PFAS Membrane Concentration and UV Photolysis Under Nitrate Interference
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Solution Overview
Problem
Existing methods for destroying PFASs are inefficient, energy-intensive, and prone to interference from other chemical species, particularly nitrates, which scavenge solvated electrons and reduce the effectiveness of UV photolysis.
Innovation Solution
A method involving pretreatment of PFAS-containing waste streams to remove interfering species, followed by UV photolysis using a photosensitizer and solvated electrons to break down PFASs, with optional post-treatment to recover valuable materials and minimize interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If UV photolysis is used to destroy PFASs, then PFAS destruction efficiency is improved, but nitrate interference reduces the effectiveness
Solution Approach 1:
The patent applies preliminary action by removing nitrates from the aqueous system before UV photolysis treatment. The method uses iron-based reductants to convert nitrates to nitrogen gas or ammonium ions, eliminating the interfering species that would otherwise scavenge solvated electrons and reduce PFAS destruction efficiency. This pretreatment step ensures that the subsequent UV photolysis proceeds without nitrate interference.
2Reliability
If supercritical water oxidation is used to break down PFASs, then destruction effectiveness is improved, but energy consumption increases
Solution Approach 1:
The patent applies parameter changes by operating at ambient temperature and pressure conditions rather than the extreme conditions required for supercritical water oxidation. The method uses UV photolysis with photosensitizers to generate solvated electrons that can break down PFAS molecules effectively under mild conditions, eliminating the need for high temperature (374°C) and high pressure (over 3000 psi) while maintaining destruction effectiveness.
3Reliability
If hydrothermal alkaline treatment is used to destroy PFAS compounds, then destruction capability is improved, but temperature and pressure requirements increase
Solution Approach 1:
The patent applies parameter changes by conducting the treatment at ambient temperature and pH conditions rather than the extreme conditions required for hydrothermal alkaline treatment. The method uses UV photolysis with photosensitizers to generate highly reactive solvated electrons that can destroy PFAS compounds effectively without requiring temperatures around 350°C and pressures around 2400 psi.
4Reliability
If electrochemical destruction is used for long chain PFASs, then destruction effectiveness is improved, but shorter chain PFASs are less prone to destruction
Solution Approach 1:
The patent applies universality by using UV photolysis with photosensitizers to generate solvated electrons that can destroy both long-chain and short-chain PFAS compounds with comparable effectiveness. The method does not rely on electrode surface adsorption which favors longer chains, but instead uses dissolved photo-generated electrons that can access and react with PFAS molecules of various chain lengths, making the treatment universally applicable to diverse PFAS contaminants.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enhances the efficiency and cost-effectiveness of PFAS destruction by minimizing reaction time and reagent use, while maintaining high PFAS removal rates and reducing interference from other contaminants.
Implementation Method 1
filtering water containing PFAS and nitrate through a membrane selective for PFAS to obtain a membrane reject containing PFAS and nitrate and a filtrate containing nitrate
Implementation Method 2
the selective membrane includes a reverse osmosis, forward osmosis, nanofiltration (NF), and/or ultrafiltration (UF) membrane
Implementation Method 3
irradiating the treatment solution with UV light in a photoreactor to destroy a portion of the PFAS
Implementation Method 4
UV photolysis using a photosensitizer and solvated electrons to break down PFASs
Implementation Method 5
combining the membrane reject with a photosensitizer, a sulfite salt, and a sufficient amount of base such that the treatment solution has a pH of about 10 or more
Data Source
AI summary
Methods and systems of PFAS destruction in water containing nitrate. The methods and systems include filtering water containing PFAS and nitrate through a membrane selective for PFAS to obtain a membrane reject containing PFAS and nitrate and a filtrate containing nitrate, forming a treatment solution using the membrane reject including diluting the membrane reject and combining the membrane reject with a photosensitizer, a sulfite salt, and a sufficient amount of base such that the treatment solution has a pH of about 10 or more, and irradiating the treatment solution with UV light in a photoreactor to destroy a portion of the PFAS. Before dilution, a concentration of PFAS in the membrane reject may be between about 3 times and about 20 times greater than before the filtering step. Dilution of the membrane reject may include between about a 3 and about a 20 times dilution.