Theme: 07. Per- and Polyfluorinated Alkyl Substances (PFAS)

Topic Area: 7q. Managing PFAS at Publicly-Owned Treatment Works (POTWs)

Formatted Title:

PFAS in RO Concentrate and Landfill Leachate: Reason for Hope

Background/Objectives:

The need to remove PFAS from aqueous solutions is expanding to include liquids that have a much more complex composition than groundwater, for example. In this context, studies have been conducted in Germany with landfill leachate from a domestic waste dump and with the concentrate of a reverse osmosis (RO) plant that treats drinking water. Such waters are characterized by high conductivities and/or elevated levels of DOC/TOC, which makes PFAS treatment difficult.

Approach/Activities:

Representative water samples from the leachate of the landfill and from the RO plant of a waterworks were subject of studies to determine whether PFAS removal is possible in the presence of a rather complex water chemistry. The technical approach for the treatment of the water consisted of the following procedure: a liquid agent which should cause precipitation was added to the water. There, this chemical generates a connection with the PFAS in the water and thus makes them accessible to filtration. By the use of filtration, the main part of the PFAS load can subsequently be removed from the respective water. In addition, it was tested whether the addition of ferric chloride can optimise the treatment step and/or the filtration process. The contaminated water was stirred with the chemicals at a set speed and for a set duration.

Results/Lessons Learned:

The following parameters characterise the leachate sample from the landfill: 134 ppm TOC, 2630 ppm Na, 3790 ppm Cl and 4.5 ppb PFAS (PFOA, PFNA, PFDA, PFHxS, PFOS). With a constant dosing rate of ferric chloride, different dosing rates of the flocculating substance were added to the water. Increasing addition rates of this substance were accompanied by an increase in the removal rate of PFAS. At 100 ppm of this substance and a dosing rate of 7 mg/l ferric chloride, 92.7 % of the specified PFAS could be removed.

The following parameters characterise the concentrate sample of the RO plant: conductivity 220 mS/cm, Ca 438 ppm, TOC 4.7 ppm and PFAS 605 ppt (PFOA, PFNA, PFDA, PFHxS, PFOS). Again, different addition rates of the flocculating substance were used. At an addition rate of 50 ppm, 92.7 % of the PFAS (5) could already be removed. Doubling the addition rate reduced the amount of dissolved PFAS (5) by 97.4%.

The results imply that this type of treatment is on the one hand not hindered by the water chemistry and on the other hand reduces the concentration of dissolved PFAS. Since the PFAS are reduced as particles (sludge) the quantity of PFAS-containing residues is low. The reduced PFAS load in the pretreated water facilitates the final cleaning (polishing) by use of GAC (granular activated carbon) and/or IX (ion exchanger resin).

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Verena Stenert