Membrane separation processes have been widely used for wastewater treatment due to their advantages over conventional processes. Key membrane processes for wastewater treatment include microfiltration, ultrafiltration, nanofiltration, reverse osmosis, and membrane bioreactors. These processes provide high quality treated water with low capital and operating costs due to their compact size and ability to automate. However, membrane fouling remains a challenge that can reduce membrane performance over time.

1. 1
Membrane Separation Processes for
Wastewater Treatment: An Overview
Dr. Z.V.P. Murthy
Professor
Department of Chemical Engineering
Sardar Vallabhbhai National Institute of Technology
Surat – 395007, Gujarat.
October 09, 2009
Presentation at the AICTE sponsored One-week Short-Term Training Programme on Treatment and Disposal of
Wastewaters, October 5-9, 2009, SVNIT, Surat

2. 2
Outline of Presentation
Introduction
Various Membrane Separation Processes
Membrane Modules
Case Study

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20. Rapid Mix
Coagulation/
Flocculation Sedimentation
Filtration
Disinfection

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24. Development of practical membrane processes
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*Loeb-Sourirajan of UCLA in early 1960’s : Breakthrough
discovery for industrial membrane application: RO for desalination.

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35. Pressure-Driven Membrane Processes
Permeate
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Membrane
Particle or Solvent
Solute Molecule
Feed
DP

36. Pressure-Driven Membrane Processes
10
Suspended Solids (Particles)
Macromolecules (Humics)
Multivalent Ions (Hardness)
Monovalent Ions (Na+,Cl-)
Water Molecules

37. 11
Membrane Fouling
macromolecules particles ions
microbes

38. 12
Membrane Fouling

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Flux: The volume of treated water obtained per unit time per
unit membrane surface area. Higher flux is often desirable.
(m3/m2/h or m/h) (MF/UF)
P
t R
J
= D
×
m
J :Flux,
P: trans-membrane pressure,
: viscosity,
Rt: total membrane resistance

43. Selectivity: For dilute aqueous mixtures of a solvent (water) and a
solute (particles), the selectivity is expressed in terms of retention
“R”
towards solute. CF and Cp are solute concentration in feed
15
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P
F
C - C
R = F P
=
F
C
C
1 -
C
and permeate
R = 100% (complete retention) of solute
R = 0% (solute and solvent pass thru membrane
Water Recovery: QP/QF
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cellulose acetate, cellulose esters,
polypropylene polyamides, polysulfones, etc.); organic- cheaper.
Ceramic: Alumina, Titania, and Zirconia: high thermal/chemical
resistant
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51. membrane constituted of two or more structural planes
of non-identical morphologies.

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60. 21
Microfiltration:
Simple screening mechanism
Pore size 0.1 m - 10 m
DP » 0.01 to 0.5 MPa

61. Molecular Weight Cut-Off (MWCO):1,00,000
Low pressure process
Most effectively remove particles and microorganisms
(bacteria)
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High flux
Colloids/Macromole --- theoretically pass through
the membrane

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76. Ultrafiltration:
Screening and Adsorption
Pore size 1 - 100 nm
DP 0.1 to 1 MPa
Membrane is classified in terms of Molecular Weight-Cut off
(MWCO) : 1000 - 100,000
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Two layers: a thin (0.1 to 0.5 μm), skin layer and
a porous substructure support layer
Separation of macromolecules
Only surface deposition - no internal pore plugging-so,
relatively easy to remove, irreversible

77. 23

78. Nanofiltration:
NF Removes molecules in the 0.001-0.01 m
DP 0.5 to 6 MPa
MWCO: upto 10,000
NF is essentially a lower-pressure version of reverse osmosis
NF performance characteristics between reverse osmosis
and ultrafiltration
Nanofiltration: Water softening, removal of organic matter,
desalting of organic reaction products.

79. 24
OSMOSIS and REVERSE OSMOSIS
Osmosis (see Figure A) is the flow of solvent through a semipermeable
membrane from the less concentrated to the more concentrated region.
A “semipermeable” membrane is a membrane, which allows solvent to pass but
completely prevents the flow of certain solutes or ions in solution. The osmotic
flow is a natural occurrence, as the system tends to come to equilibrium and
equalise chemical potentials.
Figure A. Principle of reverse osmosis.

80. 25

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85. Membrane: similar to UF, thin active layer; porous support layer
Operating Pressure: 1.0 - 10 MPa
RO has the separation range of 0.0001 to 0.001mm
Desalination (seawater and brackish water), metal plating effluent treatment,
color removal from textile effluents, production of high purity water
(boiler feed, electronics, medical, pharmaceutical)

86. The osmotic flow can be decreased by applying a pressure on the
concentrated solution.
•The higher the applied pressure the lesser the osmotic flow.
•When the osmotic flow stops, the applied pressure is the osmotic
pressure, which is given by the symbol .
Osmotic pressure is a thermodynamic property of a solution and as such values
26
can be found in various reference books.
For dilute systems, the following van’t Hoff equation may be used to calculate
osmotic pressure:
= CAiRT
where CAi is the molar concentration of solute A at location i, R is the gas
constant, and T is the absolute temperature.
Osmotic pressure is equal to 6.86 kPa (51 torr) for each 100 mg/L of dissolved
solids.

87. 27
Flux in RO and NF System:
Flux (Jw) = Kw (DR-DP)
Kw = Water mass transfer coefficient
DR = Mean imposed pressure gradient
DP = Mean osmotic pressure gradient
Collier County, FL

88. 28
MEMBRANE MODULES
Membrane module refers to the device which houses the
membrane element:
• Tubular membrane module
• Hollow fibre membrane module
•Spiral wound membrane module
• Plate and frame membrane module

89. 29
Feed Retentate
Permeate (flows radially)
•Membrane is cast inside the support tube
• Tubular membranes have a diameter of 5 - 15 mm
• High suspended solids tolerance
• Flow is usually inside out
•Mainly MF and UF
• Low packing density, high prices per module

90. 30
•Consists of a bundle of hundreds and thousands of hallow fiber
•Entire assembly is inserted into a pressure vessel
• Feed can be applied inside of the fiber (inside-out flow) outside
(outside-in flow)
• Highest packing density of all.
•Hollow fiber is used mainly for NF and RO

91. 31
Spiral wound membrane module
•Flexible permeate spacer is provided between two flat sheet membranes
•Flow is in a spiral pattern.
•Membrane envelop is spirally wound along with a feed spacer
• Filtrate is collected within the envelop and piped out
•Packing density: high
•RO and NF

92. 32
Plate-and-frame module
Two membranes are placed in a sandwich-like fashion with their feed sides facing each other.
Easy to clean and replace membranes.
Low membrane area per unit volume (a problem in high pressure application where pressure vessel costs are
significant).

93. 33
CASE STUDY
Performance of Spiral-wound TFC-PA RO Membrane for Tertiary Treatment of Effluent in
Common Effluent Treatment Plant

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Pollution Control Board norms for discharge of effluent to CETP:
pH : 6.5 $ 8.5
COD : 1000 ppm
BOD : 400 ppm
SS : 300 ppm
Detoxified toxic contaminants at each unit before discharge to CETP
Records of quantity and quality of effluent maintained by each member unit

97. 34
Materials and Methods
Experiments are performed on Perma%-pilot membrane system consisting of a spiral-wound TFC-PA
RO membrane module
Specifications of TFC-PA RO membrane module:
______________________________________________
Item Specification
______________________________________________
Membrane module Spiral-wound
Membrane type TFC-PA RO membrane
Membrane maker Permionics, Vadodara, India
Membrane material TFC Polyamide
Effective membrane area 1.0 m2
Number of modules one
Length of module 21 in.
Diameter of module 2.5 in.
_______________________________________________

98. 35
Materials and Methods……
Specifications of membrane:
TFC-PA RO membrane has three layers:
(1) First layer: 5-20 m thick TFC-PA layer
(2) Second layer: 50 m thick of polysulfone
(3) Third layer: 200 m thick of polyester
Perma-TFC membranes are capable of withstanding pH in the range 2-12, pressure up to 30 atm and
temperatures up to 50°C

99. 36
EXPERIMENTAL SET-UP:
Perma-pilot scale membrane system

100. Material and Methods……
Before actual experiments membrane is subjected to stabilization at 20 atm for 2
37
hours to avoid membrane compaction during operation.
The experiments are performed for various membrane flux rates in the range of 52-
88 L/(m2 h) or LMH with the operating pressures between 7-20 atm.

101. 38
Material and Methods……
The membrane performance can be represented in terms of normalized flux by the following relation:
J = 1.03(297- T
)
Q
…………(1)
N AP
m
where JN is the normalized flux [L/(m2 h atm)], T is the temperature in the range of 303-308 K, Q is the
volume flow rate of permeate (m3/h), A is the effective membrane area (m2), Pm is transmembrane
pressure (atm).
Performance of membrane in terms of percentage rejection (R) is given as
…………(2)
= -
Cp
100 1 % ´
Cf
R
where Cf and Cp are the individual component concentrations in the incoming feed to the RO system
and in the permeate from the system, respectively.

102. 39
Material and Methods……
The normalized flux decline rate is calculated by the following Eq. (3)
………(3)
100
initial normalized flux - final normalized flux
´
initial normalized flux operating hours
Average normalized flux
decline rate (% per hour)
´

103. =

104. The important parameters like color, pH, total solids (TS), suspended solids (SS), total dissolved solids
(TDS), phenol, ammonia, COD, BOD, sulphate, total hardness, Mg hardness, Ca hardness, zinc and
total Cr are measured in the feed and permeate samples, according to standard methods.

105. 40
Results and Discussion
Characteristics of the secondary treated wastewater from CETP used as a feed in the present study:
____________________________________________________________________________________
Parameters Unit Value
____________________________________________________________________________________
pH - 6.95
Color Pt-Co unit 1070
TS mg/L 8460
SS mg/L 296
TDS mg/L 8164
Phenol mg/L 4.19
Ammonia mg/L 210
COD mg/L 656
BOD mg/L 160
Sulphate mg/L 1027
Total Hardness mg/L 1770
Ca Hardness mg/L 1600
Mg Hardness mg/L 170
Zinc mg/L 0.03
Total Cr mg/L 0.07
______________________________________________________________________________________

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111. 42
Results and Discussion ……
Normalized flux of the RO membrane under different flux rates as a function of time are shown in Fig.
7
6
5
4
3
2
1
0
0 5 10 15 20 25 30 35 40 45
Time, h
JN, (L/m2 h atm)
87.3 LMH
78 LMH
64 LMH
52.4 LMH
64 LMH (Firs t CIP )
52.4 LMH (Firs t CIP )
64 LMH (Seco nd CIP )
(!# ;
(!# ;

112. 43
Results and Discussion ……
The results are summarized in Table
_______________________________________________________
Parameter Test-1 Test-2 Test-3 Test-4
_______________________________________________________
Flux rate (LMH) 87.3 78 64 52.4
Operating pressure 17-20 15-18 12-12.5 7
(atm)
Normalized flux, JN 3.71-3.25 4.11-3.42 4.47-4.29 6.27-4.8
[L/(m2 h atm) 25°C]
%Drop in JN per hour 1.5 1.7 0.40 0.2
%Drop after first CIP - - 0.70 1.6
%Drop after second CIP - - 0.67 -
Average % rejection 99.4 99.4 99.1 98.8
of COD
_______________________________________________________

113. 44

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Parameter unit Permeate % Rejection Specified limit**
pH - 6.7-7.3 --- 6.5-8.5
10-40 96 - 98 5-25
Pt-Co
Color unit
TS mg/L 24-80 99 – 99.7 300-600
SS mg/L 1-5 98 – 99.7 ------
TDS mg/L 24-79 99 – 99.7 300-600
Phenol mg/L 0.09-0.14 96.6 – 97.8 0.001-0.002
Ammonia mg/L 11-16 92 – 94.8 50
COD mg/L 4-8 98.8 – 99.4 100
BOD mg/L 0 100 --------
Sulphate mg/L 0 100 200-400
Total Hardness mg/L 0 100 300-600
Ca Hardness mg/L 0 100 75-200
Mg Hardness mg/L 0 100 30-100
Zinc mg/L BDL* 100 5
Total Cr mg/L 0.01-0.06 14 – 85.7 0.05
* BDL=Below Detectable Limit, ** Specified limit by pollution control authority

115. 45
Conclusions
The conclusions from the pilot study are summarized as follows:
The optimal operation flux rate of the RO membrane is found to be 64 LMH for the present application.
At a flux rate of 64 LMH and water recovery of 11%, the average operating pressure of 12 atm is noted
corresponding to a high normalized flux of 4.5 L/(m2 h atm) at 25°C.
Average rejections of the RO membrane in terms of COD and BOD are 99% and 100%, respectively.
It is found that the RO system is effective for the secondary treated industrial effluent in order to comply
with the local specified limits for discharging into the public sewerage system. In turn that can be used
for other purposes due its high quality, instead of sending it to sewerage.

116. 46
References:
1. Membrane processes for water and wastewater treatment by S.S. Khanal, Department of Civil
Engineering, Construction and Environmental Engineering, Iowa State University, USA.
2. Emerging Applications for Water Treatment and Potable Water Reuse by T.Y. Cath, Environmental
Science and Engineering Division, Colorado School of Mines, USA.
3. Z.V.P. Murthy, L.B. Chaudhari, Performance of Spiral-wound TFC-PA RO membrane for tertiary
treatment of effluent in common effluent treatment plant, Proceedings of the “2nd International
Conference on Engineering for Waste Valorisation (WasteEng08)”, University of Patras, Greece, June 3
- 5, 2008, pp 229-230.