All About Odor Control in Wastewater Treatment

Wastewater treatment odor control is about far more than keeping bad smells at bay. It’s about ensuring that local communities and nearby ecosystems are kept safe from toxic emissions, as well as giving onsite personnel a safe and pleasant place to work. It’s a crucial consideration during the wastewater treatment and management process.

Read on and discover more about odor control in wastewater treatment, including why it’s so important and how it works.

Understanding Wastewater Odor

Before we get started, let’s look at what wastewater odor actually is. In a very basic sense, wastewater odor is any bad smell produced by the process of treating the waste influent or by the waste itself. As this water tends to contain materials that humans find unpleasant, even the odors the water produces naturally can pose a serious problem for local communities. When waste materials are broken down during treatment, more intense odors are released at an even greater volume, exacerbating the problem.

Waste treatment plants release different odors at different times, due to a mix of chemicals and substances in them. These odors can resemble muddy and earthy smells, rotten vegetables or eggs, ammonia, or garlic. Odors that come from wastewater treatment plants are caused by the use of chemicals such as:

• Hydrogen sulfide (H2S)
• Skatoles
• Indoles
• Ammonia
• Sulfur dioxide
• Amines
• Mercaptans

All of these compounds may be released during treatment or simply by stagnant areas of wastewater. These compounds may be toxic in higher concentrations.

Here’s a quick idea of what each one smells like, thanks to the good folks at Evoqua:

In a more scientific sense, most odors are produced by one particular gas that is released during processing – hydrogen sulfide (H₂S). As H₂S has no color, it is invisible in the air. However, it does have a very strong smell. In addition to this, hydrogen sulfide gas can be highly toxic to humans and animals, so wastewater processing plants have a duty to keep H₂S under control, removing it where possible and preventing leaks.

Odor control is an issue right across the wastewater treatment process. From wastewater clarifiers and sedimentation basins to headworks, lift stations, and treatment lagoons, teams need to remain aware of odor levels and gas leakages.

Why Is Odor Control So Important During Wastewater Treatment?

Why is this such a big deal? Below are some of the key factors that make wastewater odor control so important.

• Odors make life unpleasant for local residents and anyone else who spends time in the local area.
• Odors may be caused by toxic gases, which can put human and animal life at risk.
• Odors may also be emitted by polluting chemicals that damage local ecosystems.
• Odors create a poor working environment for anyone onsite.
• Odors may be an indication that there are problems in the wastewater treatment process, making treatment inefficient or ineffective.

We can view odor control in two ways – removal and prevention. Removal is a reactive response, taking away odors that have already been produced. Prevention is a more proactive process, reducing the amount of odor-causing compounds produced in the first place.

Removal of Odors

Firstly, let’s take a look at three methods of removing odors from wastewater.

Biological Treatment of Vapor

Vapor from the wastewater is fed into biotowers, which are filled with inorganic matter. The vapor filters through these towers, removing much of the H₂S gas. Not all odor-causing gases can be removed in this manner, so other forms of treatment may be required to comprehensively deal with all odors.

Carbon Adsorption

Vapor can be filtered through carbon-based media to remove odor-producing compounds. The carbon media are useful in adsorbing and removing H2S gas at low concentrations. This process will also remove higher concentrations of H₂S gas, but this will wear out the media quickly and the carbon will need to be replaced. Facility managers may use other forms of medium, deployed alongside the carbon, to achieve more comprehensive removal of odor-producing compounds from the vapor mixture.

Chemical Scrubbing

Chemical scrubbing involves filtering the vapor through specially chosen chemical media in order to remove odor-causing compounds from the vapor. Removal is achieved through a process of dissolving and then absorbing (different from the adsorbing listed above) the compounds as they pass through the media. Chemical scrubbing may be better suited to treatment plants where the vapor levels fluctuate – unlike biological treatment, for example, which is better suited to applications with more consistent loads.

Prevention of Odors

Next, let’s examine how odors can be prevented to reduce the need for reactive removal during odor control.

Utilizing Aerobic Bacteria During Treatment

Using anaerobic bacteria – i.e., bacteria that digest waste in the absence of oxygen – to treat wastewater can result in unpleasant odors and the release of potentially harmful gases. This is due to the chemical reactions that take place when the bacteria break down the waste. Focusing on aerobic bacterial digestion – i.e., digestion in the presence of oxygen – can solve this problem. The byproducts of aerobic waste digestion tend to be less odorous and less toxic than those of anaerobic digestion.

Increasing Aeration within the Treatment Pool

The problem with shifting focus towards aerobic digestion is that parts of the wastewater treatment pool will naturally be devoid of oxygen. This results in anaerobic digestion, even if it is not desired. To combat this, facility teams can use aeration pipes and tubes, increasing the amount of available oxygen within the treatment tank itself.

Improving Circulation During Treatment

Even when aeration is improved, there is still the risk that oxygen-devoid areas may form within the treatment zone, particularly deep within the tank or down in the sludge layer. To prevent a resulting odor and toxic gas release, facility managers can work to improve the circulation of wastewater within the tank, ensuring that all of the waste is exposed to aerobic bacterial digestion and the conditions required to make this happen.

Odor Control Solutions for Wastewater and Other Facilities

Wastewater plants and processing facilities get bad press and are often associated with unpleasant smells and odors. There is some truth in this — wastewater odors can be seriously unpleasant for anyone in the local area. But the reputation is a little unfair. With the right odor control processes and procedures, these smells can be curtailed and even negated altogether.

Read on to learn more about six odor control solutions that work to reduce the release of unpleasant, and even harmful gases and fumes. This will make it much easier to achieve a safe and reliable operation at your facility, maintain a good relationship with all stakeholders and local residents, and remain fully compliant with all regulations in your field.

Physical Blocking of Odors

While it is a range of chemical factors that tend to cause waste water odors, you can look to non-chemical methods to control them. Physical, mechanical prevention methods are in fact highly effective in stopping odors at the source and keeping them out of the local environment. This is because the presence of odors indicates there is a weakness in your system — a place where gases and fumes are able to escape into the surrounding atmosphere and environment. Identifying this weakness and putting it right is an effective part of the process when combatting unpleasant odors.

This may seem like only a temporary solution. After all, covering a problem is generally considered inferior to actually fixing it. But it’s still an important step in odor control. There are many chemicals and pathogens in wastewater, which makes odors a natural byproduct of running this type of facility. Physical odor blocking may not be wholly effective when deployed all by itself, but it does provide an extra layer of defense.

Adequate Ventilation & Odor Removal

As mentioned above, odors are common byproducts of wastewater treatment and processing. Ensuring that there are no weaknesses in your pipework or elsewhere in your system is useful in preventing the spread of unpleasant smells. However, you also need to know what you will do if odors are released into the local environment.

A system of ventilation and fume removal is useful here. Piping odor-causing gases and fumes away from areas where they could cause problems is a must. When you operate a wastewater processing plant or other industrial facility, you need to maintain a positive relationship with your local community — implementing ventilation and odor removal that protects the community from unpleasant fumes is a big part of this.

Localized Climate Control

Often, the intensity of the odor will be influenced by the local environmental conditions. Odors caused by bacteria are likely to be much worse in the summer months or during a period of warm weather. This is because the bacteria colonies grow more quickly when temperatures rise, leading to increased enzyme activity. The enzymes break down compounds and contaminants found in the water, which means fumes and gases are released into the atmosphere.

Implementing localized climate control can help you and your team prevent this worsening of odors. This may involve controlling the temperature within the system, reducing the growth of odor-causing bacteria in the process. In addition, you may seek to remove other aspects that could cause odors, such as catalyzing agents that accelerate chemical and biological reactions.

Chemical Neutralization

In some cases, odors may be caused by volatility in the wastewater, exacerbated by excessive acidity or alkalinity. Applying chemicals with specific pHs to the wastewater mixture can neutralize the water and limit the release of odors. Of course, the specific chemical — and, most importantly, the specific pH — depends upon the nature of the wastewater itself.

Baking soda is sometimes used as a neutralizing agent. This is because baking soda is alkaline and will increase the pH of an acidic wastewater solution, bringing it up to the neutral range of around 7. If the solution is at the base/alkaline end of the pH, a substance with a lower pH may be required to neutralize it.

Odor Absorbers

We’ve mentioned enzymes above, describing how some types of enzymes can result in unpleasant odors. However, other types of enzymes work differently and may actively remove odors from a wastewater plant. This is because the enzyme will target specific chemicals and pathogens, breaking them down and destroying them. If the chemical or pathogen in question is the root cause of the odor, then enzymes become your friend in odor control.

In fact, there are lots of other substances that absorb and remove odors. These include activated charcoal, which has a porous texture that absorbs odor-causing chemicals. Another example is a plant-based oil that is used to mask the odor during the removal process.

Eliminating Specific Chemical Reactions

Odors at your plant may be caused by the release of specific chemicals. One of the most commonly encountered odors at a plant is that of hydrogen sulfide gas. Not only is this a source of unpleasant odor, but it is also highly dangerous, as it ignites and explodes easily. It is also heavier than air, which means it will collect in sunken areas around your facility and can build over time to reach a dangerous concentration.

As there are two hydrogen atoms in every water molecule, it is very difficult to remove hydrogen from your wastewater. However, you can control the levels of sulfur in the water, reducing the likelihood of hydrogen sulfide gas being created and released. Studies suggest that autotrophic denitrification of wastewater in the petrochemical industry — combined with CO2 stripping — is effective in removing sulfur and reducing resulting levels of hydrogen sulfide.

Odor Control Is a Key Industrial Responsibility

If you operate a wastewater processing plant, the community around you might often complain about foul odors and even deem your plant a nuisance to the environment. Foul odors produced by wastewater treatment plants aren’t governed by the Clean Air Act of 1990 and are exempt from federal regulation; they are not threats to public health per se. This means you are out of the purview of the United States Environmental Protection Agency. Instead, it falls on states, cities and local governments to make regulations and address odors in the neighborhoods where they are found.

While treatment plants generally are constructed away from residential areas, communities change practically every few years. New housing is constructed increasingly closer to existing treatment plants, eventually leading to more concerns and complaints about offensive odors.

In this scenario, odor control not only provides a safer environment but also allows you to remain compliant with local and national regulations. This is part of your responsibility as a facility owner, operator or manager, and so it is important to be aware of what chemicals are causing odors and work to actively control them.

Explore Our Range of Wastewater Treatment and Odor Control Products

The Chemtech range is designed to support wastewater treatment facility managers and teams as they work to achieve optimal odor control and environmental safety. Explore our odor control products and find the solutions you need or reach out to our team today and discover more.