Effective treatment of PFAS contaminated waste and process water using coagulation and flocculation - Implications for soil washing

Poster-presentation at the 33^rd SETAC conference, Dublin (May 2023)

High concentrations of Per- and Polyfluorinated compounds (PFAS) are found in different waste waters, like leachat waters from landfillls, in domestical and industrial wastewater and in soil washing water from soil washing facilities handling PFAS contaminated soil. Water treatment steps in these application commonly include a coagulation and flocculation step, where particles and parts of dissolved subtances are separated from the liquid phase. For an environmental sustainable use of soil washing as a remediation method the treatment and reuse of  washing water is crucial.

To evaluate the effectivness of different coagulants and flocculants 6, on the market available products, were tested for their PFAS reduction efficiency. The selection resembled typicall coagulants used in soil washing, waste and water treatment facilities (e.g metalloxides, polyacrylamides, activated carbon products) and one specially designed, biodegradable PFAS additive made from renewable raw materials. To mimic soil washing waste water, a silt-clay-water mixture, spiked with PFAS in concentrations typically found at AFFF contaminated sites was used. These sites are, due to their high PFAS soil concentrations favourable for soil washing as a remediation method.

Preliminary results show reduction efficiencies of standard flocculants rangig up to 50% for long chain PFAS and up to 30% for short chain PFAS. Maximum reduction rates for long chain PFAS can be reached by lower coagulant concentrations compared to short chain PFAS. The use of specially designed green additives in this study lead to high reduction of PFAS. Concentrations of long chain PFAS can hereby be reduced by over 98% and for short chain PFAS by over 85%.

The results of this study indicate that by choosing the right coagulant and flocculant in the wastewater treatment process, PFAS can be efficiently removed from the water phase. It should be noticed, that the change of a coagulant or flocculant can be done while operating these facilities and withouth bigger investments in additional treatment infrastructure, which makes this approach fast and easy to implement.