| Disinfection is one of the important links in water treatment.Although the traditional chemical disinfecting process can achieve efficient disinfection,this process also has some problems,such as producing disinfection by-products,affecting the sensory properties.At the same time,it is difficult to solve the pollution of chlorine-resistant microorganisms.Ultraviolet disinfection is one of the most efficient disinfecting processes that can solve this problem.It can be utilized alone or as a secondary treatment of traditional chemical disinfection.At present,the most widely used ultraviolet generator is mercury lamps,which have some problems such as short life,serious pollution,and recovery difficulties.The ultraviolet light-emitting diode(UV-LED)is a new type of UV generator developed in recent years with semiconductor materials,which makes up for the defects of the mercury lamps.Due to the adjustable wavelength,UV disinfection technology,based on coupling of different UV-LED wavelengths,can obviously improve the effect of UV disinfection,and is expected to replace mercury lamps as the core of the UV disinfecting process.In this paper,UVA,UVB and UVC--three different wavelengths of UV-LED were ready to carry out disinfection experiments in different water conditions.The disinfecting ability of different wavelength combinations and the influence of different water conditions during the disinfecting process were compared.UV-LED with different single wavelength,coupling wavelengths and the combination of wavelengths were used to carry out disinfecting experiments in pure water,FA solution and secondary effluent of WWTPs.The results showed that:(1)275 nm and 365 nm/275 nm have the highest disinfecting effect in single wavelength and coupling wavelength respectively,and the combination 365 nm/310 nm/275 nm acts better.(2)In the reactor considering mixing condition,when the reaction was carried out for a certain time,there was a linear relationship between the disinfection logarithm and time.Based on a mixing model,it is considered that the disinfecting effect in the reactor is affected by both the bacterial concentration and gradient.(3)Water conditions have different effects on the UV-LED disinfecting process,FA solution reduces the treatment effect,and the influence of secondary effluent on various wavelength combinations is different;(4)p H has no obvious rule on the disinfecting process,and neutral is the best p H condition.(5)Under the conditions of the present experiment,no obvious bacterial reactivation phenomenon was observed.In an ideal reactor,the corresponding active substances are knocked out by quenching experiment,and the UV wavelength combinations that can stimulate dissolved organic matter in water to generate active substances are discussed.The results show that:(1)Hydroxyl radical,singlet oxygen and triplet substance can be produced by 365 nm and 310 nm ultraviolet in FA solution and secondary effluent,and the synergistic effect of 365 nm/310 nm wavelength coupling exists,but is not significant.(2)Singlet oxygen has the highest contribution to disinfection in FA solution and secondary effluent.(3)Singlet oxygen has the highest activity.Compared with direct effect,indirect effect provided by the substance is weak,but the indirect effect can shorten the reaction time to reach the same inactivation logarithm.According to the wavelength combinations and water conditions selected in the first two parts of experiments,and related to the technical and economic factors,a set of continuous running water-circulating reactors based on UV-LED wavelength coupling was elaborated.The treatment scale is 5000 ml per 40 min,and the bacterial concentration can be reduced by 3～4 orders of magnitude in the cycle.The technology,UV-LED wavelength coupling disinfection,is suitable in different water quality and has profoundly practical meaning.The analysis of the research results shows that UV-LED wavelength coupling technology is a UV disinfecting process with great development potential.By selecting the best coupling wavelengths,adjusting the water conditions and reasonably designing the reactor form,eco-friendly and efficient disinfection can be realized in water,which provides a new technical scheme for the upgrading of the UV disinfecting process. |
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