School of Life Sciences Weihenstephan, Chair of Process Systems Engineering, Technical University of Munich, Gregor-Mendel-Str. 4, Freising 85354, Germany.
School of Life Sciences Weihenstephan, Chair of Process Systems Engineering, Technical University of Munich, Gregor-Mendel-Str. 4, Freising 85354, Germany.
Water Res. 2022 Oct 1;224:119027. doi: 10.1016/j.watres.2022.119027. Epub 2022 Aug 26.
Dissolved air flotation (DAF) is an efficient process to remove impurities from fresh or salt water. As the removal is based on the agglomeration of impurities on the generated microbubbles, the size distribution and concentration of air bubbles are key parameters in dissolved air flotation. However, the development of microbubbles in the whole flotation process remains unexplored. In this study, we show that state-of-the-art inline microscopy enables the image acquisition of bubbles in DAF. Based on image analysis, thousands of microbubbles (10-200 µm) were analyzed within 6-12 min experiments. Consequently, bubble size distributions and bubble concentrations can be determined with moderate effort. Bubble size distributions were measured in a lab-scale DAF comprising a saturation unit, a decompression valve in/after which the bubbles are formed, and the actual flotation tank. The state of the microbubbles is not only determined at different positions within the tank but also in the supply pipe from the decompression valve to the tank. All bubble size distributions were unimodal and can be described well with Burr XII distributions. For fresh water, bubble size increased while bubble concentration decreased along the supply pipe between the decompression valve and the inlet of the flotation tank, indicating bubble coalescence. Compared to freshwater, saltwater inhibited this bubble coalescence in the pipe. Within the flotation tank, the bubble size did not change drastically for neither salt- nor freshwater. However, the bubble concentration decreased for both waters, which could be explained by dilution effects. Our results demonstrate that the developed inline method is a promising tool to study the evolution of microbubbles in flotation systems. Further, it might also be applied to investigate microbubbles in other processes such as fermentation, decomposition of organic compounds, and fouling mitigation in membranes.
气浮（DAF）是一种从淡水或咸水中去除杂质的有效方法。由于去除是基于杂质在生成的微气泡上的聚集，因此空气泡的大小分布和浓度是气浮中的关键参数。然而，整个浮选过程中微气泡的发展仍未得到探索。在本研究中，我们表明最先进的在线显微镜能够实现 DAF 中气泡的图像采集。基于图像分析，可以在 6-12 分钟的实验中分析数千个（10-200µm）微气泡。因此，可以用适度的努力确定气泡大小分布和气泡浓度。在包括饱和单元、减压阀（在减压阀之后形成气泡）和实际浮选槽的实验室规模 DAF 中测量气泡大小分布。微气泡的状态不仅在槽内的不同位置确定，而且在减压阀到槽的供应管中也确定。所有气泡大小分布均为单峰分布，可用 Burr XII 分布很好地描述。对于淡水，气泡尺寸在减压阀和浮选槽入口之间的供应管中沿供应管增加，而气泡浓度减小，表明气泡聚结。与淡水相比，盐抑制了管道中这种气泡聚结。在浮选槽内，无论是盐水还是淡水，气泡尺寸都没有明显变化。然而，两种水的气泡浓度都降低了，这可以用稀释效应来解释。我们的结果表明，开发的在线方法是研究浮选系统中微气泡演变的有前途的工具。此外，它也可用于研究发酵、有机化合物分解和膜污染减轻等其他过程中的微气泡。
