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Membrane Flocculation Hybrid System as Pretreatment to Brackish and
Seawater Reverse Osmosis Desalination System:
Emphasis on Chemical Use Reduction and Recovery
Centre for Technology in Water and Wastewater (CTWW), School of Civil & Environmental Engineering,
Faculty of Engineering & Information Technology (FEIT), University of Technology Sydney (UTS), Sydney, Australia.
(E-mail: [email protected])
 Fouling is a significant problem in seawater reverse osmosis (SWRO) desalination process. It increases operational and water production costs due to frequent chemical cleaning. It is
important to eliminate organic and bio-fouling by pretreatment before passing through SWRO.
 The conventional pre-treatment systems cannot alleviate organic and bio-fouling which are the major issues in SWRO operation.
 This project establishes and evaluates a novel submerged membrane flocculation hybrid system (SMFHS) as a cost-effective pre-treatment to SWRO.
 The emphasis of this project is to reduce the use of chemical and flocculated sludge disposal through the selection of alternative chemicals, pre-adsorption and resource recovery
from chemical sludge.
Submerged membrane flocculation hybrid system (SMFHS)
with GAC pre-adsorption*
 In the SMFHS set-up,
submerged-type of hollow
fiber microfiltration (MF)
membrane (Cleanfils-S,
Polysulfone, Polyethersulfone,
Polyvinylidenefluoride (PVDF)
of pore size 0.1 µm) was used.
 The combined effective
surface area of MF was 0.1m2.
 Flocculants were dosed in-line
flocculation system.
GAC
*Granular activated carbon (GAC) filter was operated in adsorption mode at a constant filtration
rate of 10 m/h (at a down-flow mode). This was to reduce the use of flocculant (chemical).
- S. Jeong, T.V. Nguyen, S. Vigneswaran. (2011) Submerged membrane coagulation hybrid system as pretreatment to organic matter removal
from seawater. Water Science and Technology: Water Supply 11(3): 352-357.
Modelling of fouling and DOC removal
Advanced analytical methods
Organic and biological foulants and membrane autopsy were made using following methods:
 Organic characterisation:
 Detailed organic fractionation: Liquid Chromatography-Organic Carbon Detector (LC-OCD), XAD resin
 Molecular weight distribution: High Pressure Size Exclusion Chromatography (HPSEC)
 Quantification of humic-like, fulvic-like and protein-like organic foulants: Three DimensionFluorescence Excitation Emission Matrix (3D-FEEM)
 Biopolymeric organic foulant analysis: Transparent exopolymeric particles (TEP) and extracellular
polymeric substance (EPS)
 Bio-available organic fraction of dissolved organic carbon and biofouling potential: Assimilable organic
carbon (AOC)
 Structural study of organic matter: Nuclear magnetic resonance (1H-NMR), Pyrolysis-gas
chromatography–mass spectrometry(Py-GC/MS) and Liquid Chromatography–Mass Spectrometry-Ion
Trap-Time Of Flight (LC/MS-IT-TOF).
 Biological foulants: Total direct cell (TDC) count, cell viability and biomass activity (adenosine tri-phosphate;
ATP).
 The fouled membrane analysis: Environmental Scanning Electron Microscopy coupled with Energy
Dispersive Spectroscopy (SEM-EDS), Attenuated Total Reflection-Fourier Transform Infrared spectrometry
(ATR-FTIR), Zeta-potential measurement, Atomic Force Microscopy (AFM), and Contact Angle measurement.
- S. Jeong, S.-J. Kim, C.M. Kim, S. Vigneswaran, T.V. Nguyen, H.K. Shon, J. Kandasamy, I.S. Kim. (2013) A detailed organic matter characterization of
pretreated seawater using low-pressure microfiltration hybrid systems. Journal of Membrane Science 428: 290-300.
- S. Jeong, S.-J. Kim, L.H. Kim, M.S. Shin, S. Vigneswaran, T.V. Nguyen, I.S. Kim. (2013) Foulant analysis of a reverse osmosis membrane used
pretreated seawater. Journal of Membrane Science 428: 434–444..
Effect of different flocculants
- Cake formation was the predominant fouling mechanisms causing fouling in SMFHS
- An initial modelling for DOC removal was made using
conceptual method
Pore blockage
Pore constriction
 The removal occurred by adsorption of un-dissociated
compounds onto ferric hydroxide was formulated.
 DOCremaining (final DOC after coagulant is dosed into the
water) can be calculated using the following formula:
DOCremaining = DOC0-HAs-BOHs-HBnps.
Cake filtration
- S. Jeong, Y.J. Choi, T.V. Nguyen, S. Vigneswaran, T.M. Hwang. (2012) Submerged membrane hybrid systems as pretreatment in seawater
reverse osmosis (SWRO): Optimization and fouling mechanism determination. Journal of Membrane Science 411–412: 173– 181.
- S. Jeong, A. Sathasivan, G. Kastl, W.G. Shim, S Vigneswaran. (2014) Experimental investigation and modeling of dissolved organic carbon
removal by coagulation from seawater. Chemosphere 95: 310-316.
Economic analysis
FeCl3
PFS
Al2(SO4)3
PACl
TiCl4
Optimal dose (mg/L)
3.0
2.0
3.0
2.0
2.0
Flocculant price (AU$/ton)
200
180
200
260
Flocculant required (ton/d) 0.145
0.167
0.190
Cost of flocculant (AU$/d)
29.1
30.0
Sludge production (ton/d)
0.280
0.250
Sludge treatment price
PFS
Al2(SO4)3 PACl
TiCl4
Optimal dose (mg/L)
1.0
1.0
1.0
1.0
1.0
1,950
Flocculant price (AU$/ton)
200
180
200
260
1,950
0.126
0.079
Flocculant required (ton/d)
0.048
0.083
0.063
0.063
0.040
38.0
32.7
154.5
Cost of flocculant (AU$/d)
9.7
15.0
12.7
16.4
77.3
0.350
0.230
0.200
Sludge production (ton/d)
0.200
0.180
0.230
0.160
0.200
37
37
37
37
37
(AU$/ton)
Cost of sludge treatment
(AU$/d)
Incineration (AU$/d)
37
37
7.4
6.7
8.5
5.9
-
Incineration (AU$/d)
-
-
-
-
+6.6
By-product (AU$/d)
-
-
-
-
-90.0
GAC operation* (AU$/d)
13.5
13.5
13.5
13.5
13.5
Total cost (AU$/d)
30.6
35.2
34.7
35.8
7.4
Cost saving (AU$/d)
9.9
5.0
17.8
6.3
35.9
37
37
37
(AU$/ton)
Cost of sludge treatment
(AU$/d)
10.4
9.3
13.0
8.5
-
-
-
-
-
8.8
By-product (AU$/d)
-
-
-
-
-120
Total cost (AU$/d)
39.5
39.3
51.0
41.2
43.3
 Preadsorption by GAC filter will help to reduce the operational cost through reduction of the amount of
flocculant needed as well as decreased the need of sludge treatment.
 The cost for treatment of a cubic meter of seawater can reduce from 39.3-51.0 US$/d to 7.4-35.2 US$/d
based on 10,000m3/d plant.
- T.V. Nguyen, S. Jeong, T.T.N. Pham, J. Kandasamy, S. Vigneswaran. (2014) Effect of granular activated carbon filter on the subsequent flocculation
in seawater treatment. Desalination 354: 9-16.
Conclusions
- S. Jeong, F. Nateghi, T.V. Nguyen, S. Vigneswaran, T.A. Tu. (2011) Pretreatment for seawater desalination by flocculation: Performance of
modified poly ferric silicate (PFSi-δ) and ferric chloride as flocculants. Desalination 283: 106–110.
- S. Jeong, Y. Okour, T.V. Nguyen, H.K. Shon, S. Vigneswaran. (2013) Ti-salt flocculation for dissolved organic matter removal in seawater.
Desalination and Water Treatment 51(16-18): 3591-3596.
RO testing
FeCl3
Sludge treatment price
- DOC removal efficiency as a function of concentrations of five
different flocculants (initial organic matter concentration of
seawater was 1.41 mg/L)
 The chemical dose necessary with
poly ferric sulphate (PFS) and poly
aluminium chloride (PACl) was
minimal at 2 mg/L. Alum produced
the highest amount of chemical
sludge. This amount was 30% more
than that with other flocculants.
Although, TiCl4 was costly chemical,
the TiO2 production from the TiCl4
sludge makes it cost-effective.
 The results from LC-OCD showed
that most of hydrophobic organic
compounds removed and more
than 35% of hydrophilic substances
such as humic (molecular weight 
1000 Da) reduced significantly.
 SMFHS with GAC pre-adsorption removed organic compounds in the seawater. As a result, it helped to
reduce the flux decline in RO and organic fouling on the RO membrane. The reduction of organic, especially
the LMW organics and AOC compounds on the RO membrane resulted in the a lower biofouling of RO
membrane.
 The addition of GAC preadsorption also helped to reduce significantly the dose of flocculants required for
organic removal.
An energy efficient, compact submerged membrane flocculation hybrid pre-treatment system to reduce the organic fouling to RO!!
This project led to novel and practical outcomes for RO desalination.
(1) It resulted in an energy efficient, compact submerged membrane flocculation hybrid pre-treatment system to reduce the organic fouling to RO. The alleviation of membrane fouling will reduce the operational cost of
RO. The system proposed in this study alleviated the fouling problems and made the small-scale desalination process attractive.
(2) This project reduced the use of chemical usage and subsequent sludge production through the use of alternative chemicals, and effective additional pre-treatment such as pre-adsorption. Recovery of TiO2 from Tisalt based coagulant sludge reduced the amount of sludge discharged. Alternative polymeric inorganic flocculants with and without pre-adsorption reduced the chemical usage and sludge production while achieving
superior organic removal. The proposed alternative Ti-salt coagulant significantly reduced the sludge by recovery of TiO2.
Acknowledgement
This study was supported by the National Centre of Excellence in Desalination (NCED) which is funded by the Australian Government through the Water for the Future initiative.