Research can help waterworks manage PFAS
New limits for PFAS in drinking water is a concern for many waterworks. A doctoral thesis from the University of Gothenburg provides valuable insights into how PFAS can be removed safely.
At the turn of the year, the limit for PFAS concentrations in drinking water was lowered significantly in Sweden. It is now 4 nanograms per litre for four substances, compared with the previous limit of 90 ng/l for eleven PFAS substances. The new limit is equivalent to the salt concentration produced by half a grain of salt in a 50-metre swimming pool.
PFAS have been spreading through our environment since the start of their production in the 1950s. Stricter limits for drinking water mean that removing these ‘forever chemicals’ is now an issue for many water treatment plants in Sweden, not just those near an airport or another major source of emissions.
Artificially recharged groundwater
“Much of the previous research on PFAS has been carried out at heavily contaminated sites. My research instead focuses on the very low concentrations commonly found in the environment, since these sites now become relevant with the stricter drinking water regulations,” says Tabea Mumberg, doctoral student at the Department of Earth Sciences at the University of Gothenburg.
There are various ways of producing drinking water. Since Sweden has rather small groundwater volumes, around 25 per cent of Sweden’s drinking water is produced by filtering surface water from lakes or rivers through a bed of sand, allowing it to percolate down into groundwater systems. The method improves the water’s odour, taste and colour and ensures a supply of groundwater, which is then pumped to water treatment plants for further treatment.
Tabea Mumberg’s thesis investigates how this artificial filtration of surface water affects PFAS concentrations in the groundwater.
Several factors
“My research shows that some PFAS substances move rapidly down into the groundwater, almost as quickly as the water itself, while other PFAS substances can be temporarily retained. However, they can later be released, for example when groundwater levels change or operation of the infiltration system is interrupted,” says Tabea Mumberg.
Her thesis shows that PFAS concentrations entering groundwater systems depend not only on the chemical properties of the substances, but also on groundwater flow, the location of local PFAS sources and how the water treatment plant operates the system.
“Increasingly strict limits mean that low PFAS concentrations are relevant to most drinking water producers, but the presence of PFAS does not necessarily pose an immediate health risk. Completely removing PFAS also involves other risks and costs. Activated carbon, for example, can be used in the treatment process, but generate waste streams that are expensive to handle and releases greenhouse gases when incinerated,” says Tabea Mumberg.
Optimising infiltration
Her research findings show that water treatment plants can monitor the presence of PFAS in the used surface waters and adjust the operation of their infiltration systems accordingly to reduce the amount of PFAS reaching the groundwater. Tabea Mumberg has also investigated different methods for reducing the amount of PFAS before the water is infiltrated, as well as how the infiltration bed could be optimised to capture and retain more PFAS.
“Instead of relying solely on costly treatment after contamination has occurred, my research can help drinking water producers protect groundwater, reduce future drinking water treatment costs and create the conditions for safe drinking water production as PFAS limits become increasingly strict,” says Tabea Mumberg.
Thesis:PFAS in Managed Aquifer Recharge – Solution or hidden risk in drinking water production?
Contact info: Tabea Mumberg, doctoral student at the Department of Earth Sciences at the University of Gothenburg. Telephone: 076-618 1367, email: tabea.mumberg@gu.se
PFAS – per- and polyfluoroalkyl substances – are a group of man-made chemicals found in products ranging from frying pans to firefighting foam. PFAS do not break down in the environment and can remain in water and soil for long periods. PFAS are found in drinking water and, although concentrations are often very low, the chemicals have been linked to serious health problems such as cancer, hormonal disruption and impaired immune function.
