The smell of success

Both in the waste industry and in the public’s opinion, odor control is a major concern. A recent civil settlement over odor issues at the nation’s largest municipal mass-burn waste-to-energy (WTE) plant is requiring Delaware, Michigan-based companies, Michigan Waste Energy Inc. and Detroit Renewable Power LLC (DRP), to re-engineer their Detroit facility within two years with a new air ducting system, recirculating foul-smelling air into the waste-to-energy process.

While DRP declined to discuss the details of its odor control plan, Dave Beavens, chief operating officer of DRP, says, “Since acquiring the energy-from-waste facility in 2010, DRP has worked diligently to optimize technologies, processes and infrastructure and to better reduce and manage the potential for odors.”

Beavens says DRP and the Michigan Department of Environmental Quality (MDEQ) worked collaboratively for more than a year to evaluate and address the challenge of odors from the DRP facility and signed a Consent Judgment in October 2014 that addresses this challenge with a clear and achievable schedule of milestones.

“Due to an ongoing legal process, DRP cannot address specific questions regarding its odor control plan at this time. Once this period is over we’ll be able to discuss these issues,” Beavens says. “In the meantime, DRP remains committed to the long-term civic, environmental and economic health of Detroit and we believe that our odor management plan provides a strong foundation for the future.”
 

Second go-rounds

Starting off with a good plan in place can prevent legal action. In Palm Beach County, Florida, the latest design changes to the WTE facility came as the result of an upgrade and then construction of a new mass-burn facility which fired up for the first time in February 2015. In the process, the county was able to use the latest odor control technology at the new site. It is now one of the operations that have found that enclosed systems using negative air pressure can all but eliminate odor issues.

When Palm Beach County installed its second plant it had the advantage of improving on the original plant which was installed in 1989 (and upgraded in 2009-2010).

“The difference between the existing plant and the new mass-burn is the old one used RDF technology,” says Mark Hammond, executive director of the Solid Waste Authority (SWA) of Palm Beach County.

The original renewable energy facility, known as REF#1, is a three-stage process with waste getting dumped on the tipping floor. It runs through a series of magnets, shredders for size reduction and eddy currents to handle nonmagnetic material. From there it goes to a second building for RDF storage. When it is time to do the burn, the material is sent to yet another building with the boilers.

The tipping area is a drive-in, drive-out setup. That makes it easy for drivers but means that the two doors are, for all practical purposes, open all day.

“The new plant is a mass-burn operation,” Hammond explains. At REF#2, material comes in and is dropped into a pit. Cranes take the waste from the pit to one of three boilers.

Above the pit an air system takes air from the tipping area and the pit area and moves it to the boilers. The negative pressure system assures that any gases, including foul-smelling ones, go directly to the boilers.

The biggest design difference between the two systems is the RDF facility does not have the negative pressure system, Hammond says.

The old facility was upgraded in 2009-2010 from an electrostatic precipator (ESP) to a bag house. It uses selective noncatalytic reduction (SNCR) for nitrogen oxide (NOx).

The new facility has the equivalent of catalytic converters to handle odors. The under-fire and over-fire air that is drawn into the boilers is drawn from the tipping and fuel storage buildings at REF#2.

What they are doing works. The Solid Waste Authority records and investigates all odor complaints received from the community. Based upon those investigations, the number of complaints received by the SWA is actually down since 2012.

It is not just the buildings that can cause odor problems. SWA has closed 60 acres of landfill cells and has installed a synthetic liner over the landfill. It is in the process of closing the Class III landfill cells at the far northern end of the property. This will prevent further water intrustion which lessens the biological activity that causes odors. Lastly, SWA uses a landfill gas collection system which is currently collecting gas from 216 wells, including 65 new or replacement wells installed since 2012. Gas collection at the SWA has increased 30 percent in the last year.
 

California operation

Anaerobic digestion (AD) is another waste conversion technology that deals with its share of odors. “Odor control is definitely something to keep in mind when you operate one of these digesters,” says William Merry, general manager of the Monterey (California) Regional Waste Management District (MRWMD). It operates an anaerobic digester in partnership with Zero Waste Energy (ZWE), based in Lafayette, California. ZWE paid the capital cost of the facility, located two miles north of Marina, California, and the MRWMD pays the operating costs.

AD by its configuration contains odors. “Keep in mind that anaerobic digestion happens in a closed, air-tight tank,” says Patrick Serfass, executive director of the American Biogas Council, Washington, D.C.

Serfass says that AD systems almost always are an improvement over composting operations or simple landfilling.

“Generally, if there is an issue, it occurs before the material is processed. Odors do not arise from the digestion process but occur between the time of receiving the waste until it gets to the digester,” Serfass points out. “After digestion, the process is relatively odor-free.”

MRWMD’s site actually is home to four potential odor generators, including a waste water treatment facility, a 60-acre composting operation and their “SmartFerm” anaerobic digestion system, a state-of-the-industry food scrap and organics composting system. Any of the operations could produce odors. For example, the compost is turned once a week and, if the machine digs into a pile that is ripe, some smells might escape. MRWMD was one of the first in the United States to have a landfill gas-to-energy plant.

“We have an odor management plan in place for all of the operations,” Merry says. “We are very pleased with the anaerobic digester. Odors are not an issue.”

The digester operates on a mix of 70 percent commercial food scraps and 30 percent yard waste. The food scraps are hauled in three times a day in typical garbage trucks. Waste is accepted five or six days each week. The material gets dumped on a pad atop a bed of ground yard waste.

“The yard waste acts like a sponge,” Merry explains. From there, a loader moves the material to a large garage-like holding area. The roof on the building is important to keep sea gulls and other pests away.

Once a week, MRWMD opens one door on the digester itself, removes the digestate that has cooked for 21 days, and replaces it with the new, stored material. The process of loading and unloading takes a couple of hours. The material cooks for 20 days. There is one silver door to the loading chamber and four purple doors for the anaerobic digester. Since loading is done weekly and the digestion process takes 20 days, there actually is an extra door to the digester. That gives some leeway should the process take a bit longer or there be a need for repairs on one sector.

“The digester works very well as designed,” Merry says.

Merry acknowledges that there is a possibility of odors from the lettuce or squash refuse during that period but says there have been no complaints about it. Besides, he notes, odor generation will not begin until the process goes anaerobic.

Merry says he is somewhat jealous of another ZWE operation, Zero Waste Energy Development Co. in San Jose, California. “Theirs is ten times bigger than ours. It is totally enclosed and the building is under negative pressure. They filter the air.

“Not every community can afford that, but it is something for each community to look at,” Merry says.
 

Michigan case

In Detroit, residents had complained of severe odors emanating from the WTE facility. The number of complaints increased from 16 in 2009 to more than 170 complaints in 2014.

Field investigations conducted by the Michigan DEQ verified chronic “strong sour garbage odors” from the facility powerful enough to warrant violations of air pollution control laws, specifically Rule 901 of the Michigan Air Pollution Control Rules. A civil settlement was reached Oct. 21, 2014.

Under the terms of the agreement, the Michigant Waste Energy and DRP agreed to pay a $350,000 fine for past odor violations which will go into the State General Fund. In addition, they agreed to re-engineer the facility within two years with a new air ducting system, recirculating foul-smelling air into the waste-to-energy process.

Ted Michaels, president of the Energy Recovery Council (ERC), Arlington, Virginia, sees the Detroit situation as a special case. “I’ve been here for 10 years. We haven’t had it as an issue,” he says. “I don’t hear anybody talking about it at our meetings.”
 

Planning tips

Serfass says that a successful AD facility design does not have to be enclosed in order to be effective at odor control. The key is to design the facility so the waste does not have to hang out between the time it is tipped and the time it goes to the digester.

Compared with a municipal composting system, an enclosed system almost always will be more effective at odor control. In addition, it should give better results in water quality tests, Sefress adds.

An outdoor facility may work in a desert climate, but in many areas, indoor operations and negative air pressure, are required.

The author is a contributing editor to Renewable Energy from Waste based in the Cleveland area. He can be contacted at curt@curtharler.com.