Rejection of Organic Micropollutants by Nanofiltration and Reverse Osmosis Membranes

  • Emmanuel Alonso

Student thesis: Master's Thesis

Abstract

Abstract: The worldwide consumption of pharmaceuticals and personal care products for healthcare purposes has resulted in the occurrence of organic micropollutants (OMPs) in freshwater and wastewater resources. These pollutants are not entirely removed by conventional water and wastewater treatment plants, leading to potential human and animal health problems. Membranes are a promising technology capable of solving this problem. This study evaluated the ability of high-pressure driven membranes such as nanofiltration (NF) and reverse osmosis (RO) to remove OMPs. A total of 13 compounds were selected so that a broad range of molecular weights and octanol-water partition coefficients (log Kow) could be studied. Three commercial thin-film-composite polyamide membranes (NF1, NF6, and RO4) were tested. Filtration experiments were conducted using a cross-flow membrane system at pH 6 8 and 10. The membranes were characterized by atomic force microscopy and scanning electron microscopy that allowed a more profound understanding of the membrane surface structures. Experimental results showed that the permeate flux of NF6 is dependent on the pH of the feed solution. An increase in the feed pH from 6 to 10 resulted in an increase on the permeate flux from 14.5 to 24 L m-2 h-1 bar-1, which caused a drop in the rejection of some OMPs by NF6. Nevertheless, for most OMPs, as pH increased to 10, rejection increased for NF1 and RO4 due to electrostatic repulsion between the negatively charged membrane surface and the ionized OMPs. It was observed that ionic hydrophobic compounds could be highly rejected (> 95%) by NF1 and RO4. The study indicated that the rejection of non-ionic hydrophilic and hydrophobic OMPs were rejected effectively by RO4 (> 90%), and the rejection was mostly dominated by size exclusion and hydrophobic interactions between the membrane and the OMPs. Furthermore, the study revealed that the properties of the compounds, the intrinsic properties of the membrane, and the operating conditions have a significant influence on the rejection of OMPs.
Date of AwardApr 2020
Original languageEnglish (US)
Awarding Institution
  • Physical Science and Engineering
SupervisorIngo Pinnau (Supervisor)

Keywords

  • Organic micropollutants
  • Membrane separation
  • Reverse osmosis
  • Nanofiltration
  • Pharmaceuticals
  • Rejection efficiency

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