What is Turbidity
Turbidity is an indicator that measures the degree of light scattering or absorption by suspended particles in water. It reflects the clarity or turbidity of water quality. When light passes through water, if there are suspended particles in the water, these particles will scatter or absorb part of the light, making the path of light through the water blurry and the water appear turbid. The level of turbidity is directly related to the physical properties of the water body and the potential content of pollutants.
Causes of Turbidity
Suspended Solids
Solid particles suspended in water, such as silt, soil particles, algae, etc., scatter and absorb light, causing the water to become turbid. The concentration and types of these suspended solids have a direct impact on turbidity.
Organic Matter
Organic matter such as humic acids, proteins, and algal secretions can increase the turbidity of water. These organic substances may originate from biological decomposition, agricultural and industrial wastewater discharge, etc.
Water Agitation and Sedimentation
The agitation process of water will distribute suspended matter more evenly in the water, increasing water turbidity. The sedimentation process, on the other hand, leads to the gradual deposition of particulate matter to the bottom, reducing water turbidity. The agitation and sedimentation of water are influenced by environmental conditions such as wind, water flow, and water depth.
Water Temperature
Terrain and soil type can also affect it. High temperatures promote algae growth, increasing the content of suspended matter in the water, thereby raising water turbidity. Additionally, changes in water temperature affect the dissolved oxygen content and solubility of substances in the water, further influencing its turbidity.
Human Activities
Agricultural, industrial, and urban wastewater discharges contain large amounts of suspended matter, which directly or indirectly enter water bodies, raising water turbidity. Additionally, mining, river diversion, and other engineering activities can also increase water turbidity.
Applications of Turbidity in Various Industries
Drinking Water Treatment
Tap Water Treatment: It enables real-time monitoring of turbidity changes in raw and treated water, helping staff adjust treatment processes promptly to ensure that the effluent water quality meets standards. Turbidity sensors and instruments are used in various stages of water treatment plants, including pre-filtration, post-filtration, sedimentation, and final effluent, to ensure water quality standards are met.
Drinking Water Source Monitoring: It can be used to assess water quality and ensure the safety of drinking water。
Environmental Monitoring
Natural Water Body Monitoring: Widely used in environmental monitoring of rivers, lakes, reservoirs, and other natural water bodies. Real-time monitoring of turbidity changes can promptly detect water pollution issues, providing decision-making support for environmental protection departments.
Municipal Pipeline Water Quality Monitoring: Used to monitor water quality in municipal pipelines, as well as in seawater and freshwater aquaculture farms, providing a comprehensive understanding of water body conditions.
Food Processing and Pharmaceutical Manufacturing
Raw Material Purity Monitoring: An important indicator for measuring raw material purity and product quality. Real-time monitoring of water quality changes during production ensures products are clear and transparent, meeting industry standards and consumer expectations.
Production Process Control: Detects water quality issues promptly during production, preventing contaminants from entering products and ensuring product quality and safety.
Wastewater Treatment
Treatment Effect Evaluation: In wastewater treatment, turbidity is a crucial parameter for assessing treatment effectiveness. Turbidity water quality detectors monitor real-time turbidity changes, helping operators adjust treatment processes to ensure wastewater meets discharge standards.
Wastewater Reuse: In the wastewater reuse system, it is used to evaluate the quality of wastewater treatment to ensure that the reuse water meets the process requirements.
Industrial Process Water Quality Monitoring
Circulating Water Monitoring: In industrial water treatment, turbidity water quality detectors monitor water quality changes, guiding process control, optimizing treatment processes, improving water quality, and reducing energy consumption. They have significant applications in industries such as power, steel, and petrochemicals.
Cooling Water Systems: In the cooling water system, it helps to prevent microbial breeding and corrosion problems and ensure the normal operation of the system.
Methods for detecting turbidity
Colorimetric Method
Principle: Uses a colorimeter or spectrophotometer to measure the difference in absorbance between the sample liquid and a standard liquid, which is then converted into a turbidity value.
Characteristics: It has a certain quantitative capability but requires rigorous calibration and standardization. Suitable for situations requiring quantitative analysis.
Nephelometric Method
Principle: Based on the relationship between the intensity of light scattered by suspended particles in the liquid and turbidity.
Characteristics: High sensitivity and accuracy, suitable for liquids with a wide range of turbidity. Commonly used equipment includes nephelometers, scattering photometers, or laser particle size analyzers.
Light Scattering Method
Principle: It is measured by the scattering phenomenon of the light beam in the liquid, and its value is inferred by measuring the intensity of the scattered light.
Characteristics: With high sensitivity and wide measuring range, it is a commonly used measurement method. Common equipment includes scattering photometers, laser particle size analyzers, and multi-angle light scattering instruments.
Laser Scattering Method
Principle: Utilizes the principle of interference patterns generated by the scattering of laser beams with suspended particles to calculate turbidity by measuring the shape and density of the interference patterns.
Characteristics: High precision measurement, applicable to liquids with a wide range of turbidity, but usually requires specialized equipment for measurement.
Transmission Method
Principle: Obtains turbidity values indirectly by measuring the transmittance of light through the liquid. When light passes through the liquid, suspended particles scatter some of the light, leading to a decrease in transmittance. Based on changes in transmittance, the values can be calculated.
Characteristics: Accurate and stable, suitable for liquids with low turbidity. Commonly used instruments are transmission turbidimeters.
Conductivity Method
Principle: Measurement using electrical conductivity. Conductivity refers to the ability of dissolved substances or suspended particles in the liquid to conduct electricity. As the number of suspended particles increases or the concentration of dissolved substances rises, conductivity increases correspondingly. Therefore, by measuring the conductivity of the liquid, turbidity values can be indirectly obtained.
Characteristics: Sensitive and fast, suitable for liquids with high turbidity. Commonly used instruments are conductivity turbidimeters.
Other Methods
In addition to the above methods, there are other turbidity detection methods, such as particle counting, media filtration, and laser diffraction. These methods each have their unique characteristics, and the appropriate method can be selected based on actual needs for measurement.
In practical operations, it is necessary to select the appropriate measurement method based on the properties of the sample liquid and the measurement requirements, and perform accurate operations and instrument calibration to obtain reliable measurement results. Additionally, the measurement units and ranges of different methods may vary, requiring selection based on specific circumstances
Turbidity Standards Across Various Fields
For Drinking Water
The turbidity of water leaving water treatment plants is generally controlled at around 0.5 NTU, and many cities have already managed to reduce the value of their treated water to below 0.1 NTU to ensure the safety of drinking water.
For Industrial Water
In general, the turbidity limit for makeup water in open industrial recirculating cooling water systems is 5 NTU. Similarly, the value limit for boiler feed water and water used in industrial processes and product manufacturing is also 5 NTU.
For Natural Water
The turbidity of natural water is typically related to suspended matter such as silt, clay, fine organic and inorganic particles, plankton, and other microorganisms. The value of rivers in nature generally ranges from 15 to 3000 NTU, while the value of water in reservoirs and lakes is typically around 1500 NTU.
As can be seen, the value standards for various industries vary depending on the intended use and source of the water, but all aim to ensure water quality safety and meet the specific needs of different industries. In practical applications, it is crucial to strictly adhere to relevant standards and regulations to ensure that water quality meets the required standards.
The Impact of Turbidity on Human Health
The higher the turbidity of drinking water, the greater the risk of digestive diseases for consumers. This is because it may contain more suspended matter, such as bacteria and viruses, which can attach to the surface of these particles, thereby increasing the risk of human infection. This risk is particularly severe for individuals with weakened immune systems.
Long-term consumption of water with excessive turbidity can lead to symptoms such as loss of appetite, vomiting, fever, sweating, generalized pain, and fatigue. These symptoms can directly affect an individual’s daily life and work capacity.
If the iron content in water is excessive and the turbidity is high, prolonged consumption of such water can cause iron deposition in the liver, pancreas, lymph nodes, and other areas. This deposition may lead to serious illnesses such as liver cirrhosis and diabetes, and may even induce cancer.
Water with excessive turbidity often exhibits undesirable sensory characteristics such as a tea-colored appearance and a fishy odor. This not only affects the taste and comfort of the drinker but may also further erode their trust and acceptance of the water quality.
In specific environments like swimming pools, water with excessive turbidity can impair visibility, increasing the risk of accidents. Additionally, The content of suspended matter in water is high, which may damage swimmers’ eyes. Moreover, it can also cause illnesses in humans.
Application Case of Turbidity Meter in Drinking Water Testing
In a residential community, homeowners raised concerns about the quality of tap water, fearing it did not meet safety standards and could affect their health. To promptly address these concerns and ensure water safety, the property management decided to use a five-parameter turbidity detector to conduct a comprehensive test of the community’s tap water quality.
Application Process
Sampling: Property staff collected water samples from the community’s tap water pipes, ensuring they were representative.
Testing: The collected water samples were injected into the five-parameter turbidity detector, which measured the turbidity value by calculating the degree of light scattering in the water sample. Simultaneously, the detector also measured four other water quality-related parameters, including pH, dissolved oxygen, conductivity, and temperature.
Data Analysis: The detector displayed the test results in real-time on the screen and allowed data to be saved for subsequent analysis. The test revealed that the tap water contained high levels of chlorine and iron, resulting in elevated the values.
Measures Taken: Based on the test results, the property management promptly implemented corrective measures, such as adjusting the water treatment process and enhancing pipeline cleaning, to ensure water quality met safety standards.
Turbidity Effect Evaluation
Through the application of the instrument, the property found the problem in tap water in time and took effective measures to ensure the safety of drinking water for residents. At the same time, this case also reflects the important role of the detector in the detection of tap water in residential areas.
Relationship Between Turbidity and Suspended Solids
Turbidity：
It refers to the degree of obstruction caused by the solution to the passage of light, including the scattering of light by suspended matter and the absorption of light by solute molecules. It is not only related to the content of suspended substances in water, but also to their size, shape, refraction coefficient and mass concentration of suspended substances.
Suspended Solids
These are solid materials suspended in water, with particle diameters generally greater than 0.1um, often visible to the naked eye. They include insoluble inorganic and organic matter, silt, clay, microorganisms, and more. These suspended solids are the primary cause of water turbidity.
The Relationship Between Suspended Solids Content and Turbidity
The greater the mass concentration of suspended solids, the higher the turbidity of the solution. This is because suspended solids scatter light in water, increasing the obstruction to light passage, which manifests as increased turbidity.
Water containing suspended and colloidal matter such as mud, silt, fine organic and inorganic matter, plankton, and other substances can become turbid.
The Influence of Suspended Solids Characteristics on Turbidity
Apart from the content of suspended solids, their size, shape, and refractive index also affect turbidity. For instance, larger suspended particles scatter light more strongly, leading to higher Numerical values.
Different suspended solids compositions and properties also influence their ability to scatter and absorb light, further affecting Numerical values.
For other questions about turbidity meters, please click the following links:
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Working Principle of Turbidity Meter
