Published 2021-03-11This post is also available in Swedish
Mistra TerraClean: PFAS removal from drinking water
With a new technology developed in the Mistra TerraClean research programme, more than 90 per cent of per- and polyfluoroalkyl substances are removed. The method is now being tested on a larger scale at Hammarby Sjöstadsverk.
‘Per- and polyfluoroalkyl substances’ (PFASs) is a collective term for a group of industrially produced chemicals. High levels of these contaminants have previously been found in drinking water and water catchments in Sweden. In the long term, drinking water with high PFAS levels is suspected of increasing the risk of adverse health effects, according to the Swedish Food Agency. Mistra TerraClean — which is working to develop smart, safe materials and technologies that remove contaminants in air, water and soil — has come up with a technique that, in laboratory experiments, removed over 90 per cent of PFAS from water. The study was carried out jointly with RISE – Research Institutes of Sweden and IVL Swedish Environmental Research Institute. This technology is now undergoing large-scale testing in a pilot plant at Hammarby Sjöstadsverk (a municipal wastewater treatment plant in south Stockholm and also Sweden’s leading R&D and demonstration facility in water treatment technology) to see whether it works for large volumes of water over a long period. Chemical composition, levels and the toxicity of the contaminants created during capture are also being investigated.
Joydeep Dutta, Professor of Materials and Nanophysics at KTH Royal Institute of Technology, Stockholm, developed the technique based on capacitive deionization (CDI) technology. Initially used for desalination, it has now also proved to be effective for capturing PFASs. The pilot tests at Hammarby Sjöstadsverk are being carried out jointly with Stockholm Water Technology, a company founded by Dutta in 2018. ‘The technology is based on pipes made of a flexible activated-carbon material that’s rolled up like cigars, and so acts like conductive electrodes to capture the PFAS contaminants. The water flows through the pipes, and low voltage is applied to the electrodes that capture the PFAS molecules. When the electricity is turned off, the molecules are released, and can then be collected in a high concentration in the reject tank.’ He says that the lab experiments have shown good results, but that it is now a matter of relearning the process on a larger scale, with much larger volumes and different water pressure, to create a well-functioning and energy-efficient process.
Aiming well below the intervention threshold
Andriy Malovanyy, IVL Project Leader, says that in the pilot experiments they add PFASs to the water to obtain the same total concentration and the same levels of specific PFASs as in Uppsala’s raw water. Altogether, its concentration in the incoming water is 150 ng/l (nanograms per litre). ‘In some places in Sweden, the concentrations are even higher — up to several thousand ng/l. The intervention level for total PFAS is 90 ng/l, so the goal is to get far below that, but at the same time not produce degradation products. Both degradation and concentration are tested. IVL and RISE analyse purification from a life-cycle perspective and investigate which substances are formed on capture. If the main line of investigation becomes concentration, then of course we’ll look at what we do with the concentrate and whether it’s a viable solution.’ According to Dutta, there are problems with PFASs in drinking water in other countries too. The hope is that CDI technology will both generate a solution for removing PFASs from water and a water purification solution that can work to create drinking water from salt water and remove other contaminants from water. The testing at Hammarby Sjöstadsverk will continue until the end of September.
The work within Mistra TerraClean has now been awarded the VA Prize 2021, an annual award from the industry initiative VA-Fakta, which every year goes to municipalities, companies, research or individuals who make contributions to the water issue in Sweden.