人工濕地對懸浮固體排除機制之數值模擬

Numerical Investigation on Suspended Solids Removal for Constructed Wetlands

陳均美(Chun-Mei Chen)

指導教授 ： 張倉榮

國立臺灣大學/生物資源暨農學院/生物環境系統工程學研究所/碩士(2006年)

https://doi.org/10.6342/NTU.2006.10129

摘要

本研究主要目的為研析三維度自由液面之人工濕地流場在不同水生植群(Hydrophytic aquatic vegetation)排列影響下的變化情形，並比較多種人工濕地案例，分析濕地水流中懸浮固體(Suspended solids)之傳輸行為及淨化能力。研究中使用 紊流標準模式並搭配體積分率法(VOF)模擬具自由液面之人工濕地，同時引入拉格蘭日(Lagrangian)觀點之微粒軌跡追蹤模式，分析計算三維度濕地之懸浮固體移除效率，探討紊流流場對微粒傳輸行為的影響。
本研究先透過Ahmed等(1998)及Salaheldin等(2004)的水槽實驗，驗證圓柱幾何體前後區域之流速與水位。繼而設計五種人工濕地的案例，藉由不同植物高度、排列方式及植群密度分佈情形，研究其流場流況，並透過懸浮固體傳輸之軌跡，針對沈澱、懸浮、流出、截留等四種不同力學機制，做相互對照比較。
研究結果發現因植群帶阻流影響，使得動量扣除效應增大，水流平均流速減小，其中又以水生植物採加密配置其調節能力最明顯，尖峰出流量與無水生植群之濕地相比減少了24%。此外，無植群之濕地其懸浮固體流出量高達50%，顯示水質澄淨度不盡理想，但加入水生植群模擬條件之後，發現在植群所座落的區域，因為紊流動能降低、流速減緩，使植群帶截留大量懸浮固體，而挺水性植物交錯加密配置之懸浮固體移除率最顯著，其淨水能力達75.6%，而研究結果也顯示若再降低植物高度，將更影響植群淨化能力。從數據統計結果來看，應善用水生植群截留功能，藉由設計植群排列及規劃植群佔地面積，以達到淨化水質、涵養水源之功效。

關鍵字

人工濕地 ； 水生植群 ； 懸浮固體 ； 體積分率法 ； 截留

並列摘要

The main purpose of the research is to investigate 3-D free-surface flows in artificial wetlands, which is influenced by hydrophytic aquatic vegetation. Suspended solids (SS) transport behaviors and clarification efficiency of artificial wetlands are also studied. In the present study, the standard κ-ε turbulence model together with the volume of fluid (VOF) is adopted to simulate flow field of artificial wetlands. The Lagrangian particle tracking technique is used to analyze suspended solids removal efficiency of artificial wetlands.
The present model is verified by comparing through the experiments of the flow around the pier given by Ahmed et al. (1998) and Salahedin et al. (2004). Next, five sets of numerical scenario simulations are conducted to investigate the effects of plant height, plant arrangement and plant density of wetlands on water flows. In addition, suspended solids transport is calculated to demonstrate the relative importance of the four particle transport mechanisms, i.e., sedimentation, suspension, escape, and interception, in artificial wetlands.
The simulated result shows that hydrophytic aquatic vegetation effectively reduces flow velocity so that the peak flow discharge at outlet is decreased. Among the five scenarios, the scenario having the densest vegetation gives 24% reduction of the peak flow, compared to the scenario of a wetland without plantation. Moreover, a wetland without plantation can only remove at most 50% of suspended solids, whereas it can remove 75.6% of suspended solids for the scenario with unsubmerged, staggered and denser vegetation. This is because turbulent kinetic energy and mean velocity are both reduced in the vicinity of plantation area, resulting in large amounts of suspended solids intercepted in this area. On the other hand, the clarification efficiency is decreased if the height of plants is lower. It is concluded that the efficiency of purifying water quality and conserving water resource can be enhanced through planting hydrophytic aquatic vegetation in wetlands.

並列關鍵字

Artificial wetland ； Hydrophytic aquatic vegetation ； Suspended solids ； Volume of fluid ； Interception

參考文獻

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