Abstract Woodchip denitrifying bioreactors mitigate nitrate loading from agricultural tile effluents. Biochar is considered as an amendment to woodchips. Research findings are contradictory regarding the effect of biochar on nitrate removal. The current study is aimed at investigating the effect of biochar on the removal of nitrate in denitrifying bioreactors. For this purpose, laboratory and field experiments were carried out. In the laboratory, cylindrical up-flow bioreactors were used that were filled with woodchips and oxidized biochar at rates of 0%, 12.5%, 25%, 50% by volume. The removal of nitrate was investigated at two stages: unaged and aged for 16 weeks. The bioreactors were operated at four hydraulic retention times of 2, 4, 8, and 24 h. Additionally, we measured the concentrations of greenhouse gases in the laboratory bioreactors. In the field, nitrate removal over a 6-year period was investigated in two denitrifying bioreactors, one of which amended with 10% fresh biochar. The laboratory experiments showed that, on average, oxidized biochar (OB) amendment reduced nitrate removal by 9% in unaged and 13% in aged bioreactors while the respiration was equal or greater. This led us to conclude that oxidized biochar acted as an electron acceptor. In addition, oxidized biochar increased greenhouse gas concentrations. In the field bioreactors, fresh biochar initially increased nitrate removal. However, biochar became less effective over six years. In the final year, the biochar-amended bioreactor removed less nitrate than the woodchip bioreactor, which was ascribed to the electron-accepting ability of biochar due to aging. In sum, our study showed that biochar's electron acceptability significantly reduced denitrification in denitrifying bioreactors.

中文翻译：

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生物炭作为电子受体减少木屑反硝化生物反应器中硝酸盐的去除

摘要 木屑反硝化生物反应器减轻了农业瓷砖废水中的硝酸盐负荷。Biochar 被认为是对木片的一种修正。关于生物炭对硝酸盐去除的影响的研究结果相互矛盾。目前的研究旨在研究生物炭对反硝化生物反应器中硝酸盐去除的影响。为此，进行了实验室和现场试验。在实验室中，使用圆柱形上流式生物反应器，其中填充木片和氧化生物炭，体积比例为 0%、12.5%、25%、50%。在两个阶段研究硝酸盐的去除：未老化和老化 16 周。生物反应器在 2、4、8 和 24 小时的四个水力停留时间下运行。此外，我们还测量了实验室生物反应器中的温室气体浓度。在现场，在两个反硝化生物反应器中研究了超过 6 年的硝酸盐去除情况，其中一个用 10% 的新鲜生物炭进行了修正。实验室实验表明，平均而言，氧化生物炭 (OB) 修正剂使未老化的生物反应器中的硝酸盐去除率降低了 9%，而在呼吸作用相同或更高的情况下，老化的生物反应器中的硝酸盐去除率降低了 13%。这使我们得出结论，氧化生物炭充当电子受体。此外，氧化的生物炭增加了温室气体浓度。在现场生物反应器中，新鲜的生物炭最初增加了硝酸盐的去除。然而，生物炭在六年内变得不那么有效。在最后一年，生物炭改良的生物反应器去除的硝酸盐比木片生物反应器少，这归因于生物炭由于老化而具有电子接受能力。总之，我们的研究表明 biochar'