Environmental Risk Of Cement Kiln Co-processing For Disposal Of POPs Polluted Soils

Persistent organic pollutants (POPs), a class of significant environmental contaminants, can exist in environmental sinks for a long period, finally have a side effect on human health by entering the food chain. One of the important steps in POPs control is to develop an efficient cost and environment-friend strategy for the remediation of POPs contaminated sites. The technique of cement kiln co-processing is widely used for diposal of POPs polluted soils because of its high efficiency and low consumption of energy. However, environmental risk of POPs release in the application of this technology is unclear. The overall objectve of this study was:to develop an analytical method of DDT and HCH based on the passive air sampling (PAS) and to evaluate the potential risk of the technique of cement kiln co-processing during soil stack and operation processes. The results obtained in this work were addressed as follows:(1) Based on the available technologies of the air passive sampling, a new type of air passive sampler (PAS-H) was developed to monitor POPs (HCH and DDT) in the air.(2) An analytical method was developed based on polyurethane foam-air passive sampler (PAS-H)-soxhlet extraction (SE)-gas chromatography (GC-ECD), to study DDT and HCH in air. When the concentration of DDT and HCH in polyurethane foam samples were in10to100μg/kg range, the average recovery was81%to113%, relative standard deviation (RSD) was0.51%to3.3%. Another kind of accelerated solvent extraction (ASE)-gas chromatography mass spectro-metry (GC-MS) method has been established and used in the study of DDT and HCH residue in soil.(3) A greenhouse experiment was conducted to determine the diffusion of DDT and HCH in the air-soil system of a closed condition. Plistic film greenhouse to store soil contaminated with DDT and HCH, after the test of60days, DDT and HCH distribution was significantly different in different soil layers. Concentration in the layer of0-2cm was9.4±0.69mg/kg significantly lower than those in the layer of6-8cm (12.11±0.83mg/kg). The order of the concentrations of∑DTs in different soil layers were2-4cm>4-6cm>6-8cm>0-2cm, while the concentration (30.58±0.36mg/kg) of0-2cm layer was significantly lower than that(33.6±0.83mg/kg) in the2-4cm. In the air of plastic greenhouse, the concentrations of DDT and HCH attained peak values in20d.Its decreased and tend to balance after20d. The peak values of HCH and DDT were29.05±0.80μg/m3and78.90±13.2μg/m3. The oblivious variation of composition of HCH isomers and DDT degradation products was observed. p.p’-DDT was degradation of highly toxic p,p’-DDD and p,p’-DDE, and more active α-HCH was detected in the soil of greenhouse. The results imply that the promotion of air-soil exchange process was promoted and was an apparent trend of the activation of OCPs.(4) A field experiment was conducted to determine the diffusion of DDT and HCH in the air-soil system of an open condition. The characteristics of the concentrations of DDT and HCH in the air surrounding of storehouse and in the contaminated soil is generally agreed with Gaussian static wind model. Combination of experimental data and model results, it was quantitatively estimated that the range of atmospheric dispersion of DDT and HCH contaminations was22.6-83.1pg/m3in the20m areas around the storehouse.(5) the exhaust emission of pollutants were studied in the cement kiln co-processing for the disposal of POPs contaminated soils. Results showed that pollutants emission of HCl, SO2, NOx, dioxin and dust were1.90mg/m3,200mg/m3,545mg/m3,0.009I-TEQ/Nm3,20.57mg/m3, respectively, which were lower than the values in the industrial air emissions standards. Compared with the incineration process without POPs contaminated soil, tested targets in exhaust gas including acid gas, dioxin and dust were not significantly increased in cement kiln co-processing system of POPs contaminated soil. Cement quality was studied in the cement kiln disposal of POPs contaminated soil, and the chemical composition of cement clinker meets the relevant standards. Heavy metals in the cement clinker such as Hg, Cd, Sb were below the detection limit, and its basic quality could meet commercial standards.In this study, based on polyurethane foam-air passive sampler-soxhlet extraction-gas chromatography, an analytical method was developed to study DDT and HCH in air. Furthermore, the analytical method was applied to study DDT and HCH diffusion in cement kiln co-processing of soil stack in the closed and open conditions and of operation processes. The results obtained will provide not only a basis for the application of cement kiln co-processing technique, but also a theoretical basis for the establishment of the contaminated sites management and remediation technology and standards system.