Department of Civil and Environmental Engineering, University of Delaware, Newark, DE 19716, USA.
J Contam Hydrol. 2013 Sep;152:18-34. doi: 10.1016/j.jconhyd.2013.05.007. Epub 2013 Jun 3.
Rapid Infiltration Basin Systems (RIBS) are used for disposing reclaimed wastewater into soil to achieve additional treatment before it recharges groundwater. Effluent from most new sequenced batch reactor wastewater treatment plants is completely nitrified, and denitrification (DNF) is the main reaction for N removal. To characterize effects of complex surface and subsurface flow patterns caused by non-uniform flooding on DNF, a coupled overland flow-vadose zone model is implemented in the multiphase flow and reactive transport simulator TOUGHREACT. DNF is simulated in two representative soils varying the application cycle, hydraulic loading rate, wastewater quality, water table depth, and subsurface heterogeneity. Simulations using the conventional specified flux boundary condition under-predict DNF by as much as 450% in sand and 230% in loamy sand compared to predictions from the coupled overland flow-vadose zone model, indicating that simulating coupled flow is critical for predicting DNF in cases where hydraulic loading rates are not sufficient to spread the wastewater over the whole basin. Smaller ratios of wetting to drying time and larger hydraulic loading rates result in greater water saturations, more anoxic conditions, and faster water transport in the vadose zone, leading to greater DNF. These results in combination with those from different water table depths explain why reported DNF varied with soil type and water table depth in previous field investigations. Across all simulations, cumulative percent DNF varies between 2 and 49%, indicating that NO₃ removal in RIBS may vary widely depending on operational procedures and subsurface conditions. These modeling results improve understanding of DNF in RIBS and suggest operational procedures that may improve NO₃ removal.
快速渗滤系统（RIBS）用于将再生废水排入土壤中，在其补给地下水之前进行额外处理。大多数新型序批式反应器废水处理厂的出水完全硝化，反硝化（DNF）是去除氮的主要反应。为了研究非均匀淹没引起的复杂地表和地下流动模式对 DNF 的影响，多相流和反应传输模拟器 TOUGHREACT 中实现了一个地表水流-包气带模型的耦合。在两种不同的土壤中模拟 DNF，改变应用周期、水力负荷率、废水质量、地下水位和地下非均质性。与地表水流-包气带模型的预测相比，传统的指定通量边界条件下的模拟预测，在砂中 DNF 预测值低了 450%，在壤土中低了 230%，这表明在水力负荷率不足以将废水扩散到整个盆地的情况下，模拟耦合流对于预测 DNF 是至关重要的。润湿时间与干燥时间的比值较小、水力负荷率较大，会导致包气带中的水饱和度更大、缺氧条件更多、水传输更快，从而导致 DNF 更大。这些结果与不同地下水位深度的结果相结合，解释了为什么以前的现场调查中报道的 DNF 随土壤类型和地下水位深度而变化。在所有模拟中，累积 DNF 百分比在 2%至 49%之间变化，这表明 RIBS 中的 NO₃去除可能因操作程序和地下条件而异。这些建模结果提高了对 RIBS 中 DNF 的理解，并提出了可能改善 NO₃去除的操作程序。
