人工湿地生物堵塞对污染物去除效果的影响

Effect of Bio‑clogging on Removal of Pollutants in Constructed Wetland

为研究人工湿地运行过程中生物堵塞对其除污能力的影响,建立了垂直流人工湿地模型,采用连续运行的方式,研究了细(装置1)、中(装置2)、粗(装置3)3种不同粒径砾石填料装置的COD去除率随渗透系数k的变化规律,并以装置2为例,通过示踪实验考察生物堵塞过程中装置渗流水力特性的变化规律。结果表明,随着生物堵塞的发生,COD去除率随k的下降前期总体较为稳定,运行24 d后呈明显下降趋势,下降率分别达到18.2%、22.8%、22.9%。通过对比堵塞过程中各装置的累积去除负荷发现,若以k=0.5 cm/s为堵塞标准,装置3达到堵塞时的COD累积去除负荷最大,装置1最小。示踪实验结果表明,在生物堵塞初期,由于生物膜的积累使得流场分配更为均匀,真实水力停留时间变长,装置水力效率有所提升,这对装置的除污能力有利;而到运行后期,过量的生物堵塞物导致局部出现死水区,真实水力停留时间缩短,装置的水力效率明显下降,进而导致COD去除率下降。

To investigate the effect of bio‑clogging on pollutants removal capacity of constructed wetland,three vertical flow constructed wetlands with fine(device 1),medium(device 2)and coarse(device 3)packing media was established and operated continuously to reveal the variation law of COD removal rate with permeability coefficient(k),and the seepage hydraulic characteristics of device 2 during bio‑clogging was investigated by tracer experiment.With the occurrence of bio‑clogging,the COD removal rate of the three devices was generally stable with the decrease of k in the early stage,and showed an obvious downward trend after 24 days of operation,in which the decreasing rates reached 18.2%,22.8%and 22.9%,respectively.If k of 0.5 cm/s was selected as the clogging standard,the COD cumulative removal load in device 3 was the largest,while that of device 1 was the smallest.The tracer experiment results indicated that the accumulation of biofilm made the flow field more uniform and thus led to the prolong of actual hydraulic retention time(AHRT)and improvement of hydraulic efficiency in the early stage,which was beneficial to the pollutants removal.However,in the later stage,excessive bio‑clogging led to local dead zone,shortened the AHRT,and significantly decreased the hydraulic efficiency of the device,leading to the decrease of COD removal rate.