Abstract Water flow through hydroponic media beds has seldom been characterized, and little is understood about the effects of different substrate media and flow rates as they pertain to mixing within. The hydrodynamics of four hydroponic substrate media were assessed in a small-scale hydroponic media bed bioreactor using tracer tests and mixing tests. Four media commonly used in hydroponic media beds, including 12.7-mm (0.5 in) fractured rock, 25.4-mm (1.0 in) fractured rock, 25.4-mm (1.0 in) lava rock and 12.0-mm light expanded clay aggregate (LECA) were selected and placed into identical rigid plastic containers to test the mean hydraulic residence time (mean residence time (MRT)) and vessel dispersion numbers (dispersion numbers) at two water levels and two flow rates. Sodium chloride tracers were used in these tracer tests and electroconductivity (EC) was measured every second with an EC probe at the outlet to generate residence time distribution curves for each bioreactor under each set of conditions. Expanded clay had a 16–29% longer mean residence time in the low water level, low flow treatment compared to the other media. It was also the most consistent overall and did not show any significant differences between flow rates or water levels. The mean residence times of the small fractured rock treatments got longer as the water velocity decreased, with the highest mean residence time achieved at an estimated water velocity of 0.38 cm s−1. Dispersion through the expanded clay or large fractured rock was not affected by flow rate or water level. Dispersion in the small fractured rock treatment only appeared to be greater at the lowest water velocity tested. Mixing time was also significantly shorter in expanded clay treatments at the lower water level. In the mixing tests, small fractured rock was comparable to the expanded clay at the low water level, low flow treatments but mixed 59% slower than in expanded clay treatment when the velocity increased. Overall, expanded clay performed better than the other substrate media tested, while the small fractured rock only performed well at lower estimated water velocities. The large fractured rock was substandard to both of those media and the lava rock was inconclusive but appeared to slow the movement of the tracer due to its intricate structure.

中文翻译：

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不同底物介质水培床生物反应器的流体力学

摘要 通过水培介质床的水流很少被表征，并且对不同基质介质和流速的影响了解甚少，因为它们与内部混合有关。在小型水培介质床生物反应器中使用示踪剂测试和混合测试评估了四种水培基质介质的流体动力学。水培介质床中常用的四种介质，包括 12.7 毫米（0.5 英寸）裂隙岩、25.4 毫米（1.0 英寸）裂隙岩、25.4 毫米（1.0 英寸）熔岩和 12.0 毫米轻质膨胀粘土骨料 (LECA)选择并放入相同的刚性塑料容器中，以测试两个水位和两个流速下的平均水力停留时间（平均停留时间（MRT））和容器分散数（分散数）。在这些示踪剂测试中使用氯化钠示踪剂，并在出口处使用 EC 探针每秒测量电导率 (EC)，以在每组条件下生成每个生物反应器的停留时间分布曲线。与其他介质相比，膨胀粘土在低水位、低流量处理中的平均停留时间长 16-29%。它也是总体上最一致的，并且在流速或水位之间没有显示出任何显着差异。随着水流速度的降低，小裂缝岩石处理的平均停留时间变长，在估计的水流速度为 0.38 cm s-1 时达到最高平均停留时间。通过膨胀粘土或大裂缝岩石的分散不受流速或水位的影响。仅在测试的最低水速下，小裂隙岩石处理中的分散似乎更大。在较低水位的膨胀粘土处理中，混合时间也显着缩短。在混合试验中，小裂缝岩石在低水位、低流量处理下与膨胀粘土相当，但当速度增加时，混合速度比膨胀粘土处理慢 59%。总体而言，膨胀粘土的性能优于其他测试的基质介质，而小型裂缝性岩石仅在较低的估计水速下表现良好。大裂隙岩石不符合这两种介质的标准，熔岩不确定但由于其复杂的结构似乎减缓了示踪剂的运动。在较低水位的膨胀粘土处理中，混合时间也显着缩短。在混合试验中，小裂缝岩石在低水位、低流量处理下与膨胀粘土相当，但当速度增加时，混合速度比膨胀粘土处理慢 59%。总体而言，膨胀粘土的性能优于其他测试的基质介质，而小型裂缝性岩石仅在较低的估计水速下表现良好。大裂隙岩石不符合这两种介质的标准，熔岩不确定但由于其复杂的结构似乎减缓了示踪剂的运动。在较低水位的膨胀粘土处理中，混合时间也显着缩短。在混合试验中，小裂缝岩石在低水位、低流量处理下与膨胀粘土相当，但当速度增加时，混合速度比膨胀粘土处理慢 59%。总体而言，膨胀粘土的性能优于其他测试的基质介质，而小型裂缝性岩石仅在较低的估计水速下表现良好。大裂隙岩石不符合这两种介质的标准，熔岩不确定但由于其复杂的结构似乎减缓了示踪剂的运动。低流量处理，但当速度增加时，混合速度比膨胀粘土处理慢 59%。总体而言，膨胀粘土的性能优于其他测试的基质介质，而小型裂缝性岩石仅在较低的估计水速下表现良好。大裂隙岩石不符合这两种介质的标准，熔岩不确定但由于其复杂的结构似乎减缓了示踪剂的运动。低流量处理，但当速度增加时，混合速度比膨胀粘土处理慢 59%。总体而言，膨胀粘土的性能优于其他测试的基质介质，而小型裂缝性岩石仅在较低的估计水速下表现良好。大裂隙岩石不符合这两种介质的标准，熔岩不确定但由于其复杂的结构似乎减缓了示踪剂的运动。