Mitigation of bidirectional solute flux in forward osmosis via membrane surface coating of zwitterion functionalized carbon nanotubes

Shiqiang Zou; Ethan D Smith; Shihong Lin; Stephen M Martin; Zhen He

doi:10.1016/j.envint.2019.104970

Mitigation of bidirectional solute flux in forward osmosis via membrane surface coating of zwitterion functionalized carbon nanotubes

Environ Int. 2019 Oct:131:104970. doi: 10.1016/j.envint.2019.104970. Epub 2019 Jul 8.

Authors

Shiqiang Zou¹, Ethan D Smith², Shihong Lin³, Stephen M Martin⁴, Zhen He⁵

Affiliations

¹ Department of Civil and Environmental Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA.
² Department of Chemical Engineering & Macromolecules Innovation Institute, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA.
³ Department of Civil and Environmental Engineering, Vanderbilt University, Nashville, TN 37235, USA.
⁴ Department of Chemical Engineering & Macromolecules Innovation Institute, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA. Electronic address: martinsm@vt.edu.
⁵ Department of Civil and Environmental Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA. Electronic address: zhenhe@vt.edu.

PMID: 31295643
DOI: 10.1016/j.envint.2019.104970

Abstract

Forward osmosis (FO) has emerged as a promising membrane technology to yield high-quality reusable water from various water sources. A key challenge to be solved is the bidirectional solute flux (BSF), including reverse solute flux (RSF) and forward solute flux (FSF). Herein, zwitterion functionalized carbon nanotubes (Z-CNTs) have been coated onto a commercial thin film composite (TFC) membrane, resulting in BSF mitigation via both electrostatic repulsion forces induced by zwitterionic functional groups and steric interactions with CNTs. At a coating density of 0.97 g m^-2, a significantly reduced specific RSF was observed for multiple draw solutes, including NaCl (55.5% reduction), NH₄H₂PO₄ (83.8%), (NH₄)₂HPO₄ (74.5%), NH₄Cl (70.8%), and NH₄HCO₃ (61.9%). When a synthetic wastewater was applied as the feed to investigate membrane rejection, FSF was notably reduced by using the coated membrane with fewer pollutants leaked to the draw solution, including NH₄⁺-N (46.3% reduction), NO₂^--N (37.0%), NO₃^--N (30.3%), K⁺ (56.1%), PO₄^3--P (100%), and Mg²⁺ (100%). When fed with real wastewater, a consistent water flux was achieved during semi-continuous operation with enhanced fouling resistance. This study is among the earliest efforts to address BSF control via membrane modification, and the results will encourage further exploration of effective strategies to reduce BSF.

Keywords: Forward osmosis; Forward solute flux; Membrane modification; Reverse solute flux; Zwitterion.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Membranes, Artificial*
Nanotubes, Carbon*
Osmosis*
Waste Disposal, Fluid / methods
Wastewater / chemistry*
Water
Water Purification / methods*

Substances

Membranes, Artificial
Nanotubes, Carbon
Waste Water
Water