LOW-ENERGY WATER TREATMENT

Abstract

An above-ground low-energy method of dewatering highly contaminated waste e.g. leachate contaminated with at least a first group of contaminants and PFAS is described. The method comprises the step of removing the PFAS before removing the first group of contaminants. The removal of PFAS is undertaken by actively aerating the contaminated waste comprising PFAS to produce a waste stream comprising a concentration of PFAS and a liquid stream having at least some of the first group of contaminants. The one or more liquid streams are separated from the waste streams so as to dewater the contaminated waste. Optionally, the liquid streams are treated to remove the first group of contaminants.

Claims

1. An above ground low energy method of dewatering waste contaminated with at least a first group of contaminants and PFAS, the method comprising the steps of: (a) removing the PFAS before removing the first group of contaminants; (b) removing the first group of contaminants; in step (a) the removal of PFAS is undertaken by: actively aerating the contaminated waste comprising PFAS in a first vessel to produce a waste stream comprising a concentration of PFAS and a first liquid stream having at least some of the first group of contaminants; subjecting the waste stream to a second process comprising actively aerating the waste stream in a second vessel to further concentrate the PFAS in a second waste stream, and also to generate a second liquid stream having at least some of the first group of contaminants; subjecting the second waste stream to a further process to further concentrate the PFAS in the waste stream, and also to generate a third liquid stream having at least some of the first group of contaminants; wherein one or more of the first, second and third liquid streams having at least some of the first group of contaminants are separated from the waste streams so as to dewater the contaminated waste; and in step (b) the removal of at least some of the first group of contaminants is undertaken by treating the first, second and or third liquid streams either separately or together.

2. The method of claim 1, wherein the further process comprises a third stage of active aeration comprising subjecting the second waste stream to a third process comprising actively aerating the waste stream in a vessel to further concentrate the PFAS in a third waste stream, and also to generate a third liquid stream having at least some of the first group of contaminants.

3. The method of claim 2, wherein the further process comprises a fourth stage of active aeration comprising subjecting the third waste stream to a fourth process comprising actively aerating the waste stream in a vessel to further concentrate the PFAS in a fourth waste stream, and also to generate a fourth liquid stream having at least some of the first group of contaminants, wherein the fourth liquid stream can be combined with the first, second and third liquid streams prior to treatment in step (b).

4. The method of claim 1, wherein the retention time during each stage of active aeration is at least 15 minutes.

5. The method of claim 1, wherein the active aeration is foam fractionation.

6. The method of claim 1, wherein the vessel volume decreases in each subsequent stage of active aeration.

7. The method of claim 1, wherein the method comprises subjecting the first, second, third and or fourth waste streams to a solar evaporation drying process to further concentrate the PFAS.

8. The method according to claim 7, wherein prior to the solar evaporation drying process, the waste stream(s) are subject to multi-phase pass through the final stage of active aeration.

9. The method of claim 1, wherein the first group of contaminants comprises materials that contribute to TOC, materials that contribute to TDS, oil(s), heavy metal(s), materials that contribute to TN including ammonia.

10. The method of claim 1, wherein the waste has a TOC level greater than about 5 mg/L.

11. The method of claim 1, wherein the waste is selected from one or more of sewerage, leachate, contaminated surface water, municipal wastewater and industrial wastewater.

12. The method of claim 1, wherein the method reduces the sum PFAS concentration.

13. The method of claim 1, wherein the PFAS removed is perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (conjugate base perfluorooctanesulfonate) (PFOS).

14. The method of claim 1, wherein the removal of at least some of the first group of contaminants is by one or more of use of sequential batch reactor, moving bed bioreactor, and dissolved air floatation.

15. The method of claim 1, wherein the process is operated continuously with each subsequent treatment step receiving feed from a preceding step.

16. The method of claim 1, wherein the process has a Low Energy between 0 to 0.008 kW/L for a system operating at up to 500 L/hr.

17. The method of claim 1, wherein the process has a Low Energy between 0 to 0.004 kW/L for a system operating at up to 5000 L/hr.

18. The method of claim 1, wherein the process has a Low Energy between 0 to 0.001736 kW/L for a system operating at up to 8640 L/hr.

19. The method of claim 1, wherein in addition to removal of PFAS the active aeration stage(s) remove up to about 50% of the starting concentration of Total Nitrogen

20. An above ground low energy method of generating a highly PFAS concentrated waste stream from a waste, the waste comprising at least one of sewage, leachate, contaminated surface water, municipal wastewater and industrial wastewater, the waste contaminated with a first group of contaminants and having a TOC level greater than about 5 mg/L and the waste contaminated with PFAS, the PFAS including perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (conjugate base perfluorooctanesulfonate) (PFOS), the method including the steps of: actively aerating the waste in a first vessel to produce a waste stream having a first PFAS concentration, and a first stream having at least some of the first group of contaminants; actively aerating the waste stream having a first PFAS concentration in a second vessel to produce a second waste stream having a second PFAS concentration, and a second stream having at least some of the first group of contaminants; passing the second waste stream having a second PFAS concentration through a further process to produce a third waste stream having a third PFAS concentration, and a third stream having at least some of the first group of contaminants; wherein the third PFAS concentration is higher than the second PFAS concentration further wherein, at least one of the first, second and third streams having the first group of contaminants is treatable so as to remove at least some of the first group of contaminants.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0118] Embodiments of the invention and other embodiments will now be described with reference to the accompanying drawings which are not drawn to scale and which are exemplary only and in which:

[0119] FIG. 1 is a process flow diagram showing an embodiment of a process.

[0120] FIG. 2 is a schematic showing the progressive reduction in waste volume.

[0121] FIG. 3 is a graph showing PFAS concentration reduction over time.

[0122] FIG. 4 are tables showing PFAS feed concentration and the deviation in these results experienced on site.

[0123] FIG. 5 is a table showing the outcome data from experimental trials.

[0124] FIG. 6 is a process flow diagram showing an embodiment of a process.

DETAILED DESCRIPTION OF EMBODIMENTS

[0125] Foam Fractionation is a chemical engineering process in which hydrophobic molecules are preferentially separated from a liquid solution using rising columns of foam. It is commonly used, albeit on a small scale, for the removal of organic waste from aquariums; these units are known as “protein skimmers”.

[0126] The fundamental principle behind the novel technology described herein is a variation of the process of foam fractionation. Surprisingly foam fractionation can also be used for the removal of surface active contaminants from waste water streams. PFAS molecules are usually quite surface active, meaning that they are inherently attracted to air/water interfaces. This new water treatment technology takes advantage of this property of PFAS molecules.

[0127] A key element is the introduction of gas (typically air) bubbles well below the water level of a sample of PFAS contaminated water using a specific bubble diffuser system. As the bubbles mix with the water and rise to the surface, the surfaces of the bubbles are energetically stabilised by the surface active PFAS molecules, which diffuse from the bulk of the water to the bubbles and then adsorb onto the surfaces of the bubbles. This process prevents the bubbles from coalescing. When the bubbles reach the surface of the water sample, foam is formed at the surface. This foam, which is highly concentrated in PFAS, can then be removed from the surface, dewatered and transported to a treatment plant for safe disposal or destruction. By these means a PFAS can be removed from a contaminated water sample.

[0128] In FIG. 1 there is shown an above ground method of dewatering contaminated waste comprising PFAS. It also shows an above ground method for generating a highly PFAS concentrated waste stream.

[0129] Explanatory notes for FIG. 1: [0130] Stage 1 concentrate is foamate (With PFAS) [0131] Stage 2 concentrate is foamate with concentrated PFAS [0132] Stage 3 Concentrate is foamate from the treated side of Stage two [0133] 1 Aerator/Separator treating raw wastewater (bulk of material sent to clean storage tank) [0134] 2 Storage and settling of foam [0135] 3 Aerator/Separator treating Foam from stage 1 [0136] 4 clean (Stage 2 concentrate) storage/settling [0137] 5 Aerator/Separator 3 treating Tier 2 concentrate. Tier 1 (foamate) sent to settling tank [0138] 6 All fractioned waste stored here [0139] 7 Solar drying [0140] 8 Concrete pad or plastic drying bed. Could have wet weather covers [0141] 9 Dry waste scraped from the drying bed periodically and stored and destroyed

[0142] In a first vessel 10, the contaminated waste comprising PFAS is actively aerated. In an embodiment the first vessel is a foam fractionator 10 and the active aeration is the formation of bubbles in the fractionator. The PFAS contaminated waste is passed through the first foam fractionator 10 from an input (not shown) and out via an output (not shown). The process produces a waste stream 12 comprising a concentration of PFAS and a first water stream 14. The waste stream 12 can comprise a foamate having a first PFAS concentration. In an embodiment, the bulk (about 90 to 95%) of the treated wastewater from the fractionator 10 is the cleaned water stream 14 that is sent to a clean water storage tank 26. While this is referred to as “clean” water it should be understood that it is cleaned of PFAS and there may be other contaminants remaining to be removed. Waste stream 12 comprises about 4 or 5% of the separated stream. The waste stream 12 is subject to a second process comprising actively aerating the waste stream in a second vessel 16. In an embodiment the second vessel 16 is also a foam fractionator 16 and PFAS contaminated waste (which can be foamate) is passed through the second foam fractionator 16. This produces a second waste stream 18, 20 having a second PFAS concentration. Also produced is a second cleaned water stream (not shown). In an embodiment, the cleaned water stream (not shown) is about 95% of the total water input to the fractionator 16. The second waste stream 18, 20 can be treated, as shown in FIG. 1 by arrow 20, by passing it to third vessel 22. The third vessel 22 can be a foam fractionator 22. There can be waste 27 generated from the third foam fractionator 22. The clean water 24 from foam fractionator 22 can be passed to storage tank 26. Alternatively, the second waste stream shown at arrow 18 can by-pass this third treatment and instead be collected at vessel 28. In this embodiment, the waste stream 27 from the third foam fractionator 22 can be combined with the waste stream 18 from the second foam fractionator 16. The two waste streams 18, 27 can be collected at vessel 28 before being subject to further processing. In FIG. 1, the further processing is solar drying 30, to further concentrate the PFAS (a third PFAS concentration) in the waste stream 32, and to generate a third water stream 31. In an embodiment, the waste stream from vessel 28 is circulated through the solar drying 30 multiple times until salt concentration is maximised without compromising flow. The number of recirculation passes within vessel 30 depends on solar radiation rates specific to the location, flow volume relative to scale of solar drying 30 and contaminant levels in waste stream from vessel 28. The first 14, second 24 and third water streams 31 are collected into vessel 26. This treated PFAS free water can be discharged or subject to further treatment. The treated wastewater 32 from the solar drying 30 can be passed on to a further drying bed 34. The cost effectiveness of this process depends critically on the volume of the contaminated waste stream 36 that has to be shipped to a treatment plant for safe disposal or destruction. In an embodiment, starting with 100,000 litres of wastewater for treatment, the result can be as low as 65 kg of dewatered contaminated solid.

[0143] In FIG. 6 there is shown an above ground method of dewatering contaminated waste comprising PFAS and other co-contaminants (first group of contaminants). It also shows an above ground method for generating a highly PFAS concentrated waste stream. [0144] Step 1. A liquid waste stream is pumped to aerated separator 1 at a rate that enables a minimum retention time of 15 mins in the separator. [0145] Step 2. Air is introduced through the bottom of aerated separator 1 at a rate that provides the desired foam, velocity, residence time. [0146] Step 3. Foam is extracted from aerated separator 1 and flows to further aerated separator 2 at a rate to enable minimum retention time of 15 mins in the separator. [0147] Step 4. Liquid stream flows under influence of gravity to a further aerated separator 2 at a rate that enables a minimum retention time of 15 mins in the separator. [0148] Step 5. Air is introduced through the bottom of aerated separator 2 at a rate that provides the desired foam, velocity, residence time. [0149] Step 6. Foam is extracted from aerated separator 2 and flows to aerated separator 3 at a rate that enables a minimum retention time of 15 mins in the separator. [0150] Step 7. Liquid stream flows under influence of gravity to aerated separator 3 at a rate that enables a minimum retention time of 15 mins. [0151] Step 8. Air is introduced through the bottom of aerated separator 3 at a rate that provides the desired foam, velocity, residence time. [0152] Step 9. Foam is extracted from aerated separator 3 and flows to aerated separator 4 at a rate that enables minimum retention time of 15 mins in the separator. [0153] Step 10. PFAS treated liquid stream flows to holding tank for additional processing. [0154] Step 11. Air is introduced through bottom of aerated separator 4 at a rate that provides the desired foam, velocity, residence time. [0155] Step 12. Foam extracted from aerated separator 3 and flows to concentrate tank. [0156] Step 13. Treated liquid stream from aerated separator 3 moves to holding tank for additional processing of co-contaminants. [0157] Step 14. PFAS Concentrated foam is recirculated around the enclosed solar distillation unit. [0158] Step 15. Distillate from solar separation returns to treated liquid. [0159] Step 16. Treated liquid from holding tank to SBR. [0160] Step 17. Concentrate stream from enclosed solar distillation sent to covered drying bed. [0161] Step 18. Regulated Waste Disposal of solid. [0162] Step 19. Treated liquid transferred from holding tank to MBBR. [0163] Step 20. Treated liquid from MBBR sent to DAF for issue to Wetland and discharge/reuse.

[0164] In summary, FIG. 6 shows an above ground low energy method of dewatering waste contaminated with at least a first group of contaminants and PFAS, the method comprising the steps of: [0165] (a) removing the PFAS before removing the first group of contaminants (steps 1 to 15); [0166] (b) removing the first group of contaminants (steps 16 to 20).

[0167] In step (a) the removal of PFAS is undertaken by actively aerating the contaminated waste comprising PFAS in a first vessel (1) to produce a waste stream (3) comprising a concentration of PFAS and a first liquid stream (4) having at least some of the first group of contaminants. The waste stream is then subject to a second process comprising actively aerating the waste stream in a second vessel (2) to further concentrate the PFAS in a second waste stream (6), and also to generate a second liquid stream (7) having at least some of the first group of contaminants. The second waste stream is then subject to a further process comprising actively aerating the waste stream in a third (3) vessel to further concentrate the PFAS in a third waste stream (9), and also to generate a third liquid stream (10) having at least some of the first group of contaminants. The waste streams are subject to a fourth process comprising actively aerating the waste stream in a vessel (4) to further concentrate the PFAS in a fourth waste stream (12), and also to generate a fourth liquid stream (13) having at least some of the first group of contaminants. The liquid streams 4, 7, 10, 13 can be combined prior to treatment in step (b). The waste can also be subject to solar distillation. In step (b), the removal of at least some of the first group of contaminants can be undertaken. This can be undertaken by a different processing entity is desired. In which case, the liquid in the batching tank would be transferred to the location for further treatment. Alternatively, the further treatment is undertaken by the same entity on site.

[0168] FIG. 2 is a schematic showing the progressive volume reduction of the waste through the low energy process. In the first vessel, the foamate 12 is of a large volume. However, following treatment in the second vessel 16, the volume of the waste 20 is reduced. Following treatment in the third vessel 22 the volume of the waste 27 is further reduced. The further process 30 can further reduce the volume 32. An additional process 34 can further reduce the volume 36. The result is an amount of PFAS contaminated waste that is small and relatively easy and cost effective to carry by transport (e.g. truck) and destroy.

[0169] Approaches to the destruction of PFAS include high temperature incineration, plasma arc pyrolysis, thermal desorption, and cement kiln combustion. An alternative to destruction is disposal of concentrated PFAS liquid or sludge in non-biodegradable packaging at landfill. In most cases there is an economic imperative to reduce the volume of the treated waste stream containing PFAS since (a) transport of this waste stream can be expensive and proportional to the total volume of waste to be transported, and or (b) treatment costs are typically proportional to the total volume of waste to be treated.

[0170] The primary treatment technology includes: [0171] (1) A means for injecting air bubbles into a sample of contaminated water in the fractionators 10, 16 and or 22. This requires an air pump and pipe, with a specially modified element at the exit that create air bubbles of a specific size and size distribution. Typically, this element is an air diffuser—a fine pore membrane or filter element, typically with pores >25 microns and up to 100 microns, made from ceramic, polymeric of metallic materials. [0172] (2) After the bubbles so formed have risen through the water, attracting PFAS molecules, and formed foam at the surface, there is a means to remove and capture the foam. This can be via an air blower, a vacuum suction system, a physical scraping arm, gravity or other means. The foam can be captured in a separate tank. [0173] (3) Following this process optionally there can be a means to “break” the foam in order to reduce the volume and form the so-called “foamate”. Foam breaking can happen naturally by storage and settling, or it can be achieved by chemical or mechanical means. Chemical defoaming methods involve the use of an antifoam agent, typically silica based, which work by reducing the stability of the thin liquid films (lamellae) within the foam structure. Mechanical foam breakers, including turbine, vaned disk and paddle blades, destroy foam by inducing rapid pressure change and applying shear and compressive forces to the foam leading to bubble rupture. Ultrasound can be used as a mechanical foam breaking method. [0174] (4) Further reduction of foamate volume can be achieved by drying of the foamate to remove water. Drying can be achieved by solar evaporation or by one of many means of thermal evaporation with added energy (e.g. IR drying, convective drying, and others). [0175] (5) When passing to a next foam fractionate stage, the feed can be (optionally) mixed with a small volume of water in the next treatment step, and the treatment steps 1-4 described above can be repeated on this stream input, thus forming a further foamate. In some instances, the further foamate has a much higher concentration of PFAS, with all the attendant economic benefits of doing so.

[0176] The method incorporates these elements: [0177] 1. Introducing air bubbles into a PFAS contaminated water sample. [0178] 2. Collecting the PFAS concentrated foam from the surface of the contaminated water sample. [0179] 3. Optionally dewatering the foam to create a foamate. [0180] 4. Optionally transporting the foamate for destruction or disposal. [0181] 5. Preferentially, the foamate is treated in further processes.

[0182] FIG. 3 is a graph showing the PFAS concentration reduction over time.

[0183] The apparatus has a number of key elements. First is the choice of an above ground treatment, which differs from an in-situ treatment. In the in-situ treatment, PFAS contaminated water is contained in a bore or a well or a leachate pond, a clarifier, or tailings dam, or similar. The air pipe is introduced into the bottom of this water containment vessel, and the foam fractionation process takes place in-situ. The foam is removed, preferably with a suction pipe for further treatment. Typically, if a whole dam or pond of contaminated water is being treated by these means, a method for stirring the water or creating circulation is required to ensure that the all the pollutants in the water have residence time near the source of air bubbles. After a period of time from commencement of treatment, the overall concentration of PFAS in a pond, well or dam will have been reduced below a required level and the process can be halted. In essence this can be considered as a batch process.

[0184] An alternative to in-situ treatment is provided herein. The above ground treatment is undertaken in a specially constructed foam fractionation vessel, typically a tank that is brought to site, which is designed especially for the purpose of foam fractionation. Such a tank includes air diffusers and foam collection technology. Input water from a contaminated source can be continuously injected into the tank whilst an equivalent amount of treated water is extracted; the overall level of water in the tank remains constant as does the concentration of PFAS in steady state. The benefit of such a tank based system is that the foam fractionation can be operated at the most efficient rate meaning that, for the treatment of a fixed volume of contaminated water, less time is required at site compared to the in-situ treatment option. A second and optionally third and fourth specially constructed foam fractionation vessel can be used for the purposes of concentrating the foamate in a secondary waste stream process, and so on; the subsequent foam fractionation vessel can have a smaller volume than the first one.

Experimental Data

[0185] The following experiments are exemplary only and are intended to illustrate embodiments of the invention.

[0186] A total of 31 samples of leachate were collected from a wastewater in the form of leachate. Of the 31 samples collected, a significant deviation in feed concentration was identified. Surprisingly, this deviation was significantly larger than that reflected in the bench scale trials or identified in the routine sampling that had previously been undertaken at the site and would require additional steps and testing to enable continuous treatment performance without introducing significant amounts of heat or energy requirements. On one day of operation the inlet concentration of PFOS to the plant ranged from 0.8 ug/L to 2.7 ug/L. A variation of 1.37 ug/L which is equivalent to 10× the 95% guideline limit specified in the NEMP. Variations were also noted in PFOA with concentration ranging from 0.45 ug/L to 7.30 ug/L. Sum PFAS concentrations were in the range of 13 ug/L to 26.9 ug/L (Tables in FIG. 4).

[0187] Subsequently additional testing has been undertaken on foam treatment, liquid concentrations and the ability to treat PFAS in the presence of co-contaminants, most notably ammonia and TOC.

[0188] PFAS in the raw stream has already been discussed above. Concentration in the first pass foam (treated with one stage of active aeration) has been found to be in the range of 0.77 ug/L to 90.80 ug/L PFOS, 3.38 ug/L to 135 ug/L PFOA and 20.2 ug/L to 397 ug/L sum PFAS. Additional concentrations steps of foam produced more consistent yields in concentration with PFOS concentrations of 72.1 ug/L to 342 ug/L PFOS. 60.2 ug/L to 156 ug/L of PFOA and 232 ug/L to 848 ug/L of sum PFAS. Indicating a concentration step of PFOS, PFOA and other PFAS of 98%, 98% and 97% between maximums, respectively.

[0189] In solar drying applications TDS has been observed to increase from 9,510 mg/L to 182,000 mg/L with a concentration of sum PFAS in the same batch of the order of 91%.

[0190] Co-contaminant concentrations have been found to be within the same order of magnitude as those typically seen at the inlet most notably TOC concentrations and ammonia concentrations in Foamate. This observation has been noted at trials undertaken on liquids from 3 separate leachate sites: [0191] Site 1: Inlet concentration 402 mg/L TOC, 387 mg/L following active aeration. PFOS 7.5 ug/L, PFOA 2.81 ug/L. Following active aeration PFOS<0.10 ug/L, PFOA 0.22 ug/L. [0192] Site 2: Inlet range ammonia 544 mg/L outlet ammonia 540 mg/L ammonia through first pass configuration with starting PFOS concentration of 0.178 ug/L and outlet concentration of <0.002 ug/L and PFOA of 0.433 ug/L and outlet concentration of 0.003 ug/L. [0193] Site 3: Inlet median of TOC of 1220 mg/L, foamate concentration on testing of 1100 mg/L following active aeration. PFOS of 0.34 ug/L at the inlet and <0.1 ug/L following treatment and PFOA of starting concentration of 1.17 ug/L at the inlet and <0.010 ug/L following treatment.

[0194] Surprisingly, in liquid sourced from one landfill, a reduction of nearly 50% Total Kjeldahl Nitrogen was identified in the feed liquid concentrated to the foam in conjunction with PFAS removal. From 950 mg/L to 410 mg/L, 457 mg/L and 453 mg/L across three separate tests.

[0195] It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

[0196] In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

[0197] Any promises made in the present description should be understood to relate to some embodiments of the invention, and are not intended to be promises made about the invention as a whole. Where there are promises that are deemed to apply to all embodiments of the invention, the applicant/patentee reserves the right to later delete them from the description and does not rely on these promises for the acceptance or subsequent grant of a patent in any country.