Toja Ortega Sara, van den Berg Lenno, Pronk Mario, de Kreuk Merle K
Section Sanitary Engineering, Department of Water Management, Delft University of Technology, Stevinweg 1, Delft 2628CN, the Netherlands.
Department of Biotechnology, Delft University of Technology, Van der Maasweg 9, Delft, HZ 2629, the Netherlands.
Water Res X. 2022 Jul 31;16:100151. doi: 10.1016/j.wroa.2022.100151. eCollection 2022 Aug 1.
In aerobic granular sludge (AGS) reactors, granules of different sizes coexist in a single reactor. Their differences in settling behaviour cause stratification in the settled granule bed. In combination with substrate concentration gradients over the reactor height during the anaerobic plug-flow feeding regime, this can result in functional differences between granule sizes. In this study, we compared the hydrolytic activity in granules of 4 size ranges (between 0.5 and 4.8 mm diameter) collected from a full-scale AGS installation. Protease and amylase activities were quantified through fluorescent activity assays. To visualise where the hydrolytic active zones were located within the granules, the hydrolysis sites were visualized microscopically after incubating intact and sliced granules with fluorescent casein and starch. The microbial community was studied using fluorescent hybridization (FISH) and sequencing. The results of these assays indicated that hydrolytic capacity was present throughout the granules, but the hydrolysis of bulk substrates was restricted to the outer 100 µm, approximately. Many of the microorganisms studied by FISH, such as polyphosphate and glycogen accumulating organisms (PAO and GAO), were abundant in the vicinity of the hydrolytically active sites. The biomass-specific hydrolysis rate depended mainly on the available granule surface area, suggesting that different sized granules are not differentiated in terms of hydrolytic capacity. Thus, the substrate concentration gradients that are present during the anaerobic feeding in AGS reactors do not seem to affect hydrolytic activity at the granule surfaces. In this paper, we discuss the possible reasons for this and reflect about the implications for AGS technology.
在好氧颗粒污泥（AGS）反应器中，不同大小的颗粒共存于单个反应器中。它们沉降行为的差异导致沉降颗粒床中出现分层现象。在厌氧推流进料模式下，结合反应器高度上的底物浓度梯度，这可能导致不同大小颗粒之间的功能差异。在本研究中，我们比较了从一个全尺寸AGS装置收集的4个尺寸范围（直径在0.5至4.8毫米之间）颗粒中的水解活性。通过荧光活性测定法定量蛋白酶和淀粉酶活性。为了可视化水解活性区在颗粒内的位置，在用荧光酪蛋白和淀粉孵育完整颗粒和切片颗粒后，通过显微镜观察水解位点。使用荧光原位杂交（FISH）和测序研究微生物群落。这些测定结果表明，整个颗粒都具有水解能力，但大量底物的水解大约仅限于外层100微米。许多通过FISH研究的微生物，如聚磷菌和糖原积累菌（PAO和GAO），在水解活性位点附近大量存在。生物质特异性水解速率主要取决于可用的颗粒表面积，这表明不同大小的颗粒在水解能力方面没有差异。因此，AGS反应器厌氧进料期间存在的底物浓度梯度似乎不会影响颗粒表面的水解活性。在本文中，我们讨论了造成这种情况的可能原因，并思考了其对AGS技术的影响。
