Turbidity in Industrial Wastewater- How to reduce turbidity

By rana aymen On Apr 20, 2025 148 0

Contents

1 What is Turbidity?

2 How is Turbidity Measured ?

3 What Are the Effects of High Turbidity?

4 How to Reduce Water Turbidity

4.1 Coagulation-Flocculation

4.2 Settling and Decanting

4.3 Backwashing Filter

4.4 Reverse Osmosis Filtration

4.5 Ultrafiltration

5 Conclusion

6 References

Wastewater treatment is vital for ensuring environmental sustainability. Effective treatment processes eliminate pollutants and contaminants from wastewater, guaranteeing that the released water meets established quality standards. Among various parameters monitored in wastewater treatment, turbidity is a key indicator of water quality. This article explores the significance of turbidity in wastewater management and outlines various methods to reduce turbidity, ensuring compliance with environmental standards and promoting safer water reuse.

What is Turbidity?

Turbidity refers to the cloudiness or haziness of a liquid due to suspended particles. In wastewater treatment, turbidity measurements offer insights into the concentration of these particles in the water. Such particles can include suspended solids, organic matter, bacteria, and other contaminants. Turbidity is usually measured in Nephelometric Turbidity Units (NTU) and is a crucial parameter for evaluating the quality of treated wastewater. The level of cloudiness or the presence of suspended particles in the wastewater sample is generally measured in FTU, or Formazin Turbidity Units. Samples with less than 20 FTU are considered very clear, while those with 500 FTU or more appear completely opaque.

How is Turbidity Measured ?

A widely used method for measuring wastewater turbidity is Nephelometry, which relies on scattered light. Standards like ISO 7027 and EPA 180.1 dictate the use of infrared light (860 nm) or white light (500 nm) as the light sources for testing.

When light interacts with the wastewater sample, suspended particles reflect the incoming light. The scattering pattern depends on the shape, density, and size of these particles. Smaller particles usually reflect light in a perpendicular direction, while larger particles scatter light in various directions. Sensors positioned around the sample measure both the amount of reflected light and its scattering direction, enabling the assessment of turbidity, total suspended solids, and particle sizing.

High turbidity indicates a significant presence of tiny particles in the water, while low turbidity suggests minimal particles, reflecting its cleanliness. In industrial wastewater management, achieving low turbidity is essential for meeting discharge permit regulations or for reuse. Elevated turbidity often signals that wastewater treatment systems require attention.

What Are the Effects of High Turbidity?

The primary issue with high turbidity is its impact on the aesthetic quality of a water source. This can adversely affect tourism and recreational activities, as well as harm marine and aquatic life by diminishing oxygen and food availability.

From a water treatment perspective, treating water with high turbidity is more costly, as it requires more extensive filtration to eliminate sediments of various sizes. Drinking water with elevated turbidity levels can pose health risks, depending on the source of the turbidity. For example, water containing certain total suspended solids (TSS) like algae and bacteria can lead to illness. Other common turbidity causes, such as sand and dirt, may not be harmful to health, but this sediment can negatively impact your home’s plumbing, pipes, and water-based appliances.

How to Reduce Water Turbidity

Reducing water turbidity can extend the lifespan of a filtration system and help prevent water contamination. The following turbidity filtration methods can assist in removing turbidity from water:

Coagulation-Flocculation

The coagulation-flocculation treatment process destabilizes colloids in water, leading to their aggregation for physical removal. When combined with sedimentation and filtration, this process effectively reduces turbidity. Coagulation causes particles to bind together, while flocculation refers to the visible sticking of these particles.

In the coagulation-flocculation process, water is collected in a container before a coagulant is added to facilitate flocculation and settling. Common coagulants in large-scale water treatment include metal salts like ferric sulfate, aluminum sulfate, and ferric chloride. The dosing and effectiveness of coagulation depend on the water’s pH level. During sedimentation, particles settle at the bottom of a container or basin, allowing the resulting sludge to be removed before the water proceeds to filtration.

Settling and Decanting

In the settling and decanting process, water is left to sit for two to 24 hours, enabling particulates to settle at the bottom of a container. The clear water at the top can then be decanted into another container, effectively separating it from the settled particles. This method requires minimal equipment but is more time-consuming compared to other techniques.

Backwashing Filter

Water treatment filters accumulate contaminants, causing particles to adhere to the surfaces of filter grains. This filtration process can lead to particulates filling the spaces between filter grains, resulting in increased flow resistance and pressure drops. Backwashing involves reversing the water flow at a higher velocity to push water back through the filter, removing clogged particles. Sand or multimedia filtration are the most common backwashing filters used for turbidity reduction, though other media may be chosen based on turbidity loading.

Reverse Osmosis Filtration

Reverse osmosis (RO) is a water filtration system that employs a semipermeable membrane to capture particulates and larger molecules while allowing water to pass through. In the RO filtration process, high pressure forces water through the membrane to eliminate contaminants through the following steps:

Prefiltration: A pre-filter captures large particles like dirt and dust.

Reverse osmosis: The semipermeable membrane captures smaller, dissolved particles.

Drainage: Removed contaminants are drained from the filtration system.

Storage: Treated water is stored for future use.

Ultrafiltration

Ultrafiltration (UF) systems utilize hollow fiber membranes to eliminate suspended solids and finer particles from water, thereby reducing turbidity. UF systems filter solid particulates at a microscopic level. While they remove fewer types of contaminants than RO systems, they retain beneficial minerals such as magnesium and calcium.

Conclusion

Monitoring turbidity is essential in wastewater treatment. By evaluating turbidity levels, treatment facilities can gauge the effectiveness of their processes, identify contamination, enhance coagulation and flocculation, and track suspended solids. As wastewater treatment gains importance for ecological conservation, turbidity monitoring continues to be a vital tool for ensuring the quality of treated water and protecting the environment.