An ongoing large-scale demonstration project in Australia is the world’s first to apply a foam-fractionation technology to remove per- and polyfluoroalkyl substances (PFAS) in a sewage-treatment plant. The Surface-Active Foam Fractionation (SAFF®) technology developed by EPOC Enviro (Emu Plains, NSW, Australia; www.epocenviro.com) relies on charged air bubbles to manipulate amphiphilic PFAS compounds. “The double-electric layers on the air bubbles are used to harvest the hydrophobic tail chemistries on the PFAS compounds, while the hydrophilic head chemistry remains in the water. By injecting air bubbles, we reduce the Gibbs free-energy constant as much as possible, and the tail binds to the surface of the air bubble, forming a foam at the top of the system,” explains Peter Murphy, managing director of EPOC Enviro. The foam-fractionation vessel geometry narrows at the top, which helps isolate the PFAS-laden foam while cleaned water is recirculated.
Source: EPOC Systems
EPOC’s demonstration shows that SAFF technology can overcome one of the major challenges associated with sewage treatment — the presence of complex contaminants in both the solid and aqueous phases. Some technologies that work well in aqueous streams, such as membranes and solid adsorbents, cannot handle complicated sewage matrices because the solids become bound to the media very quickly, rendering them inoperable. PFAS contamination in sewage solids is a “blind spot” in many treatment ecosystems, creating additional risks for groundwater and soil pollution as sewage biosolids are increasingly used in fertilizer formulations.
While the SAFF technology has seen numerous installations globally for various wastewater streams, this trial is the first to tackle sewage waste. Ahead of the trial, EPOC completed extensive re-engineering of the SAFF process to confirm thorough PFAS removal across both liquid and solid phases. “As we moved into these almost slurry-based matrices, we had to do some pretty significant re-engineering, primarily around recirculating the solid molecules back again across the air-water interface. This creates high-energy recirculation cells in the vessels that allow us to continually bombard those molecules. Because the binding forces on lipids and fats, oil-water interfaces and colloidal-phase interactions are actually much stronger than if they just sat in an aqueous phase, we have to apply different techniques than what we do in the less-contaminated matrices,” explains Murphy, pointing to the pumping and filtration systems as particular areas of re-design focus, as well as the selection of an environmentally friendly cationic surfactant to supplement the process.
In the aqueous phase, the SAFF process removed 97% of all PFAS from sewage streams, with all criteria compounds of concern present at non-detect levels (>99% removal). Biosolids samples showed that over 80% of contamination was removed from the solids phase. Following this project in Australia, similar full-scale sewage-treatment demonstrations are planned in the U.S. and Europe later this year.