Michael Fickes

LAST APRIL, THE U.S. Environmental Protection Agency (EPA), Washington, D.C., issued its long awaited research, design and development (RD&D) rule allowing states to permit landfills for bioreactor operations. While the landfill industry cheered the new rule, some composters have lodged objections.

As opposed to conventional landfills in which waste slowly and naturally decomposes, bioreactor landfills accelerate waste decomposition by adding liquids to the waste. The acceleration process generates landfill gas (LFG) earlier in the site's lifecycle, and this increases waste consolidation so that the garbage occupies a smaller volume. This subsequently could reduce the time that a landfill requires long-term care, making the technology attractive.

However, the composters who oppose the technology say the RD&D rule upsets the EPA's waste management hierarchy by perpetuating organics disposal in landfills rather than recycling those wastes through composting. They also suggest that conventional landfill engineering has not yet adapted to bioreactor requirements. Finally, they contend that the current approach to bioreactors may add more destructive methane to the atmosphere.

The Hierarchical Argument

The EPA has ranked the most environmentally sound strategies for dealing with municipal solid waste (MSW). Source reduction and reuse top the EPA hierarchy. This is followed by recycling and composting. Finally, the hierarchy ends with disposal methods such as combustion and landfilling.

Bioreactors use organic materials, such as food waste, to fuel decomposition. So the composters argue that allowing organics to fill up landfills contradicts the EPA's hierarchical goals. Advocates, however, note that organics always have been part of the waste stream flowing into landfills.

According to industry estimates, landfills currently contain 5 billion tons of organic wastes, with 125 million to 150 million tons of new organics added to landfills every year. Further estimates indicate that proposed organic diversion programs aimed at satisfying the EPA hierarchy will decrease the flow of organic materials into landfills by 15 percent. On the other hand, proponents say bioreactors represent a way of dealing with organic materials that always will end up in landfills.

“We're not necessarily taking in more green organics,” agrees Todd Watermolen, vice president of engineering for Onyx Waste Services, Milwaukee, Wis. “Bioreactor landfill technology just enhances the technology of landfilled waste … Materials that are source separated now would still go to the composting facilities.” Onyx currently is operating 15 bioreactor landfills.

Inadequate Science

Yet the composters opposing bioreactors take issue with the technology. Landfill designs aim to create dry tombs by limiting moisture content to slow waste decomposition, they say. Theoretically, this would ensure that the decomposition that does occur could be managed.

“Current dry tomb landfill technology is a terrible solution,” says Peter Anderson, president of RecycleWorlds Consulting, Madison, Wis., a company that consults on solid waste issues. “Turning dry tombs into bioreactors acknowledges that what we have been doing isn't working.”

The term “dry tomb,” Anderson continues, never has accurately described real-world landfills. Because organic materials always have been part of the landfill waste mix, so-called dry tombs always have produced large quantities of leachate and LFG, he explains. Disposing of these byproducts is expensive, and the industry has turned to bioreactors to control those costs.

Composters concede that bioreactors may provide an eventual solution to leachate and methane disposal costs. Yet they also insist that research into potential engineering and environmental problems of bioreactors has been, so far, inadequate.

The landfilling industry responds that the RD&D rule emphasizes what its name suggests: research, design and development. The composters don't believe it. “The EPA has created the XL and CRADA programs to research bioreactors,” Anderson says. “These programs do valid research, in which the EPA reviews your study design, protocols, measurement techniques and goals.”

Project XL (eXcellence and Leadership) is an EPA initiative that started in 1995. It provides regulatory flexibility to conduct pilot projects aimed at improving landfill performance and testing bioreactors. Of the 51 pilot XL projects, four involve bioreactors.

The EPA and Waste Management Inc., Houston, have been researching several large-scale bioreactor landfills under a cooperative research and development agreement (CRADA) made in 2001. This research will continue through 2006. According to the EPA Web site, “Results of this project will be used to assist in the development of bioreactor guidance documents and standard operating procedures.”

“No one says XL and CRADA aren't working,” Anderson says, “but now with the RD&D rule, states are allowed to let anything come in. The states can do what they want. This rule basically permits the rollout of bioreactors without anyone ever validating what you need to do or having designs to test what you need to do. Under the final [RD&D] rule, there is not even a requirement that states submit a summary of what they have done for the EPA to review,” he says.

Testing Stability

Transforming a traditional landfill into one with bioreactor operations requires the addition of liquid — from captured leachate or other sources of moisture. But how much liquid?

Bioreactor proponents who have studied this issue are forming a consensus that the optimum moisture content is between 35 percent and 45 percent of the waste mass. Below 35 percent, decomposition occurs too slowly, they say. Above 45 percent, stability issues arise.

Conventional landfill designs typically prescribe a 3:1 slope in the waste mass: three horizontal feet for every foot of vertical rise. Adding too much liquid to a bioreactor landfill may destabilize conventional side-slope designs. In addressing this problem, the bioreactor landfills have focused on controlling liquid additions with engineering techniques to maintain stability.

Composting proponents quarrel with the word “controlled.” “Stability is the No. 1 issue for bioreactors,” Anderson says. “Landfills are man-made mountains, often more than 200 feet high. Adding liquids reduces the coefficient of friction in the waste mass, and this lessens site stability.”

The landfilling industry points out that the RD&D rule provides states with the authority to allow the addition of bulk liquids, but only when operators can demonstrate that the additional liquid will not cause leachate depth on the liner to exceed 30 centimeters. Composters counter by saying that bioreactor economics may lead some operators to add too much moisture anyway.

Fugitive Methane

The third issue the composters are quarreling with is that they say bioreactors increase methane gas production. This creates two benefits for landfills. First, methane production allows waste to settle, freeing up new airspace for more waste. Second, methane can be sold to energy producers as a commodity. However, the composters say a serious environmental problem may accompany increased methane production: more methane emissions.

EPA studies have shown that methane contributes to global warming. And the EPA ranks landfills as one of the main sources of human produced methane.

“According to the bioreactor people I've spoken with, it is, at best, possible to collect 50 percent of the methane produced in a bioreactor,” says James McNelly, president of Renewable Carbon Management LLC, St. Cloud, Minn. “For the sake of argument, suppose that a conventional landfill produces 100 cubic feet (cu. ft.) of methane and 50 percent is recovered. That means 50 cu. ft. are going into the atmosphere. Once you moisturize a landfill, gas production increases by a factor of four. That means you'll now produce 400 cu. ft. of methane, collect 200 and release 200 into the atmosphere — four times as much as a conventional landfill.

“This issue was covered in the Kyoto accords,” McNelly continues. “But because the [Bush] administration has withdrawn from the Kyoto agreements, these arguments are not taken seriously. But the arguments are real.”

Onyx's Watermolen believes the concern is overblown. “With bioreactors, landfill gas rates increase significantly, but bioreactor landfills are required to have active gas extraction systems,” he says. “NSPS [New Source Performance Standards] require additional air emissions monitoring at bioreactors to ensure that there are no additional air emissions. The emissions must fall within the threshold that has been established for non-bioreactor landfills.”

Furthermore, Watermolen emphasizes that more LFG is not being created. “A bioreactor generates the same amount of LFG that would be generated at a traditional landfill — just over a shorter time period,” he says. “Rather than 100 years, the gas is being generated over maybe just 10 years. I don't see that as a negative. It's more of a positive because with the greater quantity over a shorter period of time, you can use it for green energy.”

Call for Cooperation

To be sure, the composting industry's main opposition to bioreactors appears to stem from a fear that bioreactors, if broadly adopted, will reduce organic-waste feedstocks critical to the composting process. “Last year, waste management firms attempted to repeal the yard-waste ban in Iowa,” McNelly says. “There was a similar attempt in Indiana. That's unfair competition. There are plenty of organics already in landfills. Don't try to shut us down by repealing yard-waste bans.”

Yet landfill operators seem to want to reassure the composting industry that they are not going after the same feedstocks. “We're not necessarily competing with each other,” Watermolen says. “People taking the time, energy and dollars to separate waste streams will dictate where that waste stream goes.

“Composters pursing the organics fraction of the waste stream are typically doing a good job of managing green and yard waste,” Watermolen adds. “If they can extract additional organics, all the power to them. We're just trying to treat and break down the waste that normally would come into the landfill facility through the solid waste stream.”

That said, McNelly, an active member of the U.S. Composting Council, Holbrook, N.Y., also says the council hopes to find common ground with the bioreactor industry. “We'd like to share some of our research and expertise in organic management,” he says. “We're into the beneficial reuse of organics. And we have lots of resources at our disposal. Maybe the landfilling industry and the composting industry can work together to drive these new technologies.”

Michael Fickes is Waste Age's business editor based in Cockeysville, Md.