水中氯與分析 Chlorine
Why Chlorine Measurement, Testing and Analysis Matter to Water Quality 為什麼氯含量的測量和分析對水質很重要?
Chlorine (Cl2) is strong oxidizing agent and ideal disinfectant. Proper residual chlorine levels in drinking water ensure that water is safe for human consumption, but too much chlorine can have detrimental effects in pharmaceutical production, membrane treatment processes and other applications.
Proper measurement and monitoring of residual chlorine levels helps to mitigate these risks. Whether you're working in a laboratory or in the field, Hach provides a variety of chlorine analyzers, sensors, reagents and more that help offer simple and reliable measurements that you can trust.
氯（Cl2）是強氧化劑和理想的消毒劑。飲用水中適當的殘留氯含量可以確保水質對人類是安全的，但過多的氯會對藥品生產、薄膜處理流程和其他應用產生不利影響。
正確測量和監測餘氯濃度協助降低以上這些風險。無論您是在實驗室還是在現場工作，Hach 提供各種氯濃度分析儀、感測器、試劑等，協助您簡單、專業可靠的測量。
正確測量和監測餘氯濃度協助降低以上這些風險。無論您是在實驗室還是在現場工作，Hach 提供各種氯濃度分析儀、感測器、試劑等，協助您簡單、專業可靠的測量。
Why Measure Chlorine 為什麼要測量氯濃度 ?
When added to water, chlorine reacts to form free chlorine or chloramines (when ammonia is present), which 當氯加入水中時，會發生反應，形成遊離氯或氯胺（當有氨時），其作用如下 :
• act as potent germicides. 做為強效殺菌劑
• oxidize metals allowing them to be removed. 氧化金屬，使其被去除
• reduce many disagreeable tastes and odors. 減少許多令人不舒服的味道和氣味
• act as potent germicides. 做為強效殺菌劑
• oxidize metals allowing them to be removed. 氧化金屬，使其被去除
• reduce many disagreeable tastes and odors. 減少許多令人不舒服的味道和氣味
Risks Associated with the Presence of Residual Chlorine 水中殘留氯的風險
- Health 健康 - Chlorine must be removed from the water used for dialysis to prevent patients from other health issues, including cardiac arrest. 必須從透析水中去除氯，以防止患者出現心臟驟停等其他健康問題
- Environmental 環境 - Even at low levels, chlorine can cause environmental harm, especially to organisms living in water and soil. 即使是低濃度的氯也能對環境造成危害，尤其是對生活在水中和土壤中的生物
- Structures 結構 - Chlorides that may form due to the use of chlorinated water can cause stress cracks in stainless steel, potentially compromising equipment and structures. 使用氯化水可能形成的氯化物會導致不銹鋼產生應力裂紋，進而可能損壞設備和結構
- Pharmaceutical 製藥 - Chlorine can damage active pharmaceutical agents during production, resulting in poor product quality or product loss. 氯會在製藥過程中破壞活性藥劑，導致產品品質不佳或產品耗損
- Water Treatment Equipment 水處理設備 - In water treatment systems, chlorine can degrade reverse osmosis membranes and ion exchange resins. 在水處理系統中，氯會降低逆滲透膜和離子交換樹脂的效能
Dechlorination Methods 脫氯方法
Since chlorine can be detrimental, there are applications that require "dechlorination." Adsorption dechlorination uses activated carbon to remove chlorine compounds. Chemical dechlorination uses reducing agents such as sulfites, bisulfites or metabisulfites to destroy chlorine species. 由於氯是有害的，因此有些應用需要「脫氯」。吸附脫氯利用活性碳去除氯化合物。化學脫氯使用還原劑（如亞硫酸鹽、亞硫酸氫鹽或焦亞硫酸鹽）來破壞氯化物。
Since chlorine can be detrimental, there are applications that require "dechlorination." Adsorption dechlorination uses activated carbon to remove chlorine compounds. Chemical dechlorination uses reducing agents such as sulfites, bisulfites or metabisulfites to destroy chlorine species. 由於氯是有害的，因此有些應用需要「脫氯」。吸附脫氯利用活性碳去除氯化合物。化學脫氯使用還原劑（如亞硫酸鹽、亞硫酸氫鹽或焦亞硫酸鹽）來破壞氯化物。
Which Processes Require the Monitoring of Chlorine 哪些過程需要監測水中氯濃度 ?
Drinking Water Treatment and Distribution 飲用水處理和配水系統
During pre-oxidation, source water entering a plant is dosed with chlorine (pre-chlorination) to precipitate out minerals as a primary treatment step (besides disinfection) to help with suspended and dissolved matter removal before filtration. The water is then filtered to improve clarity and chlorinated again.
For chlorine to be effective, its concentration before and after filtration (as well as pH, water temperature, and contact time) must be monitored and controlled. Most treatment plants have a contact chamber (clear well) where chlorine is injected, mixed and allowed to remain in contact with the water for the required time dependent on the temperature, pH and type of microorganisms present in the water. The contact time provides a chlorine residual, intended to maintain water sanitized as it enters storage tanks and travels throughout the distribution system.
All chlorination before (pre-chlorination) and after filters (post-chlorination) is controlled at multiple points throughout the treatment process and in the distribution system. Additional booster chlorination of tap water in the network is usually conducted at pump/booster stations and must be thoroughly monitored and controlled.
It is essential to monitor chlorine levels in the distribution system to ensure that the proper level of chlorine residual is maintained to meet regulatory standards for disinfection, and to ensure that there is no excessive chlorine present.
在整個水處理過程和配水系統中，所有過濾器之前（預氯化）和之後（後氯化）的氯化都在多個點進行控制。
- Chlorine eliminates slime bacteria, molds and algae that commonly grow in water supply reservoirs, on the walls of water mains, and in storage tanks. 氯可以消滅常見於水庫中、水管壁和儲水箱中的黏菌、黴菌和藻類
- Chlorine is a potent germicide, reducing the level of many disease-causing microorganisms in drinking water to regulatory appropriate levels. 氯是一種強效殺菌劑，（在劑量控制下）可將飲用水中多種致病微生物的含量降低至適當的濃度
- Chlorine helps remove dissolved iron and manganese from raw water. 氯有助於去除原水中溶解的鐵和錳
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Chlorine reduces many disagreeable tastes and odors by 氯減少許多令人不快的味道和氣味 :
- oxidizing natural organics such a foul-smelling algae secretion, sulfides, and odors from decaying vegetations.
- destroying hydrogen sulfide, which has a rotten egg smell.
- removing ammonia and other nitrogenous compounds that may cause unpleasant tastes.
Disadvantages of Using Chlorine to Disinfect Drinking Water 使用氯消毒飲用水的缺點
- Chlorine is not effective against cryptosporidium, a life-threatening parasite. 氯對危及生命的寄生蟲隱孢子蟲無效
- During chlorination, unwanted ammonia can react with chlorine excess to form chloramines that lower the disinfection potential and may create taste/odor issues when not monitored and controlled efficiently. 在氯化過程中，多餘的氨會與過量的氯發生反應，形成氯胺，進而降低消毒潛力，並且如果沒有得到有效監測和控制，可能會產生味道/氣味問題
- When reacting with organics in water, chlorine can form disinfection by-products (DBP) that are considered harmful to human health. Due to these risks, there are regulations that limit levels of DBP as well as chlorine residual concentrations in drinking water. 氯與水中的有機物反應時，會形成對人體健康有害的消毒副產物 (DBP)。由於這些風險，因此制定了法規限制飲用水中的 DBP 含量以及氯殘留濃度
Wastewater Treatment 廢污水處理
Chlorination is used in the final stages of treatment to kill pathogens, as well as the microorganisms used in previous treatment stages to prevent the spread of waterborne diseases. To reduce the toxicity of the effluent, dechlorination is used to manage chlorine residuals and ensure compliance with regulations before effluent waters are discharged into lakes, rivers or the ocean. Chlorine is used to oxidize cyanides, which are amenable to chlorination. 在處理的最後階段使用氯化來殺死病原體，以及在先前處理階段使用的微生物，以防止水傳播疾病的傳播。為降低排放廢污水的毒性，在將排放水排入湖泊、河流或海洋之前，需要採用脫氯製程來處理氯殘留物，確保符合法規標準。
Industrial Cooling Towers 工業冷卻水塔
Chlorine levels must be monitored and controlled because if chlorine levels are too low, biogrowth can prevail and clog the water systems. However, if chlorine levels are too high, corrosion or other damage may occur. 必須監測和控制氯濃度，因為如果氯濃度太低，生物就會生長並堵塞水系統。但是，如果氯濃度過高，可能會發生腐蝕或其他損壞。
Chlorine levels must be monitored and controlled because if chlorine levels are too low, biogrowth can prevail and clog the water systems. However, if chlorine levels are too high, corrosion or other damage may occur. 必須監測和控制氯濃度，因為如果氯濃度太低，生物就會生長並堵塞水系統。但是，如果氯濃度過高，可能會發生腐蝕或其他損壞。
Food Processing 食品加工
Chlorine is often used as a sanitizing agent for fruits, vegetables, poultry and meats. Maintaining proper chlorine residuals is essential for optimizing the sanitizing power of rinse water. The recirculated water used for the rinse bath during pasteurization at the end of the packing process, accumulates contaminants. Therefore, it is necessary to maintain a chlorine residual to sanitize the water. 氯經常被用做水果、蔬菜、家禽和肉類的消毒劑。保持適當的氯殘留量對於優化清洗水的消毒能力很重要。包裝程序結束時的巴氏殺菌過程中用於沖洗槽的循環水中會積聚污染物。因此，有需要保持適當量的殘留氯來消毒水。
Clean-In-Place (CIP) Processes Used in Food, Beverage and Pharmaceutical Industries 食品、飲料和製藥產業使用的就地清洗 (CIP) 工藝
Piping and vessels used in industrial processes are periodically cleaned and sanitized in a procedure called Clean-In-Place (CIP). Chlorine must be monitored to ensure that appropriate levels exist in the CIP solution for disinfection and to prevent contamination of products due to either lack or excess of chlorine. 工業過程中使用的管道和容器會透過「就地清洗」（CIP）的程序定期進行清潔和消毒。必須對氯濃度進行監測，以確保 CIP 溶液中存在適當的消毒量，並防止因缺乏或過量的氯而導致產品受到污染。
Piping and vessels used in industrial processes are periodically cleaned and sanitized in a procedure called Clean-In-Place (CIP). Chlorine must be monitored to ensure that appropriate levels exist in the CIP solution for disinfection and to prevent contamination of products due to either lack or excess of chlorine. 工業過程中使用的管道和容器會透過「就地清洗」（CIP）的程序定期進行清潔和消毒。必須對氯濃度進行監測，以確保 CIP 溶液中存在適當的消毒量，並防止因缺乏或過量的氯而導致產品受到污染。
How is Chlorine Monitored 如何監測水中氯濃度 ?
Colorimetry 比色法
In general, this optical method uses color intensity measurements to determine the concentration of chlorine in a solution. When appropriate buffer and indicator solutions are added to the sample, a reaction occurs producing a color, which intensity is proportional to the chlorine concentration. The color intensity is measured by eye, colorimeter or spectrophotometer. This method is susceptible to interference from color and turbidity in the sample, as well as some chemical substances besides chlorine, concurrently reacting with the indicator.
DPD Method
DPD method is the most widely used colorimetric method to measure chlorine. It can be used to measure both free and total chlorine with field, lab and online instrumentation. However, DPD method is subject to interference from other oxidants such as manganese, chromium and chloramines.
DPD method is the most widely used colorimetric method to measure chlorine. It can be used to measure both free and total chlorine with field, lab and online instrumentation. However, DPD method is subject to interference from other oxidants such as manganese, chromium and chloramines.
Indophenol Method 靛酚法
Indophenol method, being selective to monochloramine, can be used to measure monochloramine and free ammonia as well as free chlorine. Monochloramine is determined directly, while for determination of both monochloramine and free ammonia in the same sample method uses additional reagent to convert free ammonia into monochloramine. Free chlorine can also be measured by the indophenol method using a two-reagent system that is not subject to the interferences that affect the DPD method. However, this method is only available for the laboratory or field analyses and not for online analyzers.
Indophenol method, being selective to monochloramine, can be used to measure monochloramine and free ammonia as well as free chlorine. Monochloramine is determined directly, while for determination of both monochloramine and free ammonia in the same sample method uses additional reagent to convert free ammonia into monochloramine. Free chlorine can also be measured by the indophenol method using a two-reagent system that is not subject to the interferences that affect the DPD method. However, this method is only available for the laboratory or field analyses and not for online analyzers.
Titration 滴定法
This method determines chlorine concentration based on a completion of chemical reaction between the chlorine and titrant added to the sample. The titrant is added incrementally until the reaction is complete. The endpoint (or equivalence point) is the point at which the titrant and chlorine are balanced. The equivalence point can be determined visually using a color indicator or by using an electrochemical sensor. Manual, visual measurements are less precise and more susceptible to interference from color or turbidity in the sample, while titration using electrodes is more accurate and not susceptible to those interferences.
DPD-FEAS Method
DPD-FEAS method uses a magenta visual indicator that is titrated to a colorless endpoint. This method measures free and total chlorine.
Iodometric MethodDPD-FEAS method uses a magenta visual indicator that is titrated to a colorless endpoint. This method measures free and total chlorine.
Iodometric method uses a blue visual indicator that disappears at the titration endpoint. This method is typically used to measure high concentrations of total chlorine.
Amperometric 安培法
This method represents amperometric titration to determine the endpoint either manually, or automatically. A small voltage is applied to the electrode and the endpoint is determined by a change in current, resulting from the reduction of chlorine by the titrant (phenylarsine oxide). The change in current and the volume of titrant are measured to correspond to the concentration of the chlorine. This method offers procedures for measuring both free and total chlorine, chlorine dioxide and chlorite, while using forward and back titration procedures.
This method represents amperometric titration to determine the endpoint either manually, or automatically. A small voltage is applied to the electrode and the endpoint is determined by a change in current, resulting from the reduction of chlorine by the titrant (phenylarsine oxide). The change in current and the volume of titrant are measured to correspond to the concentration of the chlorine. This method offers procedures for measuring both free and total chlorine, chlorine dioxide and chlorite, while using forward and back titration procedures.
Online Amperometry 線上安培法
This electrochemical method measures the change in electrical current resulting from chemical reactions taking place at the electrodes, with the current being proportional to the chlorine concentration. Different amperometric sensor designs are available, providing better selectivity for different chlorine species. This method is not susceptible to interference from color or turbidity in the sample, however, the sensor surface exposed to the sample is prone to fouling. Some amperometric analyzers do not require reagents. Amperometric sensors require maintenance and must be calibrated in-situ at a frequency dependent on the application.