Network Model Analysis of Residual Chlorine to Reduce Disinfection Byproducts in Water Supply Systems in Yangon City, Myanmar

Nwe Nwe Zin,Shinobu Kazama,Satoshi Takizawa

doi:10.3390/w13202921

Abstract

In Yangon City, chlorination commenced in January 2020 to supply drinkable water; therefore, there is as yet no information on chlorine decay and DBP formation in the water supply system. This study aimed to find methods to optimize chlorine dosage in Yangon City. Onsite sampling and laboratory analyses of residual chlorine and trihalomethane (THM) formation, as well as water quality simulations, were conducted to find the chlorine decay and THM formation kinetics. Due to a high chlorine dose of 2 mg/L for both pre- and post-chlorination, disinfection was effective despite the low removal efficiency of turbidity. However, THMs were found in high levels in both treated and tap water due to the high THM formation potential of raw water. The re-contamination and/or transformation of dissolved organic matter were found in the distribution network by increases in specific ultraviolet absorption (SUVA) values and excitation-emission matrix (EEM) fluorophores, which brought about variations of THMs in the networks. The EPANET models were run assuming there to be no water leakages; it was found that the chlorine dose could be decreased to 0.8 mg/L to meet the guidelines for THMs and residual chlorine. The methods employed in this study could be also applied in other water supply systems in tropical developing countries with limited water quality monitoring data.

Highlights

Chlorine is the most widely used disinfectant in municipal water treatment plants because of its economy and efficiency [1,2,3]
Chlorine is degraded by reactions with natural organic matter (NOM) in the water treatment processes and in water distribution networks, which may lead to the depletion of residual chlorine and the re-contamination of supplied water by infectious microbes
Aluminum concentration we found that changing the coagulant did not significantly influence other water quality In addition, the increased turbidity observed in the whenand was used as parameters, including

Summary

Introduction

Chlorine is the most widely used disinfectant in municipal water treatment plants because of its economy and efficiency [1,2,3]. Previous studies have reported that chlorine is an effective disinfectant for many kinds of pathogens, while residual chlorine prevents microbial recontamination in water supply systems [4,5]. Chlorine reacts with natural organic matter (NOM) in water and produces disinfection byproducts (DBPs), which pose risks to human health during long-term exposure [6,7]. Chlorine is degraded by reactions with NOM in the water treatment processes and in water distribution networks, which may lead to the depletion of residual chlorine and the re-contamination of supplied water by infectious microbes. Many developed countries regulate disinfection byproducts and residual chlorine in tap water; for example, the maximum permissible level of trihalomethanes (THMs) in drinking water is 0.1 mg/L and that of residual chlorine is 1 mg/L in the Japanese Drinking Water Quality

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Conclusion