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Abstract


Remtech conducted pilot tests on 440,000 gallons of fire runoff water contained in twenty-two (22) frac tanks from a chemical plant fire that was extinguished with AFFF foam. Samples were collected and laboratory analysis reported by Keith Cole, Ramboll (1) and pilot tests and design specifications were prepared by Mark Ryckman, Remtech Engineers (2).  PFAS concentrations ranged from 253,649 to 13,185,500 ppt in 6 of the 22 frac tanks. Waste from all 22 tanks were equalized and treated through a pilot treatment train consisting of screening, equalization, sedimentation, aeration, sand filtration, and three-stage granular activated carbon filtration.  27.97 percent of PFAS was removed by aeration, and 99.993% percent were removed by all unit operations.  This treatment method demonstrated that both long and short chain PFAS analytes were effectively removed.  Powdered activated carbon treatment at 1,000 mg/l (self-flocculating) removed 34.5% of PFAS following 48 hours of clarification.  Correlation curves with a field COD meter were developed with laboratory data to predict PFAS concentrations approaching target PFAS treatment values to reduce expensive PFAS lab costs.


Background


Remtech developed a mobile treatment plan to treat runoff water from a chemical plant fire that had total PFAS concentrations ranging from 253,649 ppt to 13,185,500 ppt in 6 of 22 frac tanks. Household products, fragrances, sports drinks, tapes, and road-paving materials were manufactured from processed pine tree stumps into resins, rosins, waxes, and gums.  Pilot/bench-scale tests are required to properly design a full-scale wastewater treatment system.


Waste Characterization & Preparation


Initial samples were collected from six (6) of the 22 frac tanks and tested for PFAS (using EPA Method 533) and general chemistry analytes.  The results are presented in Tables 1a and 1b.  Herbicides, heavy metals, mercury, and organochlorine pesticides were also tested on the initial 6 frac tank samples. These analytes were below pretreatment requirements of the POTW and were not run on Pilot Runs 1 and 2.


EPA analytical methods employed for PFAS and General Chemistry analyses are summarized below:


     ✦ SW846 8260D GC/MS - VOCs

     ✦ Method: SW846 8081B - Organochlorine Pesticides (GC)

     ✦ Method: SW846 8151A - Herbicides (GC)

     ✦ Method: EPA 200.7 Rev 4.4 - Metals (ICP) - Total Recoverable

     ✦ Method: SM 2340B-2011 - Total Hardness (as CaCO3) by calculation

     ✦ Method: EPA 245.1-1994 R3.0 - Mercury (CVAA)

     ✦ HEM (Oil & Grease) (1664A)

     ✦ Total Suspended Solids (SM 2540D-2015)

     ✦ Chemical Oxygen Demand (SM 5220D-2011)

     ✦ TOC (SM 5310 B-2011)

     ✦ EPA Method 533 was used for testing PFAS in the first 6 frac tanks

     ✦ EPA Method 1633 was used for pilot testing. EPA recommends this method for wastewater, surface water, and groundwater


The frac tanks contained a floating layer of resins/oils, a suspension of suspended solids, and settled solids. Samples from frac tanks had highly variable pHs (ranging from 4.25 to 11.96), general chemistry analytes and PFAS concentrations suggesting that equalization was required. Results of initial testing are presented in Tables 1a & 1b.


Due to the wide variation of analyte concentrations, one-gallon samples from all 22 frac tanks were collected and an equalized composite sample was prepared for pilot testing. This resulted in significantly lower analyte concentrations.  The “Raw Equalized” sample is depicted in the “blue highlighted” portions of Tables 1a & 1b and Table 2.  The equalized pH was10.


























Treatment Method & Goals


Environmental releases from chemical fires are known to produce toxic vapor clouds, contaminated runoff from firefighting operations, partially burnt chemicals and residues, heavy resins, and fire extinguishing agents.


A pilot test was conducted to determine if this complex mixture of concentrated organics, foam, and PFAS could be pretreated for discharge to a publicly owned wastewater treatment plant with a PFAS concentration of less than 200 ppt.  The POTW would provide further treatment.


Past treatment unit operations used by Remtech on contaminated chemical plant fire runoff water included flow/concentration equalization, sedimentation, activated granular filtration, and powdered activated carbon (PAC) at self-flocculating dosages of 1,000 mg/l combined with bentonite (8). Aeration, sediment removal, and Granular Activated Carbon (GAC) filtration are established PFAS removal technologies.  Two of the preferred PFAS GACs are Calcon’s F400M and General Carbon’s 12X40PF.  General Carbon’s GAC was selected since this vendor indicated that their product outperformed Calgon’s carbon for PFAS removal.


Six (6) EPA proposed to be regulated PFAS analytes are PFOA, PFOS, PFNA, PFHxS, PFBS, HFPO-DA, and (GenX).  Two of the most toxic long chains analytes are PFOS and PFOA.  Activated carbon filtration has been reported to be more effective in removing long chain rather than short chain PFAS analytes.  Of the six proposed compounds, GenX and PFBS were the only short chain compounds reported in this matrix during initial testing.


























Treatment Goals


     ✦ Reduce concentrations down to an acceptable pretreatment goal of less than 200 ppt

     ✦ Determine if 12 x 40PF carbon is effective in removing high concentrations of long and short chain PFAS analytes

     ✦ Determine treatment efficiency of sedimentation, aeration, GAC, and PAC

     ✦ Determine if field COD test kits could be used to develop correlations to predict  trending final PFAS concentrations to reduce               the frequency and amount of expensive PFAS laboratory costs


Pilot Plant Setup


Complex organics, surfactants, and suspended solids are known to interfere with the efficacy of GAC and PAC treatment.  Complex organics with elevated COD, TOC, and suspended solids need to be removed prior to PFAS treatment.  Particulate matter needs to be removed to reduce carbon column backwashing that decreases PFAS removal efficiencies by channeling of bed media. Wastewater was first passed through a 35 mesh (50 micron) screen to remove floating and suspended scum.


Selected unit operations were screening, sedimentation, aeration, sand filtration, and three GAC columns in series. The sand utilized was Filtersil which is a high-purity monocrystalline industrial quartz sand for mixed media and pressure filters for portable, process, and wastewater filtration.  Filtersil specifications are: Grade .85, Effective Size (mm) 0.78, Uniformity Coefficient 1.47, Prior Grade designation WG#1, Approximate Screen Slot Size (inches) 0.030), bulk density 79-80 lb/cf loose, 83-85 lb/cf compacted.


Following screening, wastewater was allowed to settle in a 30-gallon poly overpack for 24 hours.  Water was pumped with an agricultural diaphragm pump (Pentair Shurflo,12-volt,1.8 gpm) into a 10-gallon covered glass reactor that was aerated for 1 hour at 6 scfh prior to running through four identical 3" x 26" cylindrical PVC vessels. Flowrates were measured with a King Liquid Flow meter (1 to 12 gph).  Flowrates were controlled with a recirculation valve.  


Water from the aeration chamber was passed through a sand filter followed by three GAC filters. Filter volumes and media charge rates are listed in Table 3.









Two GAC runs (Runs 1 and 2) were conducted at two flowrates for carbon contact times of 10 and 20 minutes.  Raw wastewater, post aeration, and samples after each filter were collected and analyzed for removal efficiencies.  The pilot plant setup is depicted in Figures 1 and 2.  Analytical results for Run1 and Run2 are presented in Tables 4,5,6 & 7).


Raw wastewater was also treated with 1,000 ppm of PAC.  PAC was mixed with air at 6 scfh for 1 hour then allowed to settle for 48 hours then tested for PFAS.  Results are depicted in Tables 8 & 9.









































































































































Discussion & Results


GAC Run 1


The first run was at a flowrate of 0.0277 gpm and a carbon contact time of 20 minutes.  Clarified wastewater was introduced into the aeration chamber.  A significant finding was that 27.97% of PFAS was removed by aeration.  Considerable foam was generated during aeration. To prevent the covered glass reactor from surcharging foam, the aeration rate was controlled at 6 scfh for 1 hour.  Excess foaming suggests that foam fractionation would be another method of PFAS removal.


The first GAC column removed all of the following short chain PFAS analytes below laboratory detection limits: PFBA, PFPeA, PFHxA, PFHpA, PFBS, PFPeS, 4:2 FTS, GenX, PFMBA, 3:3 FTCA, and PFMPA. The long-chain PFAS analytes (PFHpS, 8:2 FTS, and 5:3 FTCA) were also removed by the first GAC column.


Only PFOS remained after the 3rd GAC column.  Each GAC column removed a reduced amount of PFOS; first column - 99.84%, second column - 81.38%, and 12.58% by the 3rd column.  A final concentration of 139 ppt remained for an overall PFAS removal efficiency of 99.993% through complete treatment train.


Total removal efficiencies for VOCs were 95.05%, COD 99.56%, TOC 96.44%, Oil & Grease 92.86%, and TSS 100%.


Note that when lab COD and TOC concentrations are less than 10 mg/l, PFAS concentration approach EPA proposed treatment goals.


GAC Run 2


Run 2 was at twice the flowrate (0.0555 gpm) and a carbon contact time of 10 minutes.  This test was initiated with mixed wastewater from the 30-gallon overpack that introduced suspended solids into the aeration chamber.  This produced a higher raw wastewater concentration of PFAS due to the suspended solids - 2,647,815 ppt suggesting that 577,625 ppt were possibly due to the increased suspended solids loading.


Two analytes remained after the 3rd GAC column, PFOS at 386 ppt, and 6:2 FTS at 134 ppt.  Short chain PFAS analytes removed below detection limits by the first GAC column were PFBA, PFPeA, PFHxA, PFHpA, PFBS, PFPeS, 4:2 FTS, GenX, PFMBA, 3:3 FTCA, and PFMPA. Long chain analytes removed by the first column were PFOA, PFNA, PFDA, PFHpS, PFOSA, NEtFOSE, 5:3 FTCA, and PFDS. A final concentration of 520 ppt or only 386 ppt of the proposed regulated PFAS analytes remained for an overall

PFAS removal efficiency of 99.985%. A higher backpressure of 5 psi was observed due to the additional TSS loadings on the sand and GAC filters.


Run 2 had higher General Chemistry values across the board except for Total VOCs which were about the same: +78.93% Oil & Grease, +78.005% TSS, +15.67% COD, and +31.05% TOC, that resulted in slightly lower treatment efficiencies.  If clarified raw wastewater had been used in this test, the total raw PFAS concentration would have been 21.82% less and it is likely that similar overall treatment efficiencies to Run1 would have been achieved at twice the flowrate and half the carbon contact time (10 min).


PAC Test


Mixed raw wastewater was placed in a 10-gallon glass reactor treated with 1,000 mg/l PAC, aerated for 1 hour at 6 scfh and allowed to settle for 48 hours to see if a synergistic removal of particulate and solution phase PFAS removal could be achieved. The overall PFAS removal was 34.5% with an estimated 28% removed by aeration.   Note that the TOC and COD final clarified concentrations were approximately 30 to 90 times higher respectively than 3rd GAC effluent concentrations for the same analytes. Consequently an elevated concentration of PFAS remained in the clarified effluent.  Coagulation with alum or other polymers should be investigated to determine if PAC treatment would perform better.


Field COD Meter PFAS Correlations


PFAS concentrations in landfill leachates have significant correlations with TOC, alkalinity, ammonia, and COD (4).  Remtech set out to see if similar PFAS laboratory and field COD correlations could be established for this wastewater matrix.

Laboratory COD correlation curves with a field COD meter resulted in a R2 value of 0.9987 (Figure 3).  PFAS versus field COD meter correlations resulted in a R2 values ranging from 0.9992 to 1.0 (Figures 4 and 5). Correlations with higher COD values resulted in a lower R2 value of 0.965 (Figure 6).  Field COD meters have the potential to reduce PFAS lab costs by identifying trends that suggest required PFAS treatment efficiencies.  


The normal turnaround time for PFAS lab analysis is 15 days. Shorter turnarounds can increase unit charges by 1.5 to 2 times. For a 5-day rush turnarounds, estimated lab costs are presented below:


     • EPA PFAS Method 533 - $600/sample

     • EPA PFAS Method 1633 - $700/sample  

     • For VOC, Oil and Grease, TSS, COD, and TOC - $217.80/sample (for all 5 parameters)


Additional parameters that may need to be run for certain matrices include; pH, alkalinity, heavy metals, pesticides, herbicides, and organochlorines.


When COD & TOC values are less than 10 mg/l after GAC filtration, PFAS concentrations are typically in the range of 4 to 100 ppt. Correlation curves need to prepared for each specific waste stream.






































Treatment System Design


Carbon Column Design Criteria


Table 3 displays the mass loading, reactor volumes, and flowrates for pilot Runs 1 & 2.

Scaling up to a flowrate of 35 gallons for Run1, an estimated 2,448.10 lbs of GAC are required for each full-scale carbon filter or a total of 7,344.03 pounds for all three GAC filters.  When the flowrate was doubled in Run2, an estimated 1,745.43 lbs of GAC is required for each full-scale filter or a total of 5,236.28 lbs for all three GAC filters.


Surface loading rates for the two runs are summarized below:


     • Pilot carbon column area = ((3.14 x 9)/4)/144 in2 = 0.049 sf

     • Run 1; Surface Loading Rate = 0.0277/0.049 = 0.565 gpm/sf @ 20 min contact time

     • Run 2; Surface Loading Rate = 0.0555/0.049 = 1.133 gpm/sf @ 10 min contact time


GAC pressurized filter design criteria for much lower PFAS feed concentrations suggest surface loading rates ranging from 2 to 10 gpm/sf for treatment plant flowrates ranging from 1 - 12 MGD and empty bed contact time ranging from 10 to 20 minutes (5,6).  GAC surface loading rates for the treatment of PFAS contaminated fire runoff water for this matrix appears to be in the range of 0.56 to 1.13 gpm/sf with an untreated PFAS concentration ranging from 2 to 2.6 mg/l providing aeration and sand filtration is provided upstream.









Suitable activated carbons show incipient breakthrough for PFOS at 30,000 to 40,000 Bed Volumes (BV) and for PFOA at 20,000 to 30,000 BV. GAC absorbers are considered to be effective and feasible taking into account operational and economic factors so long as a specific throughput of at least 15,000 BV can be achieved (5).


Using 3 carbon columns that contain 2,000 lbs of carbon with dimensions of 4 ft diameter and 6 ft tall, the BV would be 7,328 gallons for each filter.  Assuming that 15,000 to 40,000 BV would result in PFAS breakthrough, then the volume of water treated prior to media changeout could be between 109,920 to 293,120 gallons.  With 450,000 gallons to be treated one to two media changeouts may be required.


Sand Filter Design


For Runs 1 & 2: 7,266.2 lbs and 5,179.8 pounds of sand are required respectively.  An aerage of  6,203 lbs of sand sected to be placed in one of the 2,000 lb carbon reactors.


Aeration Chamber Design


Using a 21,000 gallon frac tank for batch aeration for 1 hour operating at 18,000 gallons with Remtech’s Magnetic Aeration System (9), the aeration rate is calculated below:           


               • 6 scfh/60 - 0.1 cfm, volume of wastewater treated = 5 gallons (reactor volumes and sample volumes)                   

               • 0.1/5 = X/18,000 = 360 cfm.  Aeration/mixing demonstrated by Remtech 60 to120 cfm. 120 cfm selected


Vapor Off Gas Treatment Design (optional, not currently regulated)


                • 579,126 ng/l (579.13 ug/l) of PFAS removed in Run1, 1,456 ug/l VOCs removed in Run2

                • Total of 2,035 ug/l of volatiles removed from 5 gallons of wastewater

                • 394.5 lbs of volatiles need to be removed from 440,000 gallons of wastewater

                • Assume that 1 pound carbon removes 0.4 lbs of VOCs or 986.2 pounds of carbon required

                • Selected three (3) 300 lb carbon vapor absorbers operating at 150 cfm


Full-Scale MobileTreatment Train


Wastewater from the 22 frac tanks pumped from the top manholes with adjustable suction depth hoses with screened inlets by diaphragm pumps to remove raw wastewater while leaving floatable and settleable solids in each tank.  Wastewater is then pumped to a 21,000 frac tank for settling, then pumped to a another frac tank with Remtech’s Magnetic Aeration System for pulsed aeration for 1 hour at 120 scfm.  


After settling, wastewater is pumped through a mobile treatment trailer with sand and a tri-GAC filtration system at an initial flowrate of 10 gpm to verify treatment efficiency. Flowrates will be increased with demonstrated treatment efficiencies at higher flow rates.  


Field COD vs Lab correlation curves were developed to use as predictive trending final PFAS concentrations to minimize lab analytical costs.  Additional Frac holding tanks are used to hold treated water until discharge limits are verified.  Backwash media filter water is pumped to a 9,000 gallon mini-frac settling tank with clarified water directed back to the initial 21,000 gallon settling frac tank.  


Spent GAC media is removed and sent for regeneration and reuse.  Spent sand filter and solids from the initial 22 fracs is removed by vacuum trucks, dewatered, tested and disposed of at an appropriate disposal facility.


A schematic of the full-scale system is presented in Figures 7 & 8.  The estimated cost of this system for one month of operation is $450,000 plus disposal of remaining solids in frac tanks.


Summary


Remtech has demonstrated that this type of mobile treatment system is effective in removing very concentrated short and long chain PFAS analytes using a combination treatment train consisting of sedimentation, aeration, sand filtration and carbon filtration using General Carbon’s 12 x 40PF PFAS carbon.


PFAS expensive laboratory costs can be reduced by using Remtech’s proprietary trend field COD test meter by developing correlation curves between laboratory COD and PFAS data for each specific waste stream.  


This same mobile treatment process has applications for landfill leachates, wastewater, drinking water, and other more dilute PFAS waste streams. Pilot/bench scale tests are required to determine appropriate carbon mass, flowrate loadings, carbon contact times, aeration times, and sandfilter loading rates.











































References


1.  Cole, Keith, Senior Managing Consultant, Ramboll, Sample Collection and Analysis, 2023.


2.  Eurofins Environmental Testing, Savannah, GA, 2023


3.  Ryckman, Mark, Principal Engineer, Remtech Engineers, Pilot Plant Design and Full-Scale Design, 2023.


4.  Hekai Zhang, et. al, Chemosphere Relationships between Per-and Polyfluoroalkyl Substances (PFAS) and Physical-Chemical Parameters in Aqueous Landfill Samples, July, 2023


5.  Black and Veatch Project No. 409850, WITAF 56 Technical Memorandum PFAS National Cost Model Report prepared for the American Water Works Association, March 7, 2023.


6.  Newton, Jim, Introduction to PFAS D175/D175, PDHonline.com, PE Continuing Education Course, 2023


7.  USEPA, Office of Water (4303T), Office of Science and Technology Engineering and Analysis Division, Washington, DC, EPA 821-D-23-001, 4 th Draft Method 1633* Analysis of Per- and Polyfluoroalkyl Substances (PFAS) in Aqueous, Solid, Biosolids, and Tissue Samples by LC-MS/MS, July, 2023.


8.  Ryckman, M.D., EMERGENCY RESPONSE TO A MAJOR AGRICULTURAL CHEMICAL WAREHOUSE FIRE, Proceedings of the 36th, Industrial Waste Conference, Purdue University, May 12, 13, and 14, 1981.


9.  Remtech’s FracTank Mobile Magnetic Aerations System, https://www.remtech-eng.com/store-/frac-tank-magnetic-aeration-system-frac-tank-temporary-wastewater-treatment-system-.html.





Mobile Treatment of Highly Contaminated PFAS Fire Runoff Water from Chemical Plant Fire