclic aromatic hydrocarbons（PAHs）,as a persistent pollutant,are prevalent in the environment.And the parent PAHs can be converted to their derivatives PAHs（SPAHs）by chemical or microbial action.Until now,studies on PAHs and SPAHs in the atmospheric and soil are relatively extensive.However,the studies on PAHs and SPAHs in the water are relatively limited.Both PAHs and SPAHs have durability and pose a potential threat to groundwater safety.Therefore,it is of great significance to pay attention to the existence,behavior,major sources and health risks of PAHs and SPAHs in river.To analyze the distribution characteristics of PAHs and SPAHs in the wastewater receiving rivers and Chaobai river in Beijing-Tianjin area,the concentration of PAHs and SPAHs in samples were measured by the combined method of solid extraction and gas chromatography-mass spectrometry.At the same time,the probabilistic health risk of PAHs in the river were also evaluated.In order to study the removal of PAHs,the effect of photocatalytic degradation of phenanthrene by graphitic carbon nitride（g-C₃N₄-NS）was studied.The reaction mechanism was speculated and the effects of Cl^-,NO^3-and DOM on the degradation of Phe were systematically studied.The results are as follows:（1）The contamination of PAHs and SPAHs in five typical effluents from sewage treatment plants and receiving rivers in Beijing is 59-584 ng·L^-1 and 91-1822 ng·L^-1,respectively.These PAHs are dominated by 2-and 3-ring PAHs,which account for23%-48%of the total PAHs.The proportion of oxygenated PAHs in total SPAHs was 75%,while the total proportion of methyl PAHs and chlorinated PAHs was overall low（12%and13%respectively）.The concentration of PAHs and SPAHs is generally higher in the opening period than in the closing period,the heating season is higher than the non-heating season,December 2016 is higher than December 2017,indicating that the main source of PAHs in rivers is combustion source,“urban heating without coalification”plan are conducive to environmental improvement.Through the calculation of the toxic equivalent concentration of PAHs in four rivers,it was found that the ecological risk of polycyclic aromatic hydrocarbons was significantly reduced in December 2017,possibly due to the implementation of the "coal-free urban heating" plan.（2）The contamination of PAHs and SPAHs in Chaobai river in Beijing-Tianjin area is55.06-215.02 ng·L^-1 and 92.37-227.33 ng·L^-1,respectively.PAHs and SPAHs mainly exist in the form of freely dissolved state,and the environmental risk of pollutants can be accurately estimated by the total concentration.Calculations of Toxicity equivalents of PAHs in Chaohe river and Chaobai river indicated that the carcinogenicity of PAHs in Chaohe sampling point 2 may has potential risks for adults.Compared with the four effluents receiving rivers of Beijing,it indicates the suburban river PAHs that has lower ecological risk than the urban pollution river.（3）G-C₃N₄-NS showed a good removal effect on the degradation of Phe.In the g-C₃N₄-NS/Vis photocatalytic system,there are many active species,of which·O₂^-and¹O₂ are the main active species,and photo-hole and·OH also participate in the reaction but not the main effect.Low concentration of Cl^-inhibited the degradation of Phe in the reaction system.High concentration of Cl^-promoted the degradation of Phe in the reaction system;the addition of anionic NO^3-did not significantly affect the reaction system;the addition of HA inhibited the reaction.