Daigger Glen T, Siczka John S, Smith Thomas F, Frank David A, McCorquodale J A
Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI, USA E-mail:
CH2M, Milwaukee, WI, USA.
Water Sci Technol. 2016;74(2):324-32. doi: 10.2166/wst.2016.177.
The performance characteristics of relatively shallow (3.3 and 3.7 m sidewater depth in 30.5 m diameter) activated sludge secondary clarifiers were extensively evaluated during a 2-year testing program at the City of Akron Water Reclamation Facility (WRF), Ohio, USA. Testing included hydraulic and solids loading stress tests, and measurement of sludge characteristics (zone settling velocity (ZSV), dispersed and flocculated total suspended solids), and the results were used to calibrate computational fluid dynamic (CFD) models of the various clarifiers tested. The results demonstrated that good performance could be sustained at surface overflow rates in excess of 3 m/h, as long as the clarifier influent mixed liquor suspended solids (MLSS) concentration was controlled to below critical values. The limiting solids loading rate (SLR) was significantly lower than the value predicted by conventional solids flux analysis based on the measured ZSV/MLSS relationship. CFD analysis suggested that this resulted because mixed liquor entering the clarifier was being directed into the settled sludge blanket, diluting it and also creating a 'thin' concentration sludge blanket that overlays the thicker concentration sludge blanket typically expected. These results indicate the need to determine the allowable SLR for shallow clarifiers using approaches other than traditional solids flux analysis. A combination of actual testing and CFD analyses are demonstrated here to be effective in doing so.
在美国俄亥俄州阿克伦市水回收设施（WRF）进行的一项为期两年的测试项目中，对相对较浅（直径30.5米，边水深3.3米和3.7米）的活性污泥二次沉淀池的性能特征进行了广泛评估。测试包括水力和固体负荷应力测试，以及污泥特性（区域沉降速度（ZSV）、分散和絮凝的总悬浮固体）的测量，结果用于校准所测试的各种沉淀池的计算流体动力学（CFD）模型。结果表明，只要将沉淀池进水混合液悬浮固体（MLSS）浓度控制在临界值以下，表面溢流率超过3米/小时时仍可保持良好性能。极限固体负荷率（SLR）明显低于基于测量的ZSV/MLSS关系通过传统固体通量分析预测的值。CFD分析表明，这是因为进入沉淀池的混合液被引入到沉淀污泥层中，使其稀释，并形成了一个“薄”浓度的污泥层，覆盖在通常预期的较厚浓度污泥层之上。这些结果表明，需要使用传统固体通量分析以外的方法来确定浅沉淀池的允许SLR。本文证明了实际测试和CFD分析相结合在这方面是有效的。
