Abstract
PFAS chemicals are a class of synthetic organo-fluorinated compounds widely used in industrial processes and consumer products due to their exceptional chemical stability and resistance to heat, water and oil. This stability has resulted in resistance to breakdown and designation as "Forever Chemicals" as the PFAS persists in the environment, especially in the soil and water, presenting significant long-term environmental and health issues.
Current approaches have had limited success in addressing the problem. Fresh approaches to the concentration and disposal of PFAS are therefore needed.
The innovative LAT process, which has been proven in treating landfill leachate (a significant source of PFAS), offers promising methods to treat large-scale industrial flows of water, enabling PFAS chemicals to be concentrated and facilitating easier ultimate disposal.
Introduction
Per- and polyfluoroalkyl substances (PFAS or PFASs) are a large group of synthetic organo-fluorine compounds that have multiple fluorine atoms attached to an alkyl chain, replacing some or most of the normal hydrogen atoms in the chain. The fluorine–carbon bond is one of the strongest chemical bonds, resulting in high chemical and thermal stability of PFASs. This leads to these compounds having long environmental lifetimes, hence the common nickname "forever chemicals". The first PFASs became widely used from 1938 with the invention of Teflon. PFASs have multiple applications, from packaging to fire retardants, waterproof fabrics, shampoo, adhesives and more. There are several thousand to over seven million PFAS compounds depending on the definitions used.
PFAS, due to the strength of the chemical bonds, resist natural degradation and can accumulate in groundwater, surface water and biological systems. Regulatory agencies worldwide are imposing increasingly stringent limits on PFAS concentrations in drinking water and wastewater discharges.
Concern has been raised by the accumulation of PFAS contamination in landfills and the risks this can pose in the discharge and treatment of the leachate from the landfill.
Traditional water treatment systems have proved inadequate in removal of PFAS contamination.
Current approaches
A wide variety of treatment methods are being investigated, including membranes, enhanced oxidation, adsorption, and thermal degradation. PFAS molecules typically have sizes smaller than the pore size of the membrane, preventing retention of molecules, and this has made ultrafiltration unsuccessful for their removal. Reverse osmosis (RO) and nanofiltration with smaller membrane size have shown high removal efficiency in controlled environments. However, clogging, high costs and intensive maintenance make them unsuitable for use in complex wastewater, making them unfeasible for large-scale facilities.
Adsorption methods such as the use of activated carbon and ion exchange have also shown promise, but the media involved requires recovery of the adsorption capacity. Regeneration procedures include removing the PFAS. However, in order for this to occur, economically and environmentally appropriate solutions are needed. Thermal or chemical processes are frequently used in regeneration. Despite their dangers, organic solvents are necessary for the chemical regeneration of adsorbents saturated with PFAS. High-temperature reclamation may result in the production of hazardous fluorine gases. As such, using chemical, mechanical or thermal regeneration on-site is not feasible and renders large-scale adsorption uneconomic at present.
Principle of LAT Technology
LAT is an integrated evaporation treatment solution for highly contaminated waste streams using waste heat as an energy source. The LAT system partially evaporates an incoming waste stream by heating it with the available waste heat and fragmenting the effluent into a cascade of small droplets in a sealed evaporation column. The water vapour is transferred into a second condensation column where it condenses into hot distilled water. The heat is collected from this pure water and used as a preheater for the incoming stream.
The design of the evaporation–condensation towers, together with their interconnections, distributors, and control algorithm to maximise the water recovery, are subject to a series of international patents; the control algorithm and mathematical model are kept confidential. The waste heat can be supplied by a wide range of sources such as exhaust gases, cooling liquids and renewable energy sources.
The system is economic for facilities requiring treatment of up to 25,000 m³/day. Based on operating experience, where waste heat is available LAT can generate total cost savings for clean water recovery of up to 40% versus legacy processes.
The system has been proven to process landfill leachate at landfill sites in the UK and China, achieving clean water recovery of up to 95%. To prevent volatile discharges, suitable carbon filters are installed at bleeder valves.
Potential of LAT Technology for PFAS
Given LAT Technology's experience in dealing with landfill leachate, LAT is a promising solution to preventing discharge of PFAS chemicals into the environment.
Most PFAS compounds are non-volatile and relatively small molecules. This makes them an ideal molecule for concentration using LAT Technology. Application of LAT Technology would enable water containing PFAS compounds to be concentrated, with a stream of clean water produced at a lower cost, preventing environmental discharge.
"The concentrate of a LAT system reaches a far higher concentration than filtration methods such as reverse osmosis can achieve."
The PFAS compounds would be collected in the concentrate of the LAT system, but by collecting them in this way they would be more concentrated and thus become easier to handle and dispose of. Given the advantage of evaporation systems, the concentrate of a LAT system reaches a far higher concentration than filtration methods such as reverse osmosis can achieve. Disposal would follow similar methods to filtration and ion exchange, but would be economically more favourable, without the added complexities of membrane and ion-exchange media cleaning and regeneration.
Conclusion
LAT Technology offers a simpler and more cost effective method for PFAS removal from industrial water compared to legacy systems. There will remain the issue of ultimate disposal of the PFAS compounds, but once in a more concentrated form this should be easier and cheaper. Find out whether your site has the waste heat to make this work.
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