REMOVAL OF PFAS FROM WASTEWATER THROUGH ADSORPTION AND SORBENT INCINERATION

Sammanfattning: Per- and polyfluoroalkyl substances, PFAS, are a manufactured group of chemicals that have been found to be toxic to humans and the environment. Exposure to PFAS may include birth defects for infants as well as an increased risk of cancer.  Due to PFAS exceptional traits of repelling water and oil, it has commonly been used in products such as cleaning agents, clothing, and coating for furniture. Thus, PFAS reaches the environment through deposition on landfills containing residual as well as industrial waste. Another main source of contamination is aqueous firefighting foam (AFFF) which has led to areas where military and firefighters have been practicing commonly having a high concentration of PFAS in the soil and surrounding environment. PFAS has also been found to accumulate in wastewater treatment plants. It’s partly due to its water repelling traits that PFAS has been spread efficiently over the world and has been detected in remote areas, such as Greenland. Moreover, they are persistent as they don’t naturally degrade, which has led to them being referred to as “forever chemicals”.   As of today, the main products for adsorption of PFAS are activated carbon as well as ion exchange resins, with activated carbon being the most common. The drawbacks with activated carbons are that even though they have high adsorption capacity they are non-selective, meaning that it adsorbs many other particles as well as PFAS. They are also not very effective on short-chained PFAS. Ion exchange resins are considered more selective as well as better at adsorbing short-chain PFAS. Both active carbon and ion exchange resins are expensive and require regeneration, which can only be performed so many times before they have to be disposed of.  The objectives of this master thesis were to test three adsorbents for PFAS, study incineration of PFAS in an environment similar to Swedish incineration plants as well as perform a cost analysis that ranges from production to management of ashes. The adsorbents tested are called Granular peat (float adsorb), Iron peat, and PEI-GTMAC-Pinebark (PG-PB). A batch test was performed with wastewater containing 25 mg/L PFAS on L/S 10 and 100 for the granular peat and iron peat and on L/S 100 and 1 000 for PG-PB. After the batch test, the adsorbents were incinerated at 850°C and 1 100°C, and a TGA analysis was performed in order to detect if fluorine was released during the incineration of the adsorbents.  The adsorbents tested adsorbed considerably less PFAS than the commercially available activated carbon and ion exchange resins. Of the tested adsorbents, PG-PB was the most effective adsorbent followed by iron peat, which adsorbed around half the amount of PFAS compared to PG-PB. Peat adsorbed the least amount, which was around one-third of PG-PB. Metal analysis of the wastewater showed that it contained a considerable amount of sulfur as well as sodium among other metals. As PG-PB has previously been used as an adsorbent for sulfate, the low adsorption capacity for PFAS may be due to competition with other cations for adsorption surface on the adsorbents. However, the concentration of sulfur did not change after the batch test with adsorbents, which means that the reason for the low adsorption capacity is not that sulfur occupies the surface of the adsorbents. Other metals, especially the cations, might have an impact and did change during the batch test with the adsorbents, but due to not enough data, no conclusion could be drawn. During incineration of peat, 42.6 g/kg ash was produced at 850°C and 53.3 g/kg ashes were produced while incinerated at 1100°C. Meanwhile, iron peat produces slightly more ashes with 65 g/kg ashes produced at 850°C and 63.8 g/kg ash produced during incineration at 1100°C. Pine bark was estimated to produce around 7.4 kg/g of ashes based on available literature. No PFAS was detected in the ashes. The gas composition from the TGA suggests that PFAS are emitted as flue gas with water during heating of the adsorbent. However, as incineration plants in Sweden are preheated, no conclusion of the destruction/volatile escapee of PFAS in a real incineration plant can be drawn due to different conditions.