Addressing Odor in the Wastewater Treatment Process

,

Odor control is a significant challenge for the Sanitary District of Decatur and every wastewater treatment facility in the country. Getting sewage to the treatment plant and removing contaminants is vital for safeguarding public health and the environment but can cause concentration of unpleasant odors that naturally occur along the way. Understanding the origins of these odors and effective control methods SDD undertakes is crucial for smooth operations and community awareness.

Let’s start with the sources of wastewater odor. Let’s face it sewage doesn’t exactly start out smelling good and doesn’t get any better until it has been thoroughly treated prior to returning it to the Sangamon River. The distinctive sewer smell mainly arises from gases produced during the breakdown of organic matter, including:

  • Hydrogen Sulfide (H₂S) – Known for its “rotten egg” odor, H2S is the primary source of sewer smells and is produced by the anaerobic (oxygen-free) breakdown of organic matter.
  • Ammonia (NH₃) – Most easily described as the smell of rotten fish or cat urine This compound forms during the decomposition of organic matter. Typically, it is a less intense component of sewer odor than H₂S but can be higher in Decatur due to the large-scale processing of agricultural products.
  • Methane (CH₄) – Odorless on its own, methane is lighter than air and can carry odors from other volatile organic compounds in the sewage. It is also flammable and can be a safety concern.

Weather and other outdoor factors can also increase odors, including warm temperatures and thermal inversions that can enhance gas production and trap odors. Changes in prevailing wind direction can carry odors downwind from the facility impacting neighborhoods. Other outdoor factors include:

  • Inadequate Rainfall – In a combined sewer system, like in Decatur, less rain leads to slower sewage movement and more decomposition in the sewer system.
  • Blocked or Damaged Sewer Lines – Clogs from grease or debris can slow down the flow of wastewater, causing buildup and odor.
  • Leaky Access Cover– Poorly sealed covers allow gas to escape, causing unpleasant smells in the surrounding area.
  • Pump Stations and Treatment Plants – Odors are more concentrated around areas where sewage is actively processed and more turbulent. If there are no odor control systems or the systems are not working this can lead to localized odor issues.

 Outdoor factors are not the only thing to consider. Indoor odor sources including P-traps, which are designed to hold water, but can dry out, allowing sewer gases to enter buildings. Regular flushing with 1-3 gallons of hot water can help maintain them. Also, blocked vent pipes or plumbing vents can lead to a buildup of sewer gases, giving rise to foul odors.

The following strategies are used to help reduce odors in the collection system and at the treatment plant:

  • Closed Systems with Biofilters – Enclosing processes where odor compounds are created and directing the gases to Biofilters reduces odors escaping into the open air. Biofilters, use a minimal amount of electricity and microorganisms to “scrub” foul-smelling compounds from the air as it passes through filter media, Biofilters are effective at removing hydrogen sulfide and other volatile organic compounds.
  • Activated Carbon Filters – Highly effective for certain odor compounds, particularly for treating exhaust air from enclosed spaces or small areas, absorb and trap odors without electricity.
  • Chemical Addition – Neutralize gases like H₂S with oxidizing agents, such as hydrogen peroxide (H2O2), converting it into non-odorous compounds.
  • High-intensity Combustion – Controlled burning of waste gasses at high temperatures destroys the odor causing compounds in the gases created in the treatment process.
  • Aeration – Keeping wastewater or sludge aerated can help prevent the formation of anaerobic conditions, reducing the production of odor-causing compounds.
  • Odor-Masking Agents – Temporarily reduce odor perception but do not eliminate the source. (This was done before the closed system and biofilters were installed in 2006 and is no longer used due to cost and minimal results).
  • Community Engagement and Transparency – Educating the public on proper disposal and maintaining open communication about odor control efforts helps mitigate issues. Regularly communicating odor control efforts and implementing complaint-reporting mechanisms can help identify hot spots and target areas for improved odor control measures.

 Effective odor control combines science, technology, and community cooperation and even a little help from Mother Nature as rain flushes decaying material out of the sewers. The Sanitary District of Decatur is committed to investing in sustainable solutions that minimize odors and foster positive relationships with neighboring communities, ensuring a healthier environment for all.

You can report sewage-based odors to our community hotline by calling 1-447-CALL-SDD.