Controlling Odor at Transfer Stations and MRFs: There’s More Than One Way to Reduce Complaints

Odor control at transfer stations requires special solutions.


Editor’s note: This article first appeared in the January/February 2016 edition of MSW Management.

“Odor is one of the biggest problems facing compost facilities, landfills, and transfer stations,” says Paul Relis, senior vice president at CR&R Inc. in Stanton, CA, and a veteran of the California Waste Management Board. “The problem is not going to go away; it’s only going to get more acute, which means the industry is going to have to find ways to coexist with our neighbors because the transfer station is a vital piece of municipal infrastructure.”

Although many transfer station operators, such as Daryl Smith at the Hillsborough (FL) County Solid Waste Management Department, report few or no problems with odor control (in part because the two transfer stations Smith manages are sited so “neighbors can’t get too close”), farther south in Palm Beach County, Mark Eyeington literally has neighbors outside his backdoor, making odor control strategies routine. “Odor may be a fact of life,” says Eyeington, “but there are rules; you can’t create a public nuisance.”

“The best approach is to keep it simple,” says Don Costello, national director of waste facilities for HDR Inc. in Minneapolis, MN. “Move the waste through the facility as quickly as possible. And keep the facility clean.”

Industry consultant Nat Egosi, president of RRT Design and Construction in Melville, NY, agrees. “The best way to manage odors is to have a system whereby all waste is received inside a building that is properly ventilated and then moved out as quickly as it’s brought in. You don’t want anything sitting around stewing. The odor comes from the stewing.”

Costello thinks good odor control begins with good design. “What it boils down to is designing the facility to promote good, solid housekeeping. You want to avoid nooks and crannies where waste can collect. At HDR we specify heavy-duty concrete floors and we prefer tall, reinforced concrete push walls. We also like to keep the building structure outside the walls so you don’t have columns and structural members creating places for trash to collect. If the client can afford it, we recommend interior liner panels…so dust and particulate material can easily be hosed down. In the pit there has to be easy access in and around scales; the design of the hopper above the truck should keep spillage to a minimum, and in the driveway lanes we typically call for curbs that guide the trucks and keep them where they’re supposed to be. Our experts have done tests of air being exhausted through roof fans, and the conclusion is that if the facility is operated the way it was intended to be operated, you generally won’t have an odor problem.”

“The key,” says Egosi, “is a building that’s sufficiently large that you can receive and process the waste, where the trucks can get in and out quickly and where you can close the doors. Keeping the waste confined is important; [so is] putting it where it was designed to be put because that’s what the ventilation system is designed to handle. Storing waste in a building where it wasn’t intended to be stored usually occurs when facilities begin handling more material than they were designed for, something decision-makers need to consider. One thing I like to recommend is that transfer stations install high-speed roll-up doors. Even though a permit may call for keeping entry and exit doors closed, because it takes too long to open and close a conventional door, many operators keep their doors open whether they’re receiving a load or not. But an open door is a source of odor.”

Another option for transfer station drag-out fumes is a door perimeter system being marketing by Hinsilblon Ltd. in Cape Coral, FL. The system generates an air current around a door that can be deodorized. A company spokesperson reports that Browning-Ferris Industries has experimented with the new system and likes the way it works.

A facility that’s too small, improperly designed, or inefficiently utilized can also cause a backup at the front end of the system. “Long lines are not conducive to controlling odors,” says Eyeington, whose five Florida transfer stations handle more than 1 million tpy of solid waste. “You need to get the trucks in the building, where their odors can be controlled, and just like your facilities, trucks should be cleaned regularly.”

Bob Hauser, senior vice president at Camp Dresser & McKee Inc. in Tampa, FL, thinks part of the problem is that facilities that regularly generate malodors don’t take the time to sort out what’s happening and do something about it. “If you know you have specific loads coming in that contain odorous material—maybe waste from a restaurant – plan to either dump that load directly into a transfer trailer or in a place where you can get it off the floor and into a trailer quickly. And don’t dump a load like this into a full truck; use one that’s already partly filled, then cover the odorous load with more garbage to help keep the odor down until it gets to the landfill.”

Get It Under Cover
If you can’t move all the waste in one day, store what’s left in transfer trailers. “We preload our trucks,” says Jack Gearing, solid waste manager for Montgomery County Solid Waste District in Dayton, OH, which operates two transfer stations for a daily total of 1,900 tons. “We have 12 transfer trucks of our own, and if we’ve got waste left over, all 12 are preloaded to go out the next morning.”

To keep odor down on what can’t be loaded or stored, Gearing has installed an overnight misting system. “We’ve found a neutralizing agent really helps keep the odor down. We dispense every 30 minutes at night and approximately once every hour during the day. We haven’t had any odor problems since we’ve been doing this.”

A similar loading procedure is followed at Hillsborough County’s facilities. “It’s always first in, first out,” says Smith. “If we get in 1,000 tons and have 300 tons left over, that 300 tons is the first thing to go the next day.”

How Clean Is Clean?
The jury is out about how clean a transfer station has to be to keep odors at a minimum. Costello recommends a regular, even daily, sweeping and washing down of the floors and walls. Egosi thinks cleanup is a matter of the kind of waste being handled: regular cleanups if what you’re moving is heavily organic, not so often for a stream that’s rich in paper and plastics. Egosi also points out that in some localities, the wastewater that results from hosing down a facility can be a problem. “In New York, you definitely want to do as little as you can with water. The water you collect when cleaning a transfer station is considered contaminated, and in New York you’re regulated about what you do with it.”

Smith says his crews clean the tipping floor once a week. “We don’t do it daily because our loads fluctuate too much. One day we might get 1,000 tons, another day 300.”

Keep Track of the Weather
Eyeington recommends knowing which way the wind is blowing. “We had an odor control consultant evaluate our operation, and he told us we had to be more sensitive to what’s happening with weather conditions, both so we can change our operations if the prevailing wind will affect our neighbors and so we know what we’re talking about when we handle complaints. To do this we installed an inexpensive weather station. It was a small price but a big bargain. You not only can tell what the weather is doing at that moment, you also have a historical record. This helps us a lot when it comes to tracking incidents.”

“When it’s still and quiet out, properly sized roof and wall fans do a fairly good job of pulling the air inside the building and exhausting it to the outside,” says Costello, “and where there’s enough dispersion, it’s not a problem. But if it’s windy outside and the large entry and exit doors are open, you’re kidding yourself if you think you’re sucking up all the air in a building. However, under windy conditions, the odors that get outside the building usually get dispersed quickly.”

And if the wind appears to be carrying the odors away from your facility, don’t expect a day free of complaints. “There are days when we scratch our heads and say, ‘It’s not us, it can’t be us,” says Eyeington. “But the point is you have to step up to the plate. The main thing we tell the public is to call us the minute they smell something. Don’t wait until six weeks later. All our supervisors are equipped with cell phones, and residents are informed about the hotline number they can call 24 hours a day. And when they call, we do something. Depending on what the complaint is, we may turn on the perimeter misting system or we may bring all the trucks inside and double-stack them. We might find it’s one bad load and if that’s the case, we get that out right away—maybe we’ve got a load of catfish on the floor.”

And If All Else Fails
But what if, despite your best efforts, you still get complaints? Of the available technology, misting—with either water or odor-reducing products—is still the industry’s method of choice, both inside buildings and outside, around greenwaste operations and for perimeter spraying. “Eight, 10 years ago,” says Egosi, “conventional wisdom was if you had an odor problem, you put in scrubbers. Now I see a lot of misting systems. It’s not a huge cost of operation, especially compared to scrubbers, but it’s doing something. I’ve seen some installations spray the mist into the ventilation system and then spray the masking agent or neutralizer at the point where the air is being exhausted out of the building. If you put in a misting system to control dust, which a lot of facilities do, it’s only logical on a life cycle cost basis to introduce an agent to control odor.”

Odor control agents range from products that mask malodors with something designed to smell pleasanter to new generations of neutralizers that, although widely used in other municipal applications such as wastewater treatment plants, have yet to catch on the solid waste industry.

As Doug Mason of Continuum Chemical Corporation in Houston, TX, explains it, 80% of odors humans find offensive are the result of nitrogen- or sulfur-bearing compounds. Until material containing these compounds starts to decompose, we’re unaware they’re around, usually in combination with carbon and oxygen atoms. But come decay, the nitrogen and sulfur atoms are rearranged into smaller molecules that give off odor when they’re volatilized as gases into the air. The challenge for anyone trying to control odor is that, in some cases, relatively few molecules—as little as one part per billion—need be present for sensitive noses to notice.

Masking malodors with a product designed to smell better is a traditional approach. Two others are oxidation, which inhibits the reaction that generates odor, and encapsulating agents.

“Masking agents give a black eye to everyone who is trying to do something about odors,” says Ian Howard of Ecolo Worldwide in Toronto, ON, manufacturer of essential-oil technology for odor control. “We’ve seen a trend toward odor neutralizing, and we are constantly doing research on creating improved and more effective neutralizers. In our experience, what a transfer station uses depends on a mix of variables, from the type of odorous materials present to temperature, wind direction, and climatic conditions, as well as the facility’s ventilation system and proximity to neighbors.”

In Florida, proximity to neighbors has caused Eyeington to install a perimeter misting system at the district’s largest transfer facility. The system consists of 55-gal. drums combined with stainless steel misting nozzles that are manually switched on when odor becomes a problem. The transfer stations are also equipped with portable misting devices that can be quickly dispatched to a spill or an isolated source of odor. Eyeington is also experimenting with a high-pressure misting system in his largest facility. So far he’s dispensing only water to keep dust down, but he says this also has the added advantage of cooling the buildings in warm weather. In Hillsborough County, Smith recently installed a perimeter system around the greenwaste processing area at the larger of that county’s two transfer stations. Since greenwaste pickup was separated from garbage five years ago, the amount of garden waste went from 7,000 to 50,000 tpy, and keeping it moving has been a challenge.

Transfer station operators who find pleasant odors too long ingested to be as unpleasant as the malodors they’re designed to substitute are experimenting with other chemical options. Rainbow Disposal in Huntington Beach, CA, which processes 1,800 tpd of trash, uses a product called BioMagic, which works through oxidation.

“We have found a way to put ionic oxygen—not dissolved oxygen but loosely attached oxygen radicals—in our liquids,” says BioMagic’s Paul Alfrey. “When you mist this in air that is contaminated with odor-causing sulfides, the oxygen blends with the odors and neutralizes them while adding any additional scent.”

Mike Ortiz, who has been supervising the project, says BioMagic works so well he recently injected scent to see if the malodors were actually gone or his crews had just gotten used to them. Although odor control chemicals have been typically mixed with water in a misting system, the moisture can add weight to outgoing loads. To help solve this problem, Rainbow Disposal is experimenting with a waterless delivery system that uses a venturi tube (obtained from an aircraft parts supplier) to draw the diluted fluid from a barrel and disperse it directly into the air. If the system continues to work successfully, the plan is to mount units around the facility.

From southern California, RMB Engineering is marketing Odor X, which the company describes as an odor neutralizing agent (“a water-based mix of plant oils and surfactants”) with Triad Industries’s dry vapor dispersal system.

“We vaporize the agent,” says David Ehret, company vice president, “in a vapor chamber and blow it through a blower that is connected to tubing with holes drilled in it. This creates air currents. When the Odor X is mixed with the air, the odors that pass through the air current are emulsified and carried off.”

Taking chemical odor control one step further, Continuum Chemical has developed NONOX, which converts odor-causing chemicals into materials that have no odors while encapsulating other malodorous substances to prevent their evaporation. The material can be applied by traditional spray method or atomized as a fog. The proof that the product works is the lack of scent, malodorous or pleasant.

“We decided we were going to go at this in a more scientific way,” says CEO Mason, “to identify the components that are causing the odor and actively look to eliminate them. What we came up with is a product that will literally take the odor molecule like hydrogen sulfide and put it into a container, if you will. Once it’s in a container, you can’t smell it.”

To help minimize smelly waste loads from highly organic wastestreams, Howe-Baker Engineers Ltd. in Tyler, TX, has developed a line of ozone generators. Sonozaire Odor Neutralizers electrically convert a small amount of oxygen in the air into low levels of ozone, which molecularly strips odors by breaking the carbon-to-carbon cycle, leaving behind water and carbon dioxide. The units are available for 0.5- to 50-yd. containers, and last year the company introduced a model designed for such small indoor applications as high-rise apartment buildings. The Sonozaire units are typically wall-mounted with a hose connected to the compactor or container. Output is adjustable and can be matched to the odor level in the waste collection room, stationary compactor, or rolloff container. Units can be equipped with an ozone sensors to automatically control output.

A step in a nonchemical direction from masking or neutralizing agents leads to biofilters, such as the unit CR&R Inc. developed in consultation with CH2M Hill and installed in its southern California materials recovery facility (MRF) transfer station.

“The biofilter was the result of the fact that we had ongoing nuisance violations because of land-use conflict,” says CR&R’s Relis, who was actively involved in the biofilter’s design and installation. “We are extremely close to our neighbors, 300 feet in some cases, and one of our facilities is a mixed MRF. The problems are generally seasonal—in the warm months—and the prevailing wind carries the odors toward our neighbors. The entire site is 10 acres; the MRF is an acre, and the transfer station a little under an acre. To solve the problem, we put in a comprehensive odor control program, which included moving the greenwaste out of the building so we could move material faster and installing a new misting system to cool the facility. Then two years ago, we installed the 2-to 3-acre biofilter. It’s the largest one I know of in our industry and one of the only ones at a MRF transfer station. It can take 225,000 [cubic feet per minute] of air from the two buildings with 375-horsepower fans that pull the air out and treat it through the filter. It has made a dramatic improvement. We went from an acute problem to no violations for two years.” (The facility recently received a citation, but Relis is quick to point out that it wasn’t related to the operation of the biofilter but rather the greenwaste that was stored at the facility too long.)

“The biofilter as we designed it is built out of all recycled material, including crushed concrete that we would receive normally, which we broke up,” continues Relis. “The filter media consists of wood we got from an old orchard that was being taken out – we dried the material for about six months—and we use ‘zoo doo’ from the Los Angeles Zoo for compost as a starter. In all that’s about 3,000 to 4,000 tons of recycled material. We designed the filter to be serviced in two halves so we could take it apart and replace one-half of the media at a time. The large wood material, 1 inch or larger, seems to hold up very well. In two years, there seems to be hardly any deterioration, although we are starting to see some breakdown in the smaller material. At some point we’re going to have to monitor backpressure to determine if we’re at a point where we need to replace filtering media. We’re doing quarterly inspections with CH2M Hill to see if we need to implement any refinement, and we look at the filter every day from an operational perspective. The nice thing is there are no chemicals. The cost to set it up was around half a million dollars, but operating costs are very low, much less than if we were misting chemicals.

“Before we decided on this design, we built six small filters and did the sniff test with each one. There is a slight—what I would call a musk—smell that the filter gives off, like a soil smell. For our neighbors, it would be like living next to a place that sells soil. The point is you never get 100% odor control, but if you look at the record, this is a success, a quantum leap in terms of improving our situation. In urban areas and fast-growing areas like southern California, you’re not going to find many places to site new transfer facilities, so you’ve got to make the facilities that are already operating the best they can be.”  MSW_bug_web


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