Delft University of Technology, Faculty of Civil Engineering and Geosciences, Department of Water Management, Stevinweg 1, 2628 CN Delft, the Netherlands.
Delft University of Technology, Faculty of Civil Engineering and Geosciences, Department of Water Management, Stevinweg 1, 2628 CN Delft, the Netherlands.
Water Res. 2024 Dec 1;267:122517. doi: 10.1016/j.watres.2024.122517. Epub 2024 Sep 24.
Iron (Fe), manganese (Mn), and ammonium (NH) oxidation processes were studied in three single media and three dual media full-scale rapid sand filters (RSFs) using reactive transport modelling (RTM) in PHREEQC and parameter estimation using PEST. Here, we present the insights gained into the spatial distribution of Fe and Mn mineral coatings in RSFs and its influence on the oxidation sequence and rates. Fe and Mn oxidation predominantly occurred simultaneously in the RSFs, contrary to the expected sequential oxidation based on Gibbs free energy calculations. During backwashing, RSF grains become fully mixed, which initiates heterogeneous Mn oxidation on Mn-coated grains that end up in the top layer. The resulting grains have a mixed Fe/Mn mineral coating, which is limiting heterogeneous Mn oxidation due to the limited Mn mineral surface available. Mixed coatings did not seem to affect Fe oxidation rates, instead oxidation rates were increasing at lower pH. We found that RSFs can be designed to spatially separate Fe and Mn oxidation, which results in optimal conditions for Mn oxidation. The RSF needs to consist of two layers with varying density to inhibit mixing and complete Fe oxidation should occur in the top layer. The developed RTM can be used to estimate the depth at which Fe oxidation is complete, and thus the ideal intersection depth of the two layers. A novel perspective is provided on how mineral coating distribution in single and dual media filters influence removal rates and the sequence of oxidation, which contributes to the design of more efficient groundwater filters.
铁（Fe）、锰（Mn）和铵（NH）氧化过程在三个单介质和三个双介质全规模快速砂滤器（RSF）中进行了研究，使用 PHREEQC 中的反应传输建模（RTM）和 PEST 的参数估计。在这里，我们介绍了在 RSF 中获得的关于 Fe 和 Mn 矿物涂层空间分布的深入了解，以及其对氧化顺序和速率的影响。Fe 和 Mn 的氧化主要在 RSF 中同时发生，与基于吉布斯自由能计算的预期顺序氧化相反。在反冲洗期间，RSF 颗粒完全混合，这会引发 Mn 涂层颗粒上的异相 Mn 氧化，最终导致颗粒出现在顶层。由此产生的颗粒具有混合的 Fe/Mn 矿物涂层，由于可用的 Mn 矿物表面有限，这限制了异相 Mn 氧化。混合涂层似乎并没有影响 Fe 氧化速率，相反，在较低的 pH 值下，氧化速率会增加。我们发现，可以设计 RSF 来在空间上分离 Fe 和 Mn 的氧化，从而为 Mn 氧化创造最佳条件。RSF 需要由两层组成，密度不同，以抑制混合，并且应该在顶层完全进行 Fe 氧化。开发的 RTM 可用于估计 Fe 氧化完全的深度，从而确定两层的理想相交深度。提供了一个新的视角，即单介质和双介质过滤器中的矿物涂层分布如何影响去除率和氧化顺序，这有助于设计更高效的地下水过滤器。
