Managing Liquids Extracted From Landfills
Environmental engineers specializing in landfills can successfully design disposal sites and infrastructure to mitigate how much liquid enters the waste matrix. If liquids do infiltrate the waste or gas extraction system, these professionals effectively capture and direct them to the bottom of the leachate collection system, where it belongs.
But success brings different challenges following extraction.
“You pull liquid and leachate from your landfill and landfill infrastructure, but now the question is, where do I send it? And there are no simple solutions. It’s a hard wastewater stream to manage, especially as operators grapple with increasing volumes and strength,” says Bob Dick of SCS Engineers.
As precipitation increases in many regions and operators take in wetter special wastes like sludges, finding an economically and logistically viable means to offload leachate quickly is daunting. Tightening regulations around what publicly owned treatment works (POTW) will accept adds even more pressure.
There are three main issues resulting from higher leachate quantities and its quality. Those issues are:
Storage tank capacity
“I have clients with two tanker trucks cycling 24 hours a day, taking leachate to the POTW, but they still can’t keep up with their volumes. So, they can’t be as aggressive as they want in moving it out. It’s coming out of their landfills, and they have nowhere to store it all,” Dick says.
Operators can’t transport leachate fast enough to keep pace with steadily accumulating volumes. It takes time to load tanker trucks, drive long distances, return, and repeat the process, Dick says. Even finding a facility to accept it can be difficult, compelling some of them to ship it on barges or haul it by rail—costly processes.
Wastewater treatment plant issues
Increasingly, POTWs faced with permit restrictions limit how much leachate they will take or refuse altogether, either because of the volume, quality, or characteristics.
This problem magnifies as high concentrations of several specific constituents are now often seen, including high ammonia and nitrogen. Other offenders increasingly coming into play are total suspended solids (TSS) such as clay, sand, and silt and total dissolved solids (TDS), smaller particles than TSS, including minerals and microorganisms.
Mixing leachates adds complexity
Some liquids inevitably make their way into gas extraction wells above the leachate collection system. A common solution is pumping them out so gas can enter the pipes and injecting them into nearby leachate piping. There it mixes with leachate from the bottom of the landfill.
This method may solve one problem but presents another challenge: gas dewatering liquid is a much higher strength than filtered leachate at the bottom. Mixing them could disrupt the POTW’s system due to biological changes in the material, explains Eric Peterson of SCS Engineers. He’s seen this headache escalate as POTWs adopt more sophisticated technology; it treats most leachate better, but liquids from gas wells interfere with the newer process.
“We’ve seen POTWs who refuse the liquid because it’s stronger than previously, and the plant can no longer manage it. We have also seen upsets at on-site treatment plants that may be designed for the leachate conditions at the bottom of the landfill; now they must deal with a more polluted gas dewatering liquid,” Peterson says.
Ensuring this liquid can work in either facility type requires pretreatment. Even with the more benign liquid extracted from the bottom and sent to the force main, pipes are prone to clogging, requiring due diligence in preventative maintenance.
Strategies to manage extracted leachate
Currently, three options offer alternatives to the time and money intensive process of trucking high volumes long distances:
This system heats liquids and evaporates the water molecules, reducing leachate volume by 70 to 90 percent, enabling operators to return the sludge-like residual to the landfill. Managing liquids on-site leveraging this technology eliminates dependency on drivers and the POTW.
“The idea is that the residual is small enough that you can effectively manage it in your landfill. But regulations may require another step to solidify the liquid residue,” says Zach Mahon of SCS Engineers.
Solidification of waste
Solidifying high-strength liquids entails mixing them with an amendment such as sawdust or lime that adsorbs them, removing them from the water phase, and strengthening them to dispose of in the landfill safely.
But this process is often a temporary fix. “You are typically just imposing a management technique that slows movement,” Dick says.
On-site leachate treatment
This option can clean the material to POTW-acceptable standards or enable it to discharge into the environment safely. Reverse osmosis (RO) is a common treatment of choice, where leachate flows through a membrane, separating contaminants that collect in a solution. RO can reduce contaminated water by 90 percent, typically rendering it clean enough to discharge directly to surface water with appropriate permits. Or, it can be discharged to the city sewer, eliminating the permitting step.
Mahon recently assessed all three options for a Midwestern client and a fourth solution that he believed fit this landfill’s particular needs. The operator’s 20,000-gallon tank was filling up so fast that it had to be hauled to the POTW nearly daily.
“The quality and volume were acceptable to the POTW; it was just an operational issue for the landfill. So, the solution is to install a force main that automatically pumps directly to the POTW, solving the challenges of scheduling trucks and drivers, quickly loading and unloading the vehicles,” Mahon says.
His team’s design enables the addition of RO should regulators’ requirements change or the POTW plant intensifies its discharge limits.
Still, solutions continue evolving. Landfill operators work with liquids management experts to keep up with the latest proven technologies. Many promising solutions are on the horizon, but you need a proven solution when investing capital.
Dick says the best defense is to remain proactive. Even with careful planning, some liquid will contact waste and become leachate. The best course is for robust engineering designs and sound operational practices to minimize leachate to the greatest extent possible.
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There’s science, engineering, and careful maintenance happening inside and outside of a landfill, but it’s all there to capture emissions. We thank landfill owners and operations teams across North America for strategically managing landfill system integration and running these complex systems. These well-trained and educated teams include field technicians, landfill and environmental engineers, geologists, technologists, and specialized operations staff, to name a few. They work hard and smart to make sure each landfill remains a good neighbor while delivering essential services.