Reynaert Eva, Nagappa Deepthi, Sigrist Jürg A, Morgenroth Eberhard
Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dübendorf, Switzerland.
ETH Zürich, Institute of Environmental Engineering, Zürich 8093, Switzerland.
Water Res X. 2024 Feb 22;22:100215. doi: 10.1016/j.wroa.2024.100215. eCollection 2024 Jan 1.
A growing number of cities and regions are promoting or mandating on-site treatment and reuse of wastewater, which has resulted in the implementation of several thousand on-site water reuse systems on a global scale. However, there is only limited information on the (microbial) water quality from implemented systems. The focus of this study was on two best-in-class on-site water reuse systems in Bengaluru, India, which typically met the local water quality requirements during monthly compliance testing. This study aimed to (i) assess the microbial quality of the reclaimed water at a high temporal resolution (daily or every 15 min), and (ii) explore whether measurements from commercially available sensors can be used to improve the operation of such systems. The monitoring campaign revealed high variations in microbial water quality, even in these best-in-class systems, rendering the water inadequate for the intended reuse applications (toilet flushing and landscape irrigation). These variations were attributed to two key factors: (1) the low frequency of chlorination, and (2) fluctuations of the chlorine demand of the water, in particular of ammonium concentrations. Such fluctuations are likely inherent to on-site systems, which rely on a low level of process control. The monitoring campaign showed that the microbial water quality was most closely related to oxidation-reduction potential (ORP) and free chlorine sensors. Due to its relatively low cost and low need for maintenance, the ORP emerges as a compelling candidate for automating the chlorination to effectively manage variations in chlorine demand and ensure safe water reuse. Overall, this study underscores the necessity of integrating treatment trains, operation, and monitoring for safe on-site water reuse.
越来越多的城市和地区正在推广或强制要求对废水进行现场处理和回用，这导致全球范围内实施了数千个现场水回用系统。然而，关于已实施系统的（微生物）水质信息有限。本研究的重点是印度班加罗尔的两个一流现场水回用系统，这两个系统在每月的合规测试中通常符合当地水质要求。本研究旨在（i）以高时间分辨率（每日或每15分钟）评估再生水的微生物质量，以及（ii）探索是否可以使用市售传感器的测量结果来改善此类系统的运行。监测活动揭示了微生物水质的高度变化，即使在这些一流系统中也是如此，这使得水不足以用于预期的回用应用（厕所冲洗和景观灌溉）。这些变化归因于两个关键因素：（1）氯化频率低，以及（2）水的氯需求波动，特别是铵浓度的波动。这种波动可能是现场系统固有的，因为现场系统依赖于低水平的过程控制。监测活动表明，微生物水质与氧化还原电位（ORP）和游离氯传感器最密切相关。由于其成本相对较低且维护需求较低，ORP成为自动氯化以有效管理氯需求变化并确保安全水回用的有力候选者。总体而言，本研究强调了整合处理流程、运行和监测以实现安全现场水回用的必要性。
