Gas Processing Center, Qatar University, Qatar.
Department of Chemical Engineering, Qatar University, Qatar.
Water Res. 2017 Dec 1;126:208-215. doi: 10.1016/j.watres.2017.09.024. Epub 2017 Sep 12.
The power demanded for the application of mechanically-imposed shear on an immersed flat sheet (iFS) membrane bioreactor (MBR) has been compared to that of conventional membrane air scouring. Literature correlations based on the Ostwald model were used to define the rheological characteristics of an MBR sludge. The correlation of specific power demand (P¯, in Watts per m membrane area) with shear rate γ in s was developed from first principles through a consideration of the force balance on the system in the case of mechanically-imposed shear. The corresponding aeration imposed shear correlation was interpreted from literature information. The analysis revealed the energy required to impose a shear mechanically through oscillation (or reciprocation) of the membrane to be between 20 and 70% less than that demanded for providing the same shear by conventional aeration of the immersed membrane. The energy saving increases with decreasing shear in accordance with a power demand ratio (aeration:mechanical) of 1400γ for a specific sludge rheology. Whilst the absolute P¯ value is dependent on the sludge rheology, the aeration:mechanical power demand ratio is determined by the difference in the two exponents in the respective correlations between P¯ and γ. Consequently, aeration-imparted shear becomes energetically favoured beyond some threshold shear rate value (∼180 s, based on the boundary conditions applied in the current study). The outcomes qualitatively corroborate findings from the limited practical measurement of energy demand in MBRs fitted with reciprocating immersed membranes.
已将浸没式平板膜生物反应器（MBR）机械剪切应用所需的功率与传统膜空气擦洗所需的功率进行了比较。基于奥斯特瓦尔德模型的文献相关性用于定义 MBR 污泥的流变特性。通过考虑机械剪切情况下系统的力平衡，从第一性原理出发开发了单位膜面积比功率（P¯，单位为瓦特/米）与剪切速率γ（单位为 s）的相关性。相应的曝气剪切相关性是根据文献信息解释的。分析表明，通过膜的振荡（或往复运动）施加机械剪切所需的能量比通过传统曝气浸没膜提供相同剪切所需的能量少 20%至 70%。根据特定污泥流变性的剪切需求比（曝气：机械）为 1400γ，节能效果随着剪切的减小而增加。虽然绝对 P¯值取决于污泥流变性，但曝气：机械功率需求比由两个相关性中 P¯和γ之间的两个指数的差异决定。因此，在某个剪切速率值（基于当前研究应用的边界条件，约为 180 s）之上，曝气产生的剪切在能量上变得更有利。结果从装有往复浸没式膜的 MBR 能量需求的有限实际测量中定性地证实了这一发现。
