在许多南非水处理厂，过滤器似乎没有得到充分的清洁 常规反冲洗程序。假设是这一现象的根源 这种现象存在于滤床内的高度生物活性。 这可能会在培养基颗粒上形成一层粘性生物膜，即 很难移除。絮体滞留试验被证明是一个不可或缺的工具 对目前正在进行的水过滤装置进行系统调查 检验这个假设。提高再现性，深入了解 在介质污染的情况下，絮体滞留试验以多种方式进行了改进，这是 本演示的主要重点是: 含水量校正，其中过滤器的含水量取决于 排水和取样之间经过的时间变化很大（5到10秒） 28%); 通过圆筒翻转和剧烈摇晃进行搅拌，试验确定: 该方法产生的值较低，但结果更具可重复性； 沉积物的重量法与浊度法测量 较少依赖悬浮颗粒的性质； 根据酸的溶解度和挥发性分解沉积物，这表明 沉积物的性质（生物、化学或无机）； 和 悬浮液沉积处沉积物元素组成的测量 在酸中溶解，并测定其元素组成。 在对南方八个城市的调查中，对建议的改进进行了检验 非洲植物。发现整体介质清洁度存在较大差异， 每克介质中沉积1至20毫克。然而，这是通过分裂实现的 沉积物分为不同类别（酸溶性、挥发性和惰性），其中 改进后的程序开始发挥作用。挥发性组分（生物） 占总固体的10%至60%，大致相当于 原水的富营养化状态。酸溶性部分（化学成分） 沉淀）范围为1%至79%，表明预处理不当和/或 反洗不良。元素分析显示有大量的铁和 锰浓度（除了普遍存在的钙 和镁），这可能与原水问题直接相关。 改进后的絮体滞留试验证明是对试验结果的显著改善 帮助操作员发现潜在问题，了解 他们的本质，并提出有针对性的解决方案。包括5个参考文献、表格和图表。

At many South African water treatment plants, filters appear to be inadequately cleaned by routine backwash procedures. The hypothesis is that the root of this phenomenon lies in the high degree of biological activity within filter beds. This presumably results in a sticky biofilm on the media grains, which is difficult to remove. The floc retention test proved to be an indispensable tool for a systematic survey of water filtration plants currently being carried out to test this hypothesis. To improve reproducibility and insight into the reasons for media fouling, the floc retention test was refined in a number of ways, which is the main focus of this presentation: moisture content correction where moisture content of filters is dependent on the time elapsed between draining and sampling and is highly variable (5 to 28%); agitation by cylinder inversion vs. vigorous shaking where tests determined that this method yielded lower values but resulted in more reproducible results; gravimetric vs. nephelometric measurement of deposits where the former is less dependent on the nature of the particles in suspension; splitting deposits in terms of acid solubility and volatility which indicates the nature of the deposits (biological, chemical or inorganic); and, measurement of the elemental makeup of deposits where the suspension is dissolved in acid and its elemental composition is measured. The suggested refinements were put to the test during a survey of eight South African plants. Large differences in overall media cleanliness were found, ranging from 1 to 20 mg of deposits/g of media. It was, however, by splitting the deposits into different categories (acid-soluble, volatile and inert) where the improved procedures came into their own. The volatile fraction (biological) ranged from 10 to 60% of the total solids, loosely corresponding to the eutrophic status of the raw water. The acid-soluble fraction (chemical precipitates) ranged from 1 to 79% suggesting improper pretreatment and/or poor backwashing. Where the elemental analyses showed significant iron and manganese concentrations (in addition to the ubiquitous presence of calcium and magnesium), it could directly be related to the raw water problems. The refined floc retention test proved to be a significant improvement to the old, assisting operators in the detection of potential problems, understanding their nature, and suggesting focused solutions. Includes 5 references, tables, figure.