Ahn J.C.,Waterworks Research Institute |
Lee S.W.,Waterworks Research Institute |
Choi K.Y.,Waterworks Research Institute |
Koo J.Y.,Korea University
Sustainable Environment Research | Year: 2012
The purpose of this study is to predict the level of chlorine residual and trihalomethanes (THMs) in a drinking water distribution system and to help operators to determine chlorine dose in a drinking water treatment plant (WTP) using EPANET 2.0. Water quality modelling was conducted by chlorine bulk decay and THM formation from bottle tests. Chlorine decay tests for the finished water of the WTP were performed on a monthly basis for one year. As the result, a simple equation for the target chlorine concentration in the finished water was derived by a multiple regression method in relation to initial chlorine concentrations, temperatures, total organic carbon and chlorine decay coefficients. The chlorine concentration after it leaves a WTP, before entering its distribution networks, is critical in maintaining chlorine residual levels throughout the system. It is apparent that the chlorine concen- tration of the finished water be maintained to be flexible to keep it at over 0.1 mg L-1 throughout the system because chlorine consumption is different according to the season, flow and pipe networks. These chlorine values of the finished water are the target chlorine concentrations for determining the chlorine dosage to the filtered water in a WTP. As the results of this study using a multiple regression model for chlorine decay and EPANET, the target chlorine concentrations of the finished water were set to 0.5 mg L-1 in spring and fall, 0.55 mg L-1 in summer and 0.45 mg L-1 in winter. These values are slightly lower than the existing target values. © 2012, Chinese Institute of Environmental Engineering. All rights reserved.
Choi Y.,Waterworks Research Institute |
Choi Y.-j.,Waterworks Research Institute
Water Research | Year: 2010
UV treatment is a cost-effective disinfection process for drinking water, but concerned to have negative effects on water quality in distribution system by changed DOM structure. In the study, the authors evaluated the effects of UV disinfection on the water quality in the distribution system by investigating structure of DOM, concentration of AOC, chlorine demand and DBP formation before and after UV disinfection process. Although UV treatment did not affect concentration of AOC and characteristics of DOM (e.g., DOC, UV254, SUVA254, the ratio of hydrophilic/hydrophobic fractions, and distribution of molecular weight) significantly, the increase of low molecular fraction was observed after UV treatment, in dry season. Chlorine demand and THMFP are also increased with chlorination of UV treated water. This implies that UV irradiation can cleave DOM, but molecular weights of broken DOM are not low enough to be used directly by microorganisms in distribution system. Nonetheless, modification of DOM structure can affect water quality of distribution system as it can increase chlorine demands and DBPs formation by post-chlorination. © 2009 Elsevier Ltd. All rights reserved.
PubMed | Waterworks Research Institute
Type: Journal Article | Journal: Journal of microbiology (Seoul, Korea) | Year: 2012
The impact of orthophosphate addition on biofilm formation and water quality was studied in corrosion-resistant stainless steel (STS) pipe and corrosion-susceptible ductile cast iron (DCI) pipe using cultivation and culture-independent approaches. Sample coupons of DCI pipe and STS pipe were installed in annular reactors, which were operated for 9 months under hydraulic conditions similar to a domestic plumbing system. Addition of 5 mg/L of phosphate to the plumbing systems, under low residual chlorine conditions, promoted a more significant growth of biofilm and led to a greater rate reduction of disinfection by-products in DCI pipe than in STS pipe. While the level of THMs (trihalomethanes) increased under conditions of low biofilm concentration, the levels of HAAs (halo acetic acids) and CH (chloral hydrate) decreased in all cases in proportion to the amount of biofilm. It was also observed that chloroform, the main species of THM, was not readily decomposed biologically and decomposition was not proportional to the biofilm concentration; however, it was easily biodegraded after the addition of phosphate. Analysis of the 16S rDNA sequences of 102 biofilm isolates revealed that Proteobacteria (50%) was the most frequently detected phylum, followed by Firmicutes (10%) and Actinobacteria (2%), with 37% of the bacteria unclassified. Bradyrhizobium was the dominant genus on corroded DCI pipe, while Sphingomonas was predominant on non-corroded STS pipe. Methylobacterium and Afipia were detected only in the reactor without added phosphate. PCR-DGGE analysis showed that the diversity of species in biofilm tended to increase when phosphate was added regardless of the pipe material, indicating that phosphate addition upset the biological stability in the plumbing systems.