Cyclic episodes of granules formation and disintegration took place in two lab-scale aerobic granular sludge sequencing batch reactors, one fed with synthetic wastewater (COD: 0.6 g L⁻¹ and NH₄⁺–N: 0.06 g L⁻¹) and operated at a constant organic loading rate (2.5 g COD per L d), and the other fed with real wastewater (soluble COD: 0.27–1.37 and NH₄⁺–N: 0.02–0.16 g L⁻¹) and with a variable loading rate (between 1.1 and 5.5 g COD_soluble per L d). The sludge volume index, density and diameter (mean value and relative standard deviation) of the granular biomass showed great fluctuations, without any clear tendency during the operational period. However, changes in granules fractal dimension values (both mean and relative standard deviation) matched with the formation and disintegration dynamics of the granular biomass. Statistical data analysis showed that the relative standard deviation of the granules fractal dimension could be a useful parameter for monitoring the granules status. Indeed, an increase of its value during the maturation or steady-state granulation stages is an early warning of disintegration episodes. A control strategy to maintain granules integrity based on this parameter is proposed.

中文翻译：

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分形维数法监测好氧颗粒污泥的稳定性

在两个实验室规模的好氧颗粒污泥测序批处理反应器中发生了颗粒形成和分解的循环过程，其中一个反应器供入了合成废水（COD：0.6 g L ^-1和NH ₄ ⁺ –N：0.06 g L ^-1），并在以下条件下运行恒定的有机负载量（每升d 2.5 g COD），另一种负载有实际废水（可溶性COD：0.27-1.37和NH ₄ ⁺ -N：0.02-0.16 g L ^-1），负载率可变（在1.1至5.5 g COD_{可溶性之间}每升d）。颗粒状生物质的污泥体积指数，密度和直径（均值和相对标准偏差）显示出很大的波动，在运行期间没有任何明显的趋势。但是，颗粒分形维数值的变化（均值和相对标准偏差）都与颗粒生物质的形成和分解动力学相匹配。统计数据分析表明，颗粒分形维数的相对标准偏差可能是监测颗粒状态的有用参数。实际上，在成熟或稳态制粒阶段其价值增加是崩解发作的早期警告。提出了基于该参数的维持颗粒完整性的控制策略。