Mitigating Wastewater Odors: What are my Options?
Nothing can calm you down and bring a sense of peace more than taking a few deep, controlled breaths. However, that is difficult to do if your public wastewater system has foul odor issues. And as a wastewater system owner or operator, those foul odors aren’t just your issues, they are a problem for the surrounding community too.
Wastewater odor issues are typically the result of hydrogen sulfide (H2S) produced within the wastewater during conveyance or treatment. H2S can wreak havoc in wastewater systems as it leads to infrastructure corrosion, worker safety issues and nuisance issues for people living and working near the system, leading to odor complaints and potentially affecting their quality of life. As wastewater flows through the system, it can produce a range of unpleasant odors, including the smell of rotten eggs, ammonia, and other sulfur-based compounds. These odors can be released into the air through manholes, pump stations, treatment plants, and other parts of the municipal wastewater collection and treatment system.
Liquid Phase Treatment
Liquid phase odor control involves operational optimization to minimize anaerobic biological activity. Effective wastewater collection system pipeline design criteria should aim to minimize retention times, maximize oxygen introduction, and avoid the use of metallic and concrete pipe materials. Wastewater operators should achieve scouring velocities in pumping systems, and pig lines or reroute flows where needed to keep wastewater moving through the system.
Treatment options to prevent or slow anaerobic activity include air or oxygen injection, nitrate dosing, or by introduction of microbiology-focused agents such as bacteria or enzymes.
Liquid phase treatment to remove dissolved sulfides and reduced sulfur odor-causing compounds consist of the following:
Oxidizers – hydrogen peroxide, permanganate, chlorine, and hypochlorite
Nitrate-based – alone or in conjunction with other treatments
Iron salts (only treat hydrogen sulfide)
pH adjustment – magnesium hydroxide, calcium hydroxide, or sodium hydroxide
Vapor Phase Treatment
Once odorous compounds are in the vapor phase, effective containment and ventilation are important factors in odor control success. Ductwork, covers, and fans capable of maintaining a negative headspace pressure of -0.05 inches of water relative to the atmosphere are all necessary for proper containment and ventilation. Vapor phase treatment performance is often measured by hydrogen sulfide removal and total odor removal. In addition, corrosion is effectively mitigated with a vapor phase odor control system achieving 3 to 12 air changes per hour.
Treatment technologies for vapor phase odor control include:
Biofiltration for vapor phase treatment
Biological: Biofiltration is a biological treatment process that uses microorganisms to remove or convert odorous compounds. Foul air from wastewater collection and treatment facilities is passed through a bed of organic material, such as compost, wood chips, peat moss, or engineered inorganic material, which supports the growth of microorganisms that consume the odorous compounds. Biotrickling filters combine a biofilter and a scrubber to provide high odor removal efficiency with a compact footprint.
Chemical: Chemical scrubbing involves the use of a chemical agent, such as sodium hydroxide or hydrogen peroxide, to remove or convert odorous compounds. The foul air stream is passed through a scrubber vessel that typically contains plastic packing media which provides extensive surface area for odorous gaseous compounds to come in contact with a chemical agent. The odorous compounds react with the chemical agent and are converted into less offensive substances. Dry chemical processes involve the use of impregnated media to remove odorous compounds.
Adsorption: Activated carbon is a highly porous material that can adsorb odorous compounds from foul air. In activated carbon adsorption, the air is passed through a bed of activated carbon, which captures the odorous compounds on its surface. The activated carbon must be regenerated or replaced periodically.
The choice of vapor phase treatment will depend on factors such as the type and concentration of odorous compounds, the flow rate and volume of the air or gas stream, and the specific odor control objectives of the wastewater treatment system.
Sign up to V&A’s mailing list for notifications of future blog articles that will provide in-depth information about specific odor control strategies, including important consideration factors. We hope this article provided you with a basic understanding of what your options are when it comes to wastewater odor control. Our team of odor control experts is available to answer questions and help you mitigate your specific odor issues. Feel free to reach out using the link below.