Leachate challenges the owners and operators who need to manage it — and the engineers tasked with designing effective treatment options.
Leachate and other landfill-generated liquids (gas condensate and dewatering liquids) can be one of the biggest and most expensive challenges for landfill operators, and among the most challenging industrial wastewaters to manage and treat from a technical standpoint.
The landfill system generates highly variable leachate characteristics due to waste source changes, seasonal precipitation, cell expansion, and closure phasing — not to mention the natural biological and physical process reactions of waste degradation.
The result is variable influent flow rates and constituent concentrations that must be effectively treated to comply with receiving stream or POTW limits. Typical landfill leachate includes high concentrations of organics and ammonia, but it also contains other non-biodegradable and persistent compounds such as per- and polyfluoroalkyl substances (PFAS) or even color and odor that may need to be treated or mitigated for discharge compliance or process inhibition concerns.
Nutrient-loading impacts to receiving water bodies may also force landfill owners to reduce nutrient levels, which could further require advanced forms of treatment.
These complex liquids present challenges for clients who must determine how to properly treat them. They also present a challenge for engineers who are evaluating and determining the most effective treatment options. As recycling and other waste programs have been implemented, landfill owners and operators are seeking new ways to bring in revenue, accepting types of waste they might otherwise have ignored in the past. In many instances, wastes other than municipal solid waste comprise as much as 25% of the waste stream.
“We’re on the receiving end of that,” says Greg Werner, a Principal in CEC’s Charlotte office who manages the firm’s wastewater treatment subpractice.
“What’s going into a landfill is changing and the amount that’s going into a landfill is changing. While you’re designing something or while it’s being built, the landfill might change what they’re taking in or their processes might change. There are a lot of uncontrollable factors inside a landfill.”
So how do landfills manage their leachate concerns, both at the landfill and beyond? Here is a look at some of the technology being utilized by CEC’s professionals.
Leachate treatment commonly requires biological systems be employed as primary or secondary treatment. Biological treatment includes a variety of process options including aerobic, anaerobic, and anoxic processes aimed at removing ammonia, carbonaceous organics, and nutrients such as phosphorous and nitrogen.
Typical biological treatment methods include: conventional Activated Sludge Process (ASP), Sequencing Batch Reactor (SBR), Integrated Fixed-Film Activated Sludge (IFAS), and Membrane Bioreactor (MBR). Each of these methods has its own advantages at meeting the landfill’s treatment objectives.
“One concern of treating leachate using a biological process is high solids generation, or sludge waste,” Greg says. “Solids separation and dewatering are integral to the biological process and need to be carefully considered to optimize treatment performance and operating cost.”
Primary treatment prior to biological treatment may be required to remove metals or other compounds that may inhibit the biological process. These methods can involve chemical processes aimed at precipitating dissolved metals out of the leachate, or converting compounds like odor-causing sulfur to less harmful forms. They also can involve physical processes like air stripping that transfer volatile compounds or ammonia from one phase to another.
Finally, tertiary treatment is required to meet specific limits for non-biodegradable and persistent compounds after the majority of pollutants have been removed. Tertiary treatment can be used for dissolved ions like chlorides, boron, PFAS, bacteria, odor, color, and residual ammonia and nitrogen.
“These compounds are often not very concentrated in the waste stream at this point in the treatment process, but they have limited options for removal or destruction,” Greg says.
Varying Services and Options
CEC’s work on leachate projects across the country has involved all of the aforementioned compounds and treatment technologies in some form or another. It also has involved professionals with a wide array of expertise to ensure landfill owners and operators are getting exactly what they need, including providing construction management and support services and construction quality assurance.
At a site in the mid-Atlantic, CEC’s breadth of services was on full display for a major upgrade of an existing on-site leachate treatment plant. CEC utilized Light Detection and Ranging
(LiDAR) and terrestrial survey services for an existing plant that was lacking plans. That technology helped create a model of the existing site and everything inside of it from scratch, which laid the foundation for CEC’s engineers to determine the next steps.
CEC’s experts were instrumental in ensuring the landfill was in compliance and ensured the design and upgrades were consistent with the National Pollutant Discharge Elimination System permit, which called for new discharge limits that required significant modifications to the site’s existing biological system.
Professionals from CEC offices nationwide and in numerous practice areas, including air quality, survey/geospatial, civil engineering, water resources, environmental, and waste management, pitched in on this nearly $18 million project.
At another landfill site in the mid-Atlantic, CEC provided a municipal solid waste client with a multi-disciplined team of wastewater, process, mechanical, structural, and electrical engineers to develop a leachate treatment plant on site. The owner had been transporting leachate off site, but that was increasingly difficult and expensive as outlets became limited.
Developing an on-site treatment plant would reduce the operational costs and eliminated the risk that having nearly 2,000 off-site truck trips per year would bring. CEC worked with a reverse osmosis vendor to streamline the design and solve a costly problem for the owner.
In an alternative treatment option, CEC assisted a landfill client in the Southeast by developing a system that would pretreat the leachate for discharge to the city sewer system
for final treatment and disposal at the city’s POTW.
The leachate at this site was much stronger than “typical” leachate, with high ammonia concentrations and high total dissolved solids as a result of large volumes of aluminum dross and municipal wastewater sludges disposed over the years.
CEC’s design for the leachate pretreatment system consisted of adding an additional 185,000-gallon storage tank, two 450,000-gallon bioreactor tanks, and two submerged ultrafiltration membrane tanks. As the leachate quantity and strength continued to increase, CEC was able to provide several upgrades to the plant, as well as provide staff who were responsible for daily operations for nearly a decade.
“Although landfill leachate has some general characteristics, no leachate is created the same or can be treated the same. Having as many experts as we have nationwide with diverse expertise ensures our clients are getting the specialized services their leachate concerns call for.”
— Greg Werner, CEC Principal
Landfill leachate is complex, and the appropriate treatment train must be evaluated carefully based on regulatory requirements, the life of the landfill, the capital investment, and operating costs and manpower required to maintain compliance.
Leachate projects might have some commonalities, which means the approach to treating it may be similar. But while the overarching issues for many landfills might be similar, there is no template for how to treat leachates.
“Although landfill leachate has some general characteristics, no leachate is created the same or can be treated the same,” Greg says. “From permitting to regulatory negotiation early in the process, to the design and construction, and, beyond that, monitoring and modifying as necessary, no two leachate treatment projects are similar. Having as many experts as we have nationwide with diverse expertise ensures our clients are getting the specialized services their leachate concerns call for.”