Understanding Odour Control Guidelines in Wastewater Treatment Plants

Why Odour Control Guidelines Are Important

Wastewater treatment plants (WWTP) including Sewage treatment plants (STP) and Effluent treatment plants (ETP) often emit strong, unpleasant odours due to the release of gases generated during the decomposition of organic waste and chemical reactions in the treatment process. These emissions, when it is left unchecked, can affect the health and comfort of operators and the residents nearby, it can corrode sensitive electronic equipment, and lead to complaints from nearby communities.

Government agencies such as the CPCB (India) and the U.S. EPA, and professional bodies such as the Water Environment Federation (WEF), have published reference material on odour. It covers how odour is measured, how it is regulated and which treatment technologies are available. They also guide the design and performance expectations for odour control units (OCUs).

For a waste water treatment plant, the gaseous emissions could vary depending on the waste that is coming in for treatment. For an STP, which handles only sewage, the gases emitted are known and will not vary compared to an ETP, where different chemicals come in for treatment depending on the nature of industry in which it is operated.

Hydrogen Sulfide (H₂S), which is not only the most common odour-causing agent but also highly corrosive and hazardous even at low concentrations is a critical gas which causes odour nuisance in WWTP. Outlet H₂S targets for OCUs are set for each project. They depend on the application, how close the outlet is to people or sensitive equipment, and the regulatory, permit or tender requirements that apply. AQOZA’s wastewater projects have typically been designed for an outlet H₂S below 1 ppm.

Implementing the guidelines would help to eradicate the problem at source. 

This could ensure:

• Protection of public and occupational health
• Prevention of environmental nuisance
• Compliance with legal standards
• Long-term protection of infrastructure and electronic assets

Odour Control Guidelines

Odour management in wastewater treatment plants is a key environmental and operational concern, but there is no universal regulatory standard that mandates a specific concentration limit for odorous gases like Hydrogen Sulfide (H₂S) at the outlet.

However, several global and national organizations provide guidance documents and tell of best practices that are widely followed by the industry. Some are as stated below:

• EPA (USA): While the U.S. EPA does not prescribe a fixed odour limit nationally, it provides overview-level technical guidance on odour assessment, monitoring and control through documents such as the Biosolids and Residuals Management Fact Sheet: Odor Control in Biosolids Management (EPA 832-F-00-067). Odour requirements are largely set through local ordinances, many of which treat odour as a public nuisance.
• WEF (Water Environment Federation): Manual of Practice 25 (MOP 25), Odor Emissions and Control for Collection Systems and Water Resource Recovery Facilities is a widely used engineering reference. It covers odour sampling and measurement, regulations, public outreach, and biological, chemical and physical treatment technologies.
• CPCB (India): India has no national numerical limit for odour or H₂S at sewage treatment plants. The Central Pollution Control Board’s Guidelines on Odour Pollution & its Control (May 2008) describe the sources of odour, how it is measured and the technologies used to control it. The report recommends standardised odour measurement, better data on odorous emissions, and source-specific odour standards for sectors including wastewater treatment plants. In practice, outlet targets for odour control units are set project by project, through tender specifications, consultant requirements or state pollution control board conditions.

How Should the Outlet Target for an Odour Control Unit Be Set?

There is no universal outlet limit for H₂S, so each OCU’s design target should be set for its site. Engineers usually consider: (a) regulatory or permit conditions; (b) the tender or consultant specification; (c) distance to residents, workers and sensitive equipment; (d) the inlet gas load and how much it varies.

A clearly defined outlet target helps to:

• Reduce nuisance odour for workers and neighbours
• Reduce corrosion of nearby equipment
• Show that the system meets the project specification

Why Following These Guidelines are Important and How to Achieve It

Maintaining odour control guidelines is important to protect health, prevent complaints or legal issues, and helps in smooth operation. Regular monitoring helps identify the main sources of odours, while effective solutions like Odour Control Units (OCUs) remove harmful gases such as hydrogen sulfide, VOCs and mercaptans before they cause problems. With proper maintenance, OCUs offer a practical way to meet project and regulatory requirements.

To learn more about how Odour Control Systems can help your facility, feel free to contact us for expert advice and solutions tailored to your needs.

ALSO READ

• Read the source documents: EPA odour threshold guide, WEF MOP 25, and CPCB odour guidelines.
• Explore how AQOZA provides solutions for odour control.
• Want to know more about AQOZA?