Exploring controlled hydrodynamic cavitation as a leachate treatment technology for PFAS and UVQs destruction
Investigators: Francis L. de los Reyes III & Detlef R.U. Knappe, NCSU
Start Date: 2025
Award Amount: $180,000
Project Duration: 2 years
Proposal Justification & Objectives
Landfill leachate, the liquid by-product of landfills, poses serious challenges to treatment due to the presence of recalcitrant organics, ammonia nitrogen, metals, and xenobiotics. Emerging contaminants in leachate such as per- and polyfluoroalkyl substances (PFASs) and UV quenching substances (UVQSs) are now recognized as major problems in treatment. The overall goal of the proposed research is to investigate the potential of Controlled Hydrodynamic Cavitation (CHC), as a novel and lower-cost leachate treatment approach for: (1) destruction of PFAS, and (2) improved UV transmittance after biological treatment, thereby increasing the effectiveness of UV disinfection.
The specific objectives are to:
- Quantify the removal by CHC of PFASs and UVQs in landfill leachate
- Determine the effect of cavitation intensity (cavitation number) and addition of chemicals
- on PFASs and UVQs destruction
- Develop initial guidelines for treating landfill leachate with CHC.
Description of the Research Approach and Experimental Design
We will test the effect of CHC using two systems which we designed and have already built. The lab-scale system is a pipe loop designed for initial testing of small volumes of leachate, using a 1/4-inch pipe. The pilot-scale system is a pipe loop with a variable flow pump (nominal flow of 30 gpm) and specially designed venturi, instrumented with pressure transducers. We will test 50-gal volumes of leachate and simulate different cavitation numbers (with flow and number of passes). The first phase of PFAS experiments will use ultrapure water dosed individually with PFAS species at varying levels (100, 1000, and 2000 ng/L), where destruction efficiency will be assessed using fluoride ion release. For cavitation runs (different cavitation numbers) yielding high fluoride release (>90% of F in added PFAS), more detailed quantification using LC-MS/MS and LC-QToF-MS will be performed. Promising CHC conditions will then be used in leachate experiments. PFAS levels and extractable organic fluorine (EOF) in leachate will be determined prior to CHC, and fluoride release and PFAS transformation as a result of CHC treatment will be determined. UV absorbance and transmittance (at 254 nm) will be measured before and after CHC treatment of effluent from a leachate treatment plant. In addition, fluorescence spectra and dissolved organic carbon concentrations will be determined to understand changes in dissolved organic matter concentrations and characteristics. For both PFAS and UV experiments, results will be used to estimate energy costs associated with various removal efficiencies at full scale, and to develop initial operation guidelines for treating landfill leachate with CHC.
