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Hach NH6000 氨氮監測儀協助美國德州Grapevine污水處理廠優化硝化工序
Nitrification Optimization in the Real World at Grapevine, TX, WWTP
 
City of Grapevine TX, Background  美國德州Grapevine市 - 背景介紹
The Grapevine Texas city municipal wastewater system serves a population of about 51,000 and discharges into a tributary feeding Grapevine Lake. The wastewater treatment system for this municipality consists of complete mix aeration and an average daily flow rate of 3.2 MGD.  The facility is required to meet seasonal ammonia limits of 2 mg/l daily average April to Oct and a 7 day average of 5 mg/l with slightly higher limits for the winter months of 6 mg/l daily average.
德州 Grapevine市的民生污水處理系統服務大約51,000名居民，處理後的排放水排入Grapevine湖的一條支流。此污水處理系統採用全混合曝氣，每日平均處理量為3.2百萬加侖/日（MGD）。此污水處理廠必須符合季節性氨氮限值要求，4月至10月每日平均氨氮限值 2 mg/l，7天平均氨氮限值 5 mg/l，冬季略高，每日平均氨氮限值 6 mg/l。
 
With those limits in place they’ve been operating, like many facilities, on a tight budget which requires extra care and time to make sure the facility is compliant. Grab samples and composite samples are run regularly to ensure their process is working properly. Process control samples are taken at the end of the aeration system for solids, NH4-N and others to make sure biological processes are functioning as they should.  One of the facility’s largest operational expenses is aeration to drive biological reduction of ammonia through Nitrification. The facility has traditionally used online Oxidation Reduction Potential (ORP) and Dissolved Oxygen (DO) as surrogate measurements for monitoring ammonia removal in the aeration basins.
與許多污水處理廠一樣，此污水處理廠的營運預算很緊，需要格外嚴謹管理以確保各指標符合規範。此廠最大的營運支出之一是曝氣，以透過硝化作用促進氨的生物還原。此廠傳統上使用線上監測氧化還原電位 (ORP) 和溶氧 (DO) 作為監測曝氣池中氨去除的替代測量值。
 
Maintaining consistent permit compliance for nutrients requires higher levels of attention and data for those biological systems than other types of pollutants. Nitrogen in the form of ammonia is most often the primary regulated nutrient for water quality. Many wastewater treatment plants across the globe are required to monitor ammonia nitrogen concentrations for permit compliance. Regulations for water quality can include nitrogen species such as: Total Nitrogen (TN), Total Kjeldahal (TKN), Ammonia (NH3), Nitrite (NO2) and Nitrate (NO3). This note will primarily cover the most common nitrogen species given to wastewater facilities as a numerical regulation - Ammonia. Ammonia nitrogen can be a standalone nitrogen species as a permit limit or it can be part of a larger Nitrogen form as Total Nitrogen, Total Inorganic Nitrogen and or Total Kjeldahl Nitrogen as shown above in figure 1.
氨氮通常是水質監管的主要營養物質。全球許多污水處理廠都需要監測氨氮濃度以確保其符合法規標準規定。水質標準法規可能涵蓋以下氮類型：總氮 (TN)、總凱氏氮 (TKN)、氨 (NH3)、亞硝酸鹽 (NO2) 和硝酸鹽 (NO3)。本篇主要聚焦於污水處理廠最常見的 - 氨。
 
 
Nitrification is the key biological process to remove ammonia. Ammonia is removed aerobically in oxic zones where microorganisms convert it primarily to Nitrite and Nitrate.  Controlled nitrification within wastewater treatment plants is usually the single most energy consumptive process at the plant.
Adding air to water is commonly achieved with either sub surface air addition using blowers or surface aeration using mechanical water agitation.
硝化作用是去除氨的關鍵生物過程。污水處理廠內的控制的硝化程序通常是最耗能的工序。
 
In addition to the high energy use to achieve proper nitrification it is also a very sensitive system to diurnal load changes, seasonal temperature fluctuations, toxic loads and biological solids imbalances. Any of these conditions, or combination of issues, can cause extremely rapid deterioration in effluent water quality and the possible loss of nitrification. Sometimes these conditions can be fixed quickly such as under aeration, when system air flow can be increased, but in other cases loss of nitrification can take days to recover.  There are two commonly used forms of nitrogen that are important to wastewater treatment which can be confused, ammonia and ammonium.
除了為了達到適當的硝化成效而消耗大量能源之外，系統對於晝夜負荷變化、季節性溫度波動、毒性負荷和生物固體不平衡也非常敏感。任何這些情況或這些問題的組合都可能導致排放水水質極快地惡化，並可能造成硝化成效的降低。有時，這些情況可以透過快速修復，例如在曝氣不足的情況下，增加系統空氣流量即可；但在其他情況下，硝化成效的損失可能需要數天才能恢復。
 
The Solution 解決方案
The Grapevine treatment works decided to trial the new Hach NH6000sc ammonia analyzer in one of their three aeration trains.
The new analyzer and its filtration unit was installed at the end of the aeration train shown in image 1. This allowed the plant to benefit from real-time ammonia measurements through their SCADA system for the first time. Ammonia based aeration control is gaining popularity for the following reasons:
  1. Using the specific parameter to be treated, in this case ammonia, is more effective than using surrogate measurements like DO and ORP. This is in large part is due to other interferences and demands on measurements like DO and ORP. They are not direct measurements and because of it, effective direct control for nitrification is limited.
  2. Energy savings increase with every data quality improvement. Going from ORP testing to online DO is a substantial optimization change. Further upgrading from online DO to online ammonia measurements reduces error and improves system performance even more.
  3. Overtreating for ammonia removal can have significant carbon emission implications. From a macro level, running higher blower speeds and header pressures or running blowers outside of their optimal curve, etc. when it results in over treatment increases unnecessary carbon emissions. Eia.gov states in 2023 the average US CO2 emissions was .81 lbs per kWh used. Running blowers at lower speeds within their pump curves reduces wear and extends their working life.
Grapevine 污水處理廠決定在其三個曝氣系統之一試用 Hach 新型 NH6000sc 氨氮分析儀。
如圖 1 所示，新的NH6000氨氮分析儀及其過濾裝置安裝在曝氣系統的末端。這讓該污水處理廠首次能夠透過其 SCADA 系統即時測量氨氮。根據氨氮監測數據以控制曝氣開始受到歡迎，原因如下：
  1. 在本應用案例中，監測待處理的特定水質參數 - 氨氮，比使用 DO 和 ORP 等替代測量參數更有效。很大的原因是由於 DO 和 ORP 等測量值受到其他干擾和測量要求的影響。它們並非直接測量，對硝化作用的有效直接控制因而受限。
  2. 每次監測數據品質的提升都帶來節能效果。從ORP測試到線上溶氧（DO）是一項重大的優化。而從線上溶氧（DO）測量再進一步升級到線上氨氮測量，則減少誤差並進一步提升系統效能。
  3. 過度處理氨氮去除可能會對碳排放產生重大影響。從宏觀的層面看，提高鼓風機轉速和集管壓力，或是讓鼓風機超出其最佳曲線來運行等等過度的處理會增加不必要的碳排放。 
 
This new analyzer brought a level of diurnal visibility to the facility which grab sampling and composite samples were lacking.  In figure 3 you can see the results of a few weeks of operation. The plant used the real-time ammonia values from the analyzer to slowly start reducing aeration. They closely monitored this third of the treatment plant and allowed the ammonia levels to increase to a level that’s still below their permit requirement.
In figure 3 the first data point for amps represents standard operation before making changes using the new analyzer. The following reductions in blower speed continues until they were able to completely shut off one of their two 100 hp blowers. They operated with one blower off manually for a day as successful test and then put the second blower back online. Overall, during this period, they saw a 28% decrease in power usage when the second blower was removed, and then an average power reduction of 18.4%. This reduction in aeration could represent an annualized savings of $29,953 based on the facility’s electrical rate. In addition to dollars saved this case could represent an annualized carbon emissions reduction of around 404,449 lbs. CO2.
 
Hach 新型 NH6000氨氮監測儀為此污水處理廠帶來了一定程度的全天候可視性，而在此之前，此廠缺乏抓取取樣和複合水樣。
圖3 顯示運作了數週的結果。此廠利用氨氮監測儀提供的即時氨值，開始緩慢減少曝氣量。他們密切監測了這三分之一的廠區處理系統，並允許氨濃度上升至仍然低於排放限值的濃度。
圖3 中，安培的第一個數據點代表在改用新的氨氮監測儀之前的標準運行情況。接下來，鼓風機轉速持續降低，直到他們能夠完全關閉兩台100馬力的鼓風機中的一台。他們手動關閉一台鼓風機運行了一天，成功的測試，然後再重啟運行第二台鼓風機。整體而言，在此期間，當第二台鼓風機被移除後，他們的用電量下降了28%，之後平均用電量下降了18.4%。根據此污水處理廠的電價費率，減少的曝氣量可以節省 29,953美元的年化成本。
除了節省能源費用之外，此案例還可以減少每年約 404,449 磅二氧化碳的碳排放量。
 
Conclusion 結論
The new Hach NH6000sc online ammonia analyzer proved to be a great tool for the city allowing for a new level of visibility that was not previously possible. The Hach gas sensing technology provides a fast response time unlike other technologies, providing values every 5 minutes for efficient control and monitoring in a fast-changing biological environment. In a quote from one of the system managers:
“The new analyzer from Hach allowed us the ability to confidently reduce aeration to optimize efficiency without worry of reaching our ammonia limit.”
實證顯示，全新 Hach NH6000sc 線上氨氮監測儀成為該污水處理廠之得力設備，將水質的可視度提升到新的高度。不同於其他技術，Hach 的氣體感測技術反應速度極快，每 5 分鐘提供一次數值，進而能夠在快速變化的生物環境中協助管理人員達成高效率監測和控制。一位系統經理說：“Hach 的新型監測儀讓我們能夠放心地減少曝氣量，進而優化效率，而無需擔心超出氨氮濃度限值。”
 
The new design allows for out of the box installation outdoors standing up to the elements without a second enclosure. The new reagent set-up is used at a rate which allows for replacement once every 6 months. New sample pumping and stout air backflush has all been integrated into the unit. But often analyzers are only as accurate and easy to use as their filtration system.  The new Hach FX620 filtration systems ability to deliver heavy air backflush makes manually cleaning frequency low even in high solids applications like mixed liquor. The staff pulled the filter to inspect it and found it looking great. Plant staff was surprised by how lightweight and easy to remove the filter was. The new snap in membrane design made for quick removal and secure installation.
NH6000氨氮自動監測儀全新機款設計可以直接安裝於戶外環境，抵禦天候影響。新的試劑設置頻率可以每6個月更換一次。新的水樣幫浦和強勁的空氣反吹功能都整合於儀器設備內。不過，監測儀的精確度和易用性通常也取決於搭配的過濾系統。Hach 新型 FX620 過濾系統能夠提供強勁的空氣反吹功能，即使是對於高懸浮固體濃度的混合液體的應用，也能協助降低手動清潔頻率。在實際試用中，污水處理廠的工作人員取出了過濾器進行檢查並對檢查結果滿意，包括過濾器的輕巧和容易拆卸的設計。全新的卡扣式薄膜設計能夠快速拆卸和安全安裝。
 
In the end improving plant process, protecting the environment, maintaining permit requirements, and balancing it all by being good stewards of funding and energy all play a role in a decision to use online sensors and analyzers. Hach’s innovation is moving forward to bring tools like this to the field with values rooted in simplicity and accuracy.
最後，能夠在達成各項重要目標間取得最佳平衡成為決定採用此線上監測儀的重要因素，其中包括改進污水處理廠工序、保護環境、符合排放標準、妥善運用廠區預算以及電力能源節約。
Hach 持續致力開發兼具準確度和簡便性的價值創新技術設備給全球各地客戶。
 
 
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