The main difference between turbidity and total suspended solids (TSS) lies in what they measure: TSS quantifies the mass of solid particles in a given volume of water, while turbidity measures the amount of light scattered by these solid particles.
What is the Main Difference Between Turbidity and Total Suspended Solids?
While both turbidity and total suspended solids (TSS) are crucial indicators of water quality, they assess different aspects of particulate matter in water. Understanding their distinct measurements and implications is vital for environmental monitoring, water treatment, and regulatory compliance.
What is Turbidity?
Turbidity is a measure of the relative clarity of a liquid. It describes the cloudiness or haziness of water caused by individual particles that are generally invisible to the naked eye, similar to smoke in air. These particles can include clay, silt, finely divided organic and inorganic matter, and various microscopic organisms.
- Measurement Principle: Turbidity is measured by assessing the amount of light that is scattered by the solid particles suspended in the water. A turbidimeter (or nephelometer) shines a light through a water sample and measures the light scattered at a 90-degree angle to the incident beam.
- Units: Typically expressed in Nephelometric Turbidity Units (NTU) or Formazin Turbidity Units (FTU).
- Implications: High turbidity can reduce light penetration in aquatic environments, affecting photosynthesis of aquatic plants. It can also indicate the presence of disease-causing organisms, interfere with disinfection processes in drinking water treatment, and impact the aesthetic quality of water. For more information, refer to the EPA's guidance on turbidity.
What are Total Suspended Solids (TSS)?
Total Suspended Solids (TSS), also known as non-filterable residue, refer to the dry-weight amount of particles suspended in a liquid. These particles are large enough to be retained by a filter and can include a wide range of materials such as silt, clay, plankton, organic matter, and industrial waste.
- Measurement Principle: TSS is a direct measure of mass per unit of water. It is determined by filtering a known volume of water through a pre-weighed filter, drying the filter with the retained particles, and then re-weighing it. The difference in weight provides the mass of the suspended solids.
- Units: Expressed in milligrams per liter (mg/L).
- Implications: High TSS can lead to increased water temperature (as suspended particles absorb heat), reduced dissolved oxygen levels, and can smother aquatic habitats. It also contributes to sedimentation in rivers and lakes, affecting navigation and infrastructure. TSS is a key parameter in wastewater treatment plant efficiency and environmental discharge limits. Learn more about water quality parameters from the USGS.
Key Differences at a Glance
The table below summarizes the core distinctions between turbidity and TSS:
| Feature | Turbidity | Total Suspended Solids (TSS) |
|---|---|---|
| Measurement | Optical property: measures light scattering | Gravimetric property: measures actual particle mass |
| Unit | Nephelometric Turbidity Units (NTU) | Milligrams per liter (mg/L) |
| What it Reflects | Cloudiness, haziness, visual clarity | Quantity of filterable solid material |
| Method | Turbidimeter/Nephelometer (light sensor) | Filtration, drying, and weighing |
| Sensitivity | Highly sensitive to particle size, shape, color | Direct measure of mass, less sensitive to particle optics |
| Primary Use | Indicator of water clarity, potential pathogen risk | Direct measure of particulate pollution, sediment load |
Why Both Measurements Are Important
While related, turbidity and TSS are not directly proportional, meaning a high turbidity reading doesn't always correspond to a high TSS value, and vice-versa. For example:
- Water with many very small, reflective particles (like fine clay) might have high turbidity but relatively low TSS.
- Water with fewer but larger, denser particles (like coarse sand) might have lower turbidity but higher TSS.
Therefore, both measurements are essential for a comprehensive assessment of water quality:
- Turbidity provides a rapid, real-time indicator of water clarity and potential operational issues in water treatment (e.g., filter performance). It's crucial for monitoring drinking water safety.
- TSS offers a precise quantification of the actual solid load, which is critical for understanding pollutant transport, sediment accumulation, and compliance with discharge regulations in wastewater and industrial effluents.
Understanding the unique insights provided by each parameter allows for more effective management and protection of water resources.
