Landfill operators forever work to stay on top of a diverse and complex mix of leachate contaminants—heavy metals, ammonia, and biochemical oxygen demand (BOD), among them; but lately, they think about even more. For one: how to keep concentrations of these contaminants within wastewater treatment’ plant’s tightening discharge limits. Add to this concern the possibility of more compliance pressure as the constituents’ list on regulators’ radar grows. From microplastics to PFAS and PFOA, the latter sometimes called the “elephant in the room” –some operators are preparing for what may be down the pike.
Among strategies, some are looking at are on-site leachate treatment options, and there are several. Finding the most fitting, sustainable, and cost-effective one takes vetting. This continuing blog series explores studies conducted by SCS Engineers for operators nationwide. Here you will get an inside look at what these leachate management experts found, what treatment system they recommend in each scenario, and why.
A Solution to a Nebraska Landfill’s Rising Leachate Volumes
A Nebraska landfill needs to manage its rising volumes of leachate, causing disruptions to operations. The liquid goes into a 20,000-gallon tank, is pumped into a tanker, and is driven to the municipal wastewater treatment plant. The tank was filling so fast that the operator has trouble staffing and scheduling its few commercial driver’s-licensed operators to haul it. This logistical task has become a near-daily necessity. Sometimes the liquid level indicator will go off on the weekend. Management has to move quickly, sometimes on a dime, find someone to come in, and pay overtime.
“The staffing challenge is the main issue that brought the operators to SCS. They want to understand the whole leachate management structure better, and as we answer their questions, they want to know how we can improve the overall system in the long-term, says Zach Mahon, the SCS staff professional who works on the project. “After an extensive assessment, we provide options whereby the operator no longer has to pump leachate to a holding tank and then truck it to the wastewater treatment plant. And we provide site-specific recommendations to take their leachate management practices further,” he says.
Mahon and the SCS team of leachate management experts headed to the landfill to talk to operations staff and get their historical generation records, which is the basis they start with for their assessment. “We correlate the landfill information with our research to determine yearly generation figures as well as a peak generation number over the landfill’s projected life. This site is expanding, and we want to size the equipment so that when it reaches capacity, the system can handle the higher volume,” Mahon says.
SCS plans in other ways to ensure the recommended technology will take its client into the future on solid footing. For instance, accounting for the reality that operators may one day have to remove per- and poly-fluoroalkyl substances (PFAS) to send their multi-thousands of gallons of leachate to their wastewater treatment plant each year. Operators are keenly aware that utilities and regulators are looking with more scrutiny at PFAS and other emerging contaminants of concern.
Through due diligence, SCS engineers came up with three treatment options. Mahon explains each:
Install a leachate force main. This system includes a pipe with a pump that pushes the liquid through the force main, directly to the sewer line and, ultimately, to the municipal treatment plant. The pump kicks in automatically, negating the need to have drivers in the wings at all times. This system is quick to build and fairly simple to operate. It is the least expensive of the modifications that SCS vetted.
Install a leachate evaporator, which heats the liquids and evaporates the water molecules. This system reduces leachate volume by 90%. Managing liquids on-site eliminates dependency on drivers, but on the wastewater treatment plant too. The gas-fueled system is suited for sites with surplus landfill gas to help cut their operational costs.
Install a reverse osmosis treatment (RO) system where material passes through a membrane, which separates contaminants. RO treatment can reduce contaminated water by 90%, 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.
“For each leachate treatment option, we looked at cost, the feasibility of short- and long-term implementation, and regulatory acceptance,” Mahon says. “We deliver the data with these priorities in mind, make our recommendations, and leave it to our client to decide.”
What did the SCS team recommend in this scenario?
“We suggested the force main. It solves the primary operational issue around staffing. And the economics of this comparatively inexpensive system make sense in these times when landfills are dealing with astronomical leachate management costs, among other increasing operating and capital expenses,” he says. This option does more than meet the client’s most immediate needs at a minimal cost. It provides the option to upgrade should regulators’ requirements around leachate change or should the wastewater treatment plant tighten its discharge limits. We design the modular system to add on reverse osmosis if necessary in the future. Thus, we help ensure that our client will continue having a home for its leachate.
A value-add, regardless of the operators’ decision, is more knowledge. SCS clients have a deeper understanding of industry standards. They are also more aware of how the industry is shifting in managing leachate and how these shifts could affect them. We follow up with technical bulletins explaining proposed and final federal rules in plain language influencing their operations, deadlines, and how to provide feedback to the appropriate agencies.
“We provide a lot of data to continuously inform our clients and to help them compare their operational costs now to what they would be if they invest in a new leachate management strategy. We ensure they fully understand each option’s capabilities to decide if it pencils out for their budget and operations. They have what they need to make informed decisions for a hands-off system to take them into the future,” Mahon says.
REPRINT OF USEPA PRESS RELEASE
EPA Moves Forward on Key Drinking Water Priority Under PFAS Action Plan
WASHINGTON (Dec. 4, 2019) — Yesterday, the U.S. Environmental Protection Agency (EPA) sent the proposed regulatory determination for perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) in drinking water to the Office of Management and Budget for interagency review. This step is an important part of EPA’s extensive efforts under the PFAS Action Plan to help communities address per- and polyfluoroalkyl substances (PFAS) nationwide.
“Under President Trump, EPA is continuing to aggressively implement our PFAS Action Plan – the most comprehensive cross-agency plan ever to address an emerging chemical,” said EPA Administrator Andrew Wheeler. “With today’s action, EPA is following through on its commitment in the Action Plan to evaluate PFOA and PFOS under the Safe Drinking Water Act.”
The action will provide proposed determinations for at least five contaminants listed on the fourth Contaminant Candidate List (CCL4), including PFOA and PFOS, in compliance with Safe Drinking Water Act requirements.
The Safe Drinking Water Act establishes robust scientific and public participation processes that guide EPA’s development of regulations for unregulated contaminants that may present a risk to public health. Every five years, EPA must publish a list of contaminants, known as the Contaminant Candidate List or CCL, that are known or anticipated to occur in public water systems and are not currently subject to EPA drinking water regulations. EPA publishes draft CCLs for public comment and considers those prior to issuing final lists.
After issuing the final CCL, EPA determines whether or not to regulate five or more contaminants on the CCL through a process known as a Regulatory Determination. EPA publishes preliminary regulatory determinations for public comment and considers those comments prior to making final regulatory determinations. If EPA makes a positive regulatory determination for any contaminant, it will begin the process to establish a national primary drinking water regulation for that contaminant.
For more information: www.epa.gov/ccl
Background on the PFAS Action Plan
PFAS are a large group of man-made chemicals used in consumer products and industrial processes. In use since the 1940s, PFAS are resistant to heat, oils, stains, grease, and water—properties which contribute to their persistence in the environment.
The agency’s PFAS Action Plan is the first multi-media, multi-program, national research, management and risk communication plan to address a challenge like PFAS. The plan responds to the extensive public input the agency received during the PFAS National Leadership Summit, multiple community engagements, and through the public docket. The PFAS Action Plan outlines the tools EPA is developing to assist states, tribes, and communities in addressing PFAS.
EPA is taking the following highlighted actions:
Highlighted Action: Drinking Water
Highlighted Action: Cleanup
Highlighted Action: Monitoring
Highlighted Action: Toxics
Highlighted Action: Surface Water Protection
Highlighted Action: Biosolids
Highlighted Action: Research
The agency is also validating analytical methods for surface water, ground water, wastewater, soils, sediments and biosolids; developing new methods to test for PFAS in air and emissions; and improving laboratory methods to discover unknown PFAS.
Highlighted Action: Enforcement
Highlighted Action: Risk Communications
For more information, article, and treatment options visit SCS Engineers.
PFAS are a class of synthetic fluorinated chemicals used in many industrial and consumer products, including defense‐related applications. They are persistent, found at low levels in the environment, and bio‐accumulate. Studies have shown these compounds being detected more often in surface water, sediments and/or bioaccumulated into fish tissue. Because of the greater affinity of longer chain per‐ and polyfluoroalkyl substances (PFASs) compounds for fish than other environmental matrices, certain compounds are often found in fish tissue, but not in the water or sediment. Table 1 shows average concentrations of PFOA and PFOS in landfill leachates around the world. The USEPA health advisory level is 70 ppt for PFOA and PFOS.
Table 1. Concentrations of PFAS compounds in Landfill Leachate around the world
Treatment Options for PFOS and PFOA
The removal of PFASs from drinking water has been the USEPA’s national priority. Recent discoveries of PFAS/PFOS in drinking water in multiple states in the US has heightened interest in these emerging contaminants. Federal, state, and local agencies are formulating regulatory limits that vary greatly. These limits seem to be centered on drinking water, but these developments are driving disposal of existing stores of chemicals containing PFAS/PFOS and environmental media contaminated with PFAS/PFOS
Treatment processes that can remove PFAS chemicals from drinking water may include high-pressure membrane systems such as RO, granular activated carbon (GAC), or ion exchange as shown in Figure 1. The more conventional water treatment technologies such as (e.g., aeration) are not typically effective.
Figure 1. PFAS Removal Processes (a) Membranes, (b) GAC and (c) Ion Exchange Resins
Landfill Leachate RO Treatment Plant – New Hanover County, North Carolina
New Hanover County upgraded its leachate treatment system to meet stricter regulatory standards for surface water discharges, particularly standards relating to metals (arsenic) and ammonia. Sampling by NC DEQ showed the new RO plant is filtering out PFAS. Table 2 shows the results from February 2019.
Figure 2. New Hanover County Leachate and PFAS Treatment Plant
Table 2. Concentrations of PFAS compounds in Leachate at New Hanover County Landfill
|PFAS Constituent||Raw||Treated||Surface water|
|PFOA (ppt)||1,250||< 0.6||3.9|
|PFOS (ppt)||228||< 0.6||7.1|
Comparison of GAC Types for PFOA and PFOS Removal
Four different types of GAC, i.e., Re-agglomerated Bituminous, Lignite, Enhanced Coconut and Enhanced Coconut (Blend) were evaluated under identical operating conditions and influent water quality. Figure 4 shows results from these four GAC products for PFOA/PFOS removal vs time.
Figure 4. GAC Treatability study for removal of PFOA and PFOS
Re-agglomerated bituminous coal GAC (FILTRASORB) significantly outperformed: Lignite, Enhanced Coconut and Enhanced Coconut (Blend).
PFAS compounds are of concern because they do not break down in the environment, bioaccumulate in humans and biota, and may pose risks to human health
GAC, Synthetic adsorbent, and ion exchange resins are widely used for PFAS removal. Capacity and leakage of PFASs into the treated water varies depending on the specific PFASs, the type of adsorbent used.
PFAS removal may be influenced by pH, water temperature, contact time, Natural Organic Matter, and chlorine. For complete PFAS removal, a polishing may be required.
Disposal methods for PFAS waste streams include high-temperature incineration or landfilling. Landfilling is not favored since the PFAS load would increase, and many landfills will not accept PFAS waste.
About the Author: Dr. deSilva is SCS’s Director of Wastewater Treatment. He has 30 years of progressive experience in wastewater engineering, from concept through construction and start-up, and is an international leader in operations and maintenance, energy management, solids handling processes, construction management, and commissioning wastewater treatment plants (WWTP) around the world.