The prevalence of the various per- and polyfluoroalkyl substances (PFAS) — compounds that are notoriously difficult to break down — in the water supply is causing global concern. A new partnership between Element Six (Oxford, U.K.) and Lummus Technology (Houston) is tackling the PFAS challenge by combining Element Six’s Diamox boron-doped diamond (BDD) electrochemical oxidation technology (for more, see Chem. Eng., June 2016, p. 8) with Lummus’ Zimpro Electro-Oxidation (ZEO) technology.
One of the major challenges in PFAS treatment is in the destruction of short-chain PFAS compounds. “Our system can operate at two orders of magnitude higher current density than any other electro-oxidation technology on the market, allowing for a high capacity of destruction to take place in a small footprint. The high current densities enable the destruction of short-chain PFAS, where other electro-oxidation technologies may struggle. The technology delivered by this collaboration is the only field-deployable and scalable solution proven to destroy even short-chain PFAS,” says Bruce Bolliger, head of business development, North America, for Element Six.
Image Credit: Lummus Technology
The ZEO system is a semi-batch process where liquid is sent to the system from a circulation tank. Once loaded, the PFAS concentrate is pumped across the BDD electrodes (where oxidation occurs), and then is returned to the circulation tank. In this way, long-chain PFAS compounds are broken apart to become either CO2, NaF or fractionally smaller PFAS compounds. “This is where the technology sets itself apart from others, because it can efficiently break down the shorter PFAS where other technologies have struggled. The longer the process is operated, the more oxidation occurs and, eventually, only the smaller four- and five-carbon PFAS compounds remain. Then, to avoid moving into an electrically inefficient region, the partially oxidized PFAS mixture would be re-circulated to the front end of the PFAS separation process before complete oxidation is achieved. The already treated liquid would be combined with the PFAS going into the separation process for the first time, thus forming again a concentrated PFAS stream for electro-oxidation treatment,” says Chad Felch, director of Zimpro Technology at Lummus. Because of this configuration, the ZEO system always sees a very concentrated PFAS input stream, which helps maximize efficiency.
Several pilot units for the integrated PFAS-destruction technology are operating at Lummus’ research facility in Texas. “We can also bring our pilot units directly to customer locations, and we are currently initiating our first international pilot study in the U.K.,” says Felch.