Sttp ppt msp_overview_09-10-2009_zvpm

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Membrane Separation Processes for Wastewater Treatment: An Overview

Dr. Z.V.P. MurthyProfessor

Department of Chemical EngineeringSardar 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

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Outline of Presentation

� Introduction

� Various Membrane Separation Processes

� Membrane Modules

� Case Study

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Rapid MixCoagulation/ Flocculation Sedimentation

Filtration

Disinfection

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Development of practical membrane processes

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

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Pressure-Driven Membrane Processes

SolventParticle or Solute Molecule

Membrane

PermeateFeed

P∆∆∆∆

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Pressure-Driven Membrane Processes

Suspended Solids (Particles)

Macromolecules (Humics)

Multivalent Ions (Hardness)

Monovalent Ions (Na+,Cl-)

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Water Molecules

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Membrane Fouling

particlesmacromolecules ionsmicrobes

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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)

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J :Flux, �P: trans-membrane pressure, �: viscosity, Rt: total membrane resistance

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� 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

and permeateR = 100% (complete retention) of soluteR = 0% (solute and solvent pass thru membrane

� Water Recovery: QP/QF

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� Simple screening mechanism

Pore size 0.1 �m - 10 �m

∆P ≈ 0.01 to 0.5 MPaMolecular Weight Cut-Off (MWCO):>1,00,000� Low pressure process

� Most effectively remove particles and microorganisms (bacteria)

� High flux

� Colloids/Macromole ---> theoretically pass through the membrane

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Ultrafiltration:� Screening and Adsorption

Pore size 1 - 100 nm∆P 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

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Nanofiltration:

� NF Removes molecules in the 0.001-0.01 �m

� ∆P 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.

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OSMOSIS and REVERSE OSMOSISOsmosis (see Figure A) is the flow of solvent through a semipermeablemembrane 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.

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Membrane: similar to UF, thin active layer; porous support layer

Desalination (seawater and brackish water), metal plating effluent treatment,

color removal from textile effluents, production of high purity water

(boiler feed, electronics, medical, pharmaceutical)

Operating Pressure: 1.0 - 10 MPaRO has the separation range of 0.0001 to 0.001µm

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� The osmotic flow can be decreased by applying a pressure on theconcentrated solution.

•The higher the applied pressure the lesser the osmotic flow.

•When the osmotic flow stops, the applied pressure is the osmoticpressure, which is given by the symbol �.

Osmotic pressure is a thermodynamic property of a solution and as such values can be found in various reference books.

� For dilute systems, the following van’t Hoff equation may be used to calculate osmotic pressure:� = CAiRTwhere 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.

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Flux in RO and NF System:

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Flux (Jw) = Kw (∆Ρ−∆Π) Kw = Water mass transfer coefficient ∆Ρ = Mean imposed pressure gradient ∆Π = Mean osmotic pressure gradient

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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

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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

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•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

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•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

Spiral wound membrane module

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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 aresignificant).

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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 $ 8.5COD : < 1000 ppmBOD : < 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

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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-woundMembrane type TFC-PA RO membraneMembrane maker Permionics, Vadodara, IndiaMembrane material TFC PolyamideEffective membrane area 1.0 m2

Number of modules oneLength of module 21 in.Diameter of module 2.5 in._______________________________________________

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� 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

Materials and Methods……

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EXPERIMENTAL SET-UP:

Perma�-pilot scale membrane system

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� Before actual experiments membrane is subjected to stabilization at 20 atm for 2 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.

Material and Methods……

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� The membrane performance can be represented in terms of normalized flux by the following relation:

� …………(1)

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)

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.

m

TN AP

QJ )297(03.1 −=

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R

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� The normalized flux decline rate is calculated by the following Eq. (3)

………(3)

� 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.


100hours operating flux normalized initial

flux normalized final -flux normalized initial hour)per (% rate decline

flux normalized Average×��

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Results and Discussion

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

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� Normalized flux of the RO membrane under different flux rates as a function of time are shown in Fig.

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1

2

3

4

5

6

7

0 5 10 15 20 25 30 35 40 45

Time, h

J N, (

L/m

2 h a

tm)

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 )

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Results and Discussion ……

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� The results are summarized in Table

_______________________________________________________Parameter Test-1 Test-2 Test-3 Test-4_______________________________________________________Flux rate (LMH) 87.3 78 64 52.4Operating 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 98.8of COD_______________________________________________________

Results and Discussion ……

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0.0514 – 85.70.01-0.06mg/LTotal Cr

5100BDL*mg/LZinc

30-1001000mg/LMg Hardness

75-2001000mg/LCa Hardness

300-6001000mg/LTotal Hardness

200-4001000mg/LSulphate

--------1000mg/LBOD

10098.8 – 99.44-8mg/LCOD

5092 – 94.811-16mg/LAmmonia

0.001-0.00296.6 – 97.80.09-0.14mg/LPhenol

300-60099 – 99.724-79mg/LTDS

------98 – 99.71-5mg/LSS

300-60099 – 99.724-80mg/LTS

5-2596 - 9810-40Pt-Co unitColor

6.5-8.5---6.7-7.3-pH

Specified limit**% Rejection Permeateunit Parameter

* BDL=Below Detectable Limit, ** Specified limit by pollution control authority

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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.

Conclusions

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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.

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