What are the applications of activated carbon in municipal water supply?
The safety and taste of municipal water supply (with the core being residential drinking water) are one of the most concerning livelihood topics for the public. With the upgrading of water quality standards and the increasing types of water source pollution, activated carbon has become a "key technology" in the purification process of waterworks due to its core characteristics of efficient adsorption.
1、 What is the role of activated carbon in municipal water supply?
The core role of activated carbon in municipal water supply treatment is "deep purification", which can be regarded as the "quality guardian" of tap water. Its functions cover the entire scene from basic impurity removal to sudden pollution response, and can be divided into three dimensions:
Firstly, we need to address the issues of sensory and basic pollution. The unpleasant odor (such as earthy and chlorine smell) and color (such as yellow turbidity) of tap water are the most easily perceived pain points for residents, which are mostly caused by algal metabolites, humus, residual chlorine, etc. Activated carbon, with its developed pore structure (specific surface area can reach 500-1700 ㎡/g, equivalent to a football field per gram of surface area), firmly intercepts odor molecules and pigments through physical adsorption. At the same time, it uses surface oxygen-containing functional groups to chemically react with residual chlorine, decomposing it into harmless chloride ions, completely improving the taste and appearance of drinking water. In addition, it can also absorb the precipitation hazards caused by metal ions such as iron and manganese in water, making tap water clearer and more transparent.
Next is to remove trace harmful pollutants. Conventional water treatment processes are difficult to deal with trace pollutants such as pesticide residues, endocrine disruptors (such as bisphenol A), disinfection by-products precursors (which can generate harmful substances such as trihalomethanes), and algal toxins, which may have long-term potential impacts on human health. Activated carbon has a wide adsorption spectrum and can treat over 3000 types of pollutants, especially for organic compounds with molecular weights ranging from 200 to 1000 Da. It can accurately intercept such trace impurities and reduce health risks, making it the "core defense line" to ensure the safety of drinking water.
Finally, it is necessary to address sudden pollution and supplement the shortcomings of conventional processes. When water sources encounter sudden situations such as chemical leaks or algae outbreaks, activated carbon can quickly respond and become a "weapon" for emergency response; At the same time, it can compensate for the shortcomings of conventional filtration and disinfection processes, such as small molecule organic matter that cannot be completely removed by conventional processes, or trace harmful substances remaining after disinfection, which can be deeply purified through the adsorption effect of activated carbon.
Compared to other purification technologies, activated carbon also has irreplaceable advantages: high cost-effectiveness, low unit cost of powder activated carbon treatment, suitable for large-scale municipal applications; Safe without secondary pollution, chemically stable, and will not release harmful substances into water; Strong adaptability, no need for large-scale renovation of existing water plant equipment, can be directly integrated into conventional processes, and can be flexibly applied to both small water plants and large water treatment centers.
2、 How does the water treatment plant purify water with activated carbon?
The use of activated carbon in water treatment plants is based on "on-demand adaptation and scenario specific application", with a core focus on two major scenarios: daily deep treatment and emergency response, combined with different process combinations to achieve efficient purification:
In daily routine purification, activated carbon mainly plays the role of "deep fine filtration", and there are two common core application modes: one is the pre-treatment combination of "quartz sand+activated carbon". Quartz sand first intercepts large particles of impurities such as sediment and suspended solids in water like a "coarse sieve", avoiding these impurities from blocking the pores of activated carbon. Then, the water flows into the activated carbon filter for "fine filtration", removing small molecule organic matter, residual chlorine, residual pigments, etc., reducing the burden of subsequent disinfection processes and ensuring stable water quality of the factory water; The second is the advanced treatment process of ozone biological activated carbon (O3-BAC), which is currently the mainstream high-end treatment solution: first, ozone is used to oxidize and decompose large organic molecules that are difficult to degrade in water into small molecules, improving their adsorbability and biodegradability. Then, water flows through a biological activated carbon filter - a layer of microbial film will grow on the surface of the activated carbon, which can intercept small organic molecules through physical adsorption, and microorganisms can further degrade these impurities, forming a synergistic effect of "oxidation+adsorption+biodegradation". This not only improves the purification effect, but also extends the service life of the activated carbon.
In emergency response to sudden pollution, activated carbon focuses on "rapid response" and mainly uses powdered activated carbon (PAC). When the water source encounters algae outbreaks, chemical leaks (such as toxic organic compounds like phenol), or sudden exacerbation of odors, powdered activated carbon does not require additional specialized equipment and can be quickly added to the raw water through the existing dosing system. It can take 15-30 minutes to take effect and efficiently adsorb sudden pollutants. For example, when there is an increase in algae during the rainy season, adding PAC can quickly remove the soil odor and algal toxins, avoiding a deterioration in the taste of tap water; When encountering trace amounts of toxic organic matter leakage, PAC can quickly intercept pollutants and prevent them from entering the residential water end.
In addition, the form of activated carbon will be adjusted according to the treatment process during use: daily deep treatment of multi-purpose granular activated carbon (GAC), due to its large adsorption capacity and renewability, is suitable for long-term stable operation; For emergency response, powdered activated carbon (PAC) is used because of its flexible addition and fast adsorption speed, which can quickly respond to short-term pollution. The combination of two forms enables activated carbon to achieve comprehensive coverage of "daily guarantee+emergency backup" in municipal water supply treatment.
3、 How to choose and use activated carbon in municipal water supply?
The purification effect of activated carbon not only depends on its own characteristics, but also closely related to the selection, addition, maintenance and other operations of the water plant. The core key points can be summarized into four aspects:
Selection needs to be tailored to the specific situation. The water treatment plant will choose the appropriate type of activated carbon based on water quality requirements: Powdered activated carbon (PAC) is suitable for emergency treatment and seasonal water quality fluctuations (such as increased algae during the rainy season), with low cost, flexible addition, no need for regeneration, and is discharged with the sludge in the sedimentation tank after addition; Granular activated carbon (GAC) is suitable for daily deep treatment, with a large adsorption capacity and can be reused. After failure, the adsorption capacity is restored through thermal regeneration, making it suitable for long-term stable operation. At the same time, it will also be adjusted according to the type of impurities in the water source: if there are many high molecular weight organic compounds (such as humic acid and algal toxins) in the water, choose activated carbon with an appropriate proportion of mesopores; If small molecule organic compounds (such as pesticide residues) are the main ones, activated carbon with a large specific surface area and well-developed micropores should be selected.
Adding requires precise control. The dosage and location directly affect the purification effect: during conventional odor control, the dosage is generally 5-15mg/L; In case of sudden pollution, the concentration can be increased to 100mg/L or above, which needs to be determined through static adsorption tests to avoid purification failure caused by insufficient dosage or cost increase caused by excessive dosage. The addition position also has its own requirements: powdered activated carbon should be added before the coagulant or in the middle of the reaction tank, ensuring a contact time with water of not less than 30 minutes, to avoid being wrapped by the alum produced by coagulation and affecting the adsorption effect; Granular activated carbon is usually installed after the fast filter as a deep treatment unit to receive the pre treated water flow and maximize its adsorption effect.
Replacement and regeneration need to be 'timely and standardized'. Powdered activated carbon is disposable, and the dosing frequency can be dynamically adjusted according to the water quality; After the adsorption saturation of granular activated carbon, it needs to be regenerated or replaced in a timely manner. Generally, it should be replaced every 2-3 years. Specifically, the water quality should be considered - if the tap water has a strange odor, the COD (chemical oxygen demand) index exceeds the standard, or the filter head loss is too large, the regeneration or replacement process needs to be initiated. The regenerated activated carbon can restore 70% -90% of its adsorption capacity and can be reused 3-5 times, reducing costs and solid waste pollution.
During use, it is necessary to "prevent secondary risks". One is to avoid microbial growth: After long-term operation of the granular activated carbon filter, a biofilm will form on the surface, which may release metabolic products and increase the risk of disinfection by-products. Therefore, the water plant will regularly monitor the effluent quality and backwash the filter in a timely manner; The second is to prevent carbon particle leakage: Powdered activated carbon particles are small, and if the dosage is too large or the interception effect of the filter is poor, it may enter the water distribution network and cause "black water" phenomenon. Therefore, the water plant will strictly control the dosage before filtration and strengthen the monitoring of the operation of the filter; Thirdly, avoid contact with oxidants: Activated carbon has reducing properties, and if it comes into direct contact with oxidants such as chlorine gas and potassium permanganate, it will reduce its adsorption performance. Therefore, water plants will avoid adding activated carbon immediately after pre chlorination, and if necessary, replace pre chlorination with potassium permanganate; The fourth is to prevent dust pollution: Powdered activated carbon is prone to generating dust during loading, unloading, and addition, which can affect the health of operators and the environment. Therefore, the addition equipment will be sealed and equipped with dust collection equipment if necessary.
4、 What is the development trend of activated carbon application in municipal water supply?
With the continuous strictness of water quality standards and the upgrading of water treatment technology, the application of activated carbon in municipal water supply is developing towards "high efficiency, intelligence, and greening". In the future, it will better meet the high demand of people's livelihood for drinking water quality:
In terms of technological upgrading, in response to the limited adsorption efficiency of traditional activated carbon for new hydrophilic pollutants such as short chain PFAS, functionalized modified activated carbon has become a research and development hotspot - introducing cationic functional groups through surface modification to enhance the adsorption capacity for polar pollutants; Optimize the pore structure, increase the proportion of mesopores, and adapt to the adsorption requirements of small molecule pollutants. At the same time, the combination of activated carbon and advanced oxidation processes (such as ozone) will be more extensive. Firstly, difficult to degrade pollutants will be converted into easily adsorbed intermediates through oxidation, and then deeply removed by activated carbon, forming a synergistic effect of "oxidation+adsorption", greatly improving purification efficiency.
In terms of intelligent applications, in the future, water treatment plants will use online monitoring devices (such as TOC sensors and odor detectors) to capture real-time changes in water quality, combined with PLC control systems to automatically adjust the amount of activated carbon added and backwash frequency, achieving "precise addition and dynamic optimization". At the same time, utilizing IoT technology to remotely monitor the operation status of activated carbon filters, predict adsorption saturation time, arrange regeneration or replacement in advance, reduce manual intervention, and improve the stability and economy of system operation.
In terms of green and low-carbon, the raw materials for the preparation of activated carbon will become more environmentally friendly, such as using bamboo as the raw material for activated carbon to reduce dependence on traditional resources; Regeneration technology will continue to be optimized to improve regeneration efficiency.