membrane based water purification technology(ultra filteration,dialysis and electro dialysis)

NAME-SANJEEV KUMAR SINGH

BRANCH-MECHANICAL ENGINEERING,3rd yr.

MEMBRANE BASED WATER PURIFICATION TECHNOLOGY

ROLL NO.-1457074

COLLEGE NAME-HERITAGE INSTITUTE OF TECHNOLOGY

CHECKED BY-S.D.R SIR

INTRODUCTION:

1)Membrane 10.3.b)Flow velocity 10.3.c)Flow temperature 10.3.d)Temperature 10.3.e)Multi staging 11.4)Pre-treatment 11.5)Cleaning 12)Application 13)Dialysis 14)Electro dialysis 15)Limitation of Electro dialysis 16)Advantages of using Membrane 17)Limitation of using Membrane 18)Future challenges of using membrane

2)Merit of Membrane3)Different operations4)Types of Membranes5)Ultra filtration(UF)6)Dead and Cross flow7)Principles of UF8)Membrane Fouling 8.1)Concentration Polarisation 8.2)Types of Fouling 8.2.a)Particulate deposition 8.2.b)Scaling 8.2.c)Bio fouling9)Membrane arrangments10)Process design consideration 10.1)Pre-treatment 10.2)Membrane specification 10.2.a)Material 10.2.b)Pore size 10.3)Operation strategy 10.3.a)Flow type

Membrane Processes

•A membrane is a selective barrier that permits the separation of certain species in a fluid by combination of sieving and diffusion mechanisms

•Membranes can separate particles and molecules and over a wide particle size range and molecular weights

Merits of the process:• Membrane separation consists of different process operating on a variety of physical principles

and applicable to a wide range of separations of miscible components.• These methods yield only a more concentrated liquid stream than feed. Membrane separation

processes have several advantages. These include :

1) Low energy alternative to evaporation in concentrating a dilute feed, particularly when the desired material is thermally labile or when the desired component is a clear liquid.

2) The chemical and mechanical stresses on the product are minimal and since no phase change is involve the energy requirement is modest.

3) Product concentration and purification can be achieved in a single step and the selectivity towards the desired product is good.

4) The method can easily be scaled up.

Pressure driven operation:• Micro filtration(MF)• Ultra filtration(UF)• Nano filtration(NF)• Reverse filtration(RF)

Concentration driven operations:• Dialysis• Pervaporation• Forward osmosis• Artificial lung• Gas separation

Operations in an electric potential gradient:

• Electrodialysis• Membrane electrolysis e.g. chloralkali process• Electrodeionization• Electrofiltration• Fuel cell

Operations in a temperature gradient:• Membrane distillation

ULTRA-FILTRATION

• Separates colloidal material, emulsified oils, micro biological materials, and large organic molecules.

Ultrafiltration (UF)

• Somewhat dependent on charge of the particle, and is much more concerned with the size of the particle.

• Typically not effective at separating organic streams.

1. Concentration polarisation2. Membrane fouling3. Membrane cleaning4. Operating pressure

• Membrane performance affected by:

Dead end and cross-flow:

Feed

Permeate Permeate

Feed Retentate

1. Dead-end 2. Cross-flow

J=TM/(PµRt)

Principles of UF:• The basic operating principle of ultrafiltration uses a pressure induced separation of solutes from a solvent through a

semi permeable membrane. 

• The relationship between the applied pressure on the solution to be separated and the flux through the membrane is most commonly described by the Darcy equation:

where J is the flux (flow rate per membrane area),TMP is the transmembrane pressure (pressure difference between feed and permeate stream), μ is solvent viscosity, Rt is the total resistance (sum of membrane and fouling resistance).

Membrane fouling:

1) Concentration polarization2) Types of fouling

a) Particulate deposition b) Scaling c) Biofouling

Concentration polarization:• When filtration occurs the local concentration of rejected material at the membrane surface increases and can

become saturated. 

• In UF, increased ion concentration can develop an osmotic pressure on the feed side of the membrane. This reduces the effective TMP of the system, therefore reducing permeation rate. 

•  The increase in concentrated layer at the membrane wall decreases the permeate flux, due to increase in resistance which reduces the driving force for solvent to transport through membrane surface. 

•  CP affects almost all the available membrane separation process.

• concentration polarization differs from fouling as it has no lasting effects on the membrane itself and can be reversed by relieving the TMP. 

Types of fouling:a) Particulate deposition:

The following models describe the mechanisms of particulate deposition on the membrane surface and in the pores:

•Standard blocking: macromolecules are uniformly deposited on pore walls.

•Complete blocking: membrane pore is completely sealed by a macromolecule.

•Cake filtration: accumulated particles or macromolecules form a fouling layer on the membrane surface, in UF this is also known as a gel layer.

•Intermediate blocking: when macromolecules deposit into pores or onto already blocked pores, contributing to cake formation.

b) Scaling:• As a result of concentration polarization at the membrane surface, increased ion concentrations may exceed

solubility thresholds and precipitate on the membrane surface

• These inorganic salt deposits can block pores causing flux decline, membrane degradation and loss of production. 

• The formation of scale is highly dependent on factors affecting both solubility and concentration polarization including pH, temperature, flow velocity and permeation rate.

c) Biofouling:• Microorganisms will adhere to the membrane surface forming a gel layer – known as biofilm.The film

increases the resistance to flow, acting as an additional barrier to permeation.

Membrane arrangements:1) Tubular2) Plate and frame3) Spiral wound4) Capillary hollow fibre

Process design considerations:1) Pre-treatment2) Membrane specifications

a) Materialb) Pore size

3) Operation strategya) Flowtypeb) Flow velocityc) Flow temperatured) Pressuree) Multi-stage

4) Post-treatment5) Cleaning

1) Pre-treatment:

• Treatment of feed prior to the membrane is essential to prevent damage to the membrane and minimize the effects of fouling which greatly reduce the efficiency of the separation.

• Types of pre-treatment are often dependent on the type of feed and its quality. For example in wastewater treatment, household waste and other particulates are screened.

2) Membrane specifications:a) Material:

• Polyacrylonitrile (PAN)• PVC/PAN copolymers• Polysulphone• PVDF (polyvinylidene difluoride)• PES (polyethersulfone)• Cellulose acetate (CA)

b) Pore size:• A general rule for choice of pore size in a UF system is to use a membrane with a pore size one tenth that

of the particle size to be separated. This limits the number of smaller particles entering the pores and adsorbing to the pore surface. 

3) Operation strategy:a) Flow typeb) Flow velocity:

• Flow velocity is especially critical for hard water or liquids containing suspensions in preventing excessive fouling.

• Expensive pumps are however required to achieve these conditions.

c) Flow temperature:• To avoid excessive damage to the membrane, it is recommended to operate a plant at the temperature

specified by the membrane manufacturer. In some instances however temperatures beyond the recommended region are required to minimise the effects of fouling.

d) Pressure:• Pressure drops over multi-stage separation can result in a drastic decline in flux performance in the latter stages of

the process. This can be improved using booster pumps to increase the TMP in the final stages. • This will incur a greater capital and energy cost which will be offset by the improved productivity of the process.

e) Multi-stage:• Multiple stages in series can be applied to achieve higher purity permeate streams. 

4) Post-treatment5) Cleaning:• Cleaning of the membrane is done regularly to prevent the accumulation of foulants and reverse the degrading

effects of fouling on permeability and selectivity.

• These types of foulants require chemical cleaning to be removed. The common types of chemicals used for cleaning are:

• Acidic solutions for the control of inorganic scale deposits• Alkali solutions for removal of organic compounds• Biocides or disinfection such as Chlorine or peroxide when bio-fouling is evident

When designing a cleaning protocol it is essential to consider:

Cleaning time – Adequate time must be allowed for chemicals to interact with foulants and permeate into the membrane pores. 

Aggressiveness of chemical treatment – With a high degree of fouling it may be necessary to employ aggressive cleaning solutions to remove fouling material.

Disposal of cleaning effluent – The release of some chemicals into wastewater systems may be prohibited or regulated therefore this must be considered.

Applications:• Drinking water• Protein concentration• Filtration of effluent from paper pulp mill• Cheese manufacture, see ultrafiltered milk• Removal of pathogens from milk• Process and waste water treatment• Enzyme recovery• Fruit juice concentration and clarification• Dialysis and other blood treatments

DIALYSIS

Dialysis:• Dialysis is well known in medical field as hemodialysis. Blood is drawn from a patient and passed through the lumen of

the fiber of a hollow fiber unit (artificial kidney) while water containing solutes such potassium salts is passed through the shell side

• The water contains dissolved salts so that it has the same osmotic pressure as blood to minimize transfer of water. Urea, uric acid, creatinine, phosphates and excess of chloride diffuse from the blood into water thereby purifying the blood of the waste products

• Dialysis has potential applications in bioseparations, for example separation of alcohol from beer. Dialysis involves separation of solutes by diffusion across the membrane from one liquid phase to another liquid phase, on the basis of molecular size and molecular conformation

Electrodialysis

Electrodialysis:• The method was developed fro the desalination of brackish water into potable water. Separation of ions occurs due to the imposed potential difference across the ion selective cationic and anionic ion exchanges membrane.

• The driving forces is an applied electric field which induces a current driven ionic flux across the compartments. Electrokinetic transport of positively charged species through the cationic membrane and the negatively charged species through the anionic species depends of the differing ionic mobilities of the species within the ion exchange membrane.

• In a continuous flow system, at steady state, the effluents from alternate compartments comprise concentrated and depleted streams of ionic species.

Limitations of Electro-dialysis:• Non-charged, higher molecular weight, and less mobile ionic species will not typically be significantly removed.

• In contrast to RO, electrodialysis becomes less economical when extremely low salt concentrations in the product are required.

• Electrodialysis systems require feed pretreatment to remove species that coat, precipitate onto, or otherwise "foul" the surface of the ion exchange membranes. This fouling decreases the efficiency of the electrodialysis system.

• No Complex instrumentation.• Basic concept is simple to understand.• Separation can be carried out continuously.• Membrane processes can easily be combined with other

separation processes.• Separation can be carried out under mild conditions.• Membrane properties are variable and can be adjusted.• Greater design flexibility in designing systems.• Clean technology with operational ease.

Advantages of using Membrane:

• Membranes are relatively expensive;• Certain solvents, colloidal solids, especially graphite and other residues can quickly and permanently destroy the membrane surfaces;

• Oil emulsions are not "chemically separated," so secondary oil recovery can be difficult;

• Synthetics are not effectively treated by this method;• Biofouling/membrane fouling;• Low membrane lifetime;• Generally low selectivity;

Disadvantages of using Membrane:

•Development and Advancement of Nano-materials for effective membrane strength n separations.

•Over-coming the problem of Membrane Fouling.

•To design membranes for high selectivity.

Future challenges of using Membrane:

References:• Clever, M.; Jordt, F.; Knauf, R.; Räbiger, N.; Rüdebusch, M.; Hilker-Scheibel, R. (1 December 2000). "Process water

production from river water by ultrafiltration and reverse osmosis". Desalination. 131 (1-3): 325–336. • Laîné, J.-M.; Vial, D.; Moulart, Pierre (1 December 2000). "Status after 10 years of operation — overview of UF

technology today". • Water treatment membrane processes. New York [u.a.]: McGraw Hill. 1996.• Edwards, David; Donn, Alasdair; Meadowcroft, Charlotte (1 May 2001). "Membrane solution to a "significant risk"

Cryptosporidium groundwater source"• A. Y. Membrane Processing Dairy and Beverage Applications. Chicester: Wiley.

•  Mayank Omprakash; Bansal, Bipan; Chen, Xiao Dong (1 January 2008). "Fouling and cleaning of whey protein concentrate fouled ultrafiltration membranes"

•  Munir (1998). Ultrafiltration and Microfiltration Handbook• Concentration polarization in reverse osmosis desalination with variable flux and incomplete salt rejection, Ind. Eng.

Chem. • edited by Anil Kumar Pabby, Ana Maria Sastre, Syed S.H.; Pabby, Anil Kumar; Rizvi,, Syed S.H.; Sastre, Ana Maria

(2007).