Recent bench scale test for remediation of Per- and polyfluorinated alkyl substances (PFAS) show promise, according to Jacobs.
Concerns over soil groundwater contamination by PFAS, which is found in fire-fighting foams and non-stick and stain-proofing materials, has grown in recent years as the risk to human and animal life has become better understood but effective remediation techniques have yet to be proven.
Jacobs has said that its emerging contaminants team has partnered with clients, academic partners and remediation vendors for more than five years to develop and test methods for treating PFAS.
According to Jacobs hydrogeologist and emerging contaminants leader Bill DiGuiseppi, PFAS have unique surfactant properties that make them repel both water and oil. “They have been used extensively in surface coatings and protective formulations for paper and cardboard packaging products, carpets, leather products and textiles, as well as industrial surfactants, emulsifiers, wetting agents, additives and coatings,” he said.
“PFAS have been found in almost all human blood samples collected worldwide. Some PFAS, such as PFOS, bioaccumulate and biomagnify in wildlife species such as fish and fish-eating birds. In animal studies, some PFAS disrupt normal endocrine activity, reduce immune function, cause adverse effects on multiple organs, including the liver and pancreas, and cause developmental problems in rodent offspring exposed in the womb. Low birthweight babies and elevated cholesterol have been linked to elevated PFAS in human blood, and health studies have linked firefighter cancers to exposure at training facilities using AFFF.”
In 2005, PFOA and PFOS were added to the list of 12 persistent organic pollutants—toxic chemicals that adversely affect human health and the environment—established at the 2001 Stockholm Convention. The following year, the EU restricted PFOS use and manufacture of products containing PFOS. That same year, the eight major US companies in the PFAS industry agreed to significantly reduce production of PFOA and associated compounds by 2010, and work toward elimination by 2015 under a voluntary agreement with the US Environmental Protection Agency.
“Because of their persistence and lack of partitioning to air, PFOS and PFOA resist most conventional treatment technologies such as direct oxidation, biodegradation, air stripping, vapor extraction and UV photolysis,” said DiGuiseppi.
“For extracted groundwater or drinking water, we have evaluated and/or successfully implemented several treatment technologies, including granular-activated carbon (GAC), anion exchange resin (AEX) and reverse osmosis (RO). We have also performed bench testing of several other treatment technologies, including oxidation and flocculation.
“With the immediate need to treat impacted drinking water, source area soils have largely been ignored, although they represent a substantial and ongoing contribution to groundwater plumes.”
In collaboration with Iron Creek Group vice president of operations Roger Richter and USACE Omaha District project geologist Michael Riggle, DiGuiseppi has published results of multiple bench-scale tests demonstrating that low temperature thermal desorption (LTTD) is a viable option for treatment of per- and polyfluoroalkyl substances in soil associated with AFFF impacts.
“The temperature optimisation studies used AFFF-impacted silty sand coastal plain soils from a US Navy installation, which included support from the US Navy LANTDIV, Battelle and SGS AXYS Analytical Services,” said DiGuiseppi. “During the three separate bench tests, temperatures of 250°C, 300°C, 350°C, 400°C, 550°C, and 700°C were evaluated at heating times ranging from 50 minutes to eight days. The testing identified 350°C as the lowest effective temperature, with 99.4 percent removal for the total of the 29 PFAS analysed within two days at 350°C, whereas only 40% total PFAS removal was observed at 300°C over a four-day duration.
“Longer heating durations did not improve removal at either temperature. Infrared heating for LTTD will be tested further during Jacobs’ on-going US Department of Defence-funded Strategic Environmental Research and Development Program (SERDP) research project aimed at using a portable unit for on-site treatment of PFAS-impacted investigation derived waste.
“A key to establishing the time-temperature relationship is that lower temperature, longer duration allows the flexibility to use not only batch thermal boxes but opens up the prospect of remediating excavated piles for larger scale soil treatment or implementing as an in-situ solution for areas where excavation is logistically difficult. Heating in situ source area soils to 35 °C is feasible and can be coupled with a soil vapor extraction system to capture the volatilised PFAS for destructive treatment.”