Grantee Research Project Results

Final Report: Pilot-Testing a Novel "Concentrate-&-Destroy" Technology for 'Green' and Cost-Effective Destruction of PFAS in Landfill Leachate

EPA Contract Number: 68HERC20C0023
Title: Pilot-Testing a Novel "Concentrate-&-Destroy" Technology for 'Green' and Cost-Effective Destruction of PFAS in Landfill Leachate
Investigators: Soong, Te-Yang
Small Business: CTI and Associates, Inc.
EPA Contact: Richards, April
Phase: I
Project Period: March 1, 2020 through August 31, 2020
Project Amount: $100,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2020) RFA Text |  Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Clean and Safe Water

Description:

Landfills serve as the final repository for most of Per- and Polyfluoroalkyl Substance (PFAS)-containing discarded materials. Significant amounts of PFAS in the waste mass have the potential to accumulate in landfills and, consequently, in leachate derived from the waste mass. Elevated concentrations of PFAS in leachate have raised concerns regarding disposal of leachate. Cost-effective treatment technologies for PFAS in leachate have been lacking due to the complex compositions and strong matrix effect of landfill leachate. Building upon a cutting-edge 'Concentrate-&-Destroy' technology (developed by our teaming partner Auburn University, US Patent pending 62/452,648), CTI conducted this small business innovation research (SBIR) Phase I project. The 'Concentrate-&-Destroy' technology is based on an innovative photo-regenerable adsorbent (Fe/TNTs@AC) synthesized by modifying low-cost activated carbon (AC) with a cutting-edge photocatalyst, iron-doped titanate nanotubes (Fe/TNTs). The technology works in a two-step process: first, Fe/TNTs@AC selectively adsorbs PFAS from leachate, which concentrates trace concentrations of PFAS in a large volume of leachate onto a small volume of the photoactive adsorbent; and second, the pre-concentrated PFAS on the material surface is degraded under ultraviolet or solar light, which also regenerates the material for multiple cycles of uses. 

The project aimed to preliminarily test the feasibility of using the 'Concentrate-&-Destroy' technology for removal and destruction of PFAS in municipal solid waste landfill leachate. A bench-scale laboratory treatability study was first conducted at Auburn University to evaluate the effectiveness of Fe/TNTs@AC for selective adsorption and photocatalytic degradation/regeneration of PFAS in landfill leachate. In addition, the effects of pH-value, material dosage, solid-to-liquid ratio, addition of hydrogen peroxide, and temperature on the photodegradation of PFAS were examined to determine the optimal operating conditions under field conditions. A preliminary pilot test was then conducted in a batch reactor at a landfill site to evaluate the performance of the proposed 'Concentrate-&-Destroy' technology in the field.

Summary/Accomplishments (Outputs/Outcomes):

The key findings from this research are summarized as follows: 1) Up to 18 PFAS were detected at concentrations varying from 5.47 to 2,260 nanograms per liter in the tested landfill leachate along with high concentrations (up to 440 milligrams per liter (mg/L)) of dissolved organic matter (DOM) and up to 10,000 mg/L of total dissolved solids (TDS); 2) Fe/TNTs@AC can selectively adsorb PFAS despite the strong matrix effect. The binary separation factor of Perfluorooctanoic acid (PFOA) to DOM was determined to be 110 based on laboratory adsorption tests; 3) When repeatedly used in three consecutive adsorption-photodegradation runs, Fe/TNTs@AC remained highly effective in the adsorption of detected PFAS except for perfluorobutanoic acid (PFBA). At a dosage of 10 grams per liter (g/L), the removal of 13 PFAS/precursors reached 95.2% (61.7%-100%) in Run No. 1 and 73.6% (7.3%-100%) in Run No. 3. While Fe/TNTs@AC nearly completely removed long-chain PFAS/precursors in three consecutive runs, it appeared less effective for some short-chain PFAS such as PFBA; 4) The catalytic photodegradation of PFAS performed well at normal pH-level (~7) and at ambient temperature; 5) Taking advantage of the 'Concentrate-&-Destroy' strategy, additional physical-chemical measures can be applied to a small volume of Fe/TNTs@AC with concentrated PFAS to further improve the efficacy of PFAS degradation. Experimental data indicated that the presence of 0.5 moles per liter (M) hydrogen peroxide greatly enhanced the photoactivity towards PFAS, and the presence of 0.2 M persulfate worked even better at an elevated temperature of 65 ℃; and 6) Preliminary pilot tests confirmed a strong adsorption of the PFAS under the field conditions. High concentrations of suspended solids or activated sludge should be removed from the leachate first to avoid interference with the recovery of the used Fe/TNTs@AC particles and the subsequent photocatalytic regeneration.

Conclusions:

The results showed that the 'Concentrate-&-Destroy' technology is promising for cost-effective removal and destruction of PFAS in landfill leachate. Fe/TNTs@AC could selectively concentrate low concentrations of PFAS from a large volume of leachate onto a small volume of the solid, and then directly degrade the PFAS on the solid surface representing a significant cost savings compared with treating the bulk leachate as commonly practiced. The photodegradation regenerates the material, allowing for reuse of the material. Further investigation is warranted to optimize material synthesis for more selective adsorption of PFAS (especially short-chain PFAS) and greater photoactivity. Taking advantage of the small volume of solid material, the photodegradation performance can be further improved by optimizing factors such as reaction chemistry, temperature, and addition of stronger photosensitizers or oxidants. Moreover, compared with batch adsorption reactors, a fixed-bed column would make much better use of the adsorption capacity.

The preliminary data from this project along with the material cost estimate revealed the potential of the proposed Concentrate-&-Destroy technology for destruction of PFAS in landfill leachate. In September 2020, Auburn University filed a full patent application for the technology. Several landfills, companies, and material manufactures have expressed interest in the technology. Given the current challenges associated with PFAS contamination, we expect that this technology will arm landfill engineers and decision makers with a cost-effective solution as relevant regulations are rapidly evolving. To this end, further pilot-scale experiments and field demonstration are warranted to acquire more optimized operating parameters and cost factors towards full scale applications.