Yang Min
Faculty of Geosciences and Environmental Engineering, Southwest Jiaotong University, Chengdu, China.
Water Environ Res. 2022 Jun;94(6):e10742. doi: 10.1002/wer.10742.
A one-dimensional longitudinal mixing model for an oxidation ditch with a moving symmetrical boundary and a series model for a symmetric aeration mixing unit of an aeration tank were developed in this study to analyze their mixing processes. The analysis of these models showed that the mixing process in the oxidation ditch tended to that of a continuous stirred tank reactor (CSTR) in a mode of circulation flow and dispersion; however, the mixing in the aeration tank tended to that of a CSTR in a mode of dispersion. The tracer output patterns and complete mixing times of the oxidation ditch and aeration tank with treatment capacities of 1000-50,000 m/d and hydraulic retention time 12.0 h were evaluated. The complete mixing time increased from 7.5 min to 128.5 min for the aeration tank with an increase in volume; and the oxidation ditch with same complete mixing time as that of the aeration tank was obtained. The complete mixing time for the oxidation ditch can be changed in a wider range, for matching the time scale of biochemical degradation of organic pollutants. PRACTITIONER POINTS: Mixing model of an oxidation ditch and an aeration tank were built. Mixing in oxidation ditch tends to that of CSTR in a mode of circulation flow and dispersion. Mixing in an aeration tank is in accordance with advection diffusion and tends to that of CSTR as its Peclet number is large. Complete mixing time for an oxidation ditch can be changed in a wider range.
本研究建立了具有移动对称边界的氧化沟一维纵向混合模型和曝气池对称曝气混合单元的串联模型，以分析它们的混合过程。对这些模型的分析表明，氧化沟中的混合过程在循环流动和扩散模式下趋于连续搅拌釜式反应器（CSTR）的混合过程；然而，曝气池中的混合在扩散模式下趋于CSTR的混合过程。评估了处理能力为1000 - 50000 m³/d且水力停留时间为12.0 h的氧化沟和曝气池的示踪剂输出模式和完全混合时间。曝气池的完全混合时间随着体积的增加从7.5分钟增加到128.5分钟；并获得了与曝气池具有相同完全混合时间的氧化沟。氧化沟的完全混合时间可以在更宽的范围内变化，以匹配有机污染物生化降解的时间尺度。从业者要点：建立了氧化沟和曝气池的混合模型。氧化沟中的混合在循环流动和扩散模式下趋于CSTR的混合过程。曝气池中的混合符合平流扩散，且由于其佩克莱数较大，趋于CSTR的混合过程。氧化沟的完全混合时间可以在更宽的范围内变化。
