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Contact Angle

Contact Angle

When a solid is dipped inside a liquid, the liquid surface becomes curved near the contact. For some solid–liquid interfaces, the liquid is pulled up along the solid, while for others, the liquid surface is convex or depressed near the solid surface. This phenomenon can be explained using the concept of cohesive and adhesive forces.
The adhesive force is the molecular force between molecules of different materials, that is, between the molecules of the solid and the liquid. The cohesive force...

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Related Experiment Video

Updated: Jul 17, 2026

Determination of the Settling Rate of Clay/Cyanobacterial Floccules

Determination of the Settling Rate of Clay/Cyanobacterial Floccules

Published on: June 11, 2018

Determination of denitrifying sludge settleability using contact angle measurements.

J A Lopez-Barrera¹, A Peña-Calva, R Olayo

¹Universidad Autónoma Metropolitana-Iztapalapa, Departamento de Física, Av. San Rafael Atlixco 186, col. Vicentina C. P. 09340, Mexico.

Environmental Technology

|January 6, 2007

Summary

Contact angle (CA) measurements effectively track changes in denitrifying sludge settleability. This simpler, faster CA method correlates highly with sludge settleability, outperforming the sludge volume index (SVI) test.

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Last Updated: Jul 17, 2026

Determination of the Settling Rate of Clay/Cyanobacterial Floccules

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Published on: June 11, 2018

Measurement of the Potential Rates of Dissimilatory Nitrate Reduction to Ammonium Based on 14NH4+/15NH4+ Analyses via Sequential Conversion to N2O

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Estimating Sediment Denitrification Rates Using Cores and N2O Microsensors

Estimating Sediment Denitrification Rates Using Cores and N₂O Microsensors

Published on: December 6, 2018

Area of Science:

Environmental Science
Water Treatment Engineering
Microbiology

Background:

Sludge settleability is crucial for wastewater treatment efficiency in Upflow Anaerobic Sludge Blanket (UASB) reactors.
Monitoring changes in sludge surface properties can provide insights into settleability dynamics.
Traditional methods like Sludge Volume Index (SVI) can be time-consuming and less sensitive to subtle changes.

Purpose of the Study:

To adapt and evaluate the contact angle (CA) measurement technique for monitoring denitrifying sludge settleability.
To compare the efficacy of the CA method with the conventional Sludge Volume Index (SVI) method.
To establish the correlation between CA measurements and actual sludge settleability.

Main Methods:

Denitrifying sludge was cultivated in a lab-scale Upflow Anaerobic Sludge Blanket (UASB) reactor.
Sludge settleability was intentionally reduced by decreasing the hydraulic residence time (HRT).
Contact angle (CA) was measured using air and nitrogen bubbles, and compared with Sludge Volume Index (SVI) measurements.

Main Results:

The contact angle (CA) measurement technique demonstrated a high correlation with sludge settleability.
A significant decrease in hydraulic residence time (HRT) led to a loss of sludge settleability.
The CA method proved to be simpler and required less time than the SVI method.

Conclusions:

Contact angle (CA) measurement is a reliable and efficient method for assessing denitrifying sludge settleability.
The CA technique offers a practical alternative to the Sludge Volume Index (SVI) for real-time monitoring in wastewater treatment.
This method can aid in optimizing UASB reactor operation by providing rapid feedback on sludge performance.