活性污泥好氧池曝氣效能評估模式之研究

Study on the evaluation model of aeration efficiency of activated sludge aerobic tank

楊旋(Xuan Yang)

指導教授 ： 林正芳

國立臺灣大學/工學院/環境工程學研究所/碩士(2022年)

https://doi.org/10.6342/NTU202201514

摘要

城市污水處理屬於高能耗行業，污水廠的直接成本中，所占比例最大的是動力費，而動力費中曝氣環節又佔據了50%以上的份額，可見曝氣環節是污水廠節省能耗和降低運行費用的關鍵。曝氣效果又與出流水水質是否符合標准密切相關，在保證出流水符合標准的情況下，盡可能降低曝氣環節的能源消耗和用電費用，是污水廠完成碳減量，實現碳中和目標的必要步驟。
本研究針對污水處理常見之微孔曝氣式增氧機的充氧能力進行研究，基於ASCE和兩區氧傳質模型，在不同溫度與通氣量實驗條件下進行試驗，瞭解溫度、通氣量對氧體積質傳係數(Volumetric Oxygen Mass Transfer Coefficient)的影響，檢測曝氣槽水面逸散之氧氣量，建立曝氣過程之氧質量平衡方程式，評估實際曝氣效能。
研究結果發現，清水在1 L/min通氣量條件下，25.6 °C、25.1 °C水溫時的總氧體積質傳係數（K_L a）分別爲：0.0415 /min、0.041 /min-1；1.5 L/min通氣量條件下，25.6 °C、17.3 °C水溫時的K_L a分別爲：0.0466 /min、0.0380 /min；2.5 L/min通氣量條件下，24 °C、21.6 °C水溫時的K_L a分別爲：0.0588 /min、0.0541 /min（K_L a越大，則表示氣液間氧氣質傳速率越快）；在1 L/min、1.5 L/min、2.5 L/min通氣量下之KLa20分別爲：0.0361 /min、0.0400 /min、0.0512 /min，標準曝氣效率（Standard Aeration Efficiency，SAE）分別為：0.0462 kg-O2/(kW·hr)、0.0516 kg-O2/(kW·hr)、0.0654 kg-O2/(kW·hr)，標準傳氧率（Standard Oxygen Transfer Rate，SOTR）分別爲：2.68 mg/min、3.01 mg/min、3.8 mg/min，標準傳氧效率（Standard Oxygen Transfer Efficiency，SOTE）分別爲：0.96 %、0.72 %、0.67 %，數據結果顯示溫度的增加會使K_L a增大，K_L a、SAE、SOTR隨通氣量的增大而增大，而SOTE則是隨通氣量增加而遞減。在相同功率和適當溫度下，可通過調整通氣量量來得到較佳的曝氣效率，通氣量減少時，鼓風機運轉耗電量相對會減少，可減少能源消耗。
清水之氧質量平衡方程式：曝氣機通入之氧氣量=槽內溶氧量+水面逸散之氧氣量；污泥混合液之氧質量平衡方程式：曝氣機通入之氧氣量=槽內溶氧量+污泥耗氧量+水面逸散之氧氣量。可由水面測得之氧氣量和傳氧率反向推導水中溶氧量，避免因傳感器故障所測水中溶氧量與實際值不符，達到污水廠精確曝氣控制的目的。

關鍵字

曝氣系統 ； 曝气效率 ； 氧體積質傳係數 ； 氧質量平衡 ； 精確曝氣

並列摘要

Urban wastewater treatment is a high energy consumption industry, the direct cost of sewage plants, the largest proportion of power costs, and power costs in the aeration link and accounted for more than 50% of the share, it can be seen that the aeration link is the key to saving energy and reducing operating costs of sewage plants. Aeration effect is closely related to whether the effluent quality is up to standard, to ensure that the effluent is up to standard, as far as possible to reduce the energy consumption and costs of the aeration link, is a sewage plant to complete the carbon reduction, the necessary steps to achieve the goal of carbon neutrality.
Based on ASCE and the two-zone oxygen transfer model, tests were conducted under different temperature and ventilation conditions to understand the effects of temperature and ventilation on the oxygen volumetric mass transfer coefficient, to detect the amount of oxygen escaping from the water surface of the aeration tank, to establish the oxygen mass balance equation of the aeration process, and to evaluate the actual aeration efficiency. The results of the study found that clear water in 1 L/min ventilation conditions, 25.6 °C, 25.1 °C water temperature of the total volumetric mass transfer coefficient (K_L a) are: 0.0415 /min, 0.041 /min. 1.5 L/min ventilation conditions, 25.6 °C, 17.3 °C water temperature K_L a are: 0.0466 /min, 0.038 /min. K_L a at 24 °C and 21.6 °C under 2.5 L/min ventilation: 0.0588 /min and 0.0541 /min respectively (The larger 𝐾𝐿𝑎 is, the faster the oxygen gas transfer rate between gas and liquid). 1 L/min, 1.5 L/min, 2.5 L/min ventilation KLa20 are 0.0361 /min, 0.040 /min, and 0.0512 /min, respectively; standard aeration efficiency (SAE) is 0.0462 kg-O2/(kW·hr), 0.0516 kg-O2/(kW·hr), and 0.0654 kg-O2/(kW·hr), respectively; standard oxygen transfer rate (SOTR) is 2.68 mg/min, 3.01 mg/min, and 3.8 mg/min, respectively; standard oxygen transfer efficiency (SOTE): 0.96 %, 0.72 %, 0.67 % respectively.
The data results show that the increase of temperature will increase K_L a. K_L a， SAE, SOTR will increase with the increase of ventilation volume, and SOTE will increase with the increase of ventilation volume. The SOTE is decreasing with the increase of ventilation. under the same power and appropriate temperature, the ventilation volume can be adjusted to get better aeration efficiency, when the ventilation volume decreases, the power consumption of blower operation will be reduced, which can Reduce energy consumption. Oxygen mass balance equation for clean water: Oxygen intake to the aerator = Dissolved oxygen in the tank + Oxygen escaping from the water surface; Oxygen mass balance equation for sludge mixture: Oxygen intake to the aerator = Dissolved oxygen in the tank + Oxygen consumption of sludge + Oxygen escaping from the water surface. The amount of dissolved oxygen in the water can be deduced from the oxygen measured on the water surface and the oxygen transfer rate in reverse to avoid the discrepancy between the amount of dissolved oxygen in the water measured by the sensor failure and the actual value, so as to achieve the purpose of precise aeration control in the sewage plant.

並列關鍵字

aeration system ； aeration efficiency ； volumetric mass transfer coefficient ； oxygen mass balance ； precise aeration

參考文獻

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