Layer M, Bock K, Ranzinger F, Horn H, Morgenroth E, Derlon N
Eawag, Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, 8600, Dübendorf, Switzerland.
ETH Zürich, Institute of Environmental Engineering, 8093, Zürich, Switzerland.
Water Res X. 2020 Oct 28;9:100075. doi: 10.1016/j.wroa.2020.100075. eCollection 2020 Dec 1.
Particulate substrate (X) is the major organic substrate fraction in most municipal wastewaters. However, the impact of X on aerobic granular sludge (AGS) systems is not fully understood. This study evaluated the physical retention of X in AGS sequencing batch reactor (SBR) during anaerobic plug-flow and then aerobic fully-mixed conditions. The influence of different sludge types and operational variables on the extent and mechanisms of X retention in AGS SBR were evaluated. X mass-balancing and magnetic resonance imaging (MRI) were applied. During the anaerobic plug-flow feeding, most X was retained in the first few cm of the settled sludge bed within the interstitial voids, where X settled and accumulated ultimately resulting in the formation of a filter-cake. Sedimentation and surface filtration were thus the dominant X retention mechanisms during plug-flow conditions, indicating that contact and attachment of X to the biomass was limited. X retention was variable and influenced by the X influent concentration, sludge bed composition and upflow feeding velocity (v). X retention increased with larger X influent concentrations and lower v, which demonstrated the importance of sedimentation on X retention during plug-flow conditions. Hence, large fractions of influent X likely re-suspended during aerobic fully-mixed conditions, where X then preferentially and rapidly attached to the flocs. During fully-mixed conditions, increasing floc fractions, longer mixing times and larger X concentrations increased X retention. Elevated X retention was observed after short mixing times < 60 min when flocs were present, and the contribution of flocs towards X retention was even more pronounced for short mixing times < 5 min. Overall, our results suggest that flocs occupy an environmental niche that results from the availability of X during aerobic fully-mixed conditions of AGS SBR. Therefore, a complete wash-out of flocs is not desirable in AGS systems treating municipal wastewater.
颗粒状底物（X）是大多数城市污水中主要的有机底物部分。然而，X对好氧颗粒污泥（AGS）系统的影响尚未完全了解。本研究评估了在厌氧推流然后好氧完全混合条件下，X在AGS序批式反应器（SBR）中的物理截留情况。评估了不同污泥类型和操作变量对AGS SBR中X截留程度和机制的影响。应用了X质量平衡和磁共振成像（MRI）技术。在厌氧推流进料期间，大部分X保留在沉淀污泥床最初的几厘米内的间隙空隙中，X在那里沉淀并积累，最终形成滤饼。因此，沉淀和表面过滤是推流条件下X截留的主要机制，这表明X与生物质的接触和附着有限。X截留是可变的，受X进水浓度、污泥床组成和上流进料速度（v）的影响。X截留随着X进水浓度的增加和v的降低而增加，这表明沉淀在推流条件下对X截留的重要性。因此，在好氧完全混合条件下，大部分进水X可能会重新悬浮，然后X优先且迅速地附着在絮体上。在完全混合条件下，增加絮体比例、延长混合时间和提高X浓度会增加X截留。当存在絮体时，在短混合时间<60分钟后观察到X截留增加，而对于短混合时间<5分钟，絮体对X截留的贡献更为明显。总体而言，我们的结果表明，在AGS SBR好氧完全混合条件下，絮体占据了一个因X的可利用性而形成的生态位。因此，在处理城市污水的AGS系统中，完全冲掉絮体是不可取的。
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