Turbidity Definition
Turbidity is the degree to which suspended particles in water impede the passage of light, i.e., the cloudiness of a water sample. It reflects the quantity and size of suspended particles (such as sediment, organic matter, microorganisms, etc.) in water and is one of the important indicators for assessing water cleanliness.
Importance of Turbidity
Turbidity is not only an intuitive representation of water appearance but also a key parameter for determining water safety. High turbidity water may contain pathogenic microorganisms and harmful chemicals, affecting drinking water safety, while also reducing water treatment efficiency and increasing treatment costs.
Key Points
Turbidity itself does not directly measure the number of particles in water but measures the scattering and absorption characteristics of light by these particles. Therefore, turbidity is a relative measurement value that requires standardized measurement methods and units.
Common Turbidity Units
There are various units for measuring turbidity, and different regions and fields may use different standards. The following are the main turbidity units and their application scenarios:
Turbidity Unit Conversion Table
| Unit | Full Name | Measurement Principle | Typical Applications |
|---|---|---|---|
| NTU | Nephelometric Turbidity Units | 90° Light Scattering | Drinking Water, Environmental Water Monitoring |
| FAU | Formazin Attenuation Units | Light Transmission Attenuation | Industrial Water Treatment, US Standards |
| JTU | Jackson Turbidity Units | Candle Turbidimeter | Historical Data, Some Traditional Applications |
| FTU | Formazin Turbidity Units | Formazin Standard | Parts of Europe |
Turbidity Measurement Methods
Main Measurement Techniques
Turbidity measurement is mainly based on optical principles, including:
- Scattered Light Method: Measures scattered light intensity at 90° to incident light
- Transmitted Light Method: Measures light attenuation after passing through water sample
- Scattering-Transmission Ratio Method: Combines scattering and transmission measurements to improve accuracy
Modern turbidimeters mostly use the scattered light method, complying with EPA methods and ISO 7027 international standards.
Turbidity Standards and Application Ranges
Different water uses have different turbidity requirements:
- Drinking Water: Usually requires turbidity below 1 NTU, ideal target below 0.3 NTU
- Swimming Pool Water: Recommended turbidity below 0.5 NTU to ensure clarity
- Industrial Water: Depending on process requirements, turbidity standards range from 1-10 NTU
- Wastewater Discharge: According to local regulations, usually required below 5-20 NTU
Factors Affecting Turbidity
Water turbidity is affected by various factors, including:
- Concentration, size and composition of suspended particles
- Water flow velocity and degree of water disturbance
- Seasonal changes (rainfall significantly increases turbidity)
- Human activities (agriculture, construction, industrial emissions)
Turbidity Measurement Tips
When measuring turbidity, note:
- Measure as soon as possible after sampling to avoid particle settling affecting results
- Shake sample thoroughly before measurement but avoid creating bubbles
- Calibrate turbidimeter regularly, verify accuracy with standard solutions
- Clean sample cell to avoid fingerprints or scratches affecting measurement
