Odor Complaints Need Chemistry

A rotten egg odor is commonly associated with hydrogen sulfide. If a wastewater treatment plant in the area, it can quickly become the presumed source. It is a logical conclusion, but without the chemical data to support it, it remains an assumption.

That assumption can have significant consequences. The community, municipality and regulators may look to the wastewater treatment plant to resolve the issue. The facility may face enforcement action or invest in new or modified scrubbers and other odor-control technologies designed to reduce hydrogen sulfide emissions.

What happens when the complaints continue?

This scenario outlines the challenges that landfills, wastewater treatment plants, chemical manufacturers and other industrial facilities are facing daily.

With odor becoming a leading complaint for regulators across North America and Europe, relying on human smell alone does not provide the adequate data or clarity to truly know what the odor is, where the odor is coming from, what the root cause is and how to effectively treat it.

Categorizing and identifying an odor is difficult on its own, but what if there are multiple facilities in the same area that could be potential sources of the odor?

In what became a very public example of imperfect detection, a wastewater treatment plant in Mount Dora, Florida had received numerous complaints of sewage-like and rotten-egg odors for years. Eventually, the Florida Department of Environmental Protection launched an investigation and determined there were several violations at the plant, including “failure to operate in a way that controlled objectionable odors.”While the wastewater plant was certainly capable of producing localized odors, the timing and location of measured hydrogen sulfide did not match the odors reported in surrounding neighborhoods. Without that correlation, it was concluded that the plant was unlikely to be the odor source.

Instead, a second investigation uncovered two additional potential sources of the odor, including a nearby landfill and another industrial site. Utilizing an advanced hydrogen sulfide sensor network, they found that the landfill was the cause of the odors and not the wastewater facility.

This is one of many such cases, where incomplete source-attribution data caused thousands of dollars’ worth of fines, public scrutiny and years of community distress when better science could have pointed enforcement agencies to the correct source almost immediately.

Frequent exposure to odorous compounds can lead to headaches, nausea and mental stress. Despite the business and local community risks, human perception has been the primary way to identify and locate these odors.

The odor wheel has been a useful tool for agencies and community groups in the field when trying to categorize these smells once there is a complaint.

Currently the most popular odor characterization tool in the world, the Nasal Ranger device is a field-based handheld olfactometer used to determine the strength of an odor. It takes odorous air and mixes it with clean air to determine how much dilution is needed before the bad smell no longer persists.

While Nasal Rangers are useful in certain scenarios, they are still based on the individual’s human nose. When community complaints and thousands in regulatory fines hang in the balance, that is far too subjective a tool to rely on.

What smells like rotten eggs to one person may smell like something else to another. Even with a Nasal Ranger, investigators can only qualify the strength of an odor but cannot identify the compounds causing it. Some odor-causing compounds can also be smelled at concentrations below the detection limits of standard analytical methods, meaning the chemicals driving the complaint may not appear in the results.

With some areas receiving hundreds, or thousands, of complaints weekly, regulators are taking a more active interest in regulating odors and defining “nuisance” laws. Human perception can no longer be the de facto method to manage odor.

There are two primary ways for facilities to eliminate odor. They can either mask it with something else, or you can remove it completely.

For either method, advanced odor characterization removes the human factor completely during evaluations. The goal is to be able eliminate the odorants before they even cross the fenceline, so there is nothing for the local community to smell.

Odor is not just one thing like “rotten eggs”. Odor is made up of a unique mixture of chemical compounds, each potentially requiring a different treatment. Using our mobile monitoring lab, our team has created a library of 450+ odorous compounds, allowing us to create odor fingerprints corresponding to specific locations or facilities. Once a facility’s odor fingerprint is identified, a custom, odor mitigation approach can be deployed to attack the root cause back by science, instead of perception.

Instead of asking “What does it smell like”, the questions become:

• What compounds are present?
• At what concentrations are they appearing?
• Does the odor fingerprint match one of the nearby facility processes?
• Which treatment option will reduce the odorant to below the human nose’s odor threshold?

Now, instead of addressing a complaint, facilities can address their odor issues before the local community gets a whiff.

A science-based odor investigation typically begins by deploying a mobile laboratory to monitor around a facility. This allows the field team to collect and analyze samples in near real time, rather than sending odor samples offsite and waiting for analysis results.

1. Samples are collected from potential odor sources
2. Field teams analyze the samples and let the client know how many compounds there are, what their concentrations are and whether they are above or below the odor threshold
3. Chemical fingerprints, facility conditions and monitoring data are used to evaluate and recommend changes to the treatment processes potentially contributing to the odor
4. After the new treatment regimens are established, field teams conduct follow-up measurements to ensure reduction in the targeted compounds

This approach gives facilities clarity on where to invest their time and energy, which processes to adjust and ways to verify that mitigation actions are effective. It also avoids unnecessary effort based on incorrect assumptions about the source of the odor.

For decades, human perception was the end-all, be-all when it comes to odor investigations. While great at detecting the existence of a smell, that alone does not give nearly enough information on how to fix it. By then, local communities and businesses are already being affected.

By taking a science-based approach to odor reduction, facilities are able to take a defensible path that identifies the compounds present, distinguishes between odor sources and addresses the root cause rather than just masking the issue.

Most importantly, facilities can move beyond reacting to complaints and instead understand the chemical profile of their operations. Teams can identify issues earlier, improve processes and build confidence with the surrounding communities.

Odor complaints may begin with what someone smells but resolving them requires real science.