Removal of per- and polyfluoroalkyl substances(PFAS) from contaminated leachate usingaeration foam fractionation
Sammanfattning: Leachate from landfills is contaminated in many ways and per- and polyfluoroalkyl substances (PFAS)-contamination is one of them. Recent studies have demonstrated the environmental and human concerns of PFAS. Therefore, the treatment of leachate is important. One technique to reduce the PFAS concentration is by using aeration and foam fractionation. Hovgården is a landfill northeast of Uppsala, where previous measurements have shown high levels of PFAS in the leachate. Earlier small-scale experiments using aeration foam fractionation as a treatment technique for PFAS removal have been done successfully, but with upcoming requirements of PFAS concentrations there is a need to investigate whether an upscaling is possible or not. In this study, this has been investigated by pumping PFAS contaminated leachate from the landfill in to a 0.046 square metre plastic cylinder and aerated the leachate with an airflow of ten L min-1. A total of six experiments were conducted were the contact time and fraction of extracted foam was parameters that was varying. Four experiments were done with a contact time of ten min and foam fraction of five, ten, twenty and thirty percent and two experiments were made with a foam fraction of five percent and a contact time of twenty respectively thirty min. The average ΣPFAS removal, i.e., the percentage difference in ΣPFAS concentrations between the influent and effluent water in the different runs varied between 31 % and 66 %. The removal of long chained PFAS (≥C6) was higher than the removal of short chained PFAS(≤C5) even if all experiments did reduce the PFAS concentration. Carbon chains with a functional group containing a carboxylic acid is called perfluorocarboxylic acids (PFCA) and with a functional group containing a sulfonic acid is called perfluoroalkane sulfonic acids (PFSA). Precursors are PFAS that after a reaction degrades into PFCA and PFSA. The average removal efficiency of PFCA were 48 %, of PFSA 59 % and of precursors 78 %. The highest removal efficiency was discovered in the experiment with a 30-min contact time and five percent foam fraction with an average ΣPFAS removal of 58 % and an average Σlong chained PFAS removal of 92 %. The lowest removal efficiency was discovered in the experiment with a 10-min contact time and 20 percent foam fraction with an average ΣPFAS removal of 41 % and an average Σlong chained PFAS removal of 67 %. In conclusion a connection between increased contact time and increased removal efficiency was discovered but no clear connections between foam fraction and removal efficiency were found. However, it cannot be stated beyond reasonable doubt that the contact time is the decisive factor. Another conclusion is that the enrichment of short chained PFAS are higher in the water and a higher enrichment of long chained PFAS in the foam. In general, a higher inlet concentration of PFAS in the influent water resulted in a higher removal efficiency.
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