Efficiencies and mechanisms of chemical cleaning agents for nanofiltration membranes used in produced wastewater desalination

Dongsheng Zhao; Liping Qiu; Jiyu Song; Junxia Liu; Zonghua Wang; Youbing Zhu; Guicai Liu

doi:10.1016/j.scitotenv.2018.10.221

Efficiencies and mechanisms of chemical cleaning agents for nanofiltration membranes used in produced wastewater desalination

Sci Total Environ. 2019 Feb 20:652:256-266. doi: 10.1016/j.scitotenv.2018.10.221. Epub 2018 Oct 17.

Authors

Dongsheng Zhao¹, Liping Qiu², Jiyu Song¹, Junxia Liu³, Zonghua Wang⁴, Youbing Zhu⁵, Guicai Liu⁶

Affiliations

¹ College of Civil Engineering and Architecture, Nanyang Normal University, Nanyang 473061, China.
² School of Civil Engineering and Architecture, University of Jinan, Jinan 250022, China.
³ School of Civil and Transportation Engineering, Guangdong University of Technology, Guangzhou 510006, China.
⁴ College of Civil Engineering and Architecture, Nanyang Normal University, Nanyang 473061, China; Key Laboratory of Ecological Security for Water Source Region of Mid-line Project of South-to-North Water Diversion of Henan Province, College of Chemistry and Pharmaceutical Engineering, Nanyang Normal University, Nanyang 473061, China.
⁵ State Key Laboratory of Pollution Control and Resources Reuse, School of Environmental Science and Engineering, Tongji University, Shanghai 200092, China.
⁶ School of Civil Engineering and Architecture, University of Jinan, Jinan 250022, China. Electronic address: cea_liugc@ujn.edu.cn.

PMID: 30366326
DOI: 10.1016/j.scitotenv.2018.10.221

Abstract

A spiral-wound nanofiltration (NF) membrane module harvested from a full-scale produced wastewater desalination plant was examined and cleaned to explore appropriate chemical cleaning protocols. Foulant identification and cleaning efficiency and mechanisms were investigated. For total foulants, the organic components, including anionic polyacrylamide (APAM) and crude oil, accounted for a weight percentage of 86.3%, while the remaining foulants constituted the inorganic fraction, including Na, Mg, Ca, Ba, Al, Fe and Si. Short-term cleaning experiments were designed to identify effective reagents that could be used for further evaluations of their cleaning efficiencies in long-term cleaning. For citric acid and ethylenediaminetetraacetic acid tetrasodium (EDTA-4Na), the long-term cleaning efficiencies were relatively slight or even negative, while said values varied with different surfactants. Dodecyltrimethylammonium chloride (DTAC) achieved the greatest flux recovery; conversely, cetyltrimethylammonium chloride (CTAC) provided insignificant, even negative effects, on flux recovery, as well as salt rejection, of the fouled NF membranes. FTIR and zeta potential analyses of the fouled membranes indicated that all the tested surfactants were identically effective in removing the foulants from the membrane surface, but their cleaning efficiencies differed. Moreover, a strong correlation between the flux ratio (S_f) and concentration of surfactant in the permeate (C_ps) was observed. Among the tested chemical reagents, DTAC yielded the highest C_ps and the greatest flux recovery, with an S_f of 2.25. Considering this correlation and the characteristics of the fouled membranes and surfactants, it is proposed that DTAC molecules penetrated the membrane pores and removed the foulants that were attached to the pore walls.

Keywords: Chemical cleaning; Membrane-pore cleaning; Nanofiltration membrane; Produced wastewater; Surfactant monomer molecules.