Department of Civil, Structural and Environmental Engineering, Trinity College Dublin, Ireland; MACSI, University of Limerick, Ireland.
Department of Civil, Structural and Environmental Engineering, Trinity College Dublin, Ireland.
J Contam Hydrol. 2020 Jun;232:103654. doi: 10.1016/j.jconhyd.2020.103654. Epub 2020 May 8.
Soil treatment units (STUs) receiving effluent from on-site wastewater treatment systems (OWTSs) rely on the gradual development of a microbial biomat/biozone at the infiltrative surface for optimal effluent distribution and pollutant attenuation. Here, we present the first direct measurement of gradual biomat development in the field in STU trenches receiving either primary (PE) or secondary treated effluent (SE) under identical environmental, hydrological and subsoil conditions. Two domestic OWTSs were constructed in Ireland and monitored over a period of >2 years using an automated, three-dimensional network of buried soil water content sensors tracking water flow and retention within the soil underneath the infiltrative surface. While trenches receiving PE expressed signs of biomat formation along the entire length of STU trenches, biomats in trenches receiving SE were significantly muted and did not extend further than 10 m from the inlet at the end of the study. The presence of a mature biomat helped to retain soil moisture above background levels and made the system more resilient towards drought events and desiccation stress but led, in one case, to effluent ponding within the trenches. A growth-limited non-linear model fit revealed that biomats in SE trenches are expected to remain considerably shorter and will not spread along the entire trench design length, even after 10 years of operation, which is contrary to prevalent design assumptions. Muted biomat growth, on the contrary, might lead to localized hydraulic and pollutant overloading and has been shown previously to negatively affect the ability to attenuate pollutants effectively within the soil profile before the effluent reaches the groundwater.
从现场废水处理系统（OWTS）接收污水的土壤处理单元（STU）依赖于在渗透表面逐渐形成微生物生物膜/生物区，以实现最佳的污水分布和污染物衰减。在这里，我们首次在现场 STU 沟渠中直接测量了在相同的环境、水文和底土条件下接收原水（PE）或二级处理污水（SE）的情况下逐渐形成生物膜的过程。在爱尔兰建造了两个家用 OWTS，并使用埋在土壤中的自动化、三维网络土壤水分传感器对其进行了超过 2 年的监测，该网络跟踪渗透表面下土壤中的水流和保留情况。虽然接收 PE 的沟渠沿 STU 沟渠的整个长度都表现出生物膜形成的迹象，但接收 SE 的沟渠中的生物膜则明显减弱，并且在研究结束时，其不会从末端入口延伸超过 10m。成熟的生物膜有助于将土壤水分保持在背景水平之上，并使系统更能抵抗干旱事件和干燥胁迫，但在一种情况下，导致污水在沟渠内积水。生长受限的非线性模型拟合表明，SE 沟渠中的生物膜预计仍将短得多，并且即使在运行 10 年后，也不会沿着整个沟渠设计长度传播，这与流行的设计假设相反。相反，生物膜生长减弱可能导致局部水力和污染物过载，并且以前已经表明，在污水到达地下水之前，它会对在土壤剖面中有效衰减污染物的能力产生负面影响。
