Leveraging Green Infrastructure for Efficient Treatment of Reclaimed Water

Abstract from Manuscript submission: Global water scarcity necessitates creative, yet practical, solutions to meet ever-growing demand. Green infrastructure is increasingly used in this context to provide water in environmentally friendly and sustainable ways. In this study, we focused on reclaimed wastewater from a joint gray and green infrastructure system employed by the Loxahatchee River District in Florida. The water system consists of a series of treatment stages for which we assessed 9 years of monitoring data. We measured water quality after secondary (gray) treatment, then in onsite lakes, offsite lakes, landscape irrigation (via sprinklers), and ultimately in downstream canals. Our findings show gray infrastructure designed for secondary treatment, integrated with green infrastructure, achieved lower nutrient concentrations nearly equivalent to advanced wastewater treatment systems. For example, we observed a dramatic decline in median nitrogen concentration from 19.65 mg L-1 after secondary treatment to 5.11 mg L-1 after spending an average of 42 days in the onsite lakes. Nitrogen concentration continued to decline as reclaimed water moved from onsite lakes to offsite lakes (3.54 mg L-1) and irrigation sprinklers (3.32 mg L-1). Phosphorus concentrations exhibited a similar pattern. These decreasing nutrient concentrations led to relatively low nutrient loading rates and occurred while consuming substantially less energy and producing fewer greenhouse gas emissions than traditional gray infrastructure—at lower cost and higher efficiency. There was no evidence of eutrophication in canals downstream of the residential landscape whose sole source of irrigation water was reclaimed water. This study provides an established example of how circularity in water use can be used to work toward sustainable development goals. Keywords: Eutrophication, Irrigation, Nitrogen, Phosphorus, Storage lakes, Wastewater

稿件投稿摘要：全球水资源短缺亟需兼具创新性与实用性的解决方案，以应对持续增长的用水需求。绿色基础设施（Green infrastructure）在此背景下得到愈发广泛的应用，可通过环境友好且可持续的方式供给水资源。本研究聚焦美国佛罗里达州洛哈奇奇河区（Loxahatchee River District）采用的灰绿复合基础设施系统产出的再生废水。该水处理系统包含多道处理工序，研究团队对其9年的监测数据进行了评估。我们依次检测了二级（灰色）处理后水体、现场湖泊水体、场外湖泊水体、景观灌溉（喷灌系统）出水以及最终下游河道的水质。研究结果显示，专为二级处理设计的灰色基础设施与绿色基础设施整合后，其营养盐浓度显著降低，几乎可与先进污水处理系统相媲美。例如，经二级处理后氮浓度中位数为19.65 mg·L⁻¹，在现场湖泊中平均停留42天后，氮浓度中位数降至5.11 mg·L⁻¹；随着再生水从现场湖泊流向场外湖泊（3.54 mg·L⁻¹）与灌溉喷灌系统（3.32 mg·L⁻¹），氮浓度进一步下降。磷浓度亦呈现相似的变化趋势。上述营养盐浓度的持续降低，使得系统的营养盐负荷率维持在较低水平，且相较于传统灰色基础设施，该系统能耗更低、温室气体排放量更少，同时兼具成本更低、效率更高的优势。在以该再生水为唯一灌溉水源的居住区景观下游河道中，未发现富营养化（Eutrophication）迹象。本研究为水资源循环利用助力可持续发展目标提供了可借鉴的成熟范例。关键词：富营养化、灌溉、氮、磷、储水湖泊、废水