Study On Microwave Irradiation Technology For Bioaerosol Control

Air is the fundament for human beings and living things.Since air contains a lot of biological substances,sterilization poses great significance to protect human health.Microwave technology is a rapidly developing sterilization technology which demonstrated an excellent inactivation performance on bioaerosols.In this research,we establish a microwave irradiation device and apply it to investigate the inactivation characteristics of various types of bioaerosols.Furthermore,three kinds of novel absorbing materials are fabricated and characteristiced.We analyze their chemical composition,morphology,as well as their microwave absorbing properties and microwave absorbing mechanism.Then these new microwave absorbing materials are used to evaluate their inactivation performance of various types of bioaerosols using microwave irradiation.The removal performance of direct microwave irradiation without microwave absorbing materials is firstly studied.The results show that the removal performance of various bioaerosols improve with the increase of microwave input power and irradiation time.The microwave technology presents high removal efficiencies on airborne E.coli and A.variabilis,which can reach up to 4.15-lg and 2.94-lg,respectively,under the conditions of 20 s irradiattion time and 700 W input power.Meanwhile,about 15.2%of airborne endotoxin,which is a kind of common toxic cellular metabolism products,are degraded during microwave irradiation process.However,the inactivation performance of B.subtilis and its spore bioaerosol using microwave irradiation are low,and the maximum removal efficiencies are 1.51-lg and0.71-lg,respectively.Based on Beer-Lambert law,a theoretical bioaerosol inactivation kinetic model using microwave irraidation technology is developed and found to fit well with the experimental data,which verifies the authenticity of the model.Three new kinds of microwave absorbing materials including Fe₃O₄ ceramsite,SiC foam ceramics and Fe₃O₄/SiC foam ceramics are fabricated.Fe₃O₄ ceramsite generates dielectric loss and magnetic loss in the magnetic field for microwaves absorption.The reflection loss（RL）values are samll at low frequencies ranges of microwave.When the thickness is 5 mm,the minimum RL value is-3.55 dB at 5.5GHz.Different from the Fe₃O₄ ceramsite,SiC foam ceramics only generates dielectric loss and has low RL values at medium and high frequencies ranges of microwave.After loading of Fe₃O₄,the dielectric loss of Fe₃O₄/SiC foam ceramics improve under low frequency ranges of microwave and the magnetic loss is obviously generated at low frequency ranges,but not noticeable at high frequency ranges.The corresponding minimum RL value is-5.56 dB at 7.6 GHz when the thickness is 4.5 mm.By comparing the three kinds of microwave absorbing materials,the removal performance of bioaerosol inactivation under three materials are satisfied as follows:Fe₃O₄/SiC foam ceramics>Fe₃O₄ ceramsite>SiC foam ceramics.Futhermore,the removal performance of airborne endotoxin are investigated and found the degradation efficiency can achieve as high as 40%.The EE/O（energy required to reduce the concentration of bioaerosol by one order of magnitude）are calculated and show that the Fe₃O₄/SiC foam ceramics material can reduce the energy comsumption by 31.6%-45.1%compared with the energy consumption under the conditions without microwave absorbing materials.