Top OEMs for Odor Control Systems

1. Introduction

In municipal and industrial wastewater treatment, the management of odors is not merely an aesthetic concern; it is a critical operational parameter that impacts regulatory compliance, community relations, facility safety, and infrastructure longevity. Odor Control Systems (OCS) represent the primary defense against the release of nuisance compounds—principally hydrogen sulfide (H₂S), mercaptans, ammonia, and various volatile organic compounds (VOCs)—generated during the anaerobic decomposition of organic matter.

For consulting engineers and plant superintendents, the selection of an odor control technology is rarely a one-size-fits-all proposition. The varying chemistry of airstreams, originating from collection systems, headworks, primary clarifiers, and solids handling processes, dictates a rigorous engineering approach to equipment selection. Furthermore, the corrosive nature of these gases, particularly H₂S, which converts to sulfuric acid on moist surfaces, necessitates equipment designed with robust materials and precise fabrication standards to prevent premature structural failure.

Read more4D-Printed Smart Materials For Water Treatment

The regulatory environment governing air emissions has tightened significantly. Facilities are no longer just judged by National Pollutant Discharge Elimination System (NPDES) permits for water quality but also by strict local air quality management district standards and fence-line odor monitoring requirements. An unmanaged odor release can lead to cease-and-desist orders, heavy fines, and a deterioration of public trust that can stall future capital improvement projects.

This article provides a comprehensive, engineer-focused analysis of the equipment available for odor control. It eschews marketing hyperbole in favor of technical evaluation, examining the distinct technologies, operational characteristics, and lifecycle implications of systems provided by leading Original Equipment Manufacturers (OEMs). The focus remains strictly on the engineering merits, hydraulic and pneumatic performance, and maintenance realities of these systems.

2. How to Select This Process Equipment

Read moreActivated Carbon Filtration in Water: Essential for Clean, Safe Drinking Supplies

Selecting the appropriate odor control system requires a multi-dimensional analysis that balances removal efficiency, capital cost, operating complexity, and site-specific constraints. Engineers must evaluate the following critical parameters to specify a system that provides reliable long-term performance.

Process Function and Chemical Characterization

The first step in selection is the accurate characterization of the foul air stream. Engineers must quantify not only the average concentrations of contaminants but also the diurnal and seasonal peaks.

• Hydrogen Sulfide (H₂S): The most common target. Biological systems and chemical scrubbers are generally preferred for high loads (>50 ppm), while carbon adsorption is often reserved for polishing or lower concentrations (<10 ppm) to manage media consumption costs.
• Organic Sulfurs and VOCs: Compounds such as methyl mercaptan or dimethyl sulfide are less soluble in water than H₂S, making them difficult to treat with standard chemical scrubbers or basic biotrickling filters. Multi-stage systems or specific carbon blends may be required.
• Ammonia: Often found in solids handling, ammonia requires distinct treatment chemistry (often acid scrubbing) or specific biological cultures.

Technology Evaluation

Understanding the mechanism of removal is essential for predicting performance and operational requirements.

Biological Systems (Biofilters and Biotrickling Filters)

Biological systems utilize microorganisms immobilized on a media bed to oxidize odorous compounds.

• Biofilters: Typically use organic media (wood chips, compost) with a large footprint. They function well for complex odor streams but require moisture management and media replacement every 3–5 years due to compaction and degradation.
• Biotrickling Filters (BTFs): Utilize synthetic media (polyurethane foam, glass, or plastic) in a vertical tower. Recirculating water provides nutrients and moisture. They handle high H₂S loads efficiently, have a smaller footprint, and the media can last 10–20 years. However, they may require a polishing stage for organic odors.

Chemical Scrubber Systems (Wet Scrubbers)

Packed tower scrubbers rely on gas-liquid absorption coupled with chemical oxidation.

• Mechanism: Foul air passes through a packed bed counter-current to a scrubbing liquid (typically sodium hypochlorite and sodium hydroxide).
• Pros: Immediate response to load changes, high removal efficiency for H₂S, and smaller footprint.
• Cons: High operating costs due to chemical consumption, safety risks associated with storing hazardous chemicals, and the complexity of pH/ORP control loops.

Adsorption Systems (Carbon/Media)

Dry media systems pass air through a bed of activated carbon or engineered inorganic media.

• Mechanism: Contaminants are physically adsorbed or chemisorbed onto the media surface.
• Pros: Simple operation (few moving parts), excellent polishing capability, and effective on a wide range of compounds.
• Cons: Media has a finite capacity. Once breakthrough occurs, media must be replaced. High loading leads to prohibitive Operating Expenses (OPEX). Not suitable for airstreams with high moisture/grease without pretreatment.

Empty Bed Contact Time (EBCT) and Airflow

The sizing of vessels is dictated by the EBCT required for the reaction. Biological systems typically require longer contact times (10–30 seconds for BTFs, up to 60 seconds for biofilters) compared to chemical scrubbers (1.5–3 seconds) or carbon (2–4 seconds). Engineers must verify that the OEM’s vessel dimensions allow for adequate residence time at peak airflow to prevent breakthrough.

Materials of Construction

Given the aggressive nature of H₂S and sulfuric acid generation, material selection is non-negotiable.

• Fiberglass Reinforced Plastic (FRP): The industry standard for scrubbers and BTFs. Specifications should require premium vinyl ester resins with corrosion barriers.
• Stainless Steel (304/316): Generally avoided in high H₂S environments due to corrosion risks unless specialized grades (e.g., Duplex) are used, which increases cost.
• High-Density Polyethylene (HDPE) and PVC: Used for ductwork and piping. UV stability must be considered for outdoor installations.

Operations and Maintenance (O&M) Impacts

The total lifecycle cost is heavily influenced by O&M requirements.

• Chemical Handling: Scrubbers require safe delivery zones, containment, and double-walled piping.
• Water Usage: BTFs and scrubbers consume potable or reuse water. This hydraulic load must be accounted for in the plant balance.
• Media Changeouts: Dry systems require accessibility for vacuum trucks. Engineers must design layouts that allow heavy equipment access to the vessels.
• Winterization: Liquid-based systems in cold climates require heat tracing and insulation, adding to the parasitic energy load.

3. Comparison Table

The following table compares the locked list of OEMs based on their primary engineering focus within the odor control market. Engineers should use this matrix to identify which manufacturer aligns best with the specific technology preference (biological, chemical, adsorption, or process management) and the constraints of the facility.

4. Top OEM Manufacturers

This section details the engineering capabilities, product philosophies, and specific technologies of the designated OEMs. The analysis focuses on how these manufacturers address the core challenges of odor control in water and wastewater environments.

Purafil

Purafil is widely recognized in the engineering community as a specialist in gas-phase air filtration. While they offer hardware, their core competency lies in the chemical engineering of the media itself. Unlike generic activated carbon suppliers, Purafil manufacturers engineered pellets impregnated with specific chemical oxidants (such as potassium permanganate) to target specific gases.

Engineering Philosophy and Technology

Purafil’s approach centers on Chemisorption—an irreversible chemical reaction where the contaminant is converted into a harmless solid that remains trapped within the media pellet. This differs from physical adsorption (standard carbon), where contaminants can potentially descorb under certain conditions.

Their product line includes Drum Scrubber (DS) systems and Tub Scrubber (TS) systems, often employed in wastewater treatment plants for polishing applications or protecting critical electrical gear in control rooms from H₂S corrosion. For odor control, their media blends (e.g., Odorcarb) are engineered to handle broad-spectrum odors including VOCs and aldehydes that biological systems might miss.

Best-Fit Applications

Purafil is frequently specified for:

• Control Room Pressurization: Protecting SCADA hardware and variable frequency drives (VFDs) from copper and silver corrosion caused by fugitive H₂S.
• Polishing Stages: Placed downstream of a biological system to remove residual peaks or organic odors.
• Remote Lift Stations: Passive or low-airflow active units where power availability is limited and chemical handling is impossible.

Operational Considerations

The primary operational metric for Purafil systems is Media Life Analysis. Engineers should specify coupon monitoring programs. Purafil provides analysis services that predict the remaining life of the media bed, allowing operators to budget for replacement accurately. The systems generally have low mechanical complexity, consisting mainly of a fan and the vessel.

Evoqua

Evoqua (now part of Xylem) represents one of the most diversified portfolios in the odor control market. Their acquisition history has consolidated several legacy brands, allowing them to offer biological, chemical, and adsorption technologies under one roof. This breadth allows for “technology-agnostic” recommendations where the solution is fitted to the problem rather than forcing a single technology.

Engineering Philosophy and Technology

Evoqua’s strength lies in integrated systems and service capabilities. Key product lines include:

• RJ-Series Scrubbers: The legacy RJ-2000 is a standard in the industry for packed tower chemical scrubbing. It features a compact footprint and established removal efficiencies for high-load applications.
• Midas® OCM: A proprietary odor control media based on clay and other binders, designed to offer higher H₂S capacity than standard carbons, extending bed life in adsorption applications.
• Biocube and ZABOCS: Biological systems designed for modularity. The ZABOCS (Zonal Biological Odor Control System) is a two-stage biological system designed to treat both H₂S and organic odors in a single footprint.

Best-Fit Applications

Evoqua systems are ubiquitous in municipal wastewater. They are particularly well-suited for:

• Retrofits: The modular nature of systems like the Biocube allows for installation in tight spaces.
• High-Load Headworks: The RJ-series chemical scrubbers are capable of handling the massive H₂S spikes found at large plant headworks.
• Service-Heavy Models: Municipalities that prefer to outsource maintenance often utilize Evoqua’s service branch for carbon changeouts and system tuning.

Operational Considerations

For their chemical scrubbers, operators must manage sodium hypochlorite and sodium hydroxide handling. Evoqua designs typically include robust chemical metering pumps and pH/ORP control loops. Engineers should pay close attention to the containment requirements for these chemicals. For their carbon systems, the availability of local service branches for vacuum truck dispatch reduces downtime during media exhaustion events.

Engineered Air

Engineered Air occupies a distinct niche compared to pure process equipment manufacturers. Primarily known for high-quality custom HVAC and air handling units, their relevance in the odor control sector ties to the critical need for building containment and ventilation. Effective odor control begins with capturing the foul air, which requires sophisticated air handling strategies.

Engineering Philosophy and Technology

Odor control in enclosed structures (like headworks buildings or dewatering facilities) relies on maintaining a negative pressure to prevent fugitive emissions. This requires Make-Up Air Units (MAUs) that are tightly integrated with the exhaust/odor control fans.

Engineered Air manufactures custom air handlers that can be specified with corrosion-resistant materials (coated coils, stainless steel casings) suitable for the wastewater environment. Additionally, in industrial applications, they provide thermal solutions and indirect fired heaters that can be part of a larger thermal oxidation strategy for VOC destruction.

Best-Fit Applications

Engineered Air is the OEM of choice for:

• Headworks Building Ventilation: Providing tempered make-up air to replace the volume exhausted by the odor control scrubbers, ensuring operator comfort and building integrity.
• Corrosive Environments: Where standard commercial HVAC units would fail due to H₂S attack on copper coils.
• Cold Climate Installations: Providing robust heating for intake air to prevent freezing of biological or chemical scrubber lines.

Operational Considerations

While not a manufacturer of the scrubber vessel itself, Engineered Air’s equipment is critical to the OCS ecosystem. Failure of a make-up air unit can cause building pressure alarms or starve the odor control fans, leading to system imbalance. Maintenance follows standard HVAC protocols (belt tensioning, filter changes, burner tuning) but with a focus on inspecting for corrosion.

BioAir Solutions

BioAir Solutions has carved out a strong position by focusing almost exclusively on high-efficiency biological treatment. They distinguish themselves through the use of advanced, structured synthetic media rather than random-pack organic media.

Engineering Philosophy and Technology

BioAir’s philosophy centers on the “EcoFilter” and “EcoBase” technologies.

• Structured Media: Unlike lava rock or wood chips, BioAir uses engineered synthetic media with uniform channels. This ensures consistent airflow distribution, preventing the “channeling” that plagues traditional biofilters.
• Mass Transfer: The media is designed to maximize the interface between the foul air and the biofilm layer.
• No Dangerous Chemicals: By optimizing the biological environment, they achieve high H₂S removal (>99%) without the use of caustic or bleach.

Best-Fit Applications

BioAir is a prime candidate for:

• Pump Stations in Residential Areas: The lack of chemical delivery trucks appeals to neighborhoods.
• Greenfield Plants: Where sustainability and low carbon footprint are design drivers.
• High H₂S Streams: Their biotrickling filters are capable of handling inlet concentrations in the hundreds of ppm.

Operational Considerations

BioAir systems operate with an irrigation cycle. The critical operational parameters are water pressure, nutrient supply (if required), and differential pressure. Because the media is synthetic and structured, it does not decompose or compact, significantly extending the interval between major maintenance events (often 10–20 years for media life). However, the irrigation nozzles and recirculation pumps are critical failure points that require redundancy.

Scarab Environmental

Scarab Environmental approaches odor control from a source management perspective, specifically within the realm of biosolids composting. Unlike the other OEMs that treat air in a vessel, Scarab manufactures windrow turners designed to manage the process biology of composting piles.

Engineering Philosophy and Technology

Odor in composting is largely the result of anaerobic pockets forming within the pile. When oxygen is depleted, anaerobic bacteria generate H₂S, amines, and volatile fatty acids.

• Process Control: Scarab machines are designed to thoroughly mix and aerate large windrows. The flail design ensures particle size reduction and oxygen introduction.
• Prevention vs. Treatment: By maintaining aerobic conditions, the generation of odors is suppressed at the source, reducing the load on any building ventilation or perimeter misting systems.

Best-Fit Applications

Scarab is the specific choice for:

• Biosolids Composting Facilities: Municipalities that process sludge into Class A compost.
• Yard Waste/Organics Processing: Co-digestion or co-composting facilities.

Operational Considerations

This is heavy mechanical equipment. Maintenance involves diesel engine service, hydraulic system upkeep, and wear-part replacement (flails/teeth). From an odor control perspective, the reliability of the machine is paramount; if the turner is down for a week, the piles go anaerobic, and the facility will likely generate off-site odor complaints.

5. Application Fit Guidance

Selecting the right OEM and technology requires mapping the facility’s specific constraints to the equipment capabilities. The following guidance assists engineers in matching application sectors to the most appropriate solutions.

Municipal Wastewater Headworks

Headworks areas are characterized by high, fluctuating H₂S loads and high humidity.

• Preferred Technology: Biotrickling Filters (BioAir, Evoqua) or Chemical Scrubbers (Evoqua).
• Reasoning: Biological systems are preferred for OPEX savings, but chemical scrubbers are used if space is extremely tight or if the air contains compounds toxic to bacteria. Engineered Air units are essential here for building ventilation.

Collection Systems and Lift Stations

Remote sites often lack extensive utilities, chemical containment, or daily operator presence.

• Preferred Technology: Activated Carbon (Evoqua, Purafil) or Small Footprint Biological (BioAir).
• Reasoning: Carbon is passive and simple but expensive if H₂S is high. BioAir’s EcoFilter covers are effective for wet wells where minimal maintenance is desired.

Biosolids Processing and Dewatering

These airstreams contain complex mixtures of H₂S, ammonia, amines, and mercaptans.

• Preferred Technology: Multi-stage systems. Often a biotrickling filter followed by a carbon polisher (Evoqua, BioAir + Purafil/Carbon stage).
• Composting: For open windrow composting, Scarab Environmental is the primary mechanical solution for process control.

Control Room Protection

The goal is not preventing nuisance odors but preventing corrosion of copper and silver electronics.

• Preferred Technology: Dry Chemical Scrubbing (Purafil).
• Reasoning: Purafil’s media is specifically engineered to reduce H₂S to ppb levels required by ISA standards for electronics protection.

6. Engineer & Operator Considerations

Beyond the catalog specifications, the long-term success of an odor control project hinges on practical implementation details.

Installation and Commissioning

Engineers must draft specifications that require rigorous leakage testing of ductwork and vessels. A system that pulls in clean ambient air through leaks rather than foul air from the source will fail to control odors. Commissioning should include smoke testing and velocity profiling. For biological systems, the “acclimation period” (the time for bacteria to colonize the media) must be accounted for; temporary carbon polishing may be needed during startup.

Maintenance Access

A common design failure is placing vessels where they cannot be serviced.

• Carbon Systems: Requires vacuum truck access within 50 feet. If the unit is on a roof, a permanent fill pipe and discharge piping system must be installed.
• Top Access: All towers (chemical or biological) require ladders and platforms for inspecting spray nozzles and demisters.
• Pump Redundancy: Recirculation pumps for scrubbers and BTFs should always be configured in a Duty/Standby arrangement to prevent system failure during a pump trip.

Spare Parts and Reliability

Operators should maintain critical spares on-site:

• Chemical Systems: pH and ORP probes, metering pump rebuild kits.
• Biological Systems: Spray nozzles, nutrient feed pumps.
• Mechanical: Fan belts, bearings, and motors.

Supply chain reliability is crucial. For proprietary media systems (like Purafil or Evoqua’s Midas), engineers should evaluate the lead times and availability of the media, or design the vessels to accept generic equivalents if necessary (though this may impact performance guarantees).

Operational Lessons Learned

Real-world experience dictates that grease and moisture are enemies of dry media. Mist eliminators upstream of carbon beds are mandatory. For biological systems, maintaining the correct pH in the recirculation water is vital; if the water becomes too acidic (due to sulfuric acid production), the biology can be inhibited unless the system is designed for acidophilic bacteria.

7. Conclusion

The selection of an Odor Control System is a balancing act between the chemical reality of the airstream and the operational capabilities of the utility. There is no single “best” OEM; rather, there are optimized fits for specific applications.

BioAir Solutions excels in biological treatment where chemical handling is to be avoided and long-term OPEX is the driver. Evoqua provides the versatility of a massive portfolio, ideal for complex, multi-stage treatment needs or facilities desiring a single source for various technologies. Purafil remains the gold standard for polishing and electronics protection through advanced chemisorption. Scarab Environmental addresses the specific mechanical needs of composting operations. Finally, Engineered Air ensures the fundamental physics of air movement and containment are met within the facility infrastructure.

For the consulting engineer, the task is to rigorously define the inlet loading, prioritize the lifecycle costs over initial capital expenditure, and design a layout that acknowledges the necessity of maintenance. By aligning these engineering fundamentals with the specific strengths of these top OEMs, utilities can turn the “invisible utility” of odor control into a reliable, set-it-and-forget-it asset.