Daigger Glen T, Siczka John S, Smith Thomas F, Frank David A, McCorquodale J A
Water Environ Res. 2017 Aug 1;89(8):724-731. doi: 10.2175/106143017X14839994523983. Epub 2017 Mar 22.
The need to increase the peak wet weather secondary treatment capacity of the City of Akron, Ohio, Water Reclamation Facility (WRF) provided the opportunity to test an integrated methodology for maximizing the peak wet weather secondary treatment capacity of activated sludge systems. An initial investigation, consisting of process modeling of the secondary treatment system and computational fluid dynamics (CFD) analysis of the existing relatively shallow secondary clarifiers (3.3 and 3.7 m sidewater depth in 30.5 m diameter units), indicated that a significant increase in capacity from 416 000 to 684 000 m3/d or more was possible by adding step feed capabilities to the existing bioreactors and upgrading the existing secondary clarifiers. One of the six treatment units at the WRF was modified, and an extensive 2-year testing program was conducted to determine the total peak wet weather secondary treatment capacity achievable. The results demonstrated that a peak wet weather secondary treatment capacity approaching 974 000 m3/d is possible as long as secondary clarifier solids and hydraulic loadings could be separately controlled using the step feed capability provided. Excellent sludge settling characteristics are routinely experienced at the City of Akron WRF, raising concerns that the identified peak wet weather secondary treatment capacity could not be maintained should sludge settling characteristics deteriorate for some reason. Computational fluid dynamics analysis indicated that the impact of the deterioration of sludge settling characteristics could be mitigated and the identified peak wet weather secondary treatment capacity maintained by further use of the step feed capability provided to further reduce secondary clarifier solids loading rates at the identified high surface overflow rates. The results also demonstrated that effluent limits not only for total suspended solids (TSS) and five-day carbonaceous biochemical oxygen demand (cBOD5) could be maintained, but also for ammonia-nitrogen and total phosphorous (TP). Although hydraulic limitations in other parts of the WRP prevent this full capacity to be realized, the City is proceeding to implement the modifications identified using this integrated methodology.
俄亥俄州阿克伦市水回收设施（WRF）需要提高雨季高峰时的二级处理能力，这为测试一种用于最大化活性污泥系统雨季高峰时二级处理能力的综合方法提供了契机。初步调查包括二级处理系统的过程建模以及对现有的相对较浅的二次沉淀池（直径30.5米的单元中边水深度为3.3米和3.7米）的计算流体动力学（CFD）分析，结果表明，通过在现有生物反应器中增加分步进水功能并升级现有的二次沉淀池，处理能力有可能从41.6万立方米/天大幅提高到68.4万立方米/天或更高。WRF六个处理单元中的一个进行了改造，并开展了为期两年的广泛测试计划，以确定可实现的雨季高峰时的总二级处理能力。结果表明，只要利用所提供的分步进水功能分别控制二次沉淀池的固体和水力负荷，雨季高峰时的二级处理能力接近97.4万立方米/天是可能的。阿克伦市WRF通常具有出色的污泥沉降特性，这引发了人们的担忧，即如果污泥沉降特性因某种原因恶化，已确定的雨季高峰时二级处理能力可能无法维持。计算流体动力学分析表明，可以通过进一步利用所提供的分步进水功能，在确定的高表面溢流率下进一步降低二次沉淀池的固体负荷率，从而减轻污泥沉降特性恶化的影响，并维持已确定的雨季高峰时二级处理能力。结果还表明，不仅可以维持总悬浮固体（TSS）和五日碳质生化需氧量（cBOD5）的出水限值，还可以维持氨氮和总磷（TP）的出水限值。尽管WRF其他部分的水力限制使这一满负荷能力无法实现，但该市正在着手实施使用这种综合方法确定的改造措施。
