Abstract：
In industry, treatments against biofilms need to be optimized and, in the wastewater treatment field, biofilm composition needs to be controlled. Therefore, describing the biochemical and physical structures of biofilms is now required to better understand the influence of operating parameters and treatment on biofilms. The present study aims to investigate how growth conditions influence EPS composition, biofilm physical properties and volume detachment using a 1D biofilm model. Two types of EPS are considered in the present model, proteins and polysaccharides. The main hypotheses are that: (i) the production of polysaccharides occurs mainly under strong nutrient limitation(s) while the production of proteins is coupled to both the substrate uptake rate and the lysis process; (ii) the local biofilm porosity depends on the local biofilm composition. Both volume and surface detachment occur in biofilms and volume detachment extent depends on the biofilm local cohesion and thus on the local composition of biofilms for a given shear stress. The model is based on experimental trends and aims to represent these observations on the basis of biochemical and physical processes. Four case studies covering a wide range of contrasting growth conditions such as different COD/N ratios, applied SOLR and shear stresses are investigated. The model predicts how the biochemical and physical biofilm structures change as a result of contrasting growth conditions. More precisely simulation results are in good agreement with the main experimental observations reported in the literature, such as: (i) a strong nitrogen limitation of growth induces an important accumulation of polysaccharides leading to a more porous and homogenous biofilm, (ii) a high applied surface organic loading load allows to obtain a high biofilm thickness, (iii) a strong shear stress applied during the biofilm growth leads to a reduction of the biofilm thickness and to a consolidation of the biofilm structure. Overall, this model represents a relevant decision tool for the selection of appropriate enzymatic treatments in the context of negative biofilm control. From our results, it appears that protease based treatments should be more appropriate for biofilms developed under low COD/N ratios (about 20 gCOD/gN) whereas both glucosidases and proteases based treatments should be more appropriate for biofilms developed under high COD/N ratio (about 70 gCOD/gN). In addition, the model could be useful for other applications such as resource recovery in biofilms or granules, and help to better understand biological membrane fouling.
摘要：
在工业中,生物膜的治疗需要优化，在废水处理领域，需要控制生物膜的组成。因此,现在需要描述生物膜的生化和物理结构，以更好地了解操作参数和处理对生物膜的影响。本研究旨在调查生长条件如何影响EPS组成，使用一维生物膜模型的生物膜物理性质和体积分离。在本模型中考虑了两种类型的EPS，蛋白质和多糖。主要假设是:(i)多糖的产生主要发生在强营养限制下,而蛋白质的产生与底物摄取速率和裂解过程耦合;(ii)局部生物膜孔隙率取决于局部生物膜组成。体积和表面分离都发生在生物膜中,并且体积分离程度取决于生物膜局部内聚力,因此取决于给定剪切应力下生物膜的局部组成。该模型基于实验趋势，旨在根据生化和物理过程表示这些观察结果。四个案例研究涵盖了各种不同的生长条件，如不同的COD/N比，施加的SOLR和剪切应力进行了研究。该模型预测了生化和物理生物膜结构由于不同的生长条件而如何变化。更精确的模拟结果与文献中报道的主要实验观察结果非常吻合，例如：（i）生长的强氮限制诱导多糖的重要积累，导致更多孔和均匀的生物膜，（ii）高施加的表面有机负载负载允许获得高生物膜厚度，(iii)在生物膜生长期间施加的强剪切应力导致生物膜厚度的减小和生物膜结构的固结。总的来说,该模型代表了在阴性生物膜控制的背景下选择适当的酶处理的相关决策工具。从我们的结果来看,似乎基于蛋白酶的处理应该更适合于在低COD/N比(约20gCOD/gN)下开发的生物膜,而基于葡糖苷酶和蛋白酶的处理应该更适合于在高COD/N比(约70gCOD/gN)下开发的生物膜。此外,该模型可用于其他应用，如生物膜或颗粒中的资源回收，并有助于更好地了解生物膜污染。
