| Incineration technology has become the main way of municipal solid waste treatment because of its advantages in volume reduction,quantity reduction,harmlessness and resource utilization.However,the secondary pollution,especially the emission of polychlorinated dibenzo-P-dioxins（PCDD/Fs）,has always been a sensitive issue of concern.In this study,three municipal solid waste incinerators（MSWI A,MSWI B and MSWI C,of which MSWI A and MSWI B each have two incinerators）with advanced incineration technology and complete flue gas treatment facilities were selected.the concentrations of PCDD/Fs in fly ash,stack gas,and ambient air and soil around the incinerators were sampled and measured,the characteristics of PCDD/Fs production and emission from different incinerators were compared and analyzed,the pollution characteristics of PCDD/Fs in the surrounding environment of different emission sources and their association with the incineration sources were studied,and the health risk of environmental exposure to PCDD/Fs of the surrounding population was assessed.The main research content and results of the paper are as follows:（1）The average concentration of PCDD/Fs in the fly ash of each incinerator ranged from 0.04-0.12 ng I-TEQ/g,with a small overall difference,but there were inconsistencies in the distribution characteristics of PCDD/Fs congeners and the formation mechanism of PCDD/Fs,mainly related to the characteristics of municipal solid waste components and the operation and management level of the incineration plant.The average concentration of PCDD/Fs in the stack gas ranged from 0.007-0.071ng I-TEQ/Nm3.In one of the incinerators,the“memory effect”of the bag filter resulted in abnormal emissions of PCDD/Fs in the stack gas,with significantly higher concentrations of PCDD/Fs and a different distribution characteristics of PCDD/Fs congeners than in the other incinerators.The distribution characteristics of PCDD/Fs congeners in stack gas and fly ash show some differences due to the different removal efficiency of each PCDD/Fs congener by the air pollution control system.The percentage of mass concentration of tetra-to hexachlorosubstituted PCDD/Fs congeners in stack gas is lower than in fly ash,while the percentage of OCDD and OCDF concentrations is higher.2,3,4,7,8-Pe CDF correlated best with the total toxic equivalent concentrations of PCDD/Fs in fly ash and stack gas and can be used as a potential indicator for the determination of PCDD/Fs.（2）The ambient air around each incinerator shows different pollution levels and distribution characteristics of PCDD/Fs due to the different emission levels of PCDD/Fs in the stack gas and the degree of influence of the incineration source in the study area.PCDD/Fs concentrations in the ambient air around MSWI B and MSWI C were 0.022-1.354 pg I-TEQ/m3,0.031-0.051 pg I-TEQ/m3,0.018-0.035 pg I-TEQ/m3,respectively.These incinerators are all contaminated to varying degrees with PCDD/Fs from the incineration source,and the concentrations of PCDD/Fs in the downwind direction of the prevailing wind direction were generally higher than those in the upwind direction.The mass concentrations of PCDD/Fs were overall dominated by perchlorinated PCDD/Fs,with 2,3,4,7,8-Pe CDF and 2,3,7,8-TCDD being the main TEQ concentration contributors.The distribution characteristics of PCDD/Fs congeners also vary somewhat from incineration plant to incineration plant and from point to point in the same incinerator.Seasonal monitoring of PCDD/Fs in ambient air around MSWI A revealed that the monitored values were higher in winter and autumn than in spring and summer,mainly associated with PCDD/Fs emissions from stack gas,wet deposition due to precipitation,photodegradation of gas-phase PCDD/Fs,and seasonal changes in mixed layer height.（3）The PCDD/Fs concentrations and the distribution characteristics of PCDD/Fs congeners in the soils around these incinerators do not differ significantly overall.The PCDD/Fs concentrations in the soils around MSWI A,MSWI B and MSWI C ranging from 0.32-1.23 ng I-TEQ/kg,1.04-1.69 ng I-TEQ/kg and 1.00-1.64 ng I-TEQ/kg respectively,all at very low levels.The dominant component of the mass concentration of PCDD/Fs in the soil was OCDD,with 2,3,4,7,8-Pe CDF and 2,3,7,8-TCDD being the main TEQ concentration contributors.The PCDD/Fs in the soil samples were mainly derived from emissions from MSWIs.After one year of operation of MSWI A there was a significant increase in the concentration of PCDD/Fs in the soil（2.35-3.84 ng I-TEQ/kg）and the PCDD/Fs congeners tended to be similar to the distribution characteristics of the PCDD/Fs congeners in the stack gas,indicating a significant influence by the PCDD/Fs emissions from the stack gas of the incinerator.（4）Exposure to PCDD/Fs via the inhalation,soil/dust ingestion and soil/dust dermal exposure routes for the populations（adults and children）in the study areas around the three incinerators is at the low end of the current research.The non-carcinogenic risk index for the populations in each study area is below 1 and no significant non-carcinogenic effects occur.The carcinogenic risk for the population in the study area around MSWI B and MSWI C is at an acceptable level,while the carcinogenic risk for the population around MSWI A reaches 10-5 and requires further attention. |
PDF Full Text Request