The persistence of inorganic nitrogen is assessed in a set of 21 septic system plumes located in Ontario, Canada, that were studied over a 31‐year period from 1988 to 2019. In the plume zones underlying the drainfields, site mean NO₃⁻ values averaged 34 ± 27 mg N/L and exceeded the nitrate drinking water limit (DWL) of 10 mg N/L at 16 of 21 sites. In plume zones extending up to 30 m downgradient from the drainfields, site mean NO₃⁻ values averaged 24 ± 20 mg N/L and exceeded the DWL at 9 of 13 sites. Site mean total inorganic nitrogen (TIN; NH₄⁺ + NO₃⁻ − N) removal averaged 34 ± 26% in the drainfield zones and 36 ± 44% in the downgradient plume zones, indicating that much of the removal occurred within the drainfields. Removal was much higher at nine sites where drainfield TIN included >10% NH₄⁺ (62 ± 25% removal). TIN removal was not correlated with wastewater loading rate, system age, or sediment carbonate mineral content, but was correlated with water table depth, where shallower water table sites had generally less complete wastewater oxidation. At many of these sites, both NO₃⁻ and NH₄⁺ were present together in the plumes and were lost concomitantly, suggesting that the anammox reaction was making an important contribution to the observed TIN loss. When groundwater nitrate contamination is a concern, considering on‐site treatment system designs that lead to a lesser degree of wastewater oxidation, could be a useful approach for enhancing N removal.

中文翻译：

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化粪池系统羽管中的氮衰减

无机氮的持久性在一组位于安大略省，加拿大21化粪池系统羽流，进行了研究，超过31年期间从1988年到2019年在drainfields底层羽流区被评估，现场平均NO ₃ ^-的值的平均34±27 mg N / L，在21个站点中的16个站点超过了10 mg N / L的硝酸盐饮用水极限（DWL）。在羽流区域向上从drainfields延伸至30μm下坡，现场平均NO ₃ ^-值平均为24±20毫克N / L和在超过13 9的位点DWL。站点平均总无机氮（TIN; NH ₄ ⁺  + NO ₃ ^- − N）在流失区中的去除率平均为34±26％，在下降梯度羽流区中为36±44％，这表明大部分去除发生在流失区内。在9个排水田TIN含> 10％NH ₄ ⁺（62±25％去除）的位置，去除率要高得多。TIN的去除与废水负荷率，系统年龄或沉积碳酸盐矿物含量无关，但与地下水位深度相关，在浅水位点，废水的完全氧化程度通常较低。在许多这些网站，无论是NO的₃ ^-和NH ₄ ⁺烟气中同时存在这些烟气，它们同时丢失，这表明厌氧氨氧化反应对观察到的TIN损失做出了重要贡献。当关注地下水硝酸盐污染时，考虑采用现场处理系统设计以减少废水氧化程度，这可能是提高氮去除率的有用方法。