J Environ Qual. 2019 Jan;48(1):93-101. doi: 10.2134/jeq2018.05.0199.
Woodchip bioreactors are widely used to control nitrogen export from agriculture using denitrification. There is abundant evidence that drying-rewetting (DRW) cycles can promote enhanced metabolic rates in soils. A 287-d experiment investigated the effects of weekly DRW cycles on nitrate (NO) removal in woodchip columns in the laboratory receiving constant flow of nitrated water. Columns were exposed to continuous saturation (SAT) or to weekly, 8-h drying-rewetting (8 h of aerobiosis followed by saturation) cycles (DRW). Nitrate concentrations were measured at the column outlets every 2 h using novel multiplexed sampling methods coupled to spectrophotometric analysis. Drying-rewetting columns showed greater export of total and dissolved organic carbon and increased NO removal rates. Nitrate removal rates in DRW columns increased by up to 80%, relative to SAT columns, although DRW removal rates decreased quickly within 3 d after rewetting. Increased NO removal in DRW columns continued even after 39 DRW cycles, with ∼33% higher total NO mass removed over each weekly DRW cycle. Data collected in this experiment provide strong evidence that DRW cycles can dramatically improve NO removal in woodchip bioreactors, with carbon availability being a likely driver of improved efficiency. These results have implications for hydraulic management of woodchip bioreactors and other denitrification practices.
木屑生物反应器广泛用于通过反硝化作用来控制农业中的氮素输出。有大量证据表明，干湿循环（DRW）可以促进土壤中代谢速率的提高。一项为期 287 天的实验研究了每周 DRW 循环对实验室中接受硝酸盐水恒流的木屑柱中硝酸盐（NO）去除的影响。将柱子暴露于连续饱和（SAT）或每周 8 小时干湿循环（8 小时好氧后饱和）（DRW）下。使用新型多路复用采样方法与分光光度分析相结合，每隔 2 小时测量柱出口处的硝酸盐浓度。与 SAT 柱相比，干湿循环柱表现出更大的总有机碳和溶解有机碳的输出，并增加了 NO 的去除率。尽管在重新润湿后 3 天内，DRW 的去除率迅速下降，但 DRW 柱中的硝酸盐去除率增加了高达 80％。DRW 柱中的 NO 去除率甚至在 39 次 DRW 循环后仍继续增加，每个每周 DRW 循环去除的总 NO 质量增加了约 33％。本实验中收集的数据提供了强有力的证据，表明 DRW 循环可以极大地提高木屑生物反应器中的 NO 去除率，而碳的可用性可能是提高效率的主要驱动力。这些结果对木屑生物反应器和其他反硝化实践的水力管理具有重要意义。
