- 學位論文
牡蠣殼礫間接觸水質淨化之研究
Research of Water Purification on Oyster Shell Contact Bed
摘要
本研究以廢棄的牡蠣殼作為礫間接觸基質材料，於台北縣二重疏洪道內處理民生污水，探討三個水平流槽體對於水質淨化的效果，分別為水平流曝氣牡蠣殼槽(HAOS)、水平流牡蠣殼槽(HOS)與水平流礫石槽(HG)。並在牡蠣殼模場中利用氯化鈉為追蹤劑進行脈衝式追蹤劑試驗，探討牡蠣殼礫間接觸場的水力停留時間分佈，使用地下水傳輸的縱向延散理論分析牡蠣殼模場的溶質傳輸延散效應。另外於台灣大學生物環境工程學系的農業環境實驗室外遮陽棚下架設實驗槽體，槽體內放置牡蠣殼做為材料，用於探討牡蠣殼對水質淨化的效果以及在不同流量下的延散效應。本研究可提供應用臺灣廢棄牡蠣殼作為礫間接觸處理材料之可行性及其水質淨化之效果。 結果顯示，水平流曝氣牡蠣殼槽具對污水有最佳的去除效果，對BOD5、SS、NH4-N、NO3-N、PO4-P、TP的單位面積去除量分別為18.78、58.95、11.74、-1.19、 0.50、0.87 g/m2/day，對BOD5的一階去除率為2.20/day。用牡蠣殼做為礫間接觸處理的材料對水質淨化的效果比用礫石好，而在模場中BOD5的移除有部分是由於水中SS移除所造成的，而使用牡蠣殼對於SS的攔阻效果較使傳統礫石來得好。曝氣雖然能效地移除水中的氨氮，主要是加強水中的硝化作用，將氨氮轉換為硝酸態氮，而在本實驗中，使用牡蠣殼做為礫間接觸處理的材料對於整體氮的去除效果比使用礫石為佳。 追蹤劑試驗結果顯示，出利用有效容積與平均流量計算理論水力停留時間會造成人工溼地實際水力停留時間的低估，而造成濕地的設計處理效率誤差；在距離尺度7.8公尺的牡蠣殼場中，平均水力停留時間約為理論值的2.68~2.75倍。追蹤劑實驗結果，得到牡蠣殼礫間接觸場的延散係數平均為0.014~0.016 m2/min。研究並發現於低流速環境中，延散係數可視為定值以簡化設計。 在槽體試驗中使用2.0~4.0 LPM五種不同的流量，所對應的水力停留時間為195.4~125.6 min，而延散係數為0.002~0.008 m2/min，延散數則為0.09~0.27，其延散程度介於地下流式人工溼地設計案例中莎草科植物介質和土壤介質之間，當流量增加所得到的延散數為0.27，接近有開放水域的表面流人工濕地。比較一般的柱塞流模式和一階柱塞流延散模式，如果忽略延散效應所產生的影響，則設計的污染去除去結果會被高估，在本研究中，當流量為4.0 LPM時，考慮延散影響的污染物去除效果只有原本的89.7%。 實驗槽體中生物膜於實驗初期生物膜快速生長，約至36天達到最大值，生長初期的比生速率為2.95/day，隨後生物膜數量減少，並呈現振盪增減。槽體對BOD5、NH4-N的平均除率分別為65.97 %、22.98 %，與生物膜的生長相關，去除率最大值發生於36天；PO4-P的平均去除率為17.74%，主要於實驗初期由牡蠣殼表面吸附。
並列摘要
The purpose of this study is to utilize wasted oyster shells as the media of the contact bed to purify domestic wastewater on Erchong Floodway, Taipei County. There are three horizontal flow tanks in this system, horizontal flow and aerated oyster shell tank (HAOS), horizontal flow oyster shell tank (HOS), and horizontal flow gravel tank (HG), respectively. In the experiment site, use NaCl as the tracer to perform pulse tracer tests to discuss residence time distribution of the oyster shell constructed wetland and dispersion effects of solute transport by using longitudinal dispersion theory. Besides, I set an experimental tank beside the laboratory in the Department of Bioenvironmental System Engineering in NTU. The experimental tank was set to find the water purification efficiency and the dispersion effect in different water flow condition in the oyster shell. In the results of the horizontal flow and aerated oyster shell tank (HAOS), the average mass removal of BOD5, SS, NH4-N, NO3-N, PO4-P, and TP were 18.78, 58.95, 11.74, -1.19, 0.50, and 0.87 g/m2/day. The BOD5 first-order reaction reducing rate constant in 20°C was 2.20/day. Consequently, using oyster shells as the material of the subsurface flow, constructed wetland had better water purification efficiency than using gravels. In this system, part of the BOD5 was removed because of the removal of SS, and there was better blocking effect when using oyster shells as the materials than gravels. Aeration can effectively remove ammonia nitrogen, but the main purpose was to strengthen the nitrification in the water, so that ammonia nitrogen was converted into nitrate nitrogen. Oyster shells as the material still had better removal effect of nitrogen than gravels. The results reveal that hydraulic retention time will be underestimated by using nominal retention time. Mean hydraulic retention time is about 2.68~2.75 nominal retention time in 7.8 meter length wetland. This underestimation will cause errors of the efficiency of water purification. By tracer tests, the mean dispersion coefficient of oyster shell wetlands is 0.014~0.016 m2/min. The study also points out that the dispersion coefficient can be seen as a constant in such low velocity surroundings. The relationship between flow rate and HRT of the oyster shell tank can be found by using tracer test. The average HRT was 195.4 min (Q=2.0 LPM) ~125.6 min (Q=4.0 LPM). Using oyster shells as the material, when the distance was 2.0m, and the flow rate was 2.0~4.0 LPM, the dispersion coefficient and the dispersion number was about 0.002~0.008 m2/min and 0.09~0.27, respectively. Compare the normal plug flow model and the plug flow modified by dispersion. If we ignore the dispersion effect, the treatment efficiency will be overestimated. In this study, to consider the effects of dispersion. As average HRT was 125.6 min (Q=4.0 LPM), the treatment efficiency of plug flow modified by dispersion was 89.7% of the normal plug flow model without dispersion coefficient. In the beginning of the experiment, biofilm grew fast, about 36 days to reach the maximum. In the initial of the growth, the specific growth rate was 2.95/day, then the biomass reduced and oscillated. The average removal rate of BOD5 and NH4-N in the tank were 65.97% and 22.98%. They were related to the growth of biofilm and the maximum removal occurred in 36 days. The average removal rate of PO4-P in the tank was 17.74%. Phosphate was mainly adsorbed by oyster shell in the initial of the experiment.