David Mark B, Gentry Lowell E, Cooke Richard A, Herbstritt Stephanie M
J Environ Qual. 2016 May;45(3):822-9. doi: 10.2134/jeq2015.06.0296.
Tile drainage is the major source of nitrate in the upper Midwest, and end-of-tile removal techniques such as wood chip bioreactors have been installed that allow current farming practices to continue, with nitrate removed through denitrification. There have been few multiyear studies of bioreactors examining controls on nitrate removal rates. We evaluated the nitrate removal performance of two wood chip bioreactors during the first 3 yr of operation and examined the major factors that regulated nitrate removal. Bioreactor 2 was subject to river flooding, and performance was not assessed. Bioreactor 1 had average monthly nitrate removal rates of 23 to 44 g N m d in Year 1, which decreased to 1.2 to 11 g N m d in Years 2 and 3. The greater N removal rates in Year 1 and early in Year 2 were likely due to highly degradable C in the woodchips. Only late in Year 2 and in Year 3 was there a strong temperature response in the nitrate removal rate. Less than 1% of the nitrate removed was emitted as NO. Due to large tile inputs of nitrate (729-2127 kg N) at high concentrations (∼30 mg nitrate N L) in Years 2 and 3, overall removal efficiency was low (3 and 7% in Years 2 and 3, respectively). Based on a process-based bioreactor performance model, Bioreactor 1 would have needed to be 9 times as large as the current system to remove 50% of the nitrate load from this 20-ha field.
瓦管排水是美国中西部上游地区硝酸盐的主要来源，目前已安装了诸如木屑生物反应器等瓦管末端去除技术，使当前的耕作方式得以继续，硝酸盐通过反硝化作用被去除。很少有关于生物反应器的多年研究来考察对硝酸盐去除率的控制因素。我们评估了两个木屑生物反应器在运行的前3年中的硝酸盐去除性能，并研究了调节硝酸盐去除的主要因素。生物反应器2遭受了河水泛滥，因此未对其性能进行评估。生物反应器1在第1年的月平均硝酸盐去除率为23至44克氮/平方米·天，在第2年和第3年降至1.2至11克氮/平方米·天。第1年和第2年初较高的氮去除率可能是由于木屑中含有高度可降解的碳。仅在第2年末和第3年，硝酸盐去除率才对温度有强烈响应。去除的硝酸盐中只有不到1%以一氧化氮的形式排放。由于在第2年和第3年瓦管输入的硝酸盐量大（729 - 2127千克氮）且浓度高（约30毫克硝酸盐氮/升），总体去除效率较低（第2年和第3年分别为3%和7%）。基于一个基于过程的生物反应器性能模型，生物反应器1需要比当前系统大9倍，才能从这片20公顷的田地中去除50%的硝酸盐负荷。
