Study On The Migration Characteristics Of Chlorine Ion In The Hydrothermal Treatment Of Medical Waste

As the development of healthcare industry,the treatment and disposal of medical waste attracts increasingly attention.Incineration and landfilling is the most common and popular way for MW treatment.However,these two methods will possibly cause secondary pollution or occupy the limited land resource.Interestingly,the high plastic content,mainly polyvinyl chloride(PVC),in MW makes it has high calorific value.Therefore,converting MW into clean fuel can not only reduce the waste mass but also reduce the utilization of fossil fuel.Currently,few study has been conducted on production of fuel from MW.This study proposes to production solid fuel from MW through hydrothermal treatment.The processing characteristics,especially the immigration of chlorine,in hydrothermal treatment are investigated.The possibility of utilize solid product as fuel is discussed.Additionally,the effect of hydrothermal parameters and the reaction mechanism are studied.Firstly,the solid recovery rate under different hydrothermal treatment condition is discussed.The MW and PVC derived solid products were characterized by elemental analysis,Fourier transform infrared spectroscopy(FTIR),Thermogravimetric analysis(TGA),scanning electron microscopy(SEM),etc.The TOC and pH value of the liquid products were also measured.At the same time,the chloride concentration of the solid and liquid products was detected by the chloride ion selective electrode method and Nernst equation.The main results are shown as follows(1)With the increase of hydrothermal time and temperature,the solid recovery rate of MW and PVC is reduced correspondingly.Among them,the maximum reduction of the solid recovery rate in the hydrothermal temperature range from 240? to 260?,indicating that the degradation rate of PVC in this temperature range has significantly chalged.(2)The chlorine content of solid product derived from MW and PVC decreases with the increase of hydrothermal temperature,which indicates that the higher temperature is beneficial to the dechlorination of PVC Comprehensively considering the energy consumption of the process and the chlorine content in the solid,the 260? is an optimal for dechlorination.NaOH will facilitate the decomposition as well as dechlorination of MW and PVC.(3)The scanning electron microscope(SEM)analysis of the solid product showed that surface of the solid product appeared small pores,and the porosity was very large.The thermogravimetric analysis(TGA)showed that,after hydrothermal treatment,the peak of chlorine decomposition in PVC is eliminated.In addition,the releasing of heavy matters in the solid occur at lower temperature after hydrothermal treatment,indicating that hydrothermal treatment makes the molecular chain decreases.The treated products are more prone to be combusted(4)The Fourier transform infrared(FTIR)analysis of the solid products revealed that the C-Cl bond was broken.It is proved that the dechlorination of chlorine occur in the hydrothermal process.The chlorine immigration is mainly due to the dehydrochlorination of the PVC.