Department of Agricultural and Biosystems Engineering, Iowa State University, Ames, IA 50011, USA.
Iowa State University, Dept. of Agronomy, 2104 Agronomy Hall, Ames, IA 5001, USA.
J Environ Manage. 2019 May 1;237:424-432. doi: 10.1016/j.jenvman.2019.01.025. Epub 2019 Feb 26.
Nitrate (NON) export from row crop agricultural systems with subsurface tile drainage continues to be a major water quality concern. Woodchip bioreactors are an effective edge-of-field practice designed to remove NON from tile drainage. The NON removal rate of woodchip bioreactors can be impacted by several factors, including hydraulic residence time (HRT). This study examined the impact of three HRTs, 2 h, 8 h, and 16 h, on NON removal in a set of nine pilot-scale woodchip bioreactors in Central Iowa. NON concentration reduction from the inlet to the outlet was significantly different for all HRTs (p < 0.05). The 16 h HRT removed the most NON by concentration (7.5 mg L) and had the highest removal efficiency at 53.8%. The 8 h HRT removed an average of 5.5 mg L NON with a removal efficiency of 32.1%. The 2 h HRT removed an average of 1.3 mg L NON with a removal efficiency of 9.0%. The 2 h HRT had the highest NON mass removal rate (MRR) at 9.0 g m day, followed by the 8 h HRT at 8.5 g m day, and the 16 h HRT at 7.4 g m day, all of which were statistically different (p < 0.05). Significant explanatory variables for removal efficiency were HRT (p < 0.001) and influent NON concentration (p < 0.001), (R = 0.80), with HRT accounting for 93% contribution. When paired with results from a companion study, the ideal HRT for the bioreactors was 8 h to achieve maximum NON removal while reducing the impact from greenhouse gas emissions.
地下排水暗渠中来自农作物种植系统的硝酸盐（NON）排放仍然是一个主要的水质问题。木屑生物反应器是一种有效的田边处理措施，旨在从排水中去除 NON。木屑生物反应器的 NON 去除率可能受到多种因素的影响，包括水力停留时间（HRT）。本研究在爱荷华州中部的 9 个中试规模木屑生物反应器中，考察了 3 种 HRT（2 h、8 h 和 16 h）对 NON 去除的影响。所有 HRT 对入口和出口处 NON 浓度的降低均有显著差异（p < 0.05）。16 h HRT 通过浓度去除了最多的 NON（7.5 mg L），去除效率最高，为 53.8%。8 h HRT 通过浓度去除了平均 5.5 mg L 的 NON，去除效率为 32.1%。2 h HRT 通过浓度去除了平均 1.3 mg L 的 NON，去除效率为 9.0%。2 h HRT 的 NON 质量去除率（MRR）最高，为 9.0 g m 天，其次是 8 h HRT，为 8.5 g m 天，16 h HRT 为 7.4 g m 天，所有这些都有统计学差异（p < 0.05）。去除效率的显著解释变量是 HRT（p < 0.001）和进水 NON 浓度（p < 0.001）（R = 0.80），HRT 占 93%的贡献。当与一项配套研究的结果相结合时，生物反应器的理想 HRT 为 8 h，以实现最大的 NON 去除，同时减少温室气体排放的影响。
