MSW operators must deal both with the very real odors generated by decomposing waste and with the perception of odors by neighbors. This Part 1 describes the strides that have been made in controlling and ameliorating the chemicals that cause the odors prevalent at MSW facilities. Part 2 will describe how operators work with their neighbors to deal with the perception-of-odor problem.

By Charles D. Bader

Since MSW processing and disposal inherently involves decomposition of organics, malodors represent an integral problem for MSW facility operators–and perhaps an even bigger problem for nearby neighbors. Indeed, the most widely used measure of the magnitude of a facility's odor problem is the number of neighbor complaints it receives. Largely because of neighbor complaints and the political clout they can muster, the odor-control industry has expended much effort in developing technological solutions (in both senses of that word) to mask, neutralize, encapsulate, or transform odors. Other firms have attacked malodors by accelerating the natural decomposition of MSW by adding microorganisms and/or nutrients. And as described in "In-Vessel Composting" in the January/February 2002 issue of this magazine, some operators have gone to the extent of encapsulating the MSW organics in vessels or even odor-tight buildings during the most malodorous phase of the processing.

There are three primary methods of odor treatment available, contends David Hill, CEO of Indianapolis, IN—based Global Odor Control Technologies. "The first method is by air contact. This is the atomization of reactants and deodorizers into the same air currents that are carrying the odorous gases, enabling a reaction between the molecules of the odorous gas or gases and the deodorizer upon contact in the atmosphere. The second is by surface contact. This is the topical spraying or misting of a solid or liquid surface with reactants and deodorizers to generate reactions near or on that surface. This method treats the molecules as or just before they enter the gaseous or ‘vapor' state. The third method is by incorporation. This is the addition of a substance or substances into a substrate in order to change the underlying reactions causing the odorous compounds to occur. This method, which is widely used in composting, reduces or eliminates the quantity of odor to be treated by air or surface contact."

Within these three broad categories, however, there are a variety of different product formulations and approaches to odor control that companies have marketed to the MSW industry. Each of these companies and each of these products, it would seem, has a number of satisfied users, who by definition have a number of satisfied neighbors.

The Chemical Attack

Granules inside WindScent sleeves hang along this fence every 8-10 ft. to control odors

By far the products most widely used to control MSW malodors consist of formulations of what are called "essential oils." As explained by Sylvain Savard of the Centre de Recherché Industrielle du Quebec, essential oils are made up of volatile substances that come from a physical process of extracting odorous plant materials, such as flowers, woods, leaves, and fruits. Formulations of several essential oils are marketed as active agents to control and eliminate odors. These oils consist of substance functional groups that can react with various odorous substances to create complexes or new products. The original gas-specific odor is then modified or simply eliminated.

Manufacturers insist that essential-oil formulations do much more than just mask or cover up malodors, but they differ in their explanations of how essential oils react or otherwise control odors. Perhaps the most elaborate description is offered by Bob Gaubert, who developed essential-oil—based products as the founder of Odor Control Technology and is now a knowledgeable industry consultant based in Loganville, GA.

"Essential oil formulations," he asserts, "neutralize the odors in the air by such phenomena as adsorption and interference. Adsorption is the phenomenon that occurs when the malodor molecule is absorbed into a droplet of the odor-control agent. There are attracting and repelling interactions between all molecules. The attractions in close proximity result in Van der Waals forces that hold molecules together by a weak electrical charge.

"As odor molecules [osmophores] pass through or commingle with the odor-control molecules, the positively charged atom of the odorant attracts the negatively charged portion of the odor and holds it in suspension. Once these osmophores are absorbed into the odorant molecules, their evaporation into the atmosphere is delayed until natural biodegradation or oxidation occurs.

"Odor interference or pairing occurs with Zwaadermaker pairs, which are those chemical pairs that, when added together, produce zero or close to zero odor. It is believed that certain odorants resonate at osmic frequencies, all of which are not mutually compatible but are antagonistic. Two waves that cancel each other are said to interfere. Many pairs have been identified, which neutralize each other. The phenomenon of neutralization of odor pairs was first noted by Zwaadermaker while introducing odors individually or simultaneously through each nostril. He was able to identify numerous pairs that, when breathed together, interfered with or neutralized the odor of both. When balanced and combined in the correct proportions in order for the pairs to neutralize each other completely, this phenomenon can be usefully applied in MSW odor control."

Ian Howard of Toronto, ON—based Ecolo describes the application process. "In order for a sufficient amount of transformation to occur, the odor-control molecules must be atomized to a specific size to establish and maintain contact and exposure with the odorous gases. When spread in the atmosphere by vaporization, the lighter-than-water essential oils spread over the surface of the vaporized droplets. The electrostatic forces on the droplets' surface permit a quick contact between the malodorous gas molecules and the essential oils, and this contact aids in the capture and elimination of these gases. Once malodorous gases are captured by these droplets, they no longer can be smelled at all."

As that is a strong statement, we checked with an Ecolo user, Lee Fortier, engineering and operations manager of Dry Creek Landfill in Medford, OR. "We've been using it for nine months now," he reports. "We installed a line of poles on the side of the landfill facing our neighbors' homes, and we attached the misters to these poles about 30 feet off the ground. The results have been good; unlike previous years, we haven't had a single complaint since we installed the system. We know we have to be vigilant, though. We're up against mountains, so winds change frequently. We have a windsock that we watch carefully. If the winds shift toward our neighbors' homes, we stop the intermittent misting we do during calm periods and do continuous misting as long as that wind condition persists."

This barrier type of perimeter installation is not unusual. Michelle Lang, vice president of Odor Control Company in Scottsdale, AZ, says the typical user of her company's essential oil products applies it between its MSW facility and its neighbors. "If the receptors in people's noses receive our product first, they won't smell the malodors. The product doesn't have to be in liquid form, either. If, for example, landfill users can't easily install pumps at their landfill perimeters, they may well put the neutralizer in pellet form in pails and hang them on the perimeter fence every 20 feet or so. Either way, it makes an effective barrier."

The Town of Colonie, NY, used a perimeter defense effectively to solve the odor problem of both its composting and landfilling operations. According to Joe Stockbridge, director of the town's Division of Environmental Services, it had been receiving numerous complaints from its neighbors. "Solving the landfill odor problem was straightforward," he recalls. "We just set up a perimeter defense of spray nozzles and Odor Control Company liquid neutralizers on the side of the landfill that was adjacent to neighbors. It worked fine.

"We installed a perimeter defense on three sides of our composting operation, but we found the composting required a more extensive treatment approach. Not only are this facility's neighbors much closer than at the landfill, but the odors being generated were quite strong. We pick up yardwaste in biodegradable compost bags once a week, and the waste has started to decompose in the bags before it gets to the compost facility. As soon as a decomposing batch comes in, therefore, we spray it topically with the neutralizer. Thereafter, we spray it on the windrows every time we turn them. We have mounted the odor-neutralizer control tank and the nozzles right on the Scarab turner so it is quite an efficient operation.

"Once these systems were up and running, the neighbor complaints dropped off sharply. There is still some odor, of course. We probably get 20 calls a year now, but that's a lot better than the 60 to 80 calls we used to get. To achieve this, we have to continually stay on top of things, changing frequencies and moving equipment as needed to maintain our perimeter barrier."

Movable equipment apparently is coming more and more into use. Howard reports that Ecolo has a portable system that sells well. In either a backpack or trailer/skid-mounted configuration, it enables deodorants to be sprayed at the working face of a landfill while crews are working, thereby creating a more localized barrier. In one instance, he recalls, the user actually installed atomizers on a bulldozer working the landfill face.

Other Odor-Control Methods

BAT 506 odor-control product during application

Use of essential oil products is by no means the only approach to odor control. Savard lists dozens of methods for changing or controlling odors. Included on that list are incineration, chemical oxidation, atmospheric dilution, chemical catalysis, condensation, dehydration, and even paralyzing substances (to temporarily paralyze the noses of neighbors). Most of these approaches are simply not practical for MSW operations. However, there are alternative and/or supplemental approaches to essential-oil neutralization being used in or showing promise for MSW odor control.

Bioaugmentation

Since the principal cause of malodors in solid waste is the decomposition of organics, one approach to odor control in composting is to accelerate the decomposition process and thereby reduce the time the compost piles generate malodors. Some companies raise and sell bacterial microorganisms called facultative anaerobes that do not produce odor and that accelerate the composting process.

Companies in the odor-control industry accomplish the same goals by formulating and selling nutrients that stimulate the growth and predominance of facultative anaerobes. Global Odor Control Technologies, for example, does not primarily sell bacterial products. Instead, according to Hill, it sells products that work by influencing the microbiology of the decomposing wastes in the compost or co-compost material. "By delivering selected nutrients and oxygen-rich compounds, these products increase the presence of microbes producing nonodorous waste byproducts while decreasing the presence of microbes that produce odorous byproducts."

Dennis Felt, owner of Hanaford Farms in Centralia, WA, swears by this approach to odor control. Felt once had a severe odor problem in his co-composting of 25,000 yd./yr. of yardwaste, Sheetrock, and chicken manure. About three years ago he met David Hill, and he decided to try Hill's bioaugmentation approach to odor control.

"When our feedstock comes in, we immediately spray it with the liquid enzyme, mix it in, and start the composting process," Felt says. "We grind brush and add it to the pile once a week. We roll the pile over twice a week and screen the compost after week six. Two weeks later, we do the final screen, put it in the curing area, and forget it for four months; then it's ready to ship to our customers.

"There's no such thing as no odors in a composting operation like this, but that application of the enzyme has really cut down on the odors and the complaints from my neighbors. It also has cut my labor costs by speeding up the composting cycle from six months down to two months, and I'm producing a premium soil amendment that changes the structure of our clayey soil here and turns it into a Class 1 soil."

SciCorp of Toronto produces a family of micronutrient products for various applications. Each of these products stimulate and maintain the growth of desirable, naturally occurring facultative bacteria to eliminate and prevent odors and enhance the decomposition process. According to the company's Web site, the product formulated for composting is called Biologic SRC. "The components of this product stimulate the growth and predominance of desirable facultative anaerobes that do not produce malodor. In either aerobic or anaerobic conditions, facultative anaerobes biodegrade organic material rapidly without producing odors.… There are two methods of application: It can be used during the initial processing stage of the compost material to control the most offensive odors and enhance the decomposition process, or for topical application on compost piles to address the odors associated with flare-ups or during turnovers."

Biofilters

One of the most widely used odor-control systems at composting facilities is the biofilter. Largely constructed of already composted materials, it is designed to remove odors from malodorous air pumped through it. The city of Marlborough, MA, has a 30,000-ft.² biofilter housed in an enclosed building, according to Nelson Widell of Waste Options Atlantic in Warwick, RI, which manages the facility. Air from the facility's in-vessel digesters, its tipping floor, and its aeration building are passed through the biofilter.

"There are two water-absorber scrubbers that humidify the air and remove VOCs and dust," Widell explains. "The air is then pumped into the biofilter, which is composed of pipes embedded in 18 inches of riprap covered by 42 inches of a mixture of composted yardwaste and wood chips. The air filters up through the rock and then through the compost/wood chip mixture. That's all there is to it; when the air emerges from the biofilter, most–if not all–of the malodors have been removed.

"The last time I checked, the Marlborough biofilter was operating at 95% odor removal, and it will continue to remove the odors without significant maintenance for years. Of course, since the biofilter is a biological system itself, its compost will decompose. Eventually this will impede the airflow, and we will have to rebuild the biofilter with new composted materials. Under our permit, these materials must be replaced once its resistance to airflow reaches 8 inches of backpressure. Since the current backpressure is only about 3 inches, we should be able to use the current configuration for at least two more years. And changing it will involve just replacing 4,000 yards of compost, and we expect to produce 40,000 yards of compost here at the facility each year."

Another good example is the biofilter used in the huge compost hall in the city of Davenport, IA. According to Scott Plett of the Davenport Compost Facility, there are actually two biofilters, each a half acre in size, located at the sides of the 66,000-ft.² compost hall. The system is designed to treat 210,000 cfm of malodorous air. Four 26,500-cfm fans pull a negative draft from the compost-hall piles. At each static pile, blowers pull in the air and discharge it into an aluminum header on each side of the hall and on through 196 distribution pipes (98 on each side) to the biofilters. The distribution pipes are encased in 2 ft. of clean peat gravel covered with 3 ft. of compost and wood chips that remove the odors from the compost hall.

How much odor do these biofilters remove? "A lot," Plett replies. "We didn't realize how much until one of the 196 distribution pipes broke one day. The whole place smelled just terrible until we fixed that pipe, and the smell then dispersed right away. I can't tell you exactly how much odor our biofilters are removing, but as far as I'm concerned, biofilters are the only way to treat odor."

Quantifying Odor Levels

The portable pump enables deodorants to be sprayed at the working face of a landfill while crews are working.

Too often, it seems, MSW operators and neighbors have different opinions as to when there is a malodor present. And these differences can lead to heated disagreements and even lawsuits. Unfortunately, there is no really acceptable way to measure odors on a scale that would settle these disagreements. Ecolo went to the trouble of having the University of Pierre and Marie Curie scientifically measure the drop in hydrogen sulfide and other compounds achieved with Ecolo products. The results seem impressive; for example, the concentration of hydrogen sulfide dropped from 500 to 100 ppm. However, the question still remained: Would a nearby neighbor still smell a 100-ppm concentration of hydrogen sulfide?

Of course, there are odor panels of eight or more members who evaluate odor samples using a dynamic olfactometer at an odor test facility. There, the point at which statistically 50% of the panel can just detect the sample odor is recorded as ED50 (effective dilution to 50% response) or the odor threshold value. Since the odor threshold is a dilution factor, though, it has no units. Therefore, it has little value in quantifying the variable odor conditions of an open-air landfill.

So about all we can say for sure is that odor-suppression products certainly do suppress odors–but not always enough to satisfy neighbors whose perceptions of odors differ from those of a panel or a chemist or, most importantly, an MSW operator. Unarmed with a quantitative measure of odor conditions, an MSW operator must deal with these neighbor perceptions of odors in other ways. We will explore how that is being done in Part 2 of this article in the next issue of MSW Management.

Frequent contributor Charles D. Bader is with Dateline II Communications in Los Angeles, CA.