Efficacy And Photoreactivation Control Of Inactivating Pathogenic Aspergillus Species In Water Supply System Based On UV Advanced Disinfection Process

Fungi have certain pathogenicity,sensitization and toxicity,and have a negative impact on human health and the environment in drinking water.The Aspergillus of different concentrations were detected in the water supply system,so it has become a research hotspot.At present,there are many disinfection methods for controlling fungal pollution in water.Among them,Ultraviolet（UV）and Ultraviolet chlorine system（UV/Cl₂）have been extensively studied,while the research on Ultraviolet/monochloramine system（UV/NH₂Cl）is relatively small.As a new emerging advanced oxidation process（AOPs）,UV/NH₂Cl can generate active free radicals,thereby achieving the degradation of organic pollutants and the disinfection of some pathogenic bacteria.However,there is no research on fungal pollution control.In addition,the damage of the fungi caused by UV can be repaired in the form of photoreactivation.In this paper,three common Aspergillus species（Aspergillus niger,Aspergillus flavus,Aspergillus fumigatus）were taken as the research objects in drinking water,and the inactivation efficiency and mechanism were studied through the combination of UV/NH₂Cl combination and sequential inactivation.And studied the effect of controlling the photoreactivation of Aspergillus species.In addition,a corresponding comparison was made with the UV and UV/Cl₂ systems to evaluate the applicability of the UV/NH₂Cl system.The conclusions as follows:（1）When the UV dose was 160 m J/cm²,UV alone（254 nm）could inactivate three Aspergillus species above 3.50-log₁₀.The UV resistance of Aspergillus species was:Aspergillus flavus>Aspergillus niger>Aspergillus fumigatus.UV/NH₂Cl（3.0 mg/L）was more effective than UV alone（254 nm）to inactivate three Aspergillus species,and the value of inactivation can reach more than 5.10-log₁₀.The inactivation value of UV/Cl₂（3.0 mg/L）for the three Aspergillus species could reach more than 3.50-log10,which was lower than the inactivation result of UV/NH₂Cl（3.0 mg/L）.The two combined inactivation methods have no synergistic effect on the inactivation of the three Aspergillus species.NH₂Cl-UV owned the best inactivation effect among the three sequential inactivation methods（UV-NH₂Cl,NH₂Cl-UV,UV/NH₂Cl-UV）,and the inactivation value could reach more than 4.20-log₁₀,which was higher than the result of the sequential inactivation method（UV-Cl₂,Cl₂-UV,UV/Cl₂-UV）.The inactivation process of the three Aspergillus species conformed to the first-order kinetic Chick-watson model.The reason for the differences in the inactivation of the three Aspergillus species was mainly due to the differences in size,pigment,and hydrophobicity of the spores.（2）The three Aspergillus species after 2-log₁₀ inactivation by UV（254 nm）alone showed different degrees of photoreactivation after UVA（365 nm）irradiation for 480 min,and the photoreactivation trend was consistent.The maximum survival rate was:Aspergillus niger>Aspergillus flavus>Aspergillus fumigatus,the difference in the number and activity of photolyase was the main reason for the difference in the photoreactivation rate of the three Aspergillus species.UV/NH₂Cl and UV/Cl₂ could control the photoreactivation of the three Aspergillus species more effectively than UV alone（254 nm）,and could reduce the photoreactivation rate to less than 1%and less than 2%,respectively.The NH₂Cl and Cl₂ could be added to different degrees to decrease the maximum survival rate S_m after photoreactivation and the photoreactivation rate constant k₁.After Aspergillus niger and Aspergillus fumigatus have undergone 480 min of photoreactivation,the control efficiency of UV/NH₂Cl（2.0 mg/L）was 81.50%and 81.62%,respectively,which was higher than the result of UV/Cl₂（2.0 mg/L）that it was 47.20%and 81.38%.UV/Cl₂（2.0 mg/L）has a photoreactivation control efficiency of 40.42%for Aspergillus flavus,which was higher than the result of 27.39%of UV/NH₂Cl（2.0 mg/L）.（3）UV alone（254 nm）would cause the number of damaged spores of Aspergillus fumigatus to increase by 75.80%,the high intracellular ROS level increases by 24.25%,and the number of damaged spores of Aspergillus niger and Aspergillus flavus increases less.The high intracellular ROS levels of Aspergillus flavus increased by 41.90%.Compared with UV alone（254 nm）,UV/NH₂Cl（2.0 mg/L）and UV/Cl₂（2.0 mg/L）could significantly increase the number of membrane-damaged spores and high intracellular ROS levels of the three Aspergillus species.After UV（254 nm）alone inactivation,the SEM image of Aspergillus fumigatus showed obvious depressions and wrinkles.After UV/NH₂Cl（2.0 mg/L）and UV/Cl₂（2.0 mg/L）were inactivated,Aspergillus species showed deformation and damage.And Aspergillus fumigatus was the most severely damaged.The inactivation resistance was different,and the damage was different.The cost of UV/NH₂Cl and UV/Cl₂ inactivation of the three Aspergillus species was related to the inactivation value.