Effects of combined UV and chlorine disinfection on corrosion and water quality within reclaimed water distribution systems

The effects of combined ultraviolet (UV) and chlorine disinfection on corrosion and water quality were assessed in a model reclaimed water distribution system (RWDS) using annular reactors (ARs). UV irradiation not only enhanced the inactivation of heterotrophic bacteria, but also reduced the required initial chlorine dose. Moreover, UV pretreatment induced less changes of corrosion products composition and decreased iron release and turbidity of effluents resulted from Larson-Skold Index (Li) of reclaimed water changing, enhancing the stability of water quality through RWDS. The corrosion bacteria within the biofilm on the corrosion scales could grow selectively with different disinfection processes. In the AR with combined UV and chlorine treatment, the iron-oxidizing bacterium (LOB) Acidovorax defluvii and the iron-reducing bacteria (IRB) uncultured Rhodoferax sp. and uncultured Geobacter sp. appeared on the biofilm. In contrast, in the AR treated with chlorine alone, the LOB Sediminibacterium salmoneum and the IRB uncultured Geobacter sp. were predominant in the biofilm. In the latter, S. salmoneum respiration predominantly contributed to the oxidization of Fe(II), whereas in the former, either Fe(II) or acetate acted as a donor for A. defluvii respiration, causing an increased depletion of oxygen by the oxidation of Fe(II). Therefore, under the former conditions, the composition of corrosion bacteria could result in lower corrosion rate, decreasing the effect of Li changes on iron release. All results indicated that UV irradiation enhanced water quality stability in the RWDS. (C) 2014 Elsevier Ltd. All rights reserved.