The concentration of suspended solids of effluent from secondary clarifiers often varies in a wide range, therefore the dose of ultraviolet light (UV) disinfection process need to be adjusted to meet the disinfection criterion at high frequency, and the desired disinfection effect is difficult to be ensured. The particles size and particle-associated Fecal Coliform (F.C.) contribution, and their influence on UV disinfection effects were investigated, and chlorination/UV combined disinfection process (chlorination/UV disinfection process) was used. The results showed that suspended solids content has a major impact on UV disinfection efficiency, especially the large particle size fraction. D>10µm particles associated F.C. is difficult to be disinfected and is the main part of the tailings of F.C. inactivation curve. Pre-chlorination could reduce the number of particles in effluent, and make large particles decrease to small ones. Therefore, the influence of particles on UV disinfection could be reduced after pre-chlorination, and the resistance ability to particle loadings of combined process was enhanced. Furthermore, the combined process has the advantage of low toxicity, low operational/maintenance costs, and is easy to be established not only in wastewater plants constructed already but ones to be about to be constructed.

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