Treating and disposing of leachate has been an ongoing challenge for landfill operators across the U.S. In recent years, effective leachate management has taken on greater importance due to more stringent regulations and changing waste composition that impacts leachate quality.
“Leachate management now constitutes about 30 percent of landfill operating costs and comes right off the bottom line. Opportunities to reduce costs are of great interest and importance,” says Kevin Torrens, vice president for Upper Saddle River, N.J.-based engineering firm Brown and Caldwell. Cost savings can often be found with little or minimal capital investment, he says. Also, owners should plan ahead for tightening of regulations that will contribute to cost creep and technology advancement.
But designing the leachate treatment process and ensuring that contaminated liquids do not affect nearby land and water supplies are the biggest challenges facing local operators and municipal officials.
Working with POTWs
According to Torrens, the most common and preferred method for leachate management and disposal for municipalities is to discharge to local publicly-owned treatment works (POTW) wastewater treatment plants that treat domestic sewage, via truck or the local sewer system.
“Landfill owners prefer this approach as treating water is not their business—it is the business of the POTW—and also because it is generally the least expensive,” he says.
In some cases, leachate must be pretreated prior to being sent to the POTW. This is often done via a biological treatment that reduces organic and nitrogen concentrations.
“In some cases, leachate is treated and discharged to receiving waters,” Torrens says. “In these cases the required level of treatment is significantly greater than for discharging to a POTW and often requires more advanced treatment.”
William Soukup, senior hydrogeologist and client service manager for Cornerstone Environmental Group LLC, a TetraTech Company, based in Middletown, N.Y., says there are some roadblocks to discharging leachate in this manner.
“[M]ore stringent POTW discharge limits associated with nutrients—nitrogen and phosphorous—dissolved solids, and conversion from chlorine to UV disinfection are contributing to a change in this approach,” he says.
Instead, Soukup says, the most frequent leachate treatment method is typically a biological component combined with precipitation or filtration. Aerobic biological systems are the most prevalent option, but some facilities also use anaerobic systems.
“More recent biological systems are increasingly making use of membrane separation, or a membrane bioreactor type processes or variants such as a moving bed biological reactor,” he says. “The biological component of the treatment system is typically cost-effective for reducing BOD (biochemical oxygen demand), COD (chemical oxygen demand), and ammonia concentrations common in landfill leachate. The membrane separation part of the process provides a high quality effluent.”
Frank DeOrio, technical manager for O’Brien and Gere based in Syracuse, N.Y., agrees that most landfill leachates can be adequately treated by a combination of physical-chemical and biological treatment.
“The biological treatment process … is generally selected based on the quality of effluent required, and biological systems are often challenged by the presence of elevated temperatures, inhibitory substances, and recalcitrant COD,” he says. “Biological processes include both aerobic and anaerobic processes, including fixed-film and suspended technologies. Physical-chemical methods include chemical precipitation/coagulation, chemical oxidation and chemical oxidation combined with ultraviolet (UV), dissolved air flotation, ion exchange (resin technology), reverse osmosis (RO), and ultra-filtration utilizing specialized membranes. The physical-chemical methods are employed to remove the leachate constituents that are not degradable in a biological system.”
Torrens says that in most cases, biological treatment will be used, but adds that it is typically combined with other advanced processes to achieve better quality.
“Evaporation is also commonly used and consists of evaporating the liquid fraction of the leachate. The residual material (mostly salts) is then disposed—often by placement in the landfill,” he says. “The choice of disposal location and technology requires careful analysis to consider feasibility, economics and sustainability.”
DeOrio says there are many challenges facing the treatment of leachate.
“One of the many challenges engineers and process scientists face with designing leachate treatment systems is that leachate is produced in different volumes and different qualities based on the influence of precipitation and the age and composition of the waste it travels through on its way to becoming leachate,” he says. “Combine these facts with the increasingly stringent effluent limits, and the design and operation of modern, high-tech treatment systems are indeed complicated tasks.”
Another daunting challenge operators and municipal officials face includes keeping the communities surrounding the landfills safe from leachate and other contaminants.
“Application of established landfill design practices and proper operation, maintenance, and monitoring are the keys to not impacting surface or groundwater quality or adjacent soils. Double composite liner systems are essentially the norm for a state-of-the-art landfill facility, and we have extensive data that show these systems work and do not release contaminants to groundwater,” says Soukup. “To protect surface waters, maintaining vertical drainage paths (i.e., avoid low permeability zones) and controlling buildup of landfill gas pressure help control the potential for leachate seeps on outside faces of landfills.”
Once leachate is collected, design principles and proper operation and maintenance provide the requisite controls, Soukup adds.
“For instance, in conveying leachate outside the landfill footprint dual contained pipe can be used. Once at a storage or treatment facility, secondary containment provides an important tool in controlling the potential for a discharge, just in case a tank or pipe should leak due to a defect or corrosion,” he says. “These are all tried and true methods of making sanitary landfills what they are today, environmentally sound facilities.”
DeOrio agrees that design plays an important role in proper treatment and disposal of landfill leachate.
“Leachate treatment systems are designed after a great deal of effort in assessing the treatability of the leachate in a laboratory setting, followed by pilot trials, if required. Once the design is completed and the facility built and commissioned, the most effective way of ensuring that the leachate is treated both efficiently and effectively is to have it operated by a team of skilled and experienced operations staff,” he says. “The sophistication and technological demanding aspects of a modern treatment system demands that professionals operate and maintain these significant investments. Today’s operators are highly trained and skilled and capable of meeting the demands of a challenging waste stream and the requirement to meet the strictest effluent limits.”