Mechanical Engineering Department, Northwestern University, Evanston, IL 60208, United States.
Civil and Environmental Engineering Department, Northwestern University, Evanston, IL 60208, United States.
Water Res. 2021 Sep 1;202:117394. doi: 10.1016/j.watres.2021.117394. Epub 2021 Jun 30.
Granular biofilms are dense spherical complex biological systems composed mainly of multi-microbial cells, water, and extracellular polymeric substances (EPS). They facilitate efficient purification and settling of activated sludge in wastewater treatment processes. The viscoelastic properties of these complex biofilm systems are important characteristics that control their growth and dictate how they respond to hydrodynamic forces and chemical stimuli. However, the viscoelastic properties of granular biofilms are poorly understood. In this paper, we study granular biofilms' viscoelastic properties using optical coherence elastography (OCE), a nondestructive method that integrates optical coherence tomography (OCT) with elastic wave propagation. While quantitative viscoelastic characterization of granular biofilms is challenging due to their heterogeneous properties, we show that elastic waves are suitable for this purpose. First, we employ guided elastic waves in a thin section of a granular biofilm to reveal a two-layered profile for the viscoelastic properties. Next, we utilize circumferential elastic waves that propagate near the surface of a non-sectioned spherical biofilm to quantify the layered system's viscoelastic properties. To the best of our knowledge, this work is the first quantitative study that characterizes the layered viscoelastic properties of granular biofilms. The measurement approach may provide a platform to study the interplay between the viscoelastic properties and other characteristics of granular biofilms such as the complex microbial system, morphology, and oxygen distribution.
颗粒状生物膜是由多微生物细胞、水和细胞外聚合物（EPS）组成的密集球形复杂生物系统。它们有助于在废水处理过程中有效净化和沉淀活性污泥。这些复杂生物膜系统的粘弹性是控制其生长并决定其如何响应流体动力和化学刺激的重要特性。然而，颗粒状生物膜的粘弹性特性还不太清楚。在本文中，我们使用光学相干弹性成像（OCE）研究颗粒状生物膜的粘弹性特性，这是一种将光学相干断层扫描（OCT）与弹性波传播相结合的非破坏性方法。虽然由于其不均匀的性质，对颗粒状生物膜进行定量粘弹性表征具有挑战性，但我们表明弹性波适合于这一目的。首先，我们在颗粒状生物膜的一个薄片中使用引导弹性波来揭示粘弹性的两层分布。接下来，我们利用在非切片球形生物膜表面附近传播的周向弹性波来量化分层系统的粘弹性特性。据我们所知，这项工作是首次对颗粒状生物膜的分层粘弹性特性进行定量研究。该测量方法可能为研究颗粒状生物膜的粘弹性特性与其他特性（如复杂微生物系统、形态和氧气分布）之间的相互作用提供一个平台。
