Colorful wastewater transforming into clean water with HSV color grid overlay.

Decoding Wastewater: How Color Analysis Can Revolutionize Treatment

Author's portrait.
Avery Sinclair in Climate & Environment August 2025 • 4 min read.

"Discover how a simple color-based index is transforming wastewater treatment, making it smarter, cheaper, and more effective for healthier communities."


Wastewater treatment plants (WWTPs) are essential for protecting public health and the environment. Traditionally, operators rely on a combination of laboratory tests and visual inspections to assess the health and performance of these plants. However, advancements in technology are paving the way for innovative and more efficient monitoring methods.

Among these emerging techniques, color analysis is gaining traction as a valuable tool for understanding the operational conditions of wastewater treatment processes. The color of activated sludge, a key component in wastewater treatment, can provide insights into factors such as mixing efficiency and oxygen levels. While visual observation has long been a part of wastewater management, recent research is transforming this practice into a quantifiable and data-driven approach.

A groundbreaking study has introduced a new color-based index, known as CVH/S, that correlates the color of sludge with operational conditions. This index, derived from the HSV (Hue, Saturation, Value) color space, offers a promising way to monitor mixing and oxygen deficiency in wastewater treatment plants. By leveraging readily available color information, this approach opens doors for more cost-effective and responsive management of wastewater treatment processes, with potential applications in Internet of Things (IoT) technologies.

Unlocking the Secrets of Sludge Color: What Does It Tell Us?

Colorful wastewater transforming into clean water with HSV color grid overlay.

The study, conducted by researchers at Xi'an University of Architecture and Technology and the University of Science & Technology of China, delved into the relationship between sludge color and operational conditions within wastewater treatment plants. The central finding revolves around the coordinates H (Hue) and S (Saturation) of the HSV color space. These coordinates demonstrated a strong correlation with the biological status of the sludge and the specific operational conditions, such as mixing and oxygen availability.

Researchers developed the Coefficient of Variation of H/S (CVH/S) by analyzing sludge cake images. CVH/S is not just a number; it's a revealing index. Lower CVH/S values indicate better mixing conditions. The research team substantiated these observations through a series of laboratory-scale experiments and real-world assessments at two full-scale WWTPs. This data suggests that CVH/S could serve as a reliable metric for ongoing monitoring of mixing efficiency.

  • Hue (H): Represents the type of color, indicating the nature of the sludge.
  • Saturation (S): Indicates the degree of color intensity.
  • Value (V): Represents the light intensity and brightness.
The study didn't stop at color analysis; it went deeper into biological activity. Researchers examined the Oxygen Uptake Rate (OURq) – essentially, how quickly microorganisms consume oxygen. The OURq trends mirrored CVH/S patterns. Microbial community analysis further cemented the significance of CVH/S: it reflects changes in the composition and diversity of the microbial community, hinting that CVH/S captures the effects of operational tweaks on essential biological processes. The implication? CVH/S is a biologically meaningful index. It quantifies the impact of changing operational conditions, offering a way to translate past experiences into actionable data.

Implications for the Future of Wastewater Management

This research has far-reaching implications for the future of wastewater treatment. The CVH/S index offers a simple, cost-effective, and biologically relevant method for monitoring the health and performance of activated sludge systems. By integrating color analysis with IoT technologies, wastewater treatment plants can move towards more automated, data-driven, and responsive management practices, ultimately contributing to healthier communities and a more sustainable environment.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1016/j.jenvman.2018.12.025, Alternate LINK

Title: Probing Operational Conditions Of Mixing And Oxygen Deficiency Using Hsv Color Space

Subject: Management, Monitoring, Policy and Law

Journal: Journal of Environmental Management

Publisher: Elsevier BV

Authors: Zhi-Hua Li, Dong Han, Cheng-Jian Yang, Tian-Yu Zhang, Han-Qing Yu

Published: 2019-02-01

Everything You Need To Know

1

What is CVH/S, and how does it relate to wastewater treatment processes? Does it measure nutrient levels?

The Coefficient of Variation of H/S, or CVH/S, is a color-based index derived from the HSV color space used to monitor mixing and oxygen deficiency in wastewater treatment plants. It analyzes sludge cake images, where lower CVH/S values indicate better mixing conditions. It does not directly measure nutrient levels such as nitrogen or phosphorus, which are also important factors in wastewater treatment. Additional tests are needed to monitor those parameters.

2

Can you explain what the HSV color space is, and what do Hue, Saturation, and Value represent within that space?

The HSV color space consists of three components: Hue (H), Saturation (S), and Value (V). Hue represents the type of color, indicating the nature of the sludge. Saturation indicates the degree of color intensity. Value represents the light intensity and brightness. This is different from other color spaces, such as RGB (Red, Green, Blue), which is commonly used in display technologies and may not be as intuitive for analyzing the color properties of sludge.

3

What is the Oxygen Uptake Rate (OURq), and how does it relate to the CVH/S index in wastewater treatment analysis?

The Oxygen Uptake Rate (OURq) measures how quickly microorganisms in wastewater consume oxygen. Researchers found that OURq trends mirrored the CVH/S patterns. This correlation suggests that the CVH/S index is not just a measure of color but also reflects the biological activity within the activated sludge. Measuring OURq alone doesn't give insight into mixing efficiency; the CVH/S gives additional context.

4

Which specific data points from sludge color are used to calculate the CVH/S index?

The CVH/S index uses data from the Hue (H) and Saturation (S) components of the HSV color space. Hue represents the type of color, indicating the nature of the sludge, while Saturation indicates the degree of color intensity. The Value (V) component, which represents light intensity and brightness, may also be considered, but the study emphasized the coordinates H and S to create CVH/S.

5

What are the potential benefits of integrating the CVH/S index with IoT technologies in wastewater treatment plants?

By integrating the CVH/S index with Internet of Things (IoT) technologies, wastewater treatment plants can move towards more automated, data-driven, and responsive management practices. This can lead to cost savings through optimized resource allocation, improved treatment efficiency, and proactive identification of potential problems. The integration of CVH/S with IoT enables real-time monitoring and remote control of wastewater treatment processes.

Newsletter Subscribe

Subscribe to get the latest articles and insights directly in your inbox.