Experimental Study Of Sterilization By Corona Discharge Plasma

There is a need for new sterilization method, as the society constantly makes progress, especially in medical treatment, in pharmacy and in food industry. A number of problems such as that new equipment appear in medical treatment, people need high quality foodstuff, the prevalence of viruses in environment, all need new sterilization method. The traditional sterilization methods include physical sterilization, chemical sterilization and biological sterilization, etc. The physical sterilization tend to burn out goods, costing a long time, and having a narrow application range; Chemical sterilization can be used for a lot of goods and have a good sterilization result, but it has a lot of sterilization parameters and chemical substance will remain which is a threat to people's health. Biological sterilization can not be widely used because of environment limitation. There is a need for safe, simple, low-temperature, effective and non-toxic residue generating sterilization techniques.Plasma sterilization techniques are currently under active research and development, it could overcome limitation and deficiency of the traditional methods, enhance the result of sterilization. Plasma sterilization has the potential to offer low-temperature generating sterilization, will not burn out the goods, will not destroy nourishment and colour of food. Plasma sterilization has non-toxic residue and will be safe to people who operate it.In many methods of generating plasma, corona discharge plasma could begin at room temperature and at atmospheric pressure, and the temperature of corona discharge plasma is low. So in this research, we design and set up a suit of equipment of corona discharge plasma, and design a reactor in the line-web form. This thesis has research for the characteristics of corona discharge plasma first. Including theories of corona discharge, the condition of corona discharge begins, the process of corona discharge, and the mechanisms of corona discharge; The process of corona discharge has be observed, and the phenomena of positive corona discharge and negative corona discharge were found to be different; The speciality of corona discharge and the characteristics of the corona discharge plasma were researched later.We choose Escherichia coli 8099 and Bacillus subtilis spores ATCC9372 as experimental bacterias when researching for the results of sterilization by corona discharge plasma. The sterilization results of the positive corona discharge plasma and the negative corona discharge plasma were contrasted, and the sterilization results of the positive corona discharge plasma were better. But the negative corona discharge have a wider range of voltage in corona discharge, so we choose negative corona discharge for the research of the influence of discharge perameters on the results of sterilization. In negative corona discharge condition, sterilization rate rise as discharge voltage goes up. When polar distance is 2cm, discharge time is 4min, the sterilization rate of E.coli and B.subtilis spores are 93%and 78%respectively at 18.5kV, and the sterilization rate go up to 100% and 95.2% respectively when voltage at 23kV. In addition, plasma sterilization like the other sterilization methods will be influenced by sterilization time. The sterilization rate of E.coli and B.subtilis spores are 90.6% and 73% respectively when discharge for 2min and are 100% and 90% respectively when discharge for 6min at 18.5kV. In research for the influence of polar distance on the results of sterilization, we discovered that there is a better sterilization rate at a smaller polar distance at the same voltage. The influence of different bacteria on sterilization rate were also discussed.At present, the mechanism of sterilization by plasma has not become an acknowledged one. We discussed the mechanism of sterilization by SEM photos and comparison of the experimental results. And the summarization is as follows: electric field and high energy electron bombardment have an important function for sterilization; O₃ and the other oxidative gas destroy the cellular wall of bacteria, ribose and nucleic acid, then kill bacterias, so O₃ and the other oxidative gas play an important role in sterilization; the temperature of the reactor after discharge was still low, so the function of temperature could be neglected; the function of UV irradiation was not be researched because of condition limitation; the function of free radical and active ion were mentioned at last.