Sparging regulation for destruction of PFOS and PFOA using a hydrogen-polarized vacuum ultraviolet photolysis system
The PFAS “forever chemical” problem
Perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) are two of hundreds of specific types of PFASs, or perfluoroalkyl and polyfluoroalkyl substances. These substances, nicknamed forever chemicals, are found in various industrial applications due to their excellent ability to repel both water and oil. As a result, PFASs are used in hundreds of different items, ranging from waterproof clothing, nonstick cookware, firefighter equipment, and more.
Unlike many other substances, PFASs can easily buildup in the environment since they are difficult to destroy using traditional remediation methods and are hard for natural processes to breakdown. As a result, forever chemicals present a great health risk to humans, plants, animals, and the environment and are found commonly in drinking water, food, and within homes.
Unfortunately, at even just a few parts per trillion, forever chemicals have been linked to a wide variety of human health issues. Risks from PFASs are widespread. In the US for example, almost 100 percent of Americans have already been exposed to toxic levels of these chemicals.
Some common health problems related to PFASs include:
- Low birth rates
- Severe liver and kidney issues
- Endocrine issues
- Reproductive issues
- Compromised immune system
- High cholesterol
- Increased cancer risk
New method to eliminate forever chemicals
As a result of these health risks, researchers have been working to find new strategies to mitigate human exposure to forever chemicals and to more effectively eliminate forever chemicals from the environment while manufacturers have started to limit or discontinue PFAS use in various products.
Recently, researchers at the University of California developed a novel method to destroy PFOAs and PFOSs present in water using a hydrogen-polarized vacuum ultraviolet photolysis system. By exposing the PFAS-contaminated water to a vacuum UV light at 185 nm after pre-saturating the water with 99.99% H2 for 30 min and continuously sparging with H2 throughout the reaction, it was found that up there was degradation of PFOA and PFOS up to 95% as well as defluorination up to 94%.
Flow regulation in hydrogen-polarized vacuum ultraviolet photolysis systems
In order to remove PFOA and PFOS from drinking water, hydrogen is first added to the contaminated water. After this, the water is exposed to a 185 nm vacuum UV light at a sufficient voltage and wattage while hydrogen is continuously pumped into the water. After just a few minutes to hours, the treatment is complete.
In order for this system to function properly, H2 must be accurately added to the water undergoing PFAS removal, both prior to and during the process via sparging. Additionally, nitrogen gas is used as a purge gas and pumps continuously into the lamp-housing quartz sleeves in order to reduce attenuation of the 185 nm vacuum UV light by the ambient air.
By implementing accurate and precise mass flow controllers for both the hydrogen sparging and the nitrogen purging processes, gas waste is limited, ensuring that researchers can determine a precise amount of hydrogen necessary to degrade a specific amount of PFAS using this process.
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- Repeatability ±0.1% of reading + 0.02% of full scale
- Control response times as fast as 30 ms
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- 40 g/h full scale to 100 kg/h full scale with a turndown of 2% – 100% of full scale
- NIST-traceable gas accuracy up to ±0.5% of reading or ±0.05% of full scale, whichever is greater
- Repeatability ±0.05% of reading + 0.025% of full scale
- Control response times as fast as 500 ms
- A range of serial, and industrial protocol communication options for automation using a PLC or computer