Development of Smart Flocculants for the Treatment of PFAS Contaminated Water

Project Summary Per- and polyfluoroalkyl substances (PFAS) are a family of manmade congeners with dual hydro- and oleo- phobic properties, which is why they have been widely used in firefighting foams, as well as in a multitude of other products such as food packaging, paints, pesticides, and microelectronics. Given their extensive use, high water solubility, and resistance to conventional wastewater treatment methods, PFAS have been detected in public water supplies all over the country causing concern for potential toxic human health effects given their environmental persistence. Flocculation is a widely used separation technique in the removal of suspended solids from water and wastewater. However, traditional flocculants (e.g., inorganic salts and polymeric systems) form aggregate flocs that are usually loosely packed, contain a large amount of water due to their hydrophilicity and as such, require large settling tanks due to the slow process of separation that is required to collect the solids. Furthermore, they have seldom been used to remove dissolved species like PFAS. To address these issues, BAM proposes an innovative “smart” polymeric flocculant that consists of a temperature responsive compound, N-isopropylacrylamide (NIPAAm), modified with a cationic co-monomer dimethylaminoethyl acrylate (DMAEA), and a fluorinated co-monomer short chain trifluoroethyl acrylate (TFEA) and long chain dodecafluoroheptyl acrylate (DDFHA). The combination of these three components results in a polymer which can rapidly capture the dissolved PFAS molecules and form insoluble solid aggregates at temperatures above the lower critical solution temperature (LCST) The core advantages of this system include: (1) slow water retention in the sediment, (2) fast kinetics, and (3) lower energy input by shifting the aggregation temperatures closer to ambient conditions. Specific Aim 1 of the proposed project will involve development and performance evaluation of the cationic and fluorinated modified smart flocculants. More specifically, aim 1 focuses on the material development, where the cationic and fluorinated NIPAAm copolymer with varying composition and molecular weight will be synthesized and characterized. Specific Aim 2 will investigate the flocculation efficiency of the prepared materials in the removal of PFAS, such as perfluorooctanoic acid (PFOS) and perfluorooctane sulfonic acid (PFOA), from contaminated water. To study the PFAS removal efficiency, various environmental conditions (e.g., ionic strength, pH, turbidity) and process variables (e.g., polymer dosage, initial PFAS concentration) will be examined, and the performance will be evaluated through kinetics, sediment compactness, and supernatant composition. Phase I funding of this project will produce a novel smart flocculant system with enhanced solid-liquid separation performance for removing PFAS from contaminated water. When achieved, Phase II of this project will be operated to investigate the efficacy of the prepared copolymer flocculants in drinking water and wastewater.Project Narrative In this project, a “smart” flocculant system is proposed to easily remove per- and polyfluoroalkyl substances (PFAS) from drinking water and wastewater effluents, minimizing settling times and additional dewatering steps found in current flocculant technology. The novelty of the proposed flocculant is that it combines a thermoresponsive compound (N-isopropylacrylamide (NIPAAm)) with cationic and fluorinated co-monomers, dimethylaminoethyl acrylate (DMAEA), trifluoroethyl acrylate (TFEA) and dodecafluoroheptyl acrylate (DDFHA), respectively. These co-monomers provide high affinity for PFAS molecules through a variety of electrostatic interactions, which greatly accelerates the flocculation kinetics and reduces the water retention in the resulting sediment, ultimately producing innovative smart flocculants with enhanced solid-liquid separation performance for removing PFAS from contaminated water.