倉田奨励金研究報告書 第 51 集｜2019 年度（第 51 回）助成
自然科学・工学研究部門：2 年助成（最終報告）■受領№1398

逆浸透膜のナノスケールレベルの欠陥を簡易に修復する『ナノスケールバンドエイド』の開発
代表研究者

鈴木祐麻

山口大学大学院創成科学研究科

准教授

Enhancement of solute removal efficiency of polyamide reverse osmosis
membrane without water permeability loss
Principal Researcher

Tasuma Suzuki,
Department of Sustainable Environmental Engineering, Graduate School of Sciences and Technology for Innovation,
Yamaguchi University, Associate Professor

本研究では逆浸透膜（RO 膜）を用いて下水処理水を処理した際の溶質除去率の向上を検討した。RO 膜の透過性が異なる 3 つの溶質（亜ヒ酸、電解質、ローダミン-WT）を用いてろ過実験を行った結果、バイオポリマーの代表物質として用いたアルギン酸が共存する条件下では水透過性と犠牲にすることなくローダミン-WT の透過量が 45%減少（2.0 MPa にて）した。また、亜ヒ酸と電解質の透過量は減少しなかったことから、アルギン酸が RO 膜に存在するナノスケールレベルの欠陥を塞いでいることが示された。
This study investigates the enhancement of the solute removal efficiency of reverse osmosis (RO)membranes without water permeability loss during the treatment of secondary wastewater effluent (SWE).
Filtration experiments were performed using a synthetic SWE containing three types of solutes withdifferent

membranetransport

properties,

namelyarseniousacid (H3AsO3),

electrolyte,

andrhodamine-WT (R-WT), and alginate as a representative biopolymer foulant. The flux of R-WT at 2.0
MPa decreased by up to 45% in the presence of alginate without decreasing water permeability; this trend
was not observed for H3AsO3 and the electrolyte, indicating that nanoscale imperfections that allow
unselective solute transport were plugged by alginate. These results demonstrated that nanoscale
imperfections in the RO membrane could be plugged by the biopolymer contained in SWE and that theremoval of large solutes was enhanced without forfeiting water permeability.

1．Research objective(removal percentage > 99.9999%), the virus

RO membranes are often utilized for theremoval efficiency of most RO membranes is notreclamation of municipal wastewater to produce

100%. Because of the imperfect integrity of active

drinking water. However, it is widely recognizedlayers and the incomplete rejection of contaminants,that advanced thin-film composite polyamide RO

integrated

membranes have nanoscale imperfections in themunicipal wastewater to produce drinking water

active layer that allow for the advective transport

are typically followed by ultraviolet (UV) treatmentof solutes [1-2]. Consequently, although RO

for reliable virus removal performance [3].

membranes provide an effective barrier to viruses

Our previous study [4] demonstrated that nanoscale

membranesystemsforrecovering

倉田奨励金研究報告書 第 51 集｜2019 年度（第 51 回）助成
自然科学・工学研究部門：2 年助成（最終報告）

imperfections present in the active layers ofFUJIFILM Wako Pure Chemical Corp. (Osaka,pristine polyamide RO membranes can be effectively

Japan). R-WT has a molecular weight of 480, and its

plugged by filtering an aqueous solution of polyvinyl

removal by RO membranes is well correlated with thealcohol (PVA) and subsequent cross-linking withremoval of the bacteriophage MS2; it was purchased

glutaraldehyde forming a stable plug. The key ideafrom Turner Designs, Inc. (San Jose, CA, USA). All

that makes this strategy promising is that weother chemicals used in this study were guaranteed tofiltered only a small volume of PVA aqueous solution

be of reagent-grade quality and were obtained fromto selectively plug nanoscale imperfections withoutNacalai Tesque, Inc. (Kyoto, Japan) or FUJIFILM

forming a PVA deposition layer on top of the RO

Wako Pure Chemical Corp.; they were used without

membrane. This successful demonstration of afurther purification. The commercial RO membrane“nanoscale adhesive patch” makes it reasonable toused in this study was a thin-film composite fully

assume that dissolved organic matter with a relatively

aromatic polyamide membrane, and the active layer

high molecular weight like PVA (e.g., biopolymers

was formed by interfacial polymerization between

such as polysaccharide and protein) in secondary

trimesoyl

wastewater effluent (SWE) might work as “nanoscale

According to the manufacturer, the surface of theadhesive patches” and improve solute removal

active layer was covered with PVA to improve theefficiencies

fouling propensity.

duringthetreatmentofSWE.

chlorideandm-phenylenediamine.

Biopolymers have been widely recognized as commonfoulants of RO membranes in the wastewater
reclamation process and could have a negative
influence on water permeability by forming a foulant
layer on top of the RO membrane. However, if we candemonstrate that these foulants also work as“nanoscale adhesive patches,” we could utilize thisnatural phenomenon as a strategy to improve RO
membrane performance by optimizing operationaland cleaning conditions.
Based on the abovementioned considerations, thisstudy investigates the potential enhancement in theremoval of solutes by RO membranes during thetreatment of SWE. A solution containing three typesof solutes with different membrane transport
properties and mechanisms, namely arsenious acid
(H3AsO3), electrolyte, and rhodamine-WT (R-WT),and alginate as a representative biopolymer foulant
was used as feed water to investigate the influence ofalginate on RO membrane performance.

２．Research content

2.2 Filtration experiments
2.2.1 Experiments using synthetic SWE
containing inorganic ions and alginate
5 L of synthetic SWE containing only inorganic
ions was prepared by adding 9.2 mmol/L NaCl,0.94 mmol/L NH4Cl, 0.45 mmol/L KH2PO4, 0.5mmol/L CaCl2·2H2O, 0.5 mmol/L NaHCO3, and0.6mmol/L

MgSO 4 ·7H 2 O.

Thischemicalcomposition was selected to represent SWE
quality in California [5]. Thereafter, H3AsO3 (5mg As/L, pKa=9.2) and R-WT (5 mg/L) werespiked into synthetic SWE, and the pH wasadjusted to 6.9±0.1, to fully convert H2AsO3- into
neutral H3AsO3.
The water permeability and solute removal
efficiency of the RO membrane were evaluatedusing a cross-flow closed-loop filtration systemwith a CF042 flat-leaf cell (Sterlitech Corp., Kent,WA). After installing a membrane coupon and a
CF042 high foulant spacer, the membrane wasstabilized for 14 days at 2.0 MPa for membrane

2.1 Reagent and RO membranecompaction and conditioning. The feed solution

Sodium alginate with a viscosity of 80–120 cPa·s at a

was sent to the cell using a dual pump (KP-22-33,concentration of 10 g/L was obtained fromFLOM, Inc., Tokyo, Japan) at 50 mL/min flowrate.

倉田奨励金研究報告書 第 51 集｜2019 年度（第 51 回）助成
自然科学・工学研究部門：2 年助成（最終報告）

water flux and solute rejection) at various applied

2.3.2 Water/solute transport property
characterization after adding alginate
to synthetic SWE

pressures was evaluated.

In addition to the membrane performance

After 14 days of membrane compaction andconditioning, the membrane performance (i.e.,evaluated in the absence of alginate, the closed

2.2.2 Experiments using synthetic SWE
containing inorganic ions and alginate

symbols in Fig. 1 show the performances ofAfter finishing the experiments described inμgC/L alginate. The average decrease in water

Section 2.2.1, 500 µgC/L sodium alginate waspermeability between Membrane pieces #1 and #2

spiked into the synthetic SWE used in Section

was below 5%, indicating that alginate did not

2.2.1 and operated for 14 days at 1 MPa. After 14

form a foulant layer on top of the membranes

days of operation, the membrane performance (i.e.,during 14 days of operation.

the water flux and solute rejection) at various

Spiking alginate into synthetic SWE differently

applied pressures was evaluated.

affected solute removal depending on the type ofMembrane pieces #1 and #2 after spiking with 500

solute. The addition of alginate did not
significantly have either a positive or negative

2.3 Results and discussion
2.3.1 Water/solute transport property
characterization using synthetic SWE
containing only inorganic ions
The performances of Membrane pieces #1 and #2
in the absence of alginate are shown in Fig. 1 using
opensymbols.

Thedatashowedadequate

reproducibility between Membrane pieces #1 and#2 for both water flux and the removal of the threetypes of solutes, and the solute removal efficiency
increased in the order of H3AsO3 < electrolyte <R-WT. Notably, the removal of H3AsO3 strongly
depended on the water flux, a weaker dependence
was observed for the electrolyte, and nodependence was observed for R-WT. This result
indicates that the solute permeation mechanism isdifferent depending on the type of solute. Thiswas expected because of three reasons 1) small
and neutral molecules, including H3AsO3, are noteffectively removed by a negatively charged
integrated polyamide active layer, 2) the diffusive
permeation of small but charged electrolytes iselectrically hindered by a negatively charged
integrated polyamide active layer; and 3) the
diffusive permeation of R-WT via the integrated
polyamide active layer is physically hinderedowing to its large size.

effect on H3AsO3 and electrolyte removal but had
a positive effect on R-WT removal. If we use
Membrane piece #1 for analysis, the rejection of
R-WT increased from 99.77–99.81% to 99.84–
99.89%. This study revealed that the increase in
R-WT removal from 99.78% to 99.88% (dataobtained at 2.0 MPa) is a slight improvement(0.1%); however, this is a significant decrease(45%) in the R-WT flux across the membrane.
These results show that alginate selectively
plugged nanoscale imperfections in the polyamide
active layer and blocked the pathways foradvective

solutetransport.

Thisplugging

significantly decreased the R-WT flux through themembrane and consequently improved theremoval because R-WT passes through themembrane only via advection; however, this trend
was not observed for H3AsO3 and electrolyte
because diffusion via the integrated polyamide
active layer is also an important transportmechanism for these small solutes. In summary,these results showed that the solute rejection
capability of the RO membrane could be enhancedby biopolymers in SWE without losing water
permeability as long as the following requirements
are met: i) advective transport is the dominanttransport mechanism (e.g., R-WT), and ii)

倉田奨励金研究報告書 第 51 集｜2019 年度（第 51 回）助成
自然科学・工学研究部門：2 年助成（最終報告）

nanoscale imperfections are selectively plugged by4) T. Suzuki, M. Okamura, M. Niinae, Plugging

biopolymers without forming a foulant layer on

nano-scale imperfections in the polyamide active

top of the membranes.

layer of thin-film composite reverse osmosis
membraneforinhibiting

advective

soluteReferencetransport, Desalination. 487 (2020) 114506.

1) M. Pype, M.G. Lawrence, J. Keller, W. Gernjak,5) M. S. Rahaman, H. Thérien-Aubin, M.

Reverse osmosis integrity monitoring in water

Ben-Sasson, C. K. Ober, M. Nielsen, M. Elimelech,reuse: The challenge to verify virus removal - A

Controlreview, Water Res. 98 (2016) 384–395.

polyamide membranes modified with biocidal

ofbiofouling

onreverse

osmosisnanoparticles and antifouling polymer brushes, J.

2) S.H. Yoon, Potential and limitation ofMater. Chem. B. 2 (2014) 1724-1732.

fluorescence-based membrane integrity monitoring(FMIM) for reverse osmosis membranes, Water
Res. 154 (2019) 287–297.

３．Publication of research findings3) J. E. Drewes, N. Horstmeyer, 2015. Recent

Suzuki, T.; Harada, M.; Wada, Y.; Ichimura, S.

Developments in Potable Water Reuse. In: D.

Enhancement of solute removal efficiency of

Fatta-Kassinos, D. D. Dionysiou, K. Kümmerer

polyamide reverse osmosis membrane without(Eds.). Advanced Treatment Technologies forwater permeability loss. Journal of Environmental

Urban Wastewater Reuse, The Handbook ofChemical Engineering. 2021, 9, 106818

Environmental Chemistry, Series Volume 45,Springer International Publishing, Switzerland,
pp.269-290.

Synthetic SWE containing inorganic ionsand 500 gC/L of alginate

Synthetic SWE containing
only inorganic ions

0.0
0.0 0.5 1.0 1.5 2.0 2.5
Applied pressure [MPa]Membrane piece #1
Modeling
Membrane piece #2
Modeling

100
Electrolyte rejection [%]0.5

H3AsO3 rejection [%]Water flux [m/day]

1.0

1 MPa, 14 days

100

2.0
1.5

Addition of 500 gC/L of alginate

9590
85807570

Rhodamine-WT rejection [%]Membrane piece #1
Modeling
Membrane piece #2
Modeling

9998979695

100.0
99.9
99.8
99.7
99.6
99.5

0.0 0.5 1.0 1.5 2.00.0 0.5 1.0 1.5 2.0

0.0 0.5 1.0 1.5 2.0

Water flux [m/day]

Water flux [m/day]

Water flux [m/day]Fig. 1 Experimental (symbols) and modeling (lines) results of Membrane pieces #1 and #2.
Open circles and triangles represent data obtained using synthetic SWE containing only
inorganic ions, whereas closed circles and triangles represent data obtained using synthetic
SWE containing inorganic ions and 500 μgC/L of alginate.