Technical University of Denmark, DTU Aqua, Section for Aquaculture, The North Sea Research Centre, P.O. Box 101, DK-9850 Hirtshals, Denmark; Department of Biological and Environmental Science, Nanoscience Center, University of Jyväskylä, P.O. Box 35, 40014 Jyväskylä, Finland.
Department of Biological and Environmental Science, Nanoscience Center, University of Jyväskylä, P.O. Box 35, 40014 Jyväskylä, Finland.
Sci Total Environ. 2020 Jun 25;723:138093. doi: 10.1016/j.scitotenv.2020.138093. Epub 2020 Mar 21.
Woodchip bioreactors are viable low-cost nitrate (NO) removal applications for treating agricultural and aquaculture discharges. The active microbial biofilms growing on woodchips are conducting nitrogen (N) removal, reducing NO while oxidizing the carbon (C) from woodchips. However, bioreactor age, and changes in the operating conditions or in the microbial community might affect the NO removal as well as potentially promote nitrous oxide (NO) production through either incomplete denitrification or dissimilatory NO reduction to ammonium (DNRA). Here, we combined stable isotope approach, amplicon sequencing, and captured metagenomics for studying the potential NO removal rates, and the abundance and community composition of microbes involved in N transformation processes in the three different full-scale woodchip bioreactors treating recirculating aquaculture system (RAS) effluents. We confirmed denitrification producing di‑nitrogen gas (N) to be the primary NO removal pathway, but found that 6% of NO could be released as NO under high NO concentrations and low amounts of bioavailable C, whereas DNRA rates tend to increase with the C amount. The abundance of denitrifiers was equally high between the studied bioreactors, yet the potential NO removal rates were linked to the denitrifying community diversity. The same core proteobacterial groups were driving the denitrification, while Bacteroidetes dominated the DNRA carrying microbes in all the three bioreactors studied. Altogether, our results suggest that woodchip bioreactors have a high genetic potential for NO removal through a highly abundant and diverse denitrifying community, but that the rates and dynamics between the NO removal pathways depend on the other factors (e.g., bioreactor design, operating conditions, and the amount of bioavailable C in relation to the incoming NO concentrations).
木屑生物反应器是一种可行的低成本硝酸盐（NO）去除方法，可用于处理农业和水产养殖废水。木屑上生长的活性微生物生物膜正在进行氮（N）去除，在氧化木屑中的碳（C）的同时还原 NO。然而，生物反应器的年龄以及操作条件或微生物群落的变化可能会影响 NO 的去除，并可能通过不完全反硝化或异化硝酸盐还原为铵（DNRA）来促进一氧化二氮（NO）的产生。在这里，我们结合稳定同位素方法、扩增子测序和捕获宏基因组学，研究了三个不同的全规模木屑生物反应器处理循环水产养殖系统（RAS）废水时，潜在的 NO 去除率以及参与 N 转化过程的微生物的丰度和群落组成。我们证实反硝化产生二氮气体（N）是主要的 NO 去除途径，但发现当 NO 浓度高且生物可利用的 C 量低时，有 6%的 NO 可能作为 NO 释放，而 DNRA 速率往往随 C 量的增加而增加。研究中的生物反应器之间的脱氮菌丰度相当高，但潜在的 NO 去除率与脱氮微生物群落的多样性有关。相同的核心变形菌门群体驱动着反硝化作用，而在所有三个研究的生物反应器中，Bacteroidetes 都主导着携带 DNRA 的微生物。总之，我们的研究结果表明，木屑生物反应器具有通过高度丰富和多样的脱氮微生物群落去除 NO 的高遗传潜力，但 NO 去除途径之间的速率和动态取决于其他因素（例如，生物反应器设计、操作条件以及与进入的 NO 浓度相关的生物可利用 C 的量）。
