Volatile Chlorinated Hydrocarbons Contaminated Soil And Groundwater Rapid Detection Technology

As a good organic synthesis intermediates and chemical solvents, a large number of Volatile chlorinated hydrocarbons (VCHs) are widely used in the chemical, textile, pharmaceutical, paint, electroplating and other major industries. VCHs is highly volatile and have toxic effects of teratogenic, carcinogenic and mutagenic, if used improperly, storage leak or waste disposal management incorrect,VCHs will enter the environment at that time, causing a large area of deep soil pollution, and ultimately lead to a large area of groundwater contamination not entirely consistent with surface contamination. In recent years, surveys showed that the different levels of VCHs were detected in the soil and groundwater of Beijing, Tianjin, the Yangtze River Delta, the Pearl River Delta, Northeast Industrial Area and other regions, partially of them exceeded the standard. In recent years, urban expansion, contaminated sites of after the removal is required on-site evaluation of environmental pollution before the re-development, sudden environmental pollution incidents require fast and economical means to obtain first hand information on pollution in order to select the solution, VCHs's nature of volatile also decide the importance and necessity of on-site rapid testing.On the basis of expatiated the principle of a detector tube, summarized the national and international development of detector tubes for VCHs, and gave an outlook on the future application prospects of detector tubes for on-site rapid diagnosis of soil and groundwater pollution by VCHs. Survey results show that the high price of imported detector tubes significantly depress the economization of technology,in the absence of domestic detector tubes for VCHs greatly limited the technology promotion and application in China. The electronic nose system ,which the core technology is the sensor array and the pattern reorganization, is simpleness and can be realized quickly in real time and in situ monitoring.Our group Independently developed electronic nose system which sensor array combined by a PID and 3 TGS series sensors, the test circuit designed by the same group researcher,combined with the PC form an electronic nose hardware system. On the basis of a gas sensor characterization and measurement system,generation gaseous by the standard gas generating device,,is designed and constructed,testing the response of electronic nose for TCE, PCE, chloroform, carbon tetrachloride, 1,1- dichloroethane and dichloromethane. The response signal of VCHs after signal preprocessing are analyze by pattern reorganization and the linear analysis of signal strength. The pattern reorganization used in this paper includes the principal component analysis (PCA) and back propagation artificial neural network (BP-ANN).PCA showed that the sensor array in this electronic nose have a good clustering results for different VCHs in different concentrations,but but such laws only can vague expressed clustering qualitative, not quantitative and qualitative accuracy. In the BP-ANN, through different network training and forecasting, achieve the desired objectives and post a good prediction effect in a number of iterations, to distinguish a variety of VCHs gases concentration with higher precision, but this is limited to distinguish the response of the pure substance and not effect on the mixture of VCHs gases for the purposes of accurately identify the specific components and concentration. From the linear analysis of signal strength found that the response of sensor and VCHs's concentration is a linear relarionship,and the response of the mixture gases is equal to the sum of the single substances. Therefore, on this basis, establish an method reasoning mixture of VCHs and used to monitoring the VCHs concentration trends during the process of simulate soil purification. Considering VCHs often co-exist with BTEX like toluene, ethylbenzene, benzene etc in the organic polluted soil,and each sensor have a response for BTEX, which were responsed to PID and TGS2602 more strongly,so, select halocarbon RAE-SEP tubes produced by RAE systems company as pretreatment to reduce the interference of BTEX.The five separation effects reviewes of halocarbon RAE-SEP tubes,the results show that more than 90% of BTEX can be effectively absorption without impact on VCHs by halocarbon RAE-SEP tubes.