潮汐流人工湿地的除氮效果及影响因素

为研究TF-CW(tidal flow constructed wetland,潮汐流人工湿地)的除氮效果及其主要影响因素,以连续流模拟装置(A组)为对照,设置3种潮汐进水方式〔RAT(闲置时间∶反应时间)分别为1∶1、1∶2、2∶1,依次记做B组、C组、D组〕,运行175 d,分析不同进水方式下TF-CW模拟装置对TN、NH₄+-N、NO₃--N、TOC的去除效果及其在不同处理深度上的变化. 结果表明:A、B、C、D组TN平均去除率分别为82.41%±4.84%、84.82%±5.09%、86.09%±3.99%、90.23%±3.05%. A组TN和NH₄+-N的去除效果与B、C、D组均差异显著(P<0.05),其中D组TN和NH₄+-N的去除效果均最好；A组对NO₃--N的总体去除效果较优；RAT并不影响TOC的去除率. 不同进水方式下,NH₄+-N的去除率均在0~15 cm深度内最大,ρ(TOC)处于较低水平(0~20 mg/L),二者均随处理深度的不断增加而逐渐下降；ρ(NO₃--N)在0~15 cm深度内迅速上升. 随着闲置时间的增加,ρ(DO)逐渐升高. TN和NH₄+-N的去除率随着运行时间的增加基本保持恒定,主要影响因子有ρ(DO)、RAT、ORP(oxidation reduction potential,氧化还原电位)和ρ(TOC)；而NO₃--N的去除率随着运行时间的增加而逐渐降低,其主要影响因子有pH、电导率和水温等. 

Depth Variations and Factors Influencing Nitrogen Removal in Tidal Flow Constructed Wetlands

To study the main nitrogen removal factors in a tidal flow constructed wetland (TF-CW), idle/response times (RAT) for three different water input scenarios of TF-CWs (1∶1(B), 1∶2(C) and 2∶1(D)) were compared for a continuous flow wetland versus a control group (A). After running the experiment for 175 days, the removal efficiencies and depth variations of the total nitrogen (TN), ammonium nitrogen (NH₄+-N), nitrate nitrogen (NO₃--N) and total organic carbon (TOC) were analyzed. The results showed that the average TN removal rate was 82.41%±4.84% for A, and 84.82%±5.09%, 86.09%±3.99% and 90.23%±3.05% for the three TF-CWs, B, C and D, respectively. Significant differences existed between the control (A) and the TF-CWs (B, C and D; P<0.05). Scenario D was the most efficient for TN and NH₄+-N removal. The control (A) showed higher removal efficiency for NO₃--N. In general, the idle/reaction time did not affect the removal rate of TOC. The NH₄+-N removal rate was maximally efficient when the reaction depth ranged from 0 to 15cm, and with increasing depth the removal rate slowed. The stage also showed rapidly rising ρ(NO₃--N), whereas ρ(TOC) was lower (0-20 mg/L) and further decreased with depth. A longer idle time contributed to higher ρ of dissolved oxygen (DO). The TN and NH₄+-N removal rates did not significantly temporally vary in the TF-CWs. The main factors affecting the removal of TN and NH₄+-N included DO, idle/response time, oxidation reduction potential (ORP) and TOC. The NO₃--N removal rate became slower as the time increased, while the other main factors that influenced its removal rate included pH, conductivity and water temperature.