風能葉輪曝氣促進水域氧氣傳輸之效率

Abstract

曝氣增氧機現今被廣泛利用在水產養殖業，增加水中溶氧濃度、促進靜置的水體流動、消除水體分層現象、使底層能得到氧氣行好氧分解、減少有毒氣體的產生。然而考量曝氣增氧機長時間啟動需要耗費大量能源，若能以風能轉換成為動力來源，則在節能減碳上將有極大的助益。 現地試驗利用嘉義縣明華人工溼地內設有之長臂型葉輪曝氣增氧機及噴泉式曝氣增氧機，瞭解曝氣增氧機對台灣污水處理型人工溼地淨化效能之影響，將溼地視為一處理單元，連續24hr每小時一次測量入出流的溶氧、溫度、生化需氧量、總凱氏氮。研究發現有無啟動曝氣增氧機對於標準氧氣傳輸速率 (SOTR) 並無顯著差別，但未啟動時溶氧日變化量較大，生化需氧量之去除率以啟動曝氣時效果較佳，總凱氏氮則以未啟動時效果較佳，在曝氣增氧機全開的情況下，標準曝氣效率為0.090 kg O2/kWh。 室內研究上，參考多翼型風機及葉輪式曝氣增氧機，設計小型風力葉輪曝氣機 (後文中皆以風力水車代稱)，將其置於水槽中加入污水0.0227 m3、水深0.1m，以風速2.0-4.5 m/s 測試在打水深度0.025m及0.045m下溶氧變化的情形。研究發現，水車轉速提高時氧氣體積質量傳輸係數 (KLa) 也隨之增加，但在相等低轉速時，打水深度0.045m有較高的KLa。再比較標準曝氣效率 (SAE)，打水深度0.025m為1.21 kg O2/kWh、打水深度0.045m為4.54 kg O2/kWh，相較前人的曝氣增氧機研究，風力水車有較高的SAE。利用多元線性回歸、變異數分析及T檢定評估打水深度及水車轉速對KLa的影響程度，發現水車轉速對KLa的影響較顯著，打水深度比的顯著性則較低。 研究認為，風力水車確實可節省能源電力耗用，也可提昇溶氧使水體能成為良好的生物棲息地，可應用於風況良好之河濱人工處理型溼地或沿海漁塭。

Aerator is widely used in aquaculture today. It improves dissolved oxygen increasing, promotes water body flowing, eliminates the stratification, lets oxygen down into the bottom and makes sediments become aerobic in order to reduce the noxious gas production. However, using aerator will consume massive energy. If we can use green energy such like wind power as one kind of usable power, it will be beneficial to energy conservation and carbon reduction. In the field, I used multi-paddle wheel aerators and horizontal sprayer aerators at Ming-Hua treatment wetland in Chiayi County to understand the promoting purification efficiency of aerators on wastewater treatment wetlands in Taiwan. Consider the wetland as a process unit, sampled inflow and outflow once per hour continuing 24 hours and measured dissolved oxygen, temperature, biochemical oxygen demand, total Kjeldahl nitrogen. The results showed that there are no significant differences of standard oxygen transfer rate (SOTR) whether the aerator is working or not, but dissolved oxygen had more diurnal variation when the aerator closed. Biochemical oxygen demand removal efficiency was better when the aerator operates then closed, but the total Kjeldahl nitrogen removal efficiency was contrary. The standard aeration efficiency (SAE) of Ming-Hua treatment wetland was about 0.090 kg O2/kWh. Consider the model of multi-blade windmills and paddle wheel aerators, I designed a small wind power paddle wheel aerator. Performed the aerator in laboratory, and lay it in a tank which water depth is 0.1 m and total volume is 0.0227 m3. Using deferent wind speed (2.0-4.5 m/s) and two paddle depths (0.025m, 0.045m) to test dissolved oxygen change. The results showed that no matter what depth the paddle is, when the paddle wheel rotational speed enhanced, the volumetric mass transfer coefficient (KLa) increased. However, when the paddle depth is 0.045m had higher KLa then the paddle depth is 0.025m in equal slowly rotational speed. The SAE of wind power paddle wheel aerator was 1.21 kg O2/kWh when paddle depth was 0.025m and 4.54 kg O2/kWh when 0.045m. Compared with previous aerators, the wind power paddle wheel aerator had higher SAE. Used multi factor linear regression methods to analyze the variance and use T test to estimate the affected degree of KLa of paddle depth and rotational speed. It showed that rotational speed affected KLa significantly more than paddle depth. This study showed that the wind power paddle wheel could eliminate energy consume and keep a certain concentration of dissolved oxygen, so that water body could become better habitats. It is possible to set up at treatment wetlands on floodplains or costal aquaculture ponds where the wind condition is stable and continued.