Membrane fouling and anti-fouling strategies using RO retentate from a municipal water recycling plant as the feed for osmotic power generation.
RO retentate from a municipal water recycling plant is considered as a potential feed stream for osmotic power generation in this paper. The feasibility of using RO retentate from a municipal water recycling plant was examined from two aspects: (a) the membrane fouling propensity of RO retentate, and (b) the efficacy of anti-fouling strategies. The membranes used in this study were the inner selective thin film composite polyethersulfone (TFC/PES) hollow fiber membranes, which possessed a high water permeability and good mechanical strength. Scaling by phosphate salts was found to be one possible inorganic fouling on the innermost layer of the PES membrane, whereas silica fouling was observed to be the governing fouling on the outmost surface of the PES membrane. Two anti-fouling pretreatments, i.e., pH adjustment and anti-scalant pre-treatment for the feed stream, were studied and found to be straightforward and effective. Using RO retentate at pH 7.2 as the feed and 1 M NaCl as the draw solution, the average power density was 7.3 W/m(2) at 20 bar. The average power density increased to 12.6 W/m(2) by modifying RO retentate with an initial pH value of 5.5 using HCl and to 13.4 W/m(2) by adding 1.1 mM ethylenediaminetetraacetic acid (EDTA). Moreover, the flux recovery of the fouled membranes, without the indicated pretreatments, reached 84.9% using deionized (DI) water flushing and 95.0% using air bubbling under a high crossflow velocity of 23.3 cm/s (Re = 2497) for 30 min. After pretreatment by pH adjustment, the flux recovery increased to 94.6% by DI water flushing and 100.0% by air bubbling. After pretreatment by adding 1.1 mM EDTA into RO retentate, flux was almost fully restored by physical cleaning by DI water flushing and air bubbling. These results provide insight into developing an effective pretreatment by either pH adjustment or EDTA addition before PRO and physical cleaning methods by DI water flushing and air bubbling for membrane used in osmotic power generation.
NUS Graduate School for Integrative Sciences & Engineering (NGS), National University of Singapore, 28 Medical Drive, Singapore 117456, Singapore; Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, Singapore 117585, Singapore.
Si Cong
SC
Chen
Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, Singapore 117585, Singapore; Water Desalination & Reuse (WDR) Center, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia.
Gary L
GL
Amy
NUS Graduate School for Integrative Sciences & Engineering (NGS), National University of Singapore, 28 Medical Drive, Singapore 117456, Singapore; Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, Singapore 117585, Singapore; Water Desalination & Reuse (WDR) Center, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia. Electronic address: chencts@nus.edu.sg.
Tai-Shung
TS
Chung
D008567:Membranes, Artificial; D009995:Osmosis; D010710:Phosphates / Q000737:chemistry; D011108:Polymers; D059027:Recycling; D012822:Silicon Dioxide / Q000737:chemistry; D013450:Sulfones; D014865:Waste Disposal, Fluid; D018508:Water Purification / Q000295:instrumentation* / Q000379:methods*
D008567:Membranes, Artificial; D010710:Phosphates; D011108:Polymers; D013450:Sulfones; C022840:polyether sulfone; D012822:Silicon Dioxide
Anti-fouling; Fouling; Osmotic power generation; Phosphate; Pressure retarded osmosis; Silica