HDR Engineers Discuss Potential PFAS Implications for Landfill and Wastewater Treatment PlantsHDR Engineers Discuss Potential PFAS Implications for Landfill and Wastewater Treatment Plants

Landfill operators and publicly owned treatment works (POTWs) face interconnected challenges posed by PFAS contamination. These persistent chemicals can end up in landfill leachate that is then discharged to POTWs. Conversely, POTW’s send treated biosolids to landfills that are also laden with PFAS.

Evolving policies could someday require both service provider types to invest in costly PFAS removal systems to meet discharge limits. So, given the synergy between them they should be talking to each other now to prepare. That is among messages relayed by HDR engineers Jeffrey Murray and John Schubert at an HDR-hosted webinar for operators of landfills and POTWs, regulators, engineers, and other stakeholders.

Schubert and Murray went on to discuss PFAS treatment options and pilot results of their company’s own removal technology, which they anticipate will roll out soon.

HDR’s process, froth flotation, is based on the same principles as foam fractionation, which leverages columns to separate PFAS, captured in  bubbles, from liquid—and to then further concentrate these chemicals. The idea was to provide a simpler, less expensive approach than other PFAS mitigation technologies but with similar performance.

HDR’s early research shows that froth flotation as a standalone process can remove at least 95 percent of long-chain PFAS compounds and 80 to 90 percent of short-chain compounds.

Related:EPA Expands Toxics Release Inventory to Include Nine More PFAS Chemicals

And pairing froth flotation with reverse osmosis (RO) as a preliminary step will take both technologies’ capabilities further.

RO, a high-pressure membrane system alone will typically treat to drinking water standards. But it leaves behind PFAS and other concentrates that make up 15 to 20 percent of the treated volume, Schubert says.

Beginning with RO, then leveraging froth flotation to manage the RO reject could reduce the concentrate to less than 1 percent of the treated flow, enabling it to be recirculated in landfill while bringing liquids to drinking water standards.

HDR ran pilots on its technology in several locations with different waste streams and examined three variables: surfactant dosages, air, and retention time.

“We were looking for an optimal arrangement of these variables that provided efficient removals while balancing capital cost,” Schubert says.

“What we found is the influent leachate PFAS concentrations vary by landfill type and location. But in general froth flotation can be very effective in removing long-chain PFAS with more than six carbons and get good to very good removal of shorter chain compounds with six carbons or less.

Related:Crystal Clean Expands PFAS Remediation Capabilities

“We also found that froth flotation as a singular treatment to raw leachate could be a cost-effective solution and simple to operate for significant reduction of PFAS loading on POTW.”

Existing and evolving policies around these contaminants could bring challenges for both landfills and POTWs.

Wastewater facilities have National Pollutant Discharge Elimination System (NDPES) permit obligations, and Murray anticipates increasing scrutiny of PFAS could force them to take a harder look at their industrial users beyond landfills.

“They are getting what is flushed, and the question for them is if all my industrial users reduce PFAS can I comply with the NDPES clean water program, or do I have to implement additional treatment technology?” Murray says.

The U.S. Environmental Protection Agency's (EPA) Effluent Guidelines Program Plan 15 could potentially also mean costly changes for landfill operators should they have to meet effluent limitations that would require PFAS pretreatment.

Conversations around treatment options are beginning to amplify given the reality that a landfill’s impact on a POTW’s ability to meet regulators’ discharge criteria varies. It is typically based on PFAS mass in leachate, volume of leachate discharged, and the POTW’s influent flow rate, among factors.  

Related:EPA Data Reveals Top 10 U.S. States with Contaminated Public Water

“This is why we are encouraging landfill operators and their POTWs to begin understanding the influent PFAS loading and what the landfill is contributing, so PFAS minimization and pretreatment strategies can be developed with relevant supporting information,” Murray says.    

He and Schubert say key to successful planning is to first do due diligence.  

A PFAS influent study conducted by the POTW can determine the impact landfill leachate has on its ability to meet discharge criteria for PFAS compounds (in states with such criteria). And these studies can determine just how much removal is likely necessary in what scenario.

Removal of PFAS compounds by 80 to 99 percent may be impactful for small- to mid-size POTWs but have little to no impact on large facilities’ influent stream, consequently requiring a more robust system.

Where landfills are a point source of PFAS to the POTW, they may be requested to reduce the concentrations, but a question to ask, Murray says, is how low do they need to go to be of value to the POTWs?

Schubert paused on what has come of HDR’s froth flotation pilots, particularly possible next steps for pilot participant Cumberland County in North Carolina. The County was awarded a grant by North Carolina Department of Environmental Quality for leachate pretreatment projects. A qualifying requirement is that PFAS levels be brought to drinking water standards.

In reach of this goal, HDR will be issuing a bid to construct a system pairing RO, froth flotation, a destruction technology, and a biological treatment to remove ammonia nitrogen—a system Schubert and Murray estimate will come with a $10.8M price tag.

Two underlying themes webinar attendees heard is: 1)The best system will depend on multiple variables. 2)And plan ahead for additional capital and operating costs so if and when you are required to treat PFAS in leachate you are in a position to afford it.