Patent ID: 12195377

DESCRIPTION OF EMBODIMENTS

A process for PFAS decontamination comprises exposing water comprising PFAS contaminant to gas to accumulate a PFAS concentrate and separating the PFAS concentrate.

The gas attracts fluorocarbon tail groups of the PFAS by intermolecular attraction at a water gas interface to form PFAS concentrate. As shown inFIG.1, the PFAS fluorocarbon tail101is attracted to the water gas interface of a gas bubble102with the terminal functional group103residing in the water. The accumulated PFAS concentrate can then be separated.

Preferably, a gas that exhibits a charge and/or variations in electron densities, or that can be ionised or charged is used. It is believed that Van der Waals forces of ionised or charged gasses further attract the fluorocarbon tail groups of the PFAS to the water gas interface.

The PFAS partitioning behaviour also may be affected by the alkyl chain length and the charge on the terminal functional group. In general, PFAS's with shorter alkyl chain length are more water soluble than those with longer lengths. PFAS compounds with increasing water solubility would be less likely to associate at an air water interface as they may be drawn into the aqueous phase and less likely that the tail of the molecule resides in the gas phase.

Perfluorobutyrate (PFBA) and other PSAF compounds may be an exception as some compounds can tend to form the configuration shown inFIG.7, wherein the hydrophilic end of the molecule is bound to the tail making it less likely to have surfactant qualities and associate at the air water interface, making it only miscible in water. In other words, strong bonding between H and F shown by the arrow binds the hydrophobic head group, making it less soluble in water.

As such, pH adjustment and surfactant additions may be added to facilitate attraction of the PFBA fluorocarbon tail groups to the gas water interface. It is believed the pH effect on the polar functional group end of some PFAS molecules aids in the PFAS hydrophilic end to bind to the water phase.

The process may involve bubbling gas through water wherein the PFAS contaminant is attracted to the water gas interface of bubbles which rises to the top to form a froth fractionate of PFAS concentrate.

In this regard,FIG.2shows froth concentrator apparatus104which comprises a series of columns105comprising PFAS contaminated water therein into which gas from a gas inlet107is bubbled through a gas sparge106at the bottom of each column105to form a water gas interface within each column105.

The gas interacts with the PFAS contaminated water in the aforedescribed manner to form a froth fractionate which is collected from upper froth fractionate outlets108. The columns105may be arranged in series with interconnecting overflows109therebetween. The series of columns105may comprise a wastewater inlet110and a wastewater outlet111.

The gas injected may comprise ozone in air, ozone in oxygen, oxygen, common air, nitrogen, nitrous oxide, carbon dioxide, water vapour, oxides of nitrogen and chlorine dioxide.

A hydrofluorocarbon refrigerant is added to the gas. The hydrofluorocarbon refrigerant is generally defined herein as a carbon fluorine compound that is in gas phase at standard temperature and pressure (25° C. and 1 atm) and which is compressible to form a liquid for recovery, including for reuse.

The hydrofluorocarbon refrigerant is preferably 1,1,1,2 Tetraflouroethane but may also include Difluoromethane or Pentaflouroethane.

Different types of gases may be injected into different columns105to target specific types of PFAS contaminant or multiple types of PFAS contaminant. For example, common air may be injected into a first column105whereas ozone in air (having enhanced PFAS accumulating ability which may be due to the Van der Waals forces as outlines above) may be injected into a second column105and air comprising the hydrofluorocarbon refrigerant (having enhanced PFAS accumulating ability by further attracting the carbon fluorine tail of the PFAS molecule as outlined above) may be injected into a third column105to target smaller molecular weight PFAS molecules.

Gaseous offtake from the outlets108may be collected and compressed to return the hydrofluorocarbon refrigerant to a liquid phase for recycling.

The collected froth fractionate may be decomposed by oxidation. In an embodiment, upper ends of each column105may comprise UV lamps acting on ozone (which may be introduced at concentrations from 5-5000 PPM) which generate hydroxyl free radicals to decompose the concentrated PFAS compound.

Alkalinity may be enhanced, such as to between 10-12 pH to enhance the decomposition process.

FIG.3shows a system112for reducing concentration of PFAS contamination in wastewater using the gas bubbling technique.

The system100may comprise a wastewater reservoir113and a level sensor and outlet control valve149controlled accordingly. The reservoir113may feed into the concentrator104via a pump114and flowmeter115.

Air from an air compressor150and measured through a flowmeter151may feed into the gas injection inlet116of the concentrator104.

The air may be supplemented with specific gas from a specific gas generator117via flowmeter118. Specific types of gases may include oxygen, nitrogen, nitrous oxide, carbon dioxide, water vapour, oxides of nitrogen and chlorine dioxide contained or generated by the specific gas generator117.

The air may be further supplemented with charged or ionised gas drawn from gas bottles119. The gas drawn from the gas bottles119may be ionised using a gas ioniser120.

The collected froth PFAS concentrate may be collected in reservoir121and periodically pumped for disposal such as via truck disposal.

The wastewater may flow to a wastewater reservoir122with level sensor to control an outlet valve153to periodically drain the wastewater to a sewer123.

Gaseous offtake may be collected via gaseous offtake line154which is compressed by a compressor155to compress the hydrofluorocarbon refrigerant to a liquid phase157which is stored within a liquid refrigerant container156.

Refrigerant gases may be released via refrigerant control valve158back into the gas injection inlet116.

Test results from passing regulated and non-regulated PFAS contaminant twice through the system ofFIG.3showing the difference of contamination and volume reduction by using 1,1,1,2 Tetraflouroethane are shown in the following table:

Key parameter for PFASNo hydrofluorocarbonWith hydrofluorocarbonTreatmentrefrigerant addedrefrigerant Added% reduction of regulated94-98%98-100%PFAS contamination% Reduction non-20-60%85-98%regulated PFAScontamination% Volume Reduction after1/(400-500)1/(10,000-20,000)2nd Pass

As can be seen, regulated PFAS contaminant extraction was found to increase from 94-98% to 98-100% through the addition of the hydrofluorocarbon refrigerant. Yet further, non-regulated PFAS contaminant extraction was found to increase from 20-60% to 85-98 percent.

Furthermore, the percentage volume reduction of contaminated water to PFAS froth fractionate concentrate was found to increase from 1/(400-500) to 1/(10,000-20,000) through the addition of the hydrofluorocarbon refrigerant.

FIG.5shows a soil decontamination system125which comprises a reservoir126comprising PFAS contaminated soil colloidally suspended in wash water127which is agitated by agitator128.

A water gas interface129is formed by applying an atmosphere130of gas comprising the hydrofluorocarbon refrigerant (preferably charged or ionised gas) above the soil and wash water127. As such, PFAS concentrate is formed at the interface129which is removed via collection outlet131.

In alternative embodiments, the gas may be bubbled through the water and soil suspension.

The soil may form a sludge taken via sludge outlet131for dewatering using a dewatering system124whereas clean water may be taken via clean water outlet133.

FIG.4shows the dewatering system124in accordance with an embodiment wherein sludge is pumped through a pressure screen134(preferably a 30-300 μm screen) by an auger135of a progressive cavity pump to separate the sludge into dewatered sludge159and clarified water160.

FIG.6shows PFAS scrubbing equipment137which uses gas (preferably charged or ionised gas) comprising the hydrofluorocarbon refrigerant additive to separate PFAS contaminant from wastewater.

The equipment137comprises a vessel138into which charged or ionised gas is introduced via gas inlet139. The charged or ionised gas may be provided by the aforedescribed gas ioniser120.

The vessel138comprises corrugated packing material140or similar therein to increase surface area within the vessel138.

The vessel may be pressurised to between 200-300 kPa to increase the concentration of the charged or ionised gas therein to suppress frothing.

PFAS contaminated wastewater is introduced via wastewater inlet141which flows over the packing material140to expose the wastewater to the charge or ionised gas within the vessel138which extracts the PFAS to the water gas interface.

Scrubbed wastewater flows144flows to a reservoir of water below the packing material140. The level of the reservoir of scrubbed water144may be monitored by a level sensor142which controls the addition of wastewater via the inlet141.

Charge or ionised gas may also be applied via gas distributor143to ensure that the extracted PFAS stays at the water gas interface of the scrubbed wastewater144.

The scrubbed wastewater144may be separated via three-way valve145into concentrated PFAS146and processed wastewater147.

The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that specific details are not required in order to practise the invention. Thus, the foregoing descriptions of specific embodiments of the invention are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed as obviously many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the following claims and their equivalents define the scope of the invention.