Long-term structure stability of aerobic granules is critical to maintaining stable wastewater treatment performance. In this study, granulation and long-term stability of sludge-treating synthetic wastewater with a low chemical oxygen demand to nitrogen (COD/N) ratio of 4:1 and COD concentration of 400 mg/L in anoxic-oxic conditions were investigated for over 300 days. Inoculated suspended sludge gradually transformed into granules-dominant sludge on day 80. Due to the improved sludge volume index after 30 min settling (SVI₃₀), mixed liquor suspended solids (MLSS) reached 5.2 g/L on day 140. Without any external intervention or disturbance, aerobic granules started to disintegrate from day 140, causing the increase in SVI and the decrease in biomass concentration until day 210, with the average sludge size reduced to 243 µm. From day 210, granular sludge started to be re-established by re-granulation, and the average granule size increased to 500 µm on day 302. During these disintegration and re-granulation periods, there was no obvious difference in terms of COD removal and nitrification, but microbial species were found more diverse after the re-granulation, with Thauera and Sphingomonas dominant. Although there was no external intervention, the food to microorganisms ratio (F/M) varied significantly due to the changes in biomass concentration caused by strong selective pressure and the change of sludge-settling ability in the reactor. F/M ratios should be controlled between 0.3 and 1.0 gCOD/gSS·d to maintain the stable structure of granules to minimize the fluctuation of sludge properties under the conditions used in this study. Although aerobic granular sludge is able to re-establish itself after disintegration, controlling F/M ratios in a certain range would benefit long-term stability. The findings in this study are significant to deepen the understanding of granule stability with low-strength and low COD ratio wastewater and, thus, provide guidance for maintaining the long-term stability of granules.

中文翻译：

---

低强度低C/N比废水长期运行期好氧颗粒物性的波动与再建立

好氧颗粒的长期结构稳定性对于保持稳定的废水处理性能至关重要。在本研究中，研究了在缺氧-好氧条件下化学需氧量与氮 (COD/N) 比为 4:1 且 COD 浓度为 400 mg/L 的污泥处理合成废水的造粒和长期稳定性。超过 300 天。接种的悬浮污泥在第 80 天逐渐转变为颗粒为主的污泥。由于沉降 30 分钟后污泥体积指数（SVI ₃₀)，混合液悬浮固体 (MLSS) 在第 140 天达到 5.2 g/L。在没有任何外部干预或干扰的情况下，好氧颗粒从第 140 天开始分解，导致 SVI 增加和生物量浓度下降，直到第 210 天，与平均污泥尺寸减少到 243 µm。从第 210 天开始，颗粒污泥开始通过重新造粒重新建立，平均粒径在第 302 天增加到 500 µm。在这些崩解和重新造粒期间，COD 去除率和硝化作用，但在重新造粒后发现微生物种类更加多样化，包括Thauera和鞘氨醇单胞菌主导的。虽然没有外部干预，但由于强选择压力引起的生物质浓度变化和反应器内污泥沉降能力的变化，食物微生物比（F/M）变化显着。F/M 比率应控制在 0.3 和 1.0 gCOD/gSS·d 之间，以保持颗粒的稳定结构，从而在本研究中使用的条件下最大限度地减少污泥性质的波动。尽管好氧颗粒污泥在解体后能够自我重建，但将 F/M 比控制在一定范围内将有利于长期稳定性。本研究结果对于加深对低浓度低COD比废水颗粒稳定性的理解具有重要意义，从而为保持颗粒的长期稳定性提供指导。