1. NANOFILTRATION AS A PREETREATMENT FOR
SCALING IN SWRO: A SYS
SWRO STEMATIC STUDY
Laia Llenas1, Xavier Martínez Lladó1, Andriy Yaroshch 2,3, Miquel Rovira1, Joan DePablo1,3
Martínez-Lladó huk
1 Environmental Technology Area, CTM Centre Tecnològi Av Bases de Manresa 1 08242 Manresa Spain
Area ic,
ic Av. 1, Manresa,
2 ICREA; 3Department of Chemical Engineering, Polytech
Engineering hnic University of Catalonia Av Diagonal 647 08028 Barcelona, Spain
Catalonia, Av. 647, Barcelona
INTRODUCTION AND OBJECTIVES
Seawater contains hi h concentrations of sparingly soluble salts which can cause scaling of membrane surface, li iti
S t t i high t ti f i l l bl lt hi h li f b f limiting th productivity and water recovery of seawater reverse
the d ti it d t f t
osmosis (SWRO). Nanofiltration (NF) pretreatment of seawater, prevents scaling via preferential removal of scale-forming ions [1].
( ) ( )p ,p g p g [ ]
Several studies have shown that the rejection of scale forming ions is not the same for ev
scale-forming very membrane [2] The main objective of this study was to test a number of commercially
[2].
available NF membranes with synthetic seawater in order to compare their performance and identify optimum membranes and operational conditions for shifting solubility equilibrium of
y p p d y p p g y q
compounds susceptible to cause scaling due to salt precipitation (CaSO4 ( ), MgSO4 ( ), CaCO3 ( ), etc )
(s) (s) O (s) etc.).
EXPERIMENTAL METHODOLOGY
The
Th experimental setup used consists of SEPA CF II cell (O
i l d i f ll (Osmonics).
i )
The trans membrane pressure difference and cross flow velocity were monitored and con
trans-membrane cross-flow ntrolled
automatically; pH and conductivity were also monitored.
t ti ll H d d ti it l it d
Synthetic seawater was prepared in the laboratory following the procedure described else
ewhere
[3].
[3] During the study eleven different nanofiltration membranes supplied by s
study, membranes, several
manufacturers, were tested at various trans-membrane pressure differences between 2 a
p and 20
bar,
bar and two cross-flow velocities: 0 15 and 0 30 m/s
cross flow 0,15 0,30 m/s.
Permeates obtained i th t t were analyzed i th l b t
P t bt i d in the tests l d in the laboratory b using th f ll i analytical
by i the following l ti l
methods: Total Inorganic Carbon Analysis, Ionic Chromatography and ICP-MS.
ICP MS.
Figure 1. Experimental system
1
RESULTS AND DISCUSSION
Depending on the membrane used, there were significant differences between the
p g , g
NF270 NF200 NF ESNA 1‐LF2 K‐TFCS K‐SR2 K‐SR3 DL HL ALNF99 ALNF99HF
rejections of different ions but the most important dissemblance was their
ions,
productivities.
productivities See Figure 22.
a) b)
100
The rejection of scale-forming ions is represented in Figure 2. The rejection of
scale forming 100
90
sulphate is very high for all membranes tested: only four out of eleven membranes 80
80
present a rejection l
t j ti lower th
than 90% Ab t th th
90%. About the three other scale-forming i
th l f i ions, t t l
total 70
inorganic carbon, calcium and magnesium, the rejection of different membranes is
g , g , j % R ection
ejec on
60
% Re ctio
60
more variable and it goes from 10 to 99% depending on the membrane and the
variable, 99%,
Reje
50
pressure used
used. 40 40
30
In Figures 3 and 4 the rejections of two of the most important monovalent ions in
4, 20 20
seawater,
seawater sodium and chloride are shown In contrast to divalent ions the rejection
shown. ions, 10
0 0
of monovalent i
f l t ions i much l
is h lower; even i some cases, negative rejections could b
in ti j ti ld be 0 20 40 60 80 100 120 140 160 0 20 40 60 80 100 120 140 160
observed. Permeate flow (L/h·m2)
(L/h m Permeate flow (L/h·m2)
(L/h m
c) d) 100
100
100 90
100 90
80
90 80
80 70
80 70
% Rej tion
ject n
tion
60 60
70
% Reject
% Reje on
60 50
50
R ectio
60
% Rej tion
ject n
40 40
50
40
30 30
40
20 20
30
20
10 10
20
0
10 0
0 0 20 40 60 80 100 120 140 160
0 20 40 60 80 100 120 140 160
0 0 20 40 60 80 100 120 140 160
Permeate flow (L/h·m2) Permeate flow (L/h·m2)
0 20 40 60 80 100 120 140 160
‐20
2
Permeate flow (L/h·m )
(L/h m Permeate flow (L/h·m2)
(L/h m
Figure 2. Rejection of scale forming ions for different membranes.
2 scale-forming membranes
Figure 3 Sodium rejection
3. Figure 4 Chloride rejection
4. a) Sulphate; b) Total Inorganic Carbon; c) Calcium; d) Magnesium
CONCLUSIONS REFERENCES
 Different nanofiltration membranes have been tested with synthetic seawater in order t select the
to [1] N Hilal H Al Zoubi N A Darwish A W Mohammad M Abu Arabi; A
N. Hilal, H. Al-Zoubi, N.A. Darwish, A.W. Mohammad, M.
best
b t one f th pre t t
for the treatment of reverse osmosis.
t f i comprehensive review of nanofiltration membranes: t t
h i i f filt ti b treatment,
t
p
pretreatment, modelling and atomic force microscopy; Desalination 170
, g py;
 The rejection of monovalent ions is moderate (10-40%) for all membranes. The one tha presents a
j ( ) at p (2004) 281-308
281 308
higher rejection for these ions is NF90, a membrane with very similar properties to reve
g j , y p p erse osmosis
membranes.
membranes
[ ]
[2] A.M. Hassan, A. Farooque, A. Jamaluddin, A. A1- Amoudi, M. A1-Sofi,
q
 The rejection of divalent ions is so good in all membranes tested That is very important for the
tested. A. AI Rubaian, N. Kither, I. Al Tisan
A AI-Rubaian N Kither I Al-Tisan and A Rowaili A demonstration plant
A. Rowaili,
prevention of scaling
scaling. based on the new NF SWRO process Desalination 131 (2000) 157 171
NF-SWRO process, Desalination, 157-171
 The most s itable NF membranes as a pretreatment for scaling pre ention are N
suitable prevention are: NF270 (Do
(Dow [3] Kester, D. R., Duedall, I. W., Connors, D. N. and Pytkowicz, R. M.
Chemical), K-SR2
Ch i l) K SR2 (KOCH) and AL NF99HF (Alf L
d (Alfa Laval).
l)
(1967).
(1967) Preparation of Artificial Seawater Limnology & Oceanography 12
Seawater. 12,
176—179.
176 179
ACKNOWLEDGEMENTS
C O G S
This study was financially supported by Sociedad General de Aguas de Barcelona (AGBAR within the scope of CENIT project “Desarrollos tecnológicos hacia un
R) Desarrollos
ciclo del agua urbano auto sostenible (SOSTAQUA)”.
auto-sostenible (SOSTAQUA)