Landfills’ waste streams are ever evolving, driving changes in maintenance requirements, overall protocol and in what operators will invest in moving forward.
Dwindling municipal solid waste (MSW) tonnage, mounting organics diversion and the introduction of new non-MSW materials are among the trends altering what’s entering landfills. Some of those impacts are costly while others have had little effect. For others, the true effects are still shaking out.
A drop in MSW
Waste volumes began to decrease during the 2008 recession. This decline, combined with the push to divert food scraps, spurred waste management companies to look for non-MSW sources. Some, for example, began taking in volumes of industrial and construction and demolition waste.
This focus is changing the overall waste mass, the so-called evolving ton, and has had potential consequences, prompting operation-related considerations, says Eric Chiado, vice president of Civil Environmental Consultants (CEC).
“At 5 percent of the landfills’ contents, industrial waste is not a big deal, but at the current 20 to 25 percent it does have an impact. We are seeing that we need to think more about how it’s affecting gas production, leachate and the stability of landfills,” Chiado says.
The stability issues arise due to consistency of these materials which must be addressed.
Potential change in leachate quality could necessitate pretreatment and sometimes full treatment on site.
And with regard to gas, the influx of industrial materials is interfering with production of a quality product, largely because wet industrial wastes are challenging the gas extraction process. This means that waste, coming in an as sludge or liquid needs to be solidified. Otherwise the liquid from the waste can compress, flow to gas extraction wells and flood them.
The industry is investigating solidification agents and determining what needs to be added to the waste mass for slope stability and to cut leachate. And companies are looking at ways to modify leachate and gas collection systems to anticipate issues that might result from higher percentages of industrial wastes.
On the upfront end, many waste management companies have programs focused on profiling what’s coming in, identifying what must be separated and what must be solidified.
Materials commonly vary by region
For instance, western Pennsylvania and eastern Ohio have accepted waste from processes like drilling during the shale gas boom, as have Texas and North Dakota. This has resulted in an influx of challenging materials like drilling fluids and industrial sludges.
Now the big issue, says Chiado, is residuals from coal combustion such as fly ash and bottom ash, as well as flue-gas desulfurization sludge generated during the treatment process.
Food waste, despite efforts to pump diversion, has increased over time and is the largest fraction of organic waste entering landfills today.
What would less organic waste mean?
“There’s limited research on the impact of organic waste, but we suspect it affects the quality of landfill leachate, and that the concentration of parameters like ammonia and nitrogen will be lowered if organics are removed,” says Bryan Staley, president of the Environmental and Research Education Foundation (EREF). An EREF study is now underway to further investigate the impact of leachate removal.
For now says Staley, “Because landfills are managed in different ways the impact, I think, will be all over the map.
“Some regions may be more affected, as they invest heavily in leachate treatment, like East of the Mississippi and in the northwest," he adds. "If you have had to pretreat before sending to public treatment works, you just saved a lot of money.”
Conversely, while drastically cutting food waste could cut leachate management costs, if operations are harvesting landfill gas for fuel, they could lose revenue. Plus, organics have been a way to keep volumes up. As little by little it leaves their streams and heads elsewhere, some waste management companies are considering alternative ways to capitalize on it.
Waste Management has begun partnering with wastewater treatment facilities to manage organics. Other major haulers are also considering, or actually entering, the composting and anaerobic digestion spaces as these practices ramp up.
Meanwhile, there is no definitive proof of just how much organics diversion strategies are changing what is happening on landfills now. Although evidence suggests that aggressive diversion practices are affecting gas production where collection systems are installed.
But the picture is muddled in some states. Even within the single state of California, EREF found there is much to learn. Researchers compared two sites there; Scholl Canyon in Los Angeles and Altamont in San Francisco. They found although Altamont contained more tonnage, it had less gas production.
But there were many variables EREF did not quantify.
Says Staley, “We are now looking at other landfills to see if there are trends and potential impact.”