污水處理廠操作流程優化以提供再生水 之評估方案：以內湖污水廠為例

Abstract

因應氣候變遷臺灣水資源短缺的問題越顯嚴重，如何開發穩定水資源為現況主要課題。目前各縣市逐步增加公共污水廠再生水建置計畫，期望透過污水廠穩定水源解決缺水窘境。本研究將臺北市內湖污水處理廠做為目標，透過進流水質分析，生物單元操作相關性分析以及提供現況最適合之再生水設備設置方案。 透過收集進流水數據、截流站啟閉情形瞭解各時段污水負荷，並透過箱形圖及相關性分析，將進放流水質與生物單元操作參數分析，尋找提供放流水質改善方案，再透過水質效益分析及成本分析，獲得最佳再生水設備設置方案。 分析結果顯示內湖污水廠進流污水每日水質變化較大，COD、BOD及氨氮自早上8時開始逐漸上升，至16~24時為每日高峰後至次日早上8時逐漸降低，SS高峰則延時至24~4時。1週間COD、BOD、SS在星期三、六、日較高，氨氮星期三及星期六負荷較高。1年各月COD在4、5月超過設計值，BOD 4、8月較高，SS 4月較高，氨氮1、3、4、11月超過設計值。而pH、COD、BOD、SS及氨氮等5項水質濃度皆與玉成截流站開啟時為顯著負相關，其中COD、BOD及氨氮為中度相關接近高度相關，pH及SS為中度相關接近低度相關，表示玉成截流站開啟相關水質進流濃度較低，反之較高。 厭氧池中氮物質狀態幾乎為凱氏氮，其中大部分為氨氮型態；總氮僅另一小部分為硝酸鹽氮(由缺氧池迴流)。缺氧池必須保持低溶氧才可有較好之脫氮作用。好氧池中硝化反應正常時須維持一定溶氧及硝酸鹽氮，同時降低總氮、鹼度、pH，若硝化反應不完全時可觀察到氨氮僅氧化至亞硝酸鹽氮無法完成脫氮反應進而使出流水總氮濃度增加。但若溶氧過高導致ORP過高時總氮會以硝酸鹽氮形式存在，不利脫硝反應。而MLSS對總氮、氨氮、凱氏氮具高度負相關，如需提高總氮去除率，可增加好氧池操作污泥濃度。 處理系統整體受進流水質影響大，當負荷大時COD、BOD、SS、總氮、氨氮、鹼度等濃度較高易造成F/M過高處理不完全影響放流水質，而此時放流水中亦含部分生物難分解有機物，其中大部分放流有機物為固體物流出造成，如減少放流SS即可有效降低放流COD及BOD。水溫高對於厭氧、缺氧及好氧池各污染物處理皆有正向幫助。現況前端沉砂池及初沉池處理成效佳，生物有機污泥含量高，但整體生物排泥量略為不足，當操作池數增加時系統有污泥累積的情形發生。 因放流水中大部分殘留污染物為固體物造成故於後段增加過濾設備為最具效益之再生水設置方案，比較包含UF、10 µm及18 µm盤式過濾設備與各式加藥情境，經處理水質與經費分析，如提供再生水於民生使用時選用8組10 µmm盤式過濾設備不進行加藥操作15年之每m³再生水處理成本為0.134元最具經濟效益；但若需提供予工業用時，仍須設置UF過濾設備。 依現況內湖廠設計水量為24萬CMD，而實際操作水量約為19萬CMD，廠內尚有備用池槽可供使用，由於進流負荷變化大為本廠操作上最大的隱患，具研究結果自16~24時為污染進流高峰，為避免變化風險建議平時生物池槽操作數量要大於設計處理水量，同時於高峰來臨時調整鼓風機風量，現況依初沉池、厭氧池及缺氧池各池停留時間約為4小時，故於20時至次日4時須增加風量提供足夠溶氧於好氧池以因應負荷增加。另因SS進流負荷峰值為16時至次日4時，故初沉池則可於該時段增加污泥廢棄減少生物池負荷。另可略增加好氧池內污泥濃度有利於整體除氮功能。而針對設備功能則可增加生物系統廢棄污泥量以利現場廢棄調控，另可辦理鼓風機風管保溫至好氧池，透過串池及缺氧液迴流至厭氧池可增加生物單元整體水溫，有利於整體污染物去除。 再生水設備設置考量臺北市主要以民生用水為主，可以採用10 µm盤式過濾設備不加藥作為主要再生水設施，未來可視內湖科技園區和南港軟體工業園區用水端需求，依需水量再規劃設置UF設備，減少設置成本並讓內湖廠再生水供應更具彈性及可行性，並可作為未來針對廠域周遭布設供水管線至內湖與南港園區及周遭民生需求使用為因應缺水之可行方案。

In response to the growing issue of water scarcity in Taiwan due to climate change, the main challenge currently is how to develop stable water resources. To address this, various cities are gradually increasing the construction plans for public wastewater treatment plant (WWTP) reuse systems, hoping to solve the water shortage by stabilizing water sources through wastewater treatment plants. This study takes the Neihu Wastewater Treatment Plant in Taipei City as the target. Through influent water quality analysis, biological unit operation correlation analysis, and the provision of the most suitable reclaimed water equipment setup for the current situation, the research aims to find optimal solutions. By collecting influent data and understanding the operational conditions of the interception stations during different time periods, we assess wastewater loads and analyze the influent water quality and biological unit operation parameters through box plots and correlation analysis. This helps to identify improvement measures for the effluent water quality. Through water quality benefit and cost analysis, we obtain the best reclaimed water equipment installation solution. The analysis results show that the daily water quality variation of influent wastewater at the Neihu plant is significant. COD, BOD, and ammonia nitrogen gradually increase starting from 8:00 AM, reaching a daily peak between 4:00 PM and 12:00 AM, then gradually decrease by 8:00 AM the next day. The SS peak is delayed, occurring from 12:00 AM to 4:00 AM. COD, BOD, and SS levels are higher on Wednesdays, Saturdays, and Sundays, while ammonia nitrogen loads are higher on Wednesdays and Saturdays. Monthly, the COD exceeds the design value in April and May, BOD is higher in April and August, SS is higher in April, and ammonia nitrogen exceeds the design value in January, March, April, and November. pH, COD, BOD, SS, and ammonia nitrogen levels all show a significant negative correlation with the opening of the Yucheng interception station. Among them, COD, BOD, and ammonia nitrogen are moderately to highly correlated, while pH and SS show a moderate correlation close to a low correlation, indicating that when the Yucheng interception station is open, the influent water quality concentrations are lower. Conversely, when it is closed, concentrations are higher. In the anaerobic tank, nitrogen compounds are primarily in the form of Kjeldahl nitrogen, most of which are in the ammonia nitrogen form; total nitrogen consists mostly of nitrate nitrogen (recycled from the anoxic tank). The anoxic tank must maintain low dissolved oxygen for effective denitrification. In the aerobic tank, normal nitrification requires maintaining a certain level of dissolved oxygen and nitrate nitrogen, while simultaneously reducing total nitrogen, alkalinity, and pH. If nitrification is incomplete, an increase in nitrite nitrogen and total nitrogen concentrations can be observed. However, if the dissolved oxygen is too high, leading to high ORP (oxidation-reduction potential), total nitrogen will exist in the form of nitrate nitrogen, which is unfavorable for denitrification. MLSS (Mixed Liquor Suspended Solids) shows a strong negative correlation with total nitrogen, ammonia nitrogen, and Kjeldahl nitrogen. To improve the total nitrogen removal rate, increasing the sludge concentration in the aerobic tank can be an effective approach. The overall performance of the treatment system is highly influenced by the influent water quality. When the load is high, concentrations of COD, BOD, SS, total nitrogen, ammonia nitrogen, and alkalinity are also higher, which may lead to a high F/M (food to microorganism) ratio, incomplete treatment, and poor effluent quality. At this point, the effluent may still contain some biorefractory organic matter, most of which are solids that exit the system. Reducing SS in the effluent can effectively lower the COD and BOD in the effluent. High water temperature positively affects the treatment of pollutants in the anaerobic, anoxic, and aerobic tanks. The current pre-treatment (grit and primary sedimentation) performs well, with a high concentration of biological organic sludge, but the overall biological sludge removal rate is slightly insufficient. When the number of operating tanks increases, the system may experience sludge accumulation. Since most of the remaining pollutants in the effluent are solids, adding filtration equipment in the latter stages is the most effective solution for reclaimed water setup. By comparing UF (Ultrafiltration), 10 µm, and 18 µm disk filtration equipment with various chemical dosing scenarios, and analyzing the treated water quality and costs, it is concluded that using 8 sets of 10 µm disk filters without chemical dosing has the lowest unit treatment cost of 0.134 NTD per unit over a 15-year period. The significant variation in influent load is the greatest operational risk at this plant. The research results indicate that the pollution peak occurs between 4:00 PM and 12:00 AM. To mitigate the risk of such fluctuations, it is recommended to increase the number of biological tank operations above the design treatment capacity. Additionally, during peak hours, the air blower output should be adjusted. Currently, the detention time in the primary sedimentation tank, anaerobic tank, and anoxic tank is approximately 4 hours. Thus, from 8:00 PM to 4:00 AM the next day, airflow should be increased to provide sufficient dissolved oxygen in the aerobic tank to cope with the increased load. The primary sedimentation tank should also increase sludge waste from 4:00 PM to 4:00 AM to reduce the load in the biological tanks. Furthermore, slightly increasing the sludge concentration in the aerobic tank can enhance the overall nitrogen removal performance. Regarding equipment functionality, increasing the amount of wasted biological sludge will help in field waste control. Additionally, installing insulation on the blower duct leading to the aerobic tank and introducing anoxic liquid recycling to the anaerobic tank can increase the overall temperature in the biological units, which will benefit the overall pollutant removal. Since the primary water usage in Taipei City is for domestic purposes, a 10 µm disc filtration system without chemical dosing can be adopted as the main reclaimed water treatment facility. In the future, depending on the water demand of the Neihu Technology Park and Nangang Software Industrial Park, UF (ultrafiltration) systems can be planned and installed accordingly. This approach reduces setup costs while enhancing the flexibility and feasibility of reclaimed water supply from the Neihu plant.