Kracht Oliver, Gresch Markus, Gujert Willi
Swiss Federal Institute of Aquatic Science and Technology, Eawag, 8600 Dübendorf, Switzerland.
Environ Sci Technol. 2007 Aug 15;41(16):5839-45. doi: 10.1021/es062960c.
Extraneous flows in wastewater collection systems are conventionally evaluated solely on the consideration of discharge hydrographs, which often involves a great degree of subjectivity and oversimplification. To obtain reliable information on the material fluxes within the urban environment, the use of intrinsic tracers can be the optimal choice. We demonstrate the successful use of naturally occurring stable isotopes of water (18O/16O and D/H) to accurately quantify extraneous discharge of groundwater in a combined sewer network. Fresh water supply from a distant hydrological regime provided usable isotopic separations between drinking water (proxy for real foul sewage) and local groundwater (proxy for sewer infiltration) of 1.8 per thousand in delta18O and 11.7 per thousand in 62H. Diurnal variation of wastewater isotopic composition reflected both the varying rates of foul sewage production and irregular dispersion effects in the pipe network. The latter suggest the existence of larger cumulative backwater zone volumes, which have not been attended to yet. Infiltrating groundwater contributed 39% (95% confidence interval = +/- 2.5%) of the total daily dry weather wastewater discharge. This paper discusses all relevant aspects for practical application of the method. It presents a comprehensive framework for uncertainty analysis and details on the detection and discrimination of possibly interfering effects.
传统上，仅通过考虑流量过程线来评估污水收集系统中的外来水流，这往往涉及很大程度的主观性和过度简化。为了获取城市环境中物质通量的可靠信息，使用本征示踪剂可能是最佳选择。我们展示了成功使用天然存在的水稳定同位素（18O/16O和D/H）来准确量化合流制排水管网中地下水的外来排放。来自遥远水文区域的淡水供应使得饮用水（替代实际污水）与当地地下水（替代污水管道渗漏）之间在δ18O中具有1.8‰、在δ2H中具有11.7‰的可用同位素分离。废水同位素组成的日变化既反映了污水产生速率的变化，也反映了管网中的不规则扩散效应。后者表明存在尚未得到关注的更大的累积回水区域体积。渗入的地下水占每日旱季污水排放总量的39%（95%置信区间 = ±2.5%）。本文讨论了该方法实际应用的所有相关方面。它提出了一个用于不确定性分析的综合框架以及关于可能干扰效应的检测和辨别的详细信息。
