Study On Photoreactivation Of Ultraviolet Disinfection And Its Suppression Techniques

One of the most important factors limiting the popularization of ultraviolet disinfection in water treatment is that it has no continuous disinfection ability and the microorganism in water is prone to secondary photoreactivation.Therefore,how to control the photoreactivation of ultraviolet disinfection effectively is the first problem that needs to be solved at present.Taking Escherichia coli and Bacillus subtilis in drinking water as the research object,DR ultraviolet sterilizer was used to study different ultraviolet doses.Effects of light intensity and treatment time on the photoreactivation of Escherichia coli and Bacillus subtilis.At the same time,the inhibitory effect of ultraviolet with sodium hypochlorite and peracetic acid on photoreactivation under different conditions was also investigated.The results showed that the light resurrection of Escherichia coli after ultraviolet disinfection would occur under visible light irradiation,and the increase of ultraviolet dose would help to control the degree of light resurrection of Escherichia coli.When the ultraviolet dose was 33.15 mJ/cm2,the initial inactivation rate of Escherichia coli in water could reach 100%,but the maximum recovery rate was 73.6%logarithm ratio after illumination.When the ultraviolet dose was higher than 85.75 mJ/cm2,the recovery rate of Escherichia coli reached a certain threshold after irradiation,accounting for about 25%logarithm ratio of the original inactivated quantity.When the ultraviolet radiation time is fixed,the higher the ultraviolet intensity,the lower the light resurrection rate of Escherichia coli;The longer the ultraviolet radiation time is,the lower the reactivation rate of Escherichia coli is.Because Bacillus subtilis has no photoreactivation enzyme,so Bacillus subtilis under different ultraviolet radiation dose does not produce photoreactivation phenomenon.To a certain extent,increasing the light intensity of resurrection can control the degree of light reactivation of Escherichia coli.After disinfection with low ultraviolet dose,the light resurrection of Escherichia coli was not affected by the light intensity.After high ultraviolet radiation dose disinfection,the light resurrection phenomenon of Escherichia coli was not obvious at lower resurrection light intensity.When the light intensity was higher,the light resurrection rate of Escherichia coli increased with the increase of the resurrection light time,and was proportional to the resurrection light intensity,72 hours after light exposure.Recovery of Escherichia coli at 61.02 ?W/cm2 resurrection Light intensity compared with 40.58 ? W/cm2 resurrection Light intensity.The survival rate was reduced by 0.31 logarithmic levels.The delayed exposure time of Escherichia coli to resurrection light after ultraviolet disinfection could delay and weaken the degree of light resurrection,but it could not completely control the occurrence of light resurrection.After disinfection with ultraviolet radiation,the light resurrection of Escherichia coli was delayed for a short time,but the rate of light resurrection was not affected at all.Prolonging the time of avoiding light to 24 hours,reaching the maximum time of light resurrection,the rate of light resurrection of Escherichia coli decreased slightly,and 48 hours after exposure to light,it was 1.23 logarithmic order less than that of the water without light protection.The combination of chemical disinfectants sodium hypochlorite and peracetic acid can effectively control photoreactivation to some extent.In the experiment,adding 10 mg/L of available chlorine can effectively control the phenomenon of light resurrection,and reduce the ultraviolet radiation dose by 34.48 mJ/cm2.In the experiment,PAA with 40 mg/L can achieve the effect of basically controlling the degree of light resurrection,and the ultraviolet radiation dose is reduced by 43.59 mJ/cm2.