By Steven Butel and Martin Bureau – Originally published on Water Canada.
At WEFTEC 2022, ALTRA shared their results from concrete casts made using proprietary ingredients mixed with PFAS concentrates from a landfill leachate treated by foam fractionation.
At WEFTEC 2022, we had the opportunity to present ALTRA PFAS Treatment results for two projects where 1,600 m³ of landfill leachates were treated. Results were more than promising. These projects showed that it was possible to remove very significant portions (up to 99.5 per cent) of the long-chain PFAS (PFHpA, PFHxS, 6:2 FTSA, PFOA, PFOS, PFNA, 8:2 FTSA, PFDA), using a continuous foam fractionation process at flowrates between 60 and 160 L per minute. More importantly, results showed that the sum of all PFAS detected (including short-chain) in the leachates could be removed by 70 per cent and greater, indicating that a large proportion of short-chain PFAS (PFMPA, PFPeA, PFBS, 4:2 FTSA, PFHxA, PFPeS, PFBA) could be removed by foam fractionation alone (up to 60 per cent removal of the short-chain PFAS detected). This could be achieved by using appropriate additives, or no additives, depending on the specific chemical composition of the leachates. In some cases, best results were obtained without any additives, while in others a low dosage of surfactant (e.g., soap), cationic or anionic depending on the leachate treated, helped optimize the PFAS removal process. Finally, results indicated that the volume of PFAS concentrate solution generated by this foam fractionation process could be as low as approximately 1 per cent of the incoming leachate, and even lower to 0.1 per cent if a downstream concentrator was used.
If treated leachate PFAS targets imposed by state and federal authorities in the USA warrant it, polishing of foam fractionation treated leachate using downstream media capture (granular activated carbon or ion exchange resins, and others) can be added to achieve even lower PFAS concentrations in the treated leachate. In Canada, current recommended PFAS targets remain sufficiently high and can be met using foam fractionation only without requiring downstream media capture.
These results indicate that it is possible to remove PFAS in the leachates using the foam fractionation processes prior to releasing them into downstream WWTP. Depending on the individual PFAS concentrations and PFAS types in the incoming leachates, foam fractionation alone could be enough to deal with PFAS in the landfill leachates.
A question yet remains: what do we do with the PFAS concentrate generated by foam fractionation? Since landfills are known to sequester and transform PFAS, a possibility would be to send the PFAS concentrates directly back into the landfill. Recycling PFAS concentrates back to the landfill may result in increased PFAS concentrations in the raw leachate. However, landfill operators have shared that they believe that the increase would be negligible due to inherent dilution occurring in landfills. Some could argue that the initial liability associated with the PFAS concentrates remains and even increases if recirculated back to the landfill in a never-ending cycle, but from an economic standpoint, this would appear the most cost-effective solution.
Another solution is to sequester the PFAS concentrates permanently. To this end, recent advances have been reported in the domain of PFAS encapsulation and stabilization in concrete casts. Again at WEFTEC 2022, we shared our results from concrete casts made using proprietary ingredients mixed with PFAS concentrates from a landfill leachate treated by foam fractionation. As part of the testing protocols to demonstrate the effectiveness of this method, the concrete cast was subjected to an EPA approved test method, aiming at simulating 100 years of exposure in a landfill. The cast were exposed to a synthetic leaching procedure with the resulting liquids analyzed for PFAS. The results demonstrated that using this method most of the PFAS were successfully encapsulated and stabilized within the casts. This method appears promising as a very effective, long-term way to manage the PFAS concentrates generated by foam fractionation.
Some jurisdictions will require PFAS concentrates to be destroyed. Various thermo-oxidation (for the experts, thermal desorption, sub-critical or supercritical wet air oxidation) and electro-oxidation processes are currently being developed but most are not yet commercial. However, some of these are proving to be quite appealing. PFAS destruction results from electro-oxidation (boron doped diamond electrodes) previewed at WEFTEC 2022 showed extremely effective destruction of PFAS concentrates from landfill leachates. Other technologies are also reported to be effective, based on plasma for instance. The challenge with these technologies will be cost-effectiveness and environmental permitting for on-site destruction.
While PFAS remediation remains a real challenge on many accounts, point-source treatment is part of the solution.
Irrespective of whether they are sequestered, stabilized, or destroyed, PFAS in landfill leachates as well as in other types of PFAS-contaminated streams (groundwater from firefighting training areas, industrial rejects, etc.) will still need to be concentrated by a factor of 1,000, if not more, for these PFAS end-of-life avenues to become affordable, practicably speaking.
While PFAS remediation remains a real challenge on many accounts, point-source treatment is part of the solution. For landfill operators, cost-effective solutions are being demonstrated in the field today, which brings some reasonable confidence that ultimately the PFAS challenge will be overcome.
Steven Butel and Martin Bureau are with ALTRA PFAS Solutions