Destructing PFAS in Landfill Leachate by In Situ Treatment Train: Selective Adsorption and Hydrothermal Treatment

Investigators:  Yudi Wu, Florida Polytechnic University, &  Gang Chen, Florida State University 

Start Date: 2024

Award Amount: $81,555  

Project Duration: 2 years 

Proposal Justification & Objectives

Per- and polyfluoroalkyl substances (PFASs) in the landfill leachate are presently of great health concern. Its complexity hinders in-depth understanding of the management of PFASs in the landfill leachate. Because of the effectiveness and easy operation, adsorption is the commonly adopted method in removing these contaminants from the landfill leachate. However, there is an urgent need to further the adsorption process for the following three reasons: Firstly, the adsorption efficiency is significantly affected by complicated water matrix, especially dissolved organic matter (DOC) that competes with PFASs for the sorption sites. Secondly, PFAS-saturated sorbents will leachate out the adsorbed PFASs if they are deposited back to landfills, which is typically practiced. Thirdly, the sorbent dosage requirement to efficiently adsorb PFAS stream is often very high, which is not cost-effective for landfill leachate treatment.

In this proposed research, we design a treatment train to concentrate and remove PFASs through foam fractionation coupled with biosolid biochar adsorption. Foam fractionation will be adopted as the first step to beneficially concentrate the PFASs in the landfill leachate for further biochar adsorption. As a screening process, foam fractionation helps eliminate the competition of dissolved organic matter for the sorption sites on the sorbent surface by concentrating PFASs in the treatment stream, thus reducing the high dosage requirements for the biochar sorbents. To further enhance PFAS adsorption, PFAS-tailored biochar will be constructed with designated pore structures to capture various PFAS molecules, which promote enhanced PFAS affinity through surface functional groups and/or surface charges.

In our previous study, we found that biosolid biochar showed a promising capacity of PFAS adsorption due to its positive charges and unique porous structure (i.e., hierarchical porosity). Coupling foam fractionation with biochar will be achieved in two ways: 1) foam fractionation with suspended colloidal biochar injection and 2) foam fractionation and biochar columns in series. Both strategies aim to further enhance the adsorption of short-chain PFASs, where strategy one uses colloidal biochar to enhance the biochar surfaces and second strategy uses biochar column as a barrier. PFAS-saturated foamate (strategy 1) and biochar (strategy 2) will be subject to thermal treatment for PFAS destruction. Hydrothermal treatment is increasingly drawing attention because of its cost-effectiveness and potential to completely destruct various types of PFASs. It also eliminates the needs for “drying” the foamate or biochar that is required for other treatment technologies such as pyrolysis or incineration. Currently, the destruction of PFAS-saturated sorbents has not been investigated using this method. 

The objectives of this research are to enhance the adsorption of short-chain PFASs and subsequent destruction of the sorbents with adsorbed PFASs by hydrothermal treatment to break the loop of PFAS cycling in landfills.

The specific tasks include: 

• Estimation of complicated PFAS matrix in landfill leachate using Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS); 
• Investigation of the efficacy of foam fractionation in concentrating PFASs from landfill leachate, particularly short-chain PFASs; 
• Development of PFAS-tailored biochar with optimized pore design and activation to enhance PFAS adsorption, especially short-chain PFASs; 
• Examination of coupled foam fractionation with biochar in two ways: 1) foam fractionation with suspended colloidal biochar injection and 2) foam fractionation and biochar columns in series; 
• Evaluation of the potential of hydrothermal treatment as the final treatment step to destruct PFASs adsorbed onto biochar to terminate PFAS cycling, thereby achieving zero-waste PFAS remediation. 

Description of the Research Approach & Experimental Design 

The overall logic of this proposed work will include four parts: 1) PFAS characterization and quantitative analysis using FT-ICR and LC-MS/MS; 2) understanding of the dominating mechanisms of foam fractionation coupled with biochar adsorption; 3) column studies to concentrate PFAS from complex landfill leachate matrix and remove by biochar adsorption; and 4) bench-scaled investigation of PFAS destruction using hydrothermal treatment. For PFAS hydrothermal destruction, operation parameters (e.g., pressure, temperature, and alkaline dosage) that promote fully PFAS destruction will be identified. It is therefore important to estimate the mass balance of PFASs using a suite of analytical instruments, such as LC-MS/MS, 19F-NMR and IC.