How the plant could smell better
Odor from rendering plants can be reduced with well-known, proven engineering and good daily practice. This page explains how odor control works, what state records say the East Dublin plant already has, and the practical steps we are asking for.
What the plant already has, according to state records
Darling Ingredients’ East Dublin plant at 508 Highway 80 East operates under Georgia air quality permit No. 2077-175-0042-S-05. Georgia EPD’s permit records describe five process lines (three meat and poultry rendering lines, a feather line and a blood line), a boiler plant and a wastewater treatment system.1
Odor and emission controls listed in EPD records
- The plant had a regenerative thermal oxidizer (RTO) before 2023. EPD’s 2023 review says high-intensity process emissions were already routed through venturi and packed tower scrubbers and then to the RTO before release.1
- In 2023, EPD approved a change that consolidates those scrubbers into one larger venturi scrubber (15,000 scfm) followed by two packed tower scrubbers in series, all feeding the existing RTO. Permit Amendment No. 2077-175-0042-S-05-2 was issued Sept. 28, 2023.120 The amendment keeps a bypass path: when the RTO is down for maintenance or repair, high-intensity emissions may be released directly from the last packed tower scrubber.2 We have not confirmed whether the new scrubbers have been built.
- A counter-current room scrubber and a cross-flow scrubber are also listed.1
- Wastewater is treated in covered anaerobic lagoons. Darling’s permit lists its own biogas flare.3
- A renewable natural gas (RNG) plant on the site is run by a separate company, GGUSA Dublin LLC (GreenGasUSA), under its own EPD permit, No. 1311-175-0079-B-01-0 (Aug. 2024). It draws biogas from Darling’s covered lagoons, removes CO₂ and H₂S so the gas can be sold, and burns the leftover tail gas in its own flare. That permit requires a flame check every 8 hours and does not include H₂S monitoring.202122
EPD’s draft of the 2023 amendment requires the scrubbers and RTO to run whenever the processes they serve are operating. It requires the RTO to stay at or above the combustion temperature set during its most recent approved performance test. It also requires the scrubbers’ pressure drop, liquid recirculation rate and pH to be recorded at least every four hours.2
EPD notes that its equipment list “is not intended to be a comprehensive list” of every emission source.2 We do not have performance test results or monitoring data for this plant, and we are not claiming any piece of equipment is missing or broken.
So what’s the real question?
The plant already lists the main kinds of control equipment. The open question is whether that equipment captures all the odorous air, is sized and maintained well, and works every hour of every day, including when the RTO is down. Independent checks and public monitoring data can answer that.
Where rendering odor comes from
Rendering cooks animal by-products to separate fat from protein. The U.S. EPA’s emissions guide for rendering plants (AP-42) says the main odor sources are the cookers and the screw press. Other sources include blood and feather processing, dryers, centrifuges, tallow tanks and percolator pans that are not enclosed. Raw material can also smell, but “if the material is processed in a timely manner, these emissions are minimal.”4
The compounds
EPA lists organic sulfides and disulfides, C4 to C7 aldehydes, trimethylamine and other amines, quinoline, pyrazines and organic acids. Some can be smelled at levels as low as 1 part per billion.4 Rendering air is also commonly tested for hydrogen sulfide (H₂S) and ammonia. People can usually smell H₂S, the “rotten egg” gas, at 0.0005 to 0.3 parts per million.18
High-intensity air
Vapors from the cookers are very concentrated. AP-42 explains that cooker vapor passes through a condenser, which turns steam back into water. The gases that do not condense (“noncondensibles”) carry much of the odor and must be treated.4 In an EPA-funded study, this air ranged from 5,000 to 50,000 odor units.5
Room (ventilation) air
Air from inside the buildings is much larger in volume but weaker, about 100 to 1,000 odor units in the same study.5 AP-42 says plants near homes or businesses may send plant ventilation air through a wet scrubber too.4 If that air leaks out through open doors instead, it is not treated at all.
How rendering odor is controlled
EPA sorts rendering odor controls into two groups: controls for high-intensity process air, mainly incineration in boilers or thermal oxidizers and multistage wet scrubbers, and controls for plant ventilation air, typically wet scrubbing. AP-42 says multistage wet scrubbers are “equally as effective as incineration” for high-intensity odors.4
1. Multi-stage wet scrubbers
A scrubber pulls smelly air up through a tower while a chemical solution rains down over plastic packing (a packed bed) or through spray nozzles. The packing gives the air and liquid lots of surface area to meet. A venturi scrubber is often used first to knock out grease and particles that would foul the towers.4
Acid stage: ammonia
Ammonia and amines are alkaline, so a dilute acid solution such as sulfuric acid captures them. A peer-reviewed study of a dilute (1%) sulfuric acid spray scrubber on an Ohio swine barn’s exhaust found it removed an average of 88% of ammonia over four seasons.11 EPA lists both ammonia and hydrogen sulfide among the gases packed-bed scrubbers are used for.6
Oxidizing stage: sulfur odors
Sulfur compounds and aldehydes need a chemical that breaks them apart. AP-42 calls sodium hypochlorite (bleach) the “most effective scrubbing agent for odor removal,” and notes chlorine dioxide is also used.4 In EPA-funded tests at an Iowa rendering plant, fresh alkaline hypochlorite removed about 90% of odor per stage, and two hypochlorite stages averaged 96% on high-intensity air. Hydrogen peroxide was also tested.5
Why upkeep matters
The same study found that keeping the oxidizing solution above pH 12 was “critical.” A week-long packed-bed test averaged only 85%, which the researchers attributed largely to blowdown and caustic feed being set too low; results were improving after those settings were partly corrected. The researchers recommended a continuous bleed of spent liquid with fresh make-up over dumping and refilling tanks, for more consistent performance.5 EPA’s monitoring guidance lists pressure drop, liquid flow and pH as key indicators of scrubber performance.9
What’s ORP?
Oxidation-reduction potential (ORP) is a reading, in millivolts, of how much oxidizing power is left in the scrubbing liquid. It shows whether the oxidizer is strong enough. In Maryland, a rendering plant’s permit required its scrubbers to stay at or above +125 mV, recorded continuously.15
How well a scrubber works depends on its design and operation: how long air and liquid stay in contact, liquid flow, chemical dose, pH and ORP, and the condition of nozzles and packing. EPA’s packed-bed fact sheet reports vendor estimates of 95 to 99% removal for inorganic gases.6 In a two-week plant test, a full-scale spray scrubber on room air averaged 83% odor reduction (92% excluding one sample), and no community odor complaints came in during the test.5
2. Thermal oxidation (RTOs and boilers)
Burning high-intensity vapors destroys odor compounds. Many rendering plants pipe these vapors into their boilers as combustion air.4 A regenerative thermal oxidizer (RTO) heats the gas, typically to 1,400 to 1,500°F, and reuses heat from ceramic beds. EPA reports RTO design efficiencies of 95 to 99% for organic compounds.7 In Southern California, Rule 472 has long required vapors from rendering to be incinerated at 1,202°F (650°C) or higher for at least 0.3 seconds, or treated by an equally effective method.13 An RTO helps only while it is running and hot, which is why downtime and backup plans matter.
3. Biofilters and bioscrubbers
A biofilter pushes odorous air through a moist bed of wood chips or compost, where microbes digest the odor compounds. EPA says Europeans began using biofilters on rendering plant odors decades ago, and AP-42 notes some U.S. rendering plants have installed them.104 In EPA’s summary of U.S. odor-control biofilters (mostly at compost, wastewater and food-waste sites), measured odor removal ranged from 76 to 94%, and some removed 99% of reduced-sulfur compounds. EPA lists 60 to 99.9% removal for biotrickling filters. The bed must stay damp, ideally 40 to 60% water.10 Biofilters suit large volumes of weaker air, such as room air, better than hot, concentrated cooker vapors.
4. Full enclosure under negative pressure
Even the best scrubber cannot treat air that escapes through open doors. A permanent total enclosure keeps odorous work inside a building where fans pull air inward through every opening and send it to treatment. EPA says a properly built total enclosure captures 100% of emissions.8 Southern California’s Rule 415 sets clear benchmarks:12
- Air must flow inward at 200 feet per minute or more through each opening, and at 100 feet per minute or more while a truck door is open.
- Truck doors may open only while a truck is entering or leaving.
- Routine openings may not exceed 5% of the enclosure’s surface.
- The odor control system must reduce nitrogen compounds (measured as ammonia) and sulfur compounds (measured as hydrogen sulfide) by at least 70%, as tested by an independent third party.
5. Fresh raw material and good housekeeping
Raw material that sits and spoils smells worse. Rule 415 requires incoming material to go into the cooker, a total enclosure or a covered container within 4 hours of delivery (6 hours if chilled). It also requires washing drums and containers before they leave the site and keeping receiving areas in good repair.12
6. Fenceline monitoring with public data
Monitors at the property line measure what actually leaves the site. Continuous H₂S and ammonia monitors can show when odor events happen and whether fixes are working. There is a national precedent for sharing this data: EPA requires oil refineries to monitor benzene at their fencelines and publishes the results on a public online dashboard.19
What regulators and other plants have done
| Where | What happened | Company response reported |
|---|---|---|
| Los Angeles area, CA (rendering plants in and near Vernon) | South Coast AQMD’s Rule 415 (2017) requires permanent total enclosures, odor control systems and best management practices at rendering plants. In 2022, the district reported that Darling had completed enclosures for its raw material receiving area and its grinding and cooking operations.1214 | Enclosures completed, per the regulator.14 |
| Linkwood, MD (formerly Valley Proteins, acquired by Darling in 2022) | A 2022 consent decree with Maryland’s environment department required the company to hire an air consultant with rendering odor expertise. The consultant was to evaluate scrubber integrity and capacity, air and liquid flows, fans, chemical feed, monitoring, packing, raw material management and housekeeping, and report within 120 days. The state alleged scrubber ORP readings fell below the permit’s +125 mV minimum on multiple days in 2021.15 | In September 2026, Darling told the Star Democrat it has invested tens of millions of dollars since 2022, including “several air-control improvement projects,” an upgraded air-treatment chemical program and new instrumentation-monitoring systems installed in early 2026.16 |
| Bastrop, TX | In March 2026, a court approved a temporary injunction requiring Darling to self-monitor and report to state regulators whenever hydrogen sulfide exceeds 1,000 parts per billion. The Texas Attorney General had sought an 80 ppb threshold, real-time H₂S monitoring and corrective actions overseen by independent experts. A hearing on a final injunction is set for July 2027.17 | Darling described about $40 million in improvements, largely for air and water quality, and a company representative told county commissioners, “We’re here to do better.” A county commissioner said the odors had been “much, much better.”17 |
These are examples from other places. They describe different plants, permits and situations, and are not claims about the East Dublin plant.
What we’re asking for
We want the plant to succeed as a good neighbor. These steps build on equipment the plant already lists and on practices regulators have required elsewhere.
- An independent odor audit. Hire a qualified, independent engineer to evaluate every odor source and control, as Maryland required in 2022: scrubber capacity and condition, air and liquid flows, fans, chemical feed, packing, monitoring, raw material handling and housekeeping. Share a public summary of the findings and a schedule for fixes.
- Keep the scrubbers tuned and maintained. Monitor pH and ORP continuously, not just every four hours. Automate chemical dosing, keep packing and nozzles clean, and confirm performance with periodic third-party testing.
- Capture all of the odorous air. Keep receiving, grinding, cooking and pressing inside buildings under negative pressure, with doors closed except while trucks pass through, and send that air to treatment. Rule 415’s inward-airflow standards are a good benchmark.
- Treat cooker vapors thermally around the clock. Keep high-intensity vapors going to the RTO or boilers. Minimize RTO downtime, have a backup plan for maintenance periods, and publicly report RTO downtime and bypass events, with dates and durations.
- Process raw material promptly. Keep incoming material covered and process it within hours of delivery, keep receiving areas clean, and wash trucks and containers.
- Continuous fenceline monitoring with public data. Install H₂S and ammonia monitors at the property line and post the readings online, so everyone can see when odor events happen and whether improvements are working. Add H₂S monitoring at the biogas flares, both Darling’s and the RNG plant’s.
- A community meeting. Meet with neighbors to explain current odor controls and planned improvements. Provide a staffed odor contact line and a log of complaints and responses.
Smell it right now? Your report helps document the problem. Report an odor →
Sources
- Georgia EPD, Air Protection Branch. Narrative, SIP Application No. 28914, Darling Ingredients Inc. – East Dublin (July 12, 2023).
- Georgia EPD. Draft Air Quality Permit Amendment No. 2077-175-0042-S-05-2 (2023; issued Sept. 28, 2023, per source 20).
- Georgia EPD. Narrative, SIP Application No. 28568, Darling Ingredients Inc. – East Dublin (Oct. 25, 2022).
- U.S. EPA. AP-42, Section 9.5.3: Meat Rendering Plants (Sept. 1995).
- U.S. EPA. Odor Control by Scrubbing in the Rendering Industry, EPA-600/2-76-009 (Jan. 1976; IIT Research Institute and Fats and Proteins Research Foundation).
- U.S. EPA. Air Pollution Control Technology Fact Sheet: Packed-Bed/Packed-Tower Wet Scrubber, EPA-452/F-03-015.
- U.S. EPA. Air Pollution Control Technology Fact Sheet: Regenerative Incinerator, EPA-452/F-03-021.
- U.S. EPA. Air Pollution Control Technology Fact Sheet: Permanent Total Enclosures, EPA-452/F-03-033.
- U.S. EPA. Monitoring by Control Technique: Wet Scrubber for Gaseous Control.
- U.S. EPA. Using Bioreactors to Control Air Pollution, EPA-456/R-03-003 (2003).
- Hadlocon, L.J.S., Zhao, L., Manuzon, R.B. and Elbatawi, I.E. An Acid Spray Scrubber for Recovery of Ammonia Emissions from a Deep-Pit Swine Facility. Transactions of the ASABE 57(3) (2014).
- South Coast AQMD. Rule 415: Odors from Rendering Facilities (adopted Nov. 3, 2017).
- South Coast AQMD. Rule 472: Reduction of Animal Matter.
- South Coast AQMD. Letter responding to community concerns about rendering plants (Feb. 2022). See also the district’s rendering plants page.
- Maryland Department of the Environment v. Valley Proteins. Consent Decree (Sept. 2022).
- Star Democrat. ‘You just accept it’: Residents say Darling Ingredients odor problem is going unaddressed (Sept. 3, 2026).
- Community Impact. Darling to self-monitor emissions under court order ahead of July 2027 hearing (Mar. 5, 2026).
- ATSDR (CDC). ToxFAQs: Hydrogen Sulfide.
- U.S. EPA. Benzene Fenceline Monitoring Dashboard.
- Georgia EPD. Narrative, Application No. 29349, GreenGasUSA RNG Facility at Darling Dublin (July 8, 2024).
- Georgia EPD. Air Quality Permit No. 1311-175-0079-B-01-0 (issued Aug. 15, 2024).
- Georgia EPD. Permit Amendment No. 1311-175-0079-B-01-1 (Jan. 7, 2025; name change to GGUSA Dublin LLC).
This page explains general engineering practice and summarizes public records. It is not engineering advice and does not describe the East Dublin plant’s actual performance, which we have not seen. If you spot an error, please let us know so we can correct it.