Grantee Research Project Results
Final Report: Electrochemical Mineralization of PFAS in lndustrial Wastewater
EPA Contract Number: 68HERD19C0015Title: Electrochemical Mineralization of PFAS in lndustrial Wastewater
Investigators: Legzdins, Colleen
Small Business: OXBYEL Technologies, Inc.
EPA Contact: Richards, April
Phase: I
Project Period: May 1, 2019 through October 31, 2019
Project Amount: $100,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2019) RFA Text | Recipients Lists
Research Category: SBIR - Water Quality , Small Business Innovation Research (SBIR)
Description:
Water resources are susceptible to contamination by PFAS release from industry. Consequently, there is a need for cost-effective, on-site pretreatment technologies for PFAS mineralization of industrial wastewaters. Electrochemical oxidation is gaining industrial acceptance because it is safe, does not require any costly or hazardous chemical reactants, is relatively insensitive to water quality, and does not produce any solid waste or by-products. However, current electrochemical methods are single batch processes with expensive electrodes, long treatment times and low energy efficiencies. The technology developed by OxByEl solves these problems by providing a low cost, continuous flow-through design that destroy PFASs in minutes as the wastewater flows through the reactor in a single pass. The OxByEl electro-oxidative process is automated, does not require chemicals, and can be easily integrated into existing treatment processes.
To demonstrate technical and economic feasibility, a low- cost laboratory prototype reactor for PFAS mineralization in a single pass through the reactor was designed and constructed. The prototype reactor was configured for scalability, manufacturability and component benchmarking. The reactor cell voltage breakdown and cell architecture performance were evaluated.
Three different anodes specific for PFAS destruction were designed and fabricated for process performance testing. For each electrode design, key process and operating parameters were studied, including electrode area, wastewater flow rate through the reactor, applied cell voltage, starting concentration of PFOA & PFOS, wastewater total dissolved solids (TDS), pH and temperature. Model wastewaters with PFOA, PFOS and TDS concentrations consistent with industrial wastewater concentrations were tested.
The destruction mechanism and formation of short-chain PFASs for a range of PFAS concentrations at different operating conditions and with different anodes was studied. Large wastewater sample volumes of ≥ 2 liters were used in the study which allowed the reactor to reach steady state for wastewater analysis. The analysis for 33 PFAS chemicals was performed by a commercial DOD accredited ELAP laboratory, following EPA Method 537 modified, with Isotope Dilution LC/MS/MS Compliant with QSM 5.1 Table B-15.
Given the presence of co-contaminants in industrial wastewater, pre-treatment train design was studied for technical feasibility and cost-effectiveness. Similarly, post-treatment PFAS polishing methods were examined as a function of discharge requirements and cost-effectiveness.
The validation of low operating and capital costs for a full-scale industrial wastewater pre-treatment system was performed. A scaled up reactor was designed using the results of performance testing with optimized process variables. To validate commercial feasibility, a cost comparison between carbon adsorption, ion exchange and recirculating batch electrochemical methods was made for pre-treatment of chrome plating wastewater.
Summary/Accomplishments (Outputs/Outcomes):
A prototype continuous electro-oxidative reactor with a scalable design and low cost, scalable electrodes successfully destroyed PFAS in a single pass through the reactor. The process operates at room temperature, can be automated, is not sensitive to incoming pH, does not require chemicals, can treat foaming PFAS and its low cost electrodes are durable.
The key operating parameters impacting reactor performance were cell voltage, current density, electrode area and wastewater flow rate through the reactor. A high voltage negatively impacts PFAS removal due to the increase in parasitic oxygen evolution on the anode which reduces the available catalytic active area for PFAS destruction. Conversely at lower voltages, the reaction rate is slow and PFAS removal requires a longer residence time in the reactor (i.e. slower flow rate) although the energy consumption is lower. At higher current density, the energy consumption is higher but the flow rate through the reactor is faster. For a range of PFOA and PFOS concentrations and operating parameters, the lowest cost anode design provided the best overall performance.
In general, a faster flow rate gave better PFOA and PFOS destruction performance. Flow rate also had the biggest impact reducing energy consumption. For a given PFAS concentration and cell voltage, a faster flow rate resulted in both higher PFAS destruction and lower energy consumption. The energy consumption values are low and cost competitive. For example, the energy cost for a metal finishing facility pre-treating 10,000 gal/day of wastewater with 10 mg/L PFAS, the cost would be $175 -350/day, depending on electricity cost. Similarly, a small job shop at 1,000 gal/day would only pay $18-35/day. Since the system is automated, the operating cost is primarily electricity so operating costs are very low for all users.
The main degradation products for PFOA are PFBA, PFPeA, PFHxA,PFHpA and for PFOS they are PFBA, PFPeA, PFHxA, PFHpA, PFOA, PFBS, PFHxS. The concentration of these short-chain species was very small for both treated and partially treated wastewaters, less than 1%. For example, 82% PFOS destruction of a 10mg/L wastewater solution in a single pass through the reactor with the low- cost anode resulted in less than 0.2% short-chain PFAS produced. The destruction process is direct mineralization of PFASs on the anode surface. With the low energy consumption and short reactor residence times achieved in this study, it would be cost-effective to use the OxByEl destruction process coupled with carbon and/or ion exchange polishing to reduce the operating costs and increase the capacity of the carbon bed and ion exchange resin.
A cost comparison with competing PFAS removal methods was performed to determine economic feasibility. Ion exchange, carbon adsorption and a low- cost recirculating batch electrochemical oxidation process pre-treating a chrome plating wastewater were compared to a scaled-up OxByEl continuous electro-oxidative process. The most cost-effective method was the OxByEl electro-oxidative process. Although carbon and Ion exchange have lower installation costs, their operating costs for media replacement are prohibitive due to their limited capacity. Both the calculated capital and operating costs of the OxByEl system are less than the batch electrochemical process.
Conclusions:
The technical and economic feasibility of the OxByEl continuous electro-oxidative process for PFAS destruction was successfully demonstrated. A prototype reactor and three PFAS specific anodes were designed and fabricated. Treatability testing for PFAS mineralization with PFOA and PFOS model wastewaters was conducted with different operating parameters. For a scalable, low cost anode design and optimized operating parameters, PFOA and PFOS were successfully destroyed in a single pass through the reactor. High destruction efficiencies resulted in small electrode areas, low energy consumption and faster flow rates/short reactor residence times. The destruction process was determined to be direct mineralization of PFASs on the anode surface. A commercial scale single-pass reactor was designed, using the results of this study, to pre-treat chrome plating wastewater. A comparison of the calculated operating and installation costs of the OxByEl process versus carbon adsorption, ion exchange and a low- cost recirculating batch electro-oxidation process was made. The OxByEl electro-oxidative system has the lowest cost of treatment, validating its commercial advantage.
Using experimental results from this study, a commercial scale single-pass reactor was designed to pre-treat chrome plating wastewater. A comparison of the operating and installation costs of the OxByEl process versus carbon adsorption, ion exchange and a low- cost recirculating batch electro-oxidation process was made. The OxByEl electro-oxidative system was the lowest cost treatment method validating its commercial advantage. Further optimization of the reactor design, electrode design and operating parameters will result in continued reduction in both operating and capital costs. A main technical advantage of the OxByEl process is its reactor and electrode scalability. For large volume of wastewater, the reactor footprint is small and big tanks required for batch processes with long residence times are not required. Other advantages are that the reactor runs at room temperature, can be automated, the process is not sensitive to incoming pH, does not require chemicals, can treat foaming PFAS and its low cost electrodes are durable.
Commercial applications of this technology include pre-treatment of industrial wastewaters; specifically; metal finishing, semiconductor, manufacturers using PFASs in their products such as paper and carpet mills, landfill leachate, storm water and highly contaminated groundwater. With the low energy consumption and short reactor residence times achieved in this study, it would also be cost-effective to use the OxByEl destruction process coupled with carbon and/or ion exchange polishing to reduce the operating costs and increase the capacity of carbon adsorption and ion exchange resin.
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.