Misiewicz Jakub, Datta Sujit Sankar, Lejcuś Krzysztof, Marczak Daria
Institute of Environmental Engineering, Wrocław University of Environmental and Life Sciences, 50-363 Wrocław, Poland.
Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ 08544, USA.
Materials (Basel). 2022 Jun 24;15(13):4465. doi: 10.3390/ma15134465.
Water uptake dynamics of superabsorbent polymers (SAP) in soil is of key importance for the optimum application of these materials in environmental engineering and agriculture, so goal of this paper is to determine time dependent values of coefficient of permeability for various SAP-soil mixtures. Retaining water in soil is a key requirement in critical zones to support plant growth. There is an urgent need for technologies that can increase soil water retention, given the increasing prevalence of droughts and scarcity of clean water as the climate changes, combined with the rising demand for food by a growing world population. SAPs are materials that can absorb significant amounts of water, and thus have tremendous potential to help increase water retention in soil. However, while some studies have characterized the equilibrium swelling behavior of SAPs in soil, how their addition influences the time-dependent flow of water through soil remains poorly understood. Here, we address this gap in knowledge by directly measuring the coefficient of permeability of SAP-soil mixtures, testing different soil grain sizes, SAP grain sizes, and different SAP-soil ratios. We find that SAP addition can dramatically hinder the flow rate of water through soil-reducing the permeability by several orders of magnitude, and in some cases causing complete blockage of water infiltration, at mass fractions as small as 1%. In this scenario coefficient of permeability of 1.23 × 10 m/s dropped by a factor of ~10 after 14 min, a factor of ~100 after 36 min, and by nearly a factor of ~1000 after 63 min, eventually causing complete blockage of infiltration after 67 min. Authors concluded that in this particular situation the size and quantity of SAP particles was enough to nearly completely fill the available pore space resulting in rendering the soil column almost completely impermeable. Moreover, we demonstrate that these effects are well-described by a simple hydraulic model of the mutual interactions between SAP and soil grains, providing more generally-applicable and quantitative principles to model SAP-soil permeability in applications. Ultimately, this work could help evaluate the optimal proportions and grain sizes of SAPs to use for a given soil to simultaneously achieve a desirable permeability along with increased water holding capacity in the plant root zone.
高吸水性聚合物（SAP）在土壤中的水分吸收动力学对于这些材料在环境工程和农业中的最佳应用至关重要，因此本文的目标是确定各种SAP-土壤混合物的渗透系数随时间变化的值。在关键区域保持土壤水分是支持植物生长的关键要求。鉴于随着气候变化干旱日益普遍、清洁水稀缺，以及世界人口增长对食物的需求不断上升，迫切需要能够增加土壤保水能力的技术。高吸水性聚合物是能够吸收大量水分的材料，因此在帮助增加土壤保水能力方面具有巨大潜力。然而，虽然一些研究已经描述了高吸水性聚合物在土壤中的平衡溶胀行为，但它们的添加如何影响水分在土壤中的随时间变化的流动仍知之甚少。在此，我们通过直接测量SAP-土壤混合物的渗透系数、测试不同的土壤颗粒尺寸、SAP颗粒尺寸以及不同的SAP-土壤比例，来填补这一知识空白。我们发现，添加SAP会显著阻碍水分在土壤中的流速——使渗透率降低几个数量级，在某些情况下，质量分数低至1%时就会导致水分渗透完全受阻。在这种情况下，渗透系数为1.23×10米/秒，14分钟后下降了约10倍，36分钟后下降了约100倍，63分钟后下降了近1000倍，最终在67分钟后导致渗透完全受阻。作者得出结论，在这种特殊情况下，SAP颗粒的尺寸和数量足以几乎完全填满可用的孔隙空间，导致土柱几乎完全不可渗透。此外，我们证明，这些效应可以通过一个简单的关于SAP与土壤颗粒相互作用的水力模型得到很好的描述，为在应用中模拟SAP-土壤渗透率提供了更普遍适用的定量原理。最终，这项工作有助于评估用于特定土壤的高吸水性聚合物的最佳比例和颗粒尺寸，以便在植物根区同时实现理想的渗透率和增加持水能力。
