Department of Civil and Environmental Engineering, 220 Hollister Hall, Cornell University, Ithaca, NY, USA.
Department of Molecular Biology and Genetics, 107 Biotechnology Building, Cornell University, Ithaca, NY, USA.
Water Res. 2019 Mar 15;151:456-467. doi: 10.1016/j.watres.2018.12.036. Epub 2018 Dec 27.
Septic systems inherently rely on microbial communities in the septic tank and leach field to attenuate pollution from household sewage. Operating conditions of septic leach field systems, especially the degree of water saturation, are likely to impact microbial biogeochemical cycling, including carbon (C), nitrogen (N), and phosphorus (P), as well as greenhouse gas (GHG) emissions to the atmosphere. To study the impact of flooding on microbial methane (CH) and nutrient cycling, two leach field soil columns were constructed. One system was operated as designed and the other was operated in both flooded and well-maintained conditions. CH emissions were significantly higher in flooded soils (with means between 0.047 and 0.33 g CH m d) as compared to well-drained soils (means between -0.0025 and 0.004 g CH m d). Subsurface CH profiles were also elevated under flooded conditions and peaked near the wastewater inlet. Gene abundances of mcrA, a biomarker for methanogens, were also greatest near the wastewater inlet. In contrast, gene abundances of pmoA, a biomarker for methanotrophs, were greatest in surface soils at the interface of CH produced subsurface and atmospheric oxygen. 16S rRNA, mcrA, and pmoA amplicon library sequencing revealed microbial community structure in the soil columns differed from that of the original soils and was driven largely by CH fluxes and soil VWC. Additionally, active microbial populations differed from those present at the gene level. Flooding did not appear to affect N or P removals in the soil columns (between 75 and 99% removal). COD removal was variable throughout the experiment, and was negatively impacted by flooding. Our study shows septic system leach field soils are dynamic environments where CH and nutrients are actively cycled by microbial populations. Our results suggest proper siting, installation, and routine maintenance of leach field systems is key to reducing the overall impact of these systems on water and air quality.
污水渗滤系统依靠渗滤池和渗滤场中的微生物群落来减轻家庭污水中的污染。污水渗滤场系统的运行条件，特别是水饱和程度，可能会影响微生物生物地球化学循环，包括碳（C）、氮（N）和磷（P），以及向大气排放温室气体（GHG）。为了研究洪水对微生物甲烷（CH）和养分循环的影响，构建了两个渗滤场土壤柱。一个系统按照设计运行，另一个系统在洪水和维护良好的条件下运行。与排水良好的土壤（平均值在-0.0025 和 0.004 g CH m d 之间）相比，洪水土壤中的 CH 排放明显更高（平均值在 0.047 和 0.33 g CH m d 之间）。在洪水条件下，地下 CH 剖面也升高，并在废水入口附近达到峰值。mcrA 的基因丰度，甲烷菌的生物标志物，也在废水入口附近最高。相反，pmoA 的基因丰度，甲烷氧化菌的生物标志物，在 CH 产生的地下和大气氧气界面处的表层土壤中最高。16S rRNA、mcrA 和 pmoA 扩增子文库测序显示，土壤柱中的微生物群落结构与原始土壤不同，主要受 CH 通量和土壤 VWC 驱动。此外，活性微生物种群与基因水平上存在的种群不同。洪水似乎并没有影响土壤柱中的 N 或 P 去除（去除率在 75%到 99%之间）。COD 去除率在整个实验过程中变化不定，洪水会对其产生负面影响。我们的研究表明，污水渗滤系统的渗滤场土壤是动态环境，其中 CH 和养分被微生物种群积极循环。我们的结果表明，正确选址、安装和常规维护渗滤场系统是减少这些系统对水和空气质量整体影响的关键。
