水質處理型人工溼地操作最佳化之研究-以鹿角溪溼地為例

Maintenance Strategy Optimization on Constructed Wetland System - Case Study with Lujiao Creek Constructed Wetland

高振豪(Chen-Hao Kao)

指導教授 ： 李鴻源

國立臺灣大學/工學院/土木工程學研究所/碩士(2020年)

https://doi.org/10.6342/NTU202002703

摘要

鹿角溪人工濕地為大漢溪上的污水處理型濕地，其目的在於將部分污水排入濕地後以自然工法進行處理，是大漢溪綠色廊道中的一個人工溼地，濕地設計分為五個單元池，包含沉砂池、漫地流區、近自然溪流區、草澤濕地與生態池，原始設計污水處理量為12000CMD，然而實際歷史流量紀錄顯示從未達到設計污水流量，該濕地的健康程度是需要進行科學量化之探討。傳統在評估人工濕地功能時，主要針對水質、水文、水理、生態及環境部分，而本研究使用水力效率係數作為研究方法，利用水力表現與水質進行連結，並針對影響水力效率甚鉅的流量因子進行模擬探討，藉此評估濕地健康程度。
本研究人工濕地分作以水力停留時間表現的物理性質，以及利用一階衰減係數k值表現的生化性質來呈現濕地的功能狀況，物理性質部分是以TABS-2進行數值實驗模擬鹿角溪濕地的五個單元池，並利用數值示蹤劑試驗針對溫度、曼寧n值、流量及一階衰減係數在高低流量下的因子進行模擬。而在生化性質部分，以一階衰減係數k值進行操作，本研究以固定量值k值在穩定數值示蹤劑進入濕地各單元池後的水力時間為參考基準，配合栓塞流理論的污染物削減公式以及現地量測的生化需氧量(BOD)、氮(N)、磷(P)之濃度紀錄，分別得到各自的參考一階衰減係數k_RTD。
依照不同的因子模擬後，可以依照不同因子數值模擬結果，進行最佳濕地操作，以流量為例，顯示當濕地欲達到水力效率係數λ=0.5時，污水入流量需要8000CMD，而欲達水力效率係數λ=0.75時，流量則需超過15000CMD，以季節植生為例，春夏季節因茂盛植生形成均勻流況可調降入流流量，秋冬考慮枯季因帶入的殘枝造成高濃度污染故需調升入流流量，而在生化性質為例，當入流流量低時，因容量較大的單元池對於在相同k值下影響較大，故須以該單元池作為操作依據。
最後本研究嘗試連結k_RTD與歷年事件之關聯性以藉此探討此係數當成濕地指標的可行性評估，首先將溫度與其他外在干擾利用溫度趨勢達到去因次化，結果顯示係數與溫度相關度極低，同時也顯示大面積現地濕地資料會造成溫度相關性的遮蔽。而考慮BOD、TN、TP濃度載入出口對於季節性的變化分析研究中，其結果顯示BOD在實地資料中表現變異度過大，而TP、TN削減量則相對穩定。然而本研究限於資料的非連續性以及資料不足，而得出參考一階衰減係數(k_RTD)與歷年事件連結性偏低之結果。本研究指出試驗場域如有穩定水質項目連續性濃度資料以及較小之試驗面積，參考一階衰減係數k_RTD將可為有效的人工濕地指標來呈現濕地的健康程度。

關鍵字

人工濕地 ； 水力效率係數 ； 濕地最佳入流量 ； 數值模式 ； 一階衰減係數

並列摘要

Lujiao Creek Constructed Wetland is a wastewater treatment type wetland on Dahan River, which is designed to deal with the houeshood wastewater by the natural processing method in the wetland. This wetland, belong to the Dahan Creek Green Corridor, is designed with five unit ponds, including settling pond, overflow pond, natural stream pond, marsh pond and ecological pond. The records show that the design wastewater flowrate (12,000 CMD) has never been reached, and the health of the wetland needs to be scientifically quantified. Traditionally, water quality, hydrology, hydraulics, ecology, and environment are the main components in assessing the function of the contructed wetland. The coefficient of hydraulic efficiency is used as a research method to correlate hydraulic performance with water quality, and to target flows that have a significant impact on hydraulic efficiency. In order to evaluate the health of the wetland, we carried out a numerical simulation and the index to investigate the health of the wetland.
In this study, the wetland condiction were divided into physical properties and biochemical properties. The former part, we conducted numerical experiments using TABS-2 and numerical tracers in the five ponds of the wetland. Simulation of temperature, Manning n, flow, and first-order decay coefficient (k) at high and low flowrates. The latter part , the k-values were used as the reference with the introduction of the stabilizing tracer into the wetland ponds to perform the biochemical features. In addition, the pollutant reduction formulas of the embolic flow theory and the in-situ measurements of biochemical oxygen demand (BOD), nitrogen (N), and phosphorus (P) are used as benchmarks. The first-order decay coefficients of k_RTD are used to calculate the optimal inflow for the wetland
Based on the numerical modeling with different facters, some optical maintanence strategy were mentioned . The results of flowrate show that when the wetland is intended to reach the hydraulic efficiency coefficient λ = 0.5, the wastewater inflow needs 8000 CMD as the optimal baseflow. In order to achieve the hydraulic efficiency coefficient λ = 0.75, the flow rate, on the other hand, needs to exceed 15000CMD. The seasonal vegetation provided the idea that in spring and summer, the inflow rate could be relatively decrease because the uniformly flow in the ponds; the inflow flowrate should rise to deal with the higher waste concentration brought with the withering period. The modeling result of biochemical properties(k) shows, during the low inflow condition, the unit pond with largest volume should take as the first consideration because of the greater effect among other ponds under the same k value.
Finally, this study attempts to correlate k_RTD with historical events in order to investigate the feasibility of using this coefficient as a wetland indicator. The results show a very low correlation between the coefficients and the temperature, and also a very low correlation between the coefficients and the temperature. It is also shown that large areas of in-situ wetland data cause temperature-dependent masking. The results show that BOD, TN, and TP concentrations are loaded into the export for seasonal variability analysis study. The variability in the data is too high, while the reduction in TP and TN is relatively slow. However, this study is limited by the discontinuity of the data and the insufficiency of data, and the coefficient of the first-order decay (k_RTD) and the historical data are used to calculate the coefficients. The results of this study are based on the low event linkage. This study indicates that if there are continuous concentration data and a small test area in the test area, the first-order decay coefficient k_RTD will provide a valid indicator of the health of constructed wetlands.

並列關鍵字

constructed wetlands ； hydrulic efficiency ； wetland optimal inflow ； numerical model ； irst-order decay coefficient

參考文獻

[1] Agency, U. E. P. (1988). Design manual: Constructed wetlands and aquatic plant systems for municipal wastewater treatment. In: CERI Cincinnati.

[2] Akratos, C. S., Papaspyros, J. N., Tsihrintzis, V. A. (2008). An artificial neural network model and design equations for BOD and COD removal prediction in horizontal subsurface flow constructed wetlands. Chemical Engineering Journal, 143(1-3), 96-110.

[3] Akratos, C. S., Tsihrintzis, V. A. (2007). Effect of temperature, HRT, vegetation and porous media on removal efficiency of pilot-scale horizontal subsurface flow constructed wetlands. Ecological Engineering, 29(2), 173-191.

[4] Anderson, P. (1995). Ecological restoration and creation: a review. Biological Journal of the Linnean Society, 56(suppl_1), 187-211.

[5] Association, A. P. H. (2005). APHA (2005) Standard methods for the examination of water and wastewater. APHA Washington DC, USA.