Controlling Odors: Don't Let Them Get The Drift

Del Freeman

Garbage, at its best, is not aromatic. Foul odors are a problem at almost any waste site, as organics decompose to form gaseous elements which can easily permeate the air and disturb neighboring businesses and residences.

Some wastes cause worse odor problems than others. Biosolids, for example, are among the greatest offenders, according to John Page, landfill administrator at a Chambers site in Atlanta.

Page described the site as a landfill with both business and residential neighbors. These neighbors, he said, are the best indicator of how well the site is controlling its odors.

Biosolids from a water treatment plant have been disposed at this site for the past year, during which time the odor has increased in strength and irritability. "The stench is becoming worse; we keep putting more biosolids into the landfill and compounding the problem," Page said.

About eight months ago,the neighbors decided they'd had enough and the landfill began to search for a solution.

"Now we're spritzing the air," Page said. "The current system is a drum linked up to 39 nozzles in a single row, about 10 feet in the air - almost like a wind fence for odors," he said. "We're in the process of changing the timing of the misting," he said. "We need it more often."

The landfill will continue misting, but is experimenting with other systems because "the neighbors just weren't happy enough."

One method to control odor is to change burying techniques, Page said. Originally, biosolids were buried on the landfill slopes. This, however, weakened the slopes, making them unstable for heavy equipment. Consequently, the landfill began burying the biosolids in areas where no other digging was underway.

Misting, Page said, was the first solution to placing biosolid atop bio-solid - and it wasn't enough.

"We got off the slopes and began burying the biosolids among the other trash, which helped," Page said. "We also added lime to the bio-solid burial site."

Along with the burial techniques and wind fence misting, another product is sprayed on the ground. "The dilution is pretty good and it provides a barrier for molecules of certain chemicals - sulphur and nitrogen," he said. The method "is helping a lot once waste is buried."

However, the odor problem continues from the time waste is dumped until it's buried - despite the simultaneous operation of three odor controlling methods. "I don't think the transition period is going to be solved unless we spray something during the actual disposal process," Page said.

Tony Lucente is operations manager at Fairhaven Landfill, which is located between New Bedford, Mass., and Newport, R.I. For the past six years, he's relied primarily on misting to control odors and uses landfill foam for particularly offensive and centralized problems.

"We've used several different atomization misters in a perimeter system of foggers, which we designed," Lucente said. Depending on the wind direction, misting solutions can be sprayed from lines running along the North, South, East and West perimeters of the site.

Lucente uses a solution that reportedly kills odor-causing bacteria, and "is environmentally friendly" - an important factor at Fairhaven. The product's scent is also important to Lucente. "If you cover one odor with another, you may create a worse one," he said.

Landfill odors could be burned off as well, to avoid being able to smell them at all, according to More-trench's Carl Asprinio. "You'd have some odors from the burning of the gas, but they'd be minimal," he said.

The secret to burning off odor, however, is drawing it rapidly from the ground, containing it at ground level and then flaring it.

"You follow this method because you want it to come out in quantity," said Asprinio. Depending on the site's size, such flaring could take years, but it also should not have to be repeated, Asprinio said. However, if garbage continues to be deposited at a landfill, the job is never done because new deposits will continue to decompose and form odor.

In addition, older sites often don't have controls in place. But "odor is going to be in the landfill, and unless you punch a hole in the clay cover, it'll stay there," he said.

Of course, landfill gas can produce useful end products, such as electricity. "If you burn it in a generator, it creates electricity, and the exhaust doesn't smell," Asprinio added.

Landfill gas is composed of nearly a dozen different items, including hydrogen sulfide, or the "sour egg smell," said LFG Specialties' Ray Nardelli. Gas migration can be controlled in several ways, including oxidizing, masking or using a combination of gas combustion and oxidizing the compounds," he said.

Landfill gas is gathered in an active or a passive system. In a passive system, pressure created by gas formation pushes the gas through a vented collection system into a flare. Due to the gases' natural combustibility, the flare will burn it at sufficient temperatures to oxidize the odor-creating compounds.

In an active system, the gas is drawn up using a vacuum suction and is then pumped into the flare for combustion. Both open and enclosed flares are available, Nardelli added.

"Some odors are due to an aerobic reaction when the air mixes with the garbage, as well as with the landfill gas itself. Other odors come from construction debris. For example, decomposing wall-board generates hydrogen sulfide gas," he said.

Landfills also can have odor-producing leachate systems. "Normally, when a leachate system is pumped down, it exposes areas in the gathering system that will allow leachate gas to migrate out. That's where you'll pick up odors," Nardelli said.

Several methods exist to filter odors, including pumping hydrogen sulfide through an iron screen or using activated woodchips. But treating sufficiently high levels of material will curtail the useful life of such systems, he added.

"Odor can be a nuisance or a safety concern," said Neal Linnihan of Odor Management. "The neighbors of industry are often the catalysts for changing the way companies treat their odor problems."

Waste collection methods, particularly wet processes involving bio-technology, will generate some odor that needs to be controlled, he said.

Scrubbers or incinerators generally are used to dispose of dangerous emissions resulting from odor control, Linnihan said. Misting, unlike scrubbing or flaring, is an odor neutralizer by absorption.

"[Misting involves] a precipitation of the odor molecule with a droplet of oil, which then precipitates onto the surrounding flora and fauna," Linnihan said.

The difference between masking agents and absorption agents, he said, is that masking agents lay a pleasant scent atop an unpleasant one, while an absorption method absorbs the offensive odor, converting it to an acceptable - or even a pleasant - odor.

There seems to be no escape from odor in this industry. It's as constant a factor as the ongoing quest to subvert, contain and eliminate it.