Development of effective removal methods of PFCs (perfluorinated compounds) in water by adsorption and coagulation

Research output: ThesisDoctoral Thesis

Abstract

Perfluorinated compounds (PFCs) have been used for decades to make products that resist heat, oil, stains, grease and water. In the past, PFCs were not regulated. Common uses include nonstick cookware, stain-resistant carpets and fabrics, components of fire-fighting foam, industrial applications, coatings for packaging, such as milk cartons, cosmetic additives, and other personal products. Huge amount of PFCs have been already released in to the environment, which have been trickled down up to the glaziers in Antarctica. The chemical structure of PFCs makes them extremely resistant to breakdown in the environment. Although PFCs have been used for decades, limited studies on human health effects have been carried out. In animal studies, high concentrations PFCs have shown adverse affects on the liver and other organs. It is a reported fact by researchers that the conventional water and wastewater treatment facilities can not eliminate PFCs. Many studies have showed a positive correlation between the PFOS concentration in raw water and tap water samples suggesting minimum removal efficiency of conventional water purification systems. The main reason for the persistancy of PFCs is C-F bonds. The C-F bond length is shorter than any other carbon–halogen bonds, and shorter than the C-N and the C-O bonds.The high electro-negativity of fluorine gives the carbon–fluorine bond a significant polarity/dipole moment. The overall objective of this research was to investigate on possible techniques to eliminate PFCs in water. Since PFCs are negatively charged by its atomic structure, the stagergy was to eliminate them by adsorption process. In this experiment, seven granular materials and nine coagulants were studied in detail for PFCs eliminations. Six kind of synthetic resins and GAC were tested with a series of batch experiments for PFCs adsorption (Chapter 4). The batch experiment for kinetic and isotherm characteristics of each maretial was carried out in a shaker with 100 hrs shaking duration. Out of seven materials five were first time tested for PFCs. Faster kinetic characteristics were observed for GAC and ion exchange resins than non ion exchange resins. Considering the adsorption isotherms, synthetic resins were identified as better filter materials (in terms of adsorption capacity) to eliminate PFCs in water at a low concentration (1μg/L). The magnitude of Freundlich isotherm constants (Kf ) decreases in the following order for most of the long chain and the medium chain PFCs tested: Ion-exchange polymers > Non ion-exchange polymers > GAC, sometimes at a further low equilibrium concentration (100 ng/L) non ion-exchange polymers showed higher adsorption capacity than other adsorbents. Amb IRA- 400 was identified as the best filter material to eliminate PFOS at equilibrium concentrations of >1 g/L. Considering both adsorption isotherms and adsorption kinetics, Amb XAD 4 and Dow MarathonA were best candidate materials for eliminating PFOS at ng/L equilibrium concentrations. From the results for kinetic experiments, chemisorption was identified as the main attaching process in PFCs adsorption. The process of coagulation was studied by a series of jar tests for PFCs elimination in this research (Chapter 5). There is limited published data on PFCs coagulation, especially by organic coagulants. Six long chain cationic coagulants were tested for anionic PFCs coagulation and the results were compared with three conventional inorganic coagulants. The results of the experiments with deionized water and wastewater spiked with PFCs showed that the PFCs coagulation by organic coagulants is double than that of inorganic coagulants. Among organic coagulants FL 2749 was identified as the best candidate material to eliminate PFCs. Jar test results with actual PFCs related industrial wastewater indicated that organic coagulants are not effective (as it showed in wastewater spiked with PFCs) to coagulate PFCs. The PFCs that appear in real wastewater seems to be incorporated with other polar molecules in wastewater. Organic coagulation followed by microfiltration was identified as an effective combination to eliminate PFCs for some wastewaters, but further studies have to be done on this topic. The results of batch experiments (chapter 4 and 5) were further consolidated by the long run continuous experiments (60 days and 130 days). Non ion exchange polymers were further studied with a column experiment (Chapter 6) (60 days continuous run) and Amb XAD 4 was recognized as the best candidate among the tested four filter materials to eliminate PFOS. Amb XAD 4 removed 99.99% PFOS up to 23,000 bed volumes pass through with the condition of 10 μg/L inflow concentration and flow rate of 15 ml/min (0.75 bed volumes/min). At the end of the column test, PFOS adsorbed granular materials were used to examine the material regeneratability with an organic solvent. Within 80 min, all most 100% PFOS was recovered from synthetic resins suggesting that synthetic polymers can be effectively regenerated by an organic solvent. A long run continuous experiment (130 days) showed the combined treatment process of coagulation (by organic coagulants) followed by adsorption and filtration is an excellent method to treat PFCs in water. The combination with some adsorbents, more than 99% removal was obtained even after 100 days of continuous run. Economical analysis with different scenarios for the level of treatment and regenerations indicated that AmbXAD 4 was the cheapest option for PFOS adsorption. This experiment was limited for six synthetic resins and six long chain cationic organic coagulants. The results highly reccomend to repeat the same experiments with more adsorbants and coagulants for material optimization. The materials tested in this experiment were limited for lab scale models and the same materials to be tested in the field. As the first step a filter column with Amb XAD4 can be installed at the discharge point of a wastewater treatment plant in a PFCs related industry.
Original languageEnglish
Thesis sponsors
Place of PublicationJapan
Publisher
DOIs
Publication statusPublished - 24 Sep 2010

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