Inhibition Of PCDD/Fs Formation During Medical Waste Incineration And Research Of Environmental Impact Of Incinerator

Medical waste incinerator (MWI) would emit higher concentration of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) than municipal solid waste incinerator (MSWI), so it needs more work to limit dioxins emission from MWI, and correctly estimate the exact environmental impact of MWI. According these objectives, a lot of research work were conducyted during my PhD. study, and got several valuable conclusions as following:1) According this survey, only9.52%of MWI can meet EU standard of dioxin emission in flue gas (0.1ng I-TEQ/Nm3), and accounting for42.86%under0.5ng I-TEQ/Nm3set by Chinese Ministry of Environmental Protection, however, still47.62%samples above the emission standard. By calculation, the emission factor of dioxins in big scale medical waste incinerator is248.7μg I-TEQ/t. In addition, chlorobenzene (CBz) is the great indicator of PCDD/Fs in the flue gas collected in the front of bag house, the correlation coefficient (R2) between CBz and dioxins/TEQ is bigger than0.8.2) The key factors influencing dioxins formation, including temperature, moisture, metal catalyst, chlorine source and oxygen concentration, have similar effect on CBz formation. For instance, the optimum temperature window for CBz is in the range of350-400℃; little moisture can improve CBz formation, and decrease chlorination degree. This consistent effect of parameters on CBz and dioxins formation might be the main reason or mechanism of the great correlation between CBz and PCDD/Fs.3) The inhibition of N-containing compounds on CBz formation is observed during different condition and processes. For example,5%additive of (NH4)2SO4suppressed99.1%CBz formation from model fly ash (MA). CBz is pollutant in environment too, and CBz concentration in water and soil is limited by State Standard, especially pentachlorobenzene and hexachlorobenzene are also in the list of persistent organic pollutants. Hence, the emission of CBz from incinerator must be controlled.4) The evolved gas from sewage sludge is firstly used to control CBz and dioxins formation in flue gas, and series simulation experiments were carried out to clarify the effect of co-combustion of sludge and MW on dioxin emission. Many different detecting methods were performed to understand the inhibition mechanism, in summary according to experimental results.(NH4)2SO4reacts with metal catalyst and converts active catalyst to metal sulfate without catalysis, urea can effectively affect the Deacon reaction and reduce Cl2yield. Ammonia, urea and (NH4)2SO4have the significant inhibition in dioxins formation. In the present study,98.5%(98.0%) of PCDD/Fs (TEQ) was less detected after 5%(NH4)2SO4into MA.5) A long-term monitoring of dioxins level in the soils around a specific MWI was conducted, and the soil samples in the first survey were collected before the start-up operation of the MWI. The results demonstrate the dioxins concentration slightly increased, for instance, the average level of PCDD/Fs (TEQ) in2007year is205.11pg/g (1.09pg I-TEQ/g), while308.77pg/g (4.14pg I-TEQ/g) in2011, respectively. The PCDD/Fs variation values between before operation and after operation decreases with the increasing distance away from MWI, and looks an exponential relation. A safe area with500～600radius is proposed. The fingerprint of PCDD/Fs homologue patterns in soil became more similar with the character in MWI samples, which implies the impact of MWI in this region. The results of PCDD/Fs concentration in air also shows the bad situation of MWI operation and management, definitely suggests the staff take health protection in this factory.