Freshwater quality is deteriorating worldwide. In populated areas, urban pollution is the main pressure on surface continental waters, but intensive wastewater treatment is costly. Setting standards for treatment of wastewater before discharge is a major policy instrument for water authorities, balancing environmental gains and operational costs. Discharge permits usually define concentration limits at the discharge point of the plant effluent. This approach, however, may not guarantee the good status of the receiving waters. Discharge permits should be directly linked to pollutant concentration in the river. Our paper develops an approach to adaptively adjust discharge permits and applies it to Madrid and the Manzanares river, a city of more than 3 million inhabitants discharging its treated wastewater to a stream having less than 2 m³ s⁻¹ average flow. Stricter limits to 5-day biological oxygen demand (11 mg O₂ L⁻¹), ammonium (0.5 mg N-NH₄ L⁻¹), nitrate (5.9 mg N-NO₃ L⁻¹), and phosphate (0.17 mg P-PO₄ L⁻¹) at plant effluent are required to meet the river environmental objectives. The results can be generalized to assess wastewater management decisions in other geographical areas.

全球淡水质量正在恶化。在人口稠密地区，城市污染是大陆表层水域的主要压力，但密集的废水处理成本很高。制定排放前废水处理的标准是水务部门的一项重要政策工具，可以平衡环境收益和运营成本。排放许可证通常定义了工厂废水排放点的浓度极限。但是，这种方法可能无法保证接收水的良好状态。排放许可证应与河流中的污染物浓度直接相关。我们的论文开发了一种适应性调整排放许可证的方法，并将其应用于马德里和曼萨纳雷斯河，这是一个拥有超过300万居民的城市，其排放的污水经过处理后的流量小于2 m³  s ^-1平均流量。5天的生物需氧量（11 mg O ₂ L ^-1），铵（0.5 mg N-NH ₄ L ^-1），硝酸盐（5.9 mg N-NO ₃ L ^-1）和磷酸盐（0.17 mg为了满足河流环境目标，需要在工厂废水中添加P-PO ₄ L ^-1）。可以对结果进行概括，以评估其他地理区域的废水管理决策。