| Domestic sewage contains a lot of pathogens, and the secondary effluents alsoinclude plenty of plenty of pathogens which are harmful to the ecological environmentand human health. Recently, frequent outbreaks of pathogens pollution incidents makepeople concern more about sewage disinfection. Normal disinfection techniques includeultraviolet (UV) disinfection, chlorine disinfection, ozone disinfection, peracetic acid(PAA) disinfection and so on. Ultraviolet disinfection is welcome by the public for theadvantages in high disinfection efficiency, short contact time, no additional chemicals,no DBPs and no residual toxicity.In this article, the secondary effluents of MSBR process in A wastewater treatmentplant are main study objects. Influencing factors of UV disinfection, photoreactivationof fecal coliform, and combined disinfection of UV combined NaClO and UV combinedPAA were studied through lab-scale and full-scale experiments. NaClO is aconventional disinfection reagent in municpal wastewater plant, and PAA is widelystudied and have wide application in Europe but an emerging disinfection forwastewater in China.The experimental results suggest that UV disinfection efficiency has greatrelationship with water quality, and ultraviolet transmittance (UVT) is the main factor ofwater quality influencing UV disinfection. Turbidity, color and SS can decrease UVT,and then decrease UV disinfection efficiency. When turbidity is higher than10NTU,color is above30degree, or SS is more than22mg/L, the UV disinfection efficiencywill decrease greatly. The number of fecal coliform is related to particles which with10μm~40μm diameters. Regular maintain of UV disinfection system is necessary forensuring stable and high disinfection efficiency.Microorganism has the ability of reactivation after UV disinfection. Bothphotoreactivation and dark repair can occur with high degree at the experimentalconditions which can increase the risk of UV disinfection. Photoreactivation can becontrolled by improve UV dose and UV intensity. Increase light intensity forphotoreactivation can promote photoreactivation rate. Nutrient elements such as aceticacid, phosphate can improve photoreactivation, and seawater can increasephotoreactivation rate by10%. Different light sources have different photoreactivationrates at test conditions: fluorescence> low sunlight> indoor sunlight> strong sunlight.There are very high disinfection efficiency were observed in UV/PAA andUV/NaClO combined disinfection process, and both of them have synergistic effectwhen PAA or NaClO added before UV irradiation. The disadvantages of UV disinfection such as easily affected by water quality can be overcome by combineddisinfection process which still has high disinfection efficiency when turbidity and SS ishigh. UV/PAA and UV/NaClO combined disinfection process can also inhibitphotoreactivation of fecal coliform with very low combined doses.In general, UV combined with PAA or NaClO disinfection process can eliminatethe disadvantages of single UV disinfection, and the disinfection efficiency can bedouble guaranteed by combined disinfection. |
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