OCR Text |
Show pyrolysis temperature was increased from 900 to 1200 °C, The mutagenicity of PUF extracts is weaker than the mutagenicity of particules extracts. Moreover, the mutagenicity is much higher in presence of rat liver microsomal fraction (S9 mixture) than the observed in its absence . INTRODUCTION During the incineration process of organic compound [1], the aIr emlSSlons might possess certain highly toxic compounds such as dioxins, polycyclic aromatic hydrocarbons (PARs). The PARs, which are thought to be the prescursors of soot and have been also known to be mutagenic or carcinogenic after being metabolized, commonly produced from the incomplete combusion process [2-4]. The propensity to form PARs and soot is strictly dependent upon the incineration temperature, residence time and supply of oxygen in the incineration process of plastic. Most plastic materials decompose thermally at the temperature range of 200 to 400°C. In principle, the decomposed and fragmented molecules mix with oxygen to produce C02 and R20 in the complete combustion reaction . From a thermodynamic point of view ,PAHs and soot formation should begin at a C/O ratio of unity, corresponding to the condition m=2y 2y CO + n/2 R2 0 + (m-2y) Cs Thus even v.ell mixed incineration systems are observed to form PAHs and soot when the c/o ratio is greater than 0.5. That also indicates that some of the oxygen is tied up in the relatively sta ble com bustion products C02 and H2 and is thus unavailable for reaction with Cs on the time scale of incineration systems [5,6]. PAHs and soot to be decreased by oxidation occurs predominantly VIa molecular oxygen attack on aromatic radicals when the oxidants. such as 02 and OH are supplied in the incineration process. Also, due to similar reactions of 02 with C4H3 and C4H3 radicals (and of OH with C2H3, etc), the concentrations of these precusors of PAHs formation are decreased, 2 |