Prediction of removal of Per- and Poly-fluoroalkyl Substances (PFAS) from drinking water by nanofiltration and reverse osmosis membranes : Analysing membrane flux variation over time and their ion removal efficiency

Abstract

Per- and Poly-fluoroalkyl substances (PFAS) are persistent environmental contaminants with significant health risks due to their resistance to natural degradation and potential adverse effects on human health. This study aims to evaluate the effectiveness of 8 commercial nano-filtration (NF) and reverse osmosis (RO) membranes in treating PFAS-contaminated drinking water. The objective was to assess the removal efficiency of total organic carbon (TOC), and various ions using a lab-scale membrane unit and thereby predict the PFAS removal of the membranes. The membranes were evaluated for their performance in terms of flux rates, ion rejections, and PFAS removal rate. The water quality was analysed before and after treat-ment to determine the efficiency of each membrane. Key operational parameters, such as transmembrane pressure and crossflow velocity, and their impacts on membrane flux, foul-ing, and cleaning efficiency were also examined. The study observed that the NF membranes exhibited increased flux over time, whereas the RO membranes experienced a significant decrease in flux, however, the ion removal efficiency was greater for the RO membranes, owing to their denser structure. Lastly, PFAS rejection rates of these membranes were predicted based on previous studies. In summary, NF and RO membranes were both effective in re-moving PFAS from drinking water, but each had specific operational and cleaning considerations. Future research should focus on addressing membrane fouling, optimising operational conditions, and integrating advanced treatment technologies to enhance PFAS removal efficiency for full-scale water treatment applications.

Popular Abstract

There are some harmful chemicals in the environment that pose significant health risks. These chemicals are called PFAS. Like many things, PFAS can end up in water and if that water is used as a drinking water source, PFAS can enter the human body and cause potential health issues including cancer and other chronic diseases. Therefore, it is important to ensure the safety of drinking water. To do this, water needs to be treated before using it for drinking purposes. Besides PFAS, there can be other harmful substances and minerals in the water that make it unsafe to drink. One way to treat water is through filtration, which helps separate the dirt or contaminants from the water.
Filtration can be considered as a filter paper that is used to make coffee, which separates the coffee grounds from the water. In water filtration, the water passes through membranes (similar to filter paper) that hold back the contaminants or dirt present/mixed in the water. There are different types of filter papers (membranes), and this study evaluated eight different water filter papers, known as nanofiltration (NF) and reverse osmosis (RO), to see how well they can remove the other contaminants from drinking water and thereby predict their effectiveness in removing PFAS.
Using a laboratory setup, the membranes were tested to measure their performance in terms of water flow and their ability to separate contaminants. The water quality was tested before and after filtration to determine how effective the filtration process was with the two different types of filter papers (membrane) used. It was found that NF membranes allowed more water to flow through over time because they have larger openings, similar to a coffee filter with bigger holes. The opposite was seen in the case of RO membranes because they have tighter openings, like a coffee filter with smaller holes. Because RO membranes have small-er openings, they were better at stopping contaminants from passing through, making the treated water much cleaner than water treated with NF membranes. However, one of the NF membranes also performed well at removing contaminants. As both NF and RO membranes were able to remove many contaminants, they are expected to be good at removing PFAS as well.
However, one limitation is that these membranes can get clogged over time. This is like filter paper getting dirty and jammed, making it harder for water to pass through. RO membranes usually have more of this problem because their openings are smaller, but this clog-ging behavior was not evident in this study. Membranes have another limitation; again, con-sidering coffee filters, once coffee is ready, the coffee grains left on the paper are thrown afterwards in the waste, they cannot be broken down into smaller particles. Similarly, mem-brane filtration cannot break down the contaminants present in water and are released as waste which eventually ends up in the environment.
Therefore, future research should focus on finding ways to minimize clogging and integrating new technologies with NF and RO membranes to break down these contaminants and make the treatment technologies even more effective.

• author: Kakati, Suneeta
• supervisor: Frank Lipnizki; Tobias Hey
• organization: Chemical Engineering (M.Sc.Eng.)
• course: VVAM01 20241
• year: 2024
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Nanofiltration, Reverse Osmosis, Membrane flux, Ion removal, PFAS, Water and Environmental Engineering
• language: English
• id: 9162636
• date added to LUP: 2024-06-13 15:34:17
• date last changed: 2024-06-13 15:34:17