Electro-oxidation: How to sustainably destroy PFAS in water

WSP* has achieved a significant breakthrough in the development of an innovative electro-oxidation technology.

The technology solves a particularly challenging and urgent problem in wastewater and groundwater treatment: the destruction of per-and poly-fluoroalkyl substances, or PFAS. These compounds have been widely used for more than 50 years in several industrial and household products, and their presence in the environment is now widespread.

Based on the needs we are seeing in various sectors, finding a solution for destruction of PFAS was paramount. So, the PFAS team set out to find a sustainable, cost-effective, commercially available, modular and scalable technology that could be easily applied at various types of sites and water.

Electro-oxidation – an efficient way to destroy PFAS in effluent streams

We focused on electro-oxidation technology using a unique kind of long-lasting boron-doped diamond (BDD) electrodes. In this technology, the PFAS-laden water passes by an array of electrodes, a positively charged anode, and a negatively charged cathode, and similar to the firm’s other pioneering work on electrocoagulation.

In BDD electrodes, the anode generates the oxidation process and forms oxidizing radicals and electrons, that, through a complex chemical process, break down the PFAS molecules into shorter molecules and eventually carbon dioxide for organics molecules and fluorides. The cathode produces primarily hydrogen gas and provides reduction reactions. Electro-oxidation can be viewed as a chemical combustion of compounds in water.

The first electro-oxidation tests focused on two types of PFAS – known as PFOS and PFOA – that are some of the most persistent and recalcitrant, and are regulated by health authorities worldwide. The large-scale test removed 100 percent of PFOS and 100 percent of PFOA to meet the Health Canada and the U.S. Environmental Protection Agency guidelines for drinking water for these two substances.

As expected, based on the PFAS EO team experience, the process has been found to generate some by-products – including hypochlorite and perchlorate. However, by optimizing the process, the team was able to significantly reduce these problematic constituents, including reducing the formation of perchlorate by more than 99 percent.

Since fluoride is one of the building blocks of all PFAS molecules, some fluoride will be produced by the electro-oxidation process as the final breakdown product of these molecules. The team focused on making sure that the effluent from the process has fluoride levels that are within applicable regulatory standards.

All of the treatability tests have been done out of our treatability center in Montreal. The water analysis for PFAS has been carried out by state-of-the-art analytical laboratories in the Civil Engineering department at Montreal’s McGill University, which has supported the project with its PFAS analytical expertise since inception in 2019.

There has been growing concern about PFAS impacting the environment in areas where firefighting foams were used, certain manufacturing facilities, landfill leachate and other impacted sites. However, most current technologies used to remove PFAS from groundwater, industrial wastewater and leachate have significant drawbacks.

• Activated carbon, the most commonly applied technology, offers low capital cost, but high operating costs because the used media, which needs to be regularly replaced, must be transported to an accredited disposal facility where it is treated by high-temperature incineration to destroy the problematic PFAS molecules.
   
• Ion exchange resins are also becoming a mainstream technology for PFAS removal in water. However, most of the time they involve a single-use resin, which must then also be incinerated. If a regenerable resin is employed, the PFAS-impacted regenerant stream needs to be transported and disposed of at high cost – again, in an accredited waste management facility.
   
• Membrane technologies, such as reverse osmosis, can remove PFAS from water, but they also require disposal of their PFAS-contaminated reject stream. This could be a significant volume, depending on the volume of water to treat and the initial water quality, such as its total dissolved solids concentration. For remote area, this could simply not be applicable.

Cost savings over conventional methods

One of the keys to our successful use of electro-oxidation technology has been using unique long-lasting boron-doped diamond (BDD) electrodes. While these electrodes increase the capital cost of the equipment, the electrodes are expected to have a lifespan of up to 25 years, so that the initial cost is spread over a long operational life. Furthermore, the capital cost can be mitigated by leasing the equipment. These special electrodes also allow for generation of lower concentrations of by-products compared to other electro-oxidation electrode materials.

Our team has been encouraged to find that by optimizing the electro-oxidation process, we were able to provide a cost-competitive solution compared to activated carbon technology over the long term. The only operating cost of electro-oxidation is electricity to charge the electrodes and operate the process pump.

In brief, this boron-doped diamond electro-oxidation system for PFAS treatment:

• destroys PFAS molecules so there is no transfer of PFAS to other media, thereby eliminating costs for media purchase, transport, disposal or regeneration;
• uses no chemicals, produces no sludge, and the absence of filter media eliminates costly disposal;
• offers easy scalability with more arrays of boron-doped diamond plates or reactors and application of more electricity to treat a larger water flow; and
• delivers low operating costs by needing only electricity and no human intervention. Initial capital costs can be mitigated by leasing equipment.

Electro-oxidation has great potential for treating PFAS. Prime applications of this technology are sites where PFAS-containing firefighting foam has been used, stocked or disposed of, such as landfills, mine sites, oil and gas plants, including oil rigs; waste management sites, military sites, ships and transportation sites, including airports, train stations and locomotive maintenance centers.

WSP’s EO has been successfully tested to destroy PFAS below the US EPA Drinking Water Health Advisory Levels, the Health Canada Criteria and several more stringent standards. The technology is effective for all types of PFAS, scalable, long-lasting and typically treats PFAS in one to two hours, thereby making the technology highly efficient with minimal operation and maintenance requirements. The technology has been successfully tested and optimized in the lab on several effluents and is ready for commercial applications.

Contact our PFAS Team today for more information on this and other PFAS treatments.

About the Author

Note: The research and development of this technology was initially conducted by Golder professionals who joined WSP in an acquisition completed in 2021.