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Hydraulic shear stress calculation in a sequencing batch biofilm reactor with granular biomass

机译：颗粒生物质序批式生物膜反应器中的水力剪切应力计算

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This paper reports the results of an experimental study specifically aimed at developing a simple methodology for calculating hydrodynamic shear forces in a sequencing batch biofilm reactor (SBBR) system with granular biomass. Using such a methodology, the hydrodynamic shear forces are simply calculated by measuring bed porosity and pressure losses. In addition, by applying this methodology an explanation for the biomass evolution from biofilm to granules under aerobic conditions has been provided and the following mechanism has been proposed: (i) formation of a thin biofilm that fully covers the carrier; (ii) increase of biofilm thickness; (iii) break-up of the attached biofilm with release of biofilm particles; (iv) rearrangement of biofilm particles in smooth granules. The hydrodynamic shear forces trend during the start-up period provides an explanatory key for the generation process of granular biomass. In fact, during the first two steps, the SBBR is characterized by rather weak shear forces values (lower than 1 dyn/ cm(2)). Under these weak shear forces, the biofilm grows by increasing its thickness through a porous structure and weak adhesion strengths. Such a continuous increase of biofilm thickness produces an increase of the shear forces with negative effect on biomass stability, causing the detachment of biofilm particles. In turn, such detachment causes a further sharp increase of shear forces (more than 10 times) that promotes the rearrangement of the detached biofilm particles in smooth granules, A correlation between biomass density and hydrodynamic shear forces was observed. In particular, the biomass density linearly increases with the increase of shear stress.
机译：本文报告了一项实验研究的结果，该研究旨在开发一种简单的方法来计算具有颗粒生物质的测序批生物膜反应器（SBBR）系统中的流体动力剪切力。使用这种方法，可以通过测量床的孔隙率和压力损失来简单地计算流体动力剪切力。另外，通过采用这种方法，提供了在有氧条件下生物质从生物膜向颗粒演变的解释，并提出了以下机理：（i）形成完全覆盖载体的薄生物膜； （ii）增加生物膜厚度； （iii）附着的生物膜破裂并释放生物膜颗粒； （iv）将生物膜颗粒重新排列成光滑的颗粒。启动期间的流体动力剪切力趋势为颗粒状生物质的生成过程提供了一个解释性的关键。实际上，在前两个步骤中，SBBR的剪切力值很弱（低于1 dyn / cm（2））。在这些弱的剪切力作用下，生物膜通过多孔结构和较弱的粘附强度而增加其厚度，从而生长。生物膜厚度的这种连续增加会产生剪切力的增加，从而对生物质稳定性产生负面影响，从而导致生物膜颗粒的脱离。继而，这种分离引起剪切力的进一步急剧增加（超过10倍），其促进了分离的生物膜颗粒在光滑颗粒中的重排。观察到生物质密度与流体动力剪切力之间的相关性。特别地，生物质密度随着剪切应力的增加线性增加。

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