Good Business Scents

Lynn Merrill

Beyond good housekeeping, there are techniques to help control odors in containers and at facilities.

Odors are as much a part of the waste industry as collection trucks and landfills. The byproducts of the decomposition process, odors start when putriscible garbage is placed in a container for disposal, or when materials are prepared for composting.

With the exception of dry recyclables, each decaying item dropped into a waste container emits its own unique olfaction, which blends with molecules from other components until they combine to produce a stench cologne. These unique smells may be tolerable to those that have grown used to the bouquet. But to the rest of the public - those who must sleep, work or play downwind from a composting plant, landfill or transfer facility - such smells are an insidious intrusion. And when those smells intrude on a community's daily life, there is a good chance something will need to be done - and fast.

The Route to the Smell Treating odors starts with the waste container itself. In dry climates such as in the Southwest, container odors generally are not a problem, because the materials dry rapidly, which reduces odor potential. But in warm, damp climates that allow for decomposition, odor complaints may be frequent. In these situations, a variety of products may be used.

For example, dry, granular products that absorb odor molecules may be sprinkled in the bottom of the garbage bin. Chemical masking agents or deodorizers also may be sprayed. However, applying these products will require additional time and costs to the collection operation.

A recent advancement for container odor control involves automatic spray systems that are installed on the forks of front-loading refuse trucks. When a bin is dumped and still inverted, a spray manifold located on the forks shoots a chemical solution into the bin to clean and deodorize it while the lid is still open over the hopper.

Food service operations, such as grocery stores, restaurants and fast-food franchises are notorious waste generators, but regular cleaning of their bins can reduce the sources of odors.

In addition to treating stationary containers, maintaining the proper cleanliness of trucks also can help to reduce the number of odor complaints. Operators can steam clean the inside of the collection trucks at the end of a shift, as well as regularly clean drip containment areas under the tailgate, the clean-out areas behind packer blades and other places where materials can collect and rot.

At the Compost Facility Beyond the odor control techniques available for containers and trucks, it is possible to minimize the release of offsite odors at facilities through proper design, engineering and operation.

The Akron Composting Facility operated by KD Composting Service, Akron, Ohio, for instance, is located in a river valley where odors can accumulate because of temperature inversions. "That odor just sort of hangs in there while it's cool," says Annette Berger, plant manager. "Once the temperature starts rising, that air mass lifts through the tree line. Until the sun breaks out, those people smell us."

In producing its compost, the Akron facility operates an in-vessel composting system that processes 64 dry tons daily into a soil amendment that is marketed to topsoil blenders, nurseries, landscapers, golf courses and area residents. Each of the four reactor bays is 700 feet long by 20 feet wide and 10 feet deep. Odor-laden air is collected from the reactor bays using manually lowered covers that span the width of each bay. The air is collected and scrubbed using 12 two-stage towers.

The first stage tower is a column of packing 6 feet high composed mostly of 2-inch plastic balls to create surface area. Water then is trickled through the packing to scrub out the ammonia. This water then is treated with sulfuric acid to bring the pH back to neutral. Once the air has gone through the first stage, sodium hypochlorite is injected to remove the sulfides and amines in the system. The air then travels up through the second tower through another set of identical packing, and then the air is released into the atmosphere.

Each scrubber supply fan feeds one set of towers, and each one can pull 37,000 cubic feet per minute of air into one tower.

In choosing the best system for the facility, Berger says they hired a consulting firm that created an odor panel of local residents who wanted to help find a solution to the odor problem. Working with the panel, the consultants "experimented to find out at what level the people could no longer detect the odor."

"We needed to meet a threshold of 20 dilutions off the stacks for us not to offend the residents around us," she says. Eventually, a scrubber system was selected because it was effective during a trial. "We have better removal of the sulfides and amines," she says.

Just knowing that the city was working on the odor problem was enough to see a reduction in the number of odor complaints, Berger reports. "[Residents] were very patient in [the construction] phase. Once we had the system online, we initially still had some complaints, but most of that was due to aeration problems."

Berger says some of the facility's operations changed, such as handling curing piles outside, to eliminate the last remaining odor issues. "We had to tweak some of the operations," she says. "For example, we couldn't move material at night or if the temperature was going to drop. People think if you put an odor control system in, it's going to take care of everything. That's not realistic."

The Bio Option Sometimes, biofilters can provide a solution. For example, a southeastern Michigan biosolids composting facility used a biofilter in its paint sludge odor control project. "We'd heard of many success stories using biofilters," says Nicole Chardoul, a project engineer with RRS, Ann Arbor, Mich. "There's all different kinds of designs, but ours is quite simple."

The biofilter includes several layers. The first is a plastic liner and drainage system to collect run-off. The second layer consists of 1 foot of stones. Polyvinyl chloride (PVC) pipes are imbedded in this layer to collect the air and send it to the biofilter. The third layer includes compost, wood chips and peat moss. Pine bark is spread over the top of the entire biofilter to hold down fines that could blow away. The entire filter was five feet deep with a surface area of 120 feet by 70 feet wide.

Chardoul explains that the air inside the enclosed building is captured, then sent through a biofilter before it is released. "The bacteria inside materials such as compost and wood chips thrive," she says, noting that "that's the kind of bacteria we want." "They eat [the odor-causing] compounds found in composting facilities, so it's important to keep the biofilter moist so the bacteria can thrive."

To ensure its system works, Chardoul says RRS created an "odor panel" to critique the design of the biofilter. "The odor panel included people that either worked in the township offices or administrative offices where they weren't used to smelling the compost or working in the compost building daily," she says. "They went around the fence line and the surrounding roads [of the facility] and marked the intensity of odors and what type of odor they detected."

Out on the Landfill Site Even in the most rural environments, odors can be problematic. For example, at the Waste Management Inc. Temple Landfill in Temple, Texas, most of the facility's neighbors are farmers. The landfill services approximately 60,000 customers, and receives between 800 and 1,000 tons per day.

"We didn't really have a complaint, but you could smell an odor as you drove by," says Frank Hawkins, site supervisor. According to Hawkins, the odors were originating from risers going underneath the landfill to the leachate sump. Odors were most prevalent during the rainy season.

Hawkins said the landfill opted for a liquid odor control product to neutralize smells because the district manager had used the product at another site and it had proven effective. The liquid is used primarily during the rainy season, when odors are most prevalent. "When it's not raining, we don't seem to have any problem," Hawkins says.

To treat odors, Hawkins says the liquid treatment is applied every three weeks. "We dilute it, and then we pour it down into the risers," he says.

Hawkins also notes that good housekeeping prevents odor problems. "We keep our sump pumped," he says, noting that he tries to keep his pumped dry. "After you get the [sumps] pumped completely out, then you start getting the smell. But if you do this for two or three months, your smell usually [will be] gone. You don't have to use [treatment] again unless you have another rainy season."

At the West Edmonton Landfill in Edmonton, Alberta, Canada, odor problems also are seasonal. Operated by Canadian Waste Services Inc., the facility handles approximately 17,000 tons of municipal waste each month. Originally, the landfill was located on the town's outskirts. However, now the facility is surrounded by a heavy industrial area, so odors are more noticeable. "The area is saturated in population, especially during the day when everybody is at work," says Rhonda Rudnitski, environmental compliance manager.

Nevertheless, an odor suppressant only is used in the summer, "and sometimes in the spring and fall, depending on the temperature," Rudnitski says. "We're below freezing for three months of the year in most years," she says, noting that when it's freezing, odors are more or less nonexistent.

According to Rudnitski, the suppressant, manufactured by Odor Control Co., Scottsdale, Ariz., has "a fresh, piney odor." "When we mix that with either leachate or water and apply it to our roads, we can sort of smell traces of it," she says, noting that she chose this product because she was able to test it first. The suppressant is mixed into a tank truck that pumps and recirculates the leachate for dust control.

"We put a little bit of odor suppressant directly into the truck that collects the leachate," she says. "We find that the odor suppressant will work on the leachate before we even start recirculating it."

"We also have sprayed [the odor suppressant] directly onto the working face if the garbage has a lot of odor. We notice it the most when it rains," she adds, noting this has reduced odor problems.

Additionally, Rudnitski uses water as dust control on all the facility's haul and perimeter roads, "and we've started adding a little bit of odor suppressant to that as well," she says.

Many of the recent odor complaints were the result of a recently approved vertical landfill expansion, Rudnitski says. "We are the highest point in the area, and we'll eventually be the highest point in the city of Edmonton," she says. "With the vertical expansion, we have lots of hills and valleys around our site [which has been trapping odor]. "By applying odor suppressant along the haul roads, it seems to mitigate the odor pockets that were collecting in the low-lying areas."

Finding What Works The types of odors may vary in the waste industry, depending on what's causing them. Consequently, what may work in one setting and climate to control smells may not succeed in another. The best approach, however, is to identify the odor source and then determine a strategy to combat it.

No strategy or odor control product, however, can substitute for good basic housekeeping. Whether it's a transfer station, composting operation or refuse bin, you should regularly clean the container or facility. Then, identify and quantify the types and sources of remaining odors. Also consider who is complaining. If they are neighbors, it's important to involve them in the control process and to communicate regularly and openly.

It also may help to hire consultants who specialize in odor control problems. They can develop and implement techniques such as establishing an odor control panel of local residents or affected parties.

In addition, research the various odor control techniques and products. If possible, visit sites that are using the products or equipment, and evaluate how well they are working and whether they'll fit your application. Whenever possible, perform pilot tests of different products to determine their effectiveness and ease of handling. While the latest state-of-the-art system may look appealing, always try to address the lowest cost solution first, then work up.

Odor issues are not something to be taken lightly, especially in the waste business. Controlling these problems is not just a matter of being a good neighbor, it makes good business sense.

Contributing Editor Lynn Merrill is the director of public services for the city of San Bernardino, Calif.

To treat odors, it is important to understand what is generating them in the first place. There are a variety of sources of odors that are generated within waste and composting systems. The most common source is generated by oxidation - when air and an organic compound come into contact with each other. During this process, oxygen molecules exchange with another molecule to generate a new, and possibly smelly, compound.

Some compounds emit odors when mixed with other components. While these compounds may not themselves be smelly, when blended, these mixes cause a chemical reaction that generates various odors. Other odors are the byproduct of gases emitted by bacteria as they consume waste materials for food. For example, anaerobic digestion, the process of decomposition in the absence of oxygen, can generate ammonia odors as a byproduct. Other compounds are just plain smelly. The variety of odors can range from the familiar rotten egg smell of sulfides to the sickly-sweet garbage smell generated from amines.

Odor control products minimize odors through a variety of control strategies. One type of product masks odors by covering them up with a pleasant-smelling perfume. However, masking agents combined with the offending odor sometimes may produce a more noticeable odor. Another type of product neutralizes the odor molecule by creating a chemical reaction that renders the odor molecule inoffensive. Other products literally cancel the odor out, similar to raising or lowering the pH value to make it less alkaline or acidic.

Odors also may be physically filtered out of the air stream using various media such as carbon or wood chips.

While the science of odor control requires an understanding of both the chemical and physical properties of their molecules, the art of odor control can be trickier because not everyone reacts to an odor in the same way or in the same concentrations. If you have two neighbors next door to each other and across the street from a composting facility, one may react strongly to the faintest smell, where the other may not smell anything at all, or may even find the odor pleasant. Therefore, any odor control strategy must deal with the most sensitive recipient - who also may be the most vocal.