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 12 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 nutrient concentrations nearly equivalent to advanced wastewater treatment systems. For example, we observed a dramatic decline in mean nitrogen concentration from 19.42 mg L⁻¹ after secondary treatment to 5.26 mg L⁻¹ after spending an average of 30 days in the onsite lakes. Nitrogen concentration continued to decline as reclaimed water moved from onsite lakes to offsite lakes (3.87 mg L⁻¹) and irrigation sprinklers (3.27 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 a long-term example of how circularity in water use can be used to work toward sustainable development goals. <em>Keywords: </em>Eutrophication, Irrigation, Nitrogen, Phosphorus, Storage lakes, Wastewater投稿论文摘要：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）在此背景下愈发广泛应用，可通过环境友好且可持续的方式供给水资源。本研究聚焦于美国佛罗里达州洛哈奇奇河区（Loxahatchee River District）所采用的灰绿基础设施联合系统（joint gray and green infrastructure system）产出的再生废水（reclaimed wastewater）。该水处理系统包含多组处理工序，我们对其12年的监测数据进行了全面评估。我们分别在二级（灰色）处理后、场内湖泊、场外湖泊、景观灌溉（喷淋系统）以及最终的下游河道中开展水质测定。研究结果表明，集成绿色基础设施的二级处理灰色基础设施，其出水营养盐浓度可与先进污水处理系统近乎持平。例如，经二级处理后，平均氮浓度为19.42 mg L⁻¹；再生水在经过场内湖泊平均停留30天后，氮浓度降至5.26 mg L⁻¹，降幅显著。随着再生水从场内湖泊流向场外湖泊（3.87 mg L⁻¹）及灌溉喷淋系统（3.27 mg L⁻¹）时，氮浓度仍持续下降。磷浓度亦呈现相似的变化趋势。营养盐浓度的持续降低使得系统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，该系统能耗与温室气体排放量均显著降低，同时兼具成本更低、运行效率更高的优势。在仅以再生水作为唯一灌溉水源的居民区下游河道，未出现富营养化（Eutrophication）现象。本研究提供了一个长期实践案例，展示了用水循环模式如何助力可持续发展目标的实现。<em>Keywords: </em>富营养化（Eutrophication）、景观灌溉、氮、磷、储水湖泊、废水