Decay process of free residual chlorine concentration affected by travel time in water distribution systems

Abstract Chlorination is the most widely used method for disinfecting water for human consumption. While the chlorinated water travels through a distribution system, the concentration of free residual chlorine (FRC) declines depending on the natural water characteristics. This study investigated FRC decay in two types of water sources - ground and surface water - with varied concentrations of organic compounds. The travel time variable depended on water consumption patterns of both distribution systems which attend low density populations and their initial project needs. Based on mathematical simulation techniques of water quality models, the study also investigated the effects of water temperature and total organic carbon (TOC) on the kinetic constants (kb) of chlorine decay. Results show that travel time in the most critical locations in the water networks and the minimum disinfectant concentrations required at the entry points were 40 hours and 0.27-0.28 mg L-1 at Vale dos Pássaros housing complex, and 144 hours and 0.30-0.36 mg L-1 at Terras Alphaville housing complex.

摘要：氯化消毒是当前人类饮用水消毒最广泛应用的技术手段。当经氯化处理的水在输配管网中输送时，游离余氯（free residual chlorine, FRC）的浓度会随水体的自然属性发生衰减。本研究针对两类水源——地下水与地表水——开展了不同有机化合物浓度条件下的FRC衰减规律研究。输水停留时间这一变量，取决于两座服务低密度人口的输配管网的用水模式与初始工程设计需求。本研究依托水质模型的数学模拟技术，同时探究了水温与总有机碳（Total Organic Carbon, TOC）对氯衰减动力学常数（kb）的影响。研究结果表明，在Vale dos Pássaros住宅小区的供水网络中，最关键点位的输水停留时间与管网入口处所需的最低消毒剂浓度分别为40小时与0.27~0.28 mg/L；而在Terras Alphaville住宅小区，上述两项参数分别为144小时与0.30~0.36 mg/L。