Wet landfill technology has become more commonplace now, but early on it seemed scary to many operators.
By Adam Jochelson, P. E., MOLO
“You want us to do what?!”
In the early days, that was a typical response to descriptions of the principles behind what is commonly known as a bioreactor landfill. By now, pretty much everyone in the industry knows about wet landfill technologies and their potential benefits. But not too long ago, the idea of adding liquids to a landfill’s waste mass ran counter to everything landfill managers had learned. To understand why, it’s important to think about the primary purpose of landfills.
Liquids Lead to Zombies
Disposal is the process by which items are removed from your general vicinity and transported to some distant locale, never to be seen or heard from again. For most of the U.S., the “distant locale” is whichever landfill is the most convenient for the outfit hauling your garbage away. Thus, standard landfill operating procedures were established to encourage the appropriate flow of materials, favoring ingress and minimizing egress. Over time, operators recognized that the most likely escapees from landfills were liquids flowing out of and gases emanating from the facility. These two nuisances were like zombies emerging from their landfill grave to terrorize the community—and they did.
Considered separately, each of these presents unique containment and safety challenges. Keeping liquids from escaping the landfill requires an impermeable liner system—difficult to achieve over the long time horizon of a landfill’s lifespan. Thinking about it reminds me of an old engineering adage about underground storage tanks—they come in two varieties: those that are leaking and those that will eventually leak. Liquid discharge through a landfill liner could contaminate local groundwater, presenting a potential threat to all members of the surrounding ecosystem, including humans. Landfill gas is a triple-threat: its varied composition includes methane, hydrogen sulfide and carbon dioxide, among other trace components. The first is explosive; the second is toxic; and all three are greenhouse gases. If trapped underground, it will gather in pockets that can (and historically have) become fire hazards. But venting to the atmosphere is both noxious and potentially adds to global warming concerns. From the start, landfill operators worked to mitigate these potential hazards.
During the search for ways to curtail their actions, moisture in the waste surfaced as a major source of both. A combination of physics and chemistry turns water into leachate. The simple action of gravity encourages liquids in garbage to trickle to the bottom of the facility. And during its journey through the waste mass, water will dissolve much of what it encounters, resulting in a fluid resembling tea or coffee in color (but not in flavor or smell). Higher moisture levels also increase biological activity, stimulating anaerobic microbes that produce gaseous wastes that combine to produce the unique components of landfill gas. The short story was that wetter waste led to more headaches, so we devised ways to keep moisture out as much as possible, a path that resulted in so-called “dry tomb landfilling.” (See? The graveyard metaphor isn’t too outlandish.)
To be fair, there’s no doubt that this style of landfill management is rooted in a strong desire to protect human health and the environment. And for many decades, dry entombment was the most advantageous way to minimize leachate and slow down gas production. But then technological advances intervened in two ways.
Adversity Breeds Opportunity
First, the plastics revolution dramatically improved liner systems. Innovations in plastic production led to the ready availability of materials that could enhance impermeability. By the mid-1990s federal mandates placed new requirements on landfill liner systems. Compacted clay containment gave way to composite liners using extrusion welded sheets of high density polyethylene (HDPE) to supplement the earthen barriers. Plus, rather than simply contain the liquids trickling to the bottom of the landfill, operators also implemented collection systems to pump the leachate out of the waste mass for transport to a treatment facility. These collection pipelines are also typically constructed of HDPE—it’s a pretty versatile plastic!
Second, gas processing technology improved in ways that would allow recapture of the energy content in the methane component of landfill gas. If you live somewhere that uses natural gas for heating and/or cooking, the product delivered to your home is nearly pure methane gas, an efficient and relatively clean burning source of energy. Turns out that landfill gas is as much as half (or more) methane. And because it’s also a powerful greenhouse gas, federal standards require installation of gas control systems at landfills of significant size. Not content to simply capture and destroy it, innovative entrepreneurs developed facilities to tap into that rich supply of energy. Today, landfills turn their collected gas into heat, electricity, and even pipeline quality natural gas—and can earn a tidy profit doing so.
So, now we’ve reached a point in history where implementation of appropriate technologies can easily minimize the risks associated with landfill fugitives. Combine that with the potential to reap a financial benefit, and you’ll find that many landfill operators now prefer wetter waste to the point that they’re looking for ways to increase their garbage moisture content. And here’s where a major paradigm shift comes into play. Whereas traditional landfill operations involved considerable efforts to prevent introduction of moisture into the waste mass, now many facilities seek out soggy garbage. Some go so far as to actually pump additional liquids into their landfill.
Of course, even the most successful new technologies endure periods of skepticism—consider the historical reluctance to adopt usage of the “horseless carriage” in the early 20th century. But as more and more facilities reap the benefits of implementing wet landfill technologies, eventually everyone will be wondering if it would work for them. And when you propose the idea of adding liquid to your landfill, rather than respond with “Do what?” your staff will ask “How much?” | WA
Tune in next month to learn about specific experiences transitioning into wet landfill operations.
Adam Jochelson, P. E., MOLO, is a Landfill Engineer and Facility Specialist working for GeoShack, Inc. (Dallas, TX), where he promotes the application of cutting edge technologies to improve the efficiency and effectiveness of landfill operations. Adam built his knowledge and techniques over a nine-year period as the on-site engineer at McCommas Bluff Landfill in Dallas, TX. His unique experiences in engineering and other fields have combined to create an exceptional understanding of the various challenges inherent in landfill planning, design, and operations. Adam can be reached at (972) 342-3055 or via e-mail at [email protected].