Membrane Technology

Bernard A. Agana, PhD

University of Santo Tomas

Faculty of Engineering

Membrane Technology

- A physical separation process (similar to a filter)

- Has the advantage that the separated materials are neither

thermally nor chemically or biologically modified

- Applications include:

separation of activated sludge in municipal wastewater

treatment (up to the molecular range)

retention of dissolved salts in seawater desalination

- Important terms:

Feed or raw solution

Permeate or filtrate

Brine or concentrate

transmembrane pressure difference or transmembrane pressure

Membrane Technology

- Important terms cont’d:

Selectivity – ability to differentiate components of a mixture

Capacity or flow (volumetric flow rate per unit surface area; L m-2 hr-1)

- Operating principle of micro- and ultrafiltration membranes

Membrane Technology

- Filtration operating modes

Dead-end or static filtration

Cross-flow or dynamic filtration

Membrane Technology

- Filtration resistances

Membrane Technology

- Classifications of membranes

Pure pore membranes (“porous” membranes)

Pure solution-diffusion membranes (“dense” membranes)

based on sieving effect

differences in solubility and diffusivity are responsible for

selectivity

Membrane Technology

- Pressure-driven membrane processes in wastewater treatment

Membrane Processes Phase

Separation

Driving Force Application

Microfiltration (MF) Liquid/Solid P, 0.1 – 3 bars Separation of solid matter

from suspensions

Ultrafiltration (UF) Liquid/Solid P, 0.5 – 10 bars Separation of macromolecular

or colloids, disinfection

Nanofiltration (NF) Liquid/Solid P, 2 – 40 bars Separation of dissolved

organic molecules and

polyvalent inorganic ions

Reverse Osmosis (RO) Liquid/Solid P, 5 – 70 bars

In special cases

up to 120 bars

Separation of organic

molecules and of all ions

Membrane Technology

- Characteristic features of micro- and ultrafiltration

Microfiltration (MF) Ultrafiltration (UF)

Operation mode cross-flow and dead-end-

operation

cross-flow and dead-end-

operation

Operating pressure 0.1 – 3 bars (transmembrane) 0.5 – 10 bars (transmembrane)

Separating mechanism Screening controlled by

covering layer, if necessary

Screening controlled by

covering layer, if necessary

Molecular separation size Solids > 0.1 µm Colloids: 20,000 – 200,000

Dalton*

Solids > 0.005 µm

Membrane types Predominantly symmetric

polymer or ceramic

membranes

Asymmetric polymer composite

or ceramic membranes

Module types Spiral wound, hollow fiber and

tube modules, plate or

cushion modules

Spiral wound, hollow fiber and

tube modules, plate or cushion

modules

* Dalton, numerically equivalent to the molecular weight (MW) in [g mol-1]

Membrane Technology

- Typical applications of micro- and ultrafiltration

Municipal wastewater treatment

separation of activated sludge and water

disinfection

pretreatment prior to a reverse osmosis plant

phosphate removal after precipitation

Industrial wastewater treatment

Wastewater recycling and reuse as process water for different

uses

Recovery of water-based paint from spray booth effluents by

concentration

Concentration of water-oil emulsions

Membrane Technology

- Characteristic features of nanofiltration

Nanofiltration (NF)

Operation mode cross-flow-operation

Operating pressure 2 – 40 bars (transmembrane)

Separating mechanism Solubility/diffusion/charge (ion selectivity)

Molecular separation size Dissolved matter: 200 – 20,000 Dalton

Solids > 0.001 µm

Membrane types Asymmetric polymer or composite membrane

Module types Spiral-wound, tube, and cushion modules

Membrane Technology

- Typical applications of nanofiltration

Industrial wastewater treatment

removal of color in textile, pulp and paper industry wastewater

demineralization of wastewater containing surfactants

In general:

Retention of multivalent ions (e.g. SO4-2, Cd2+, Cr2+) but

permeation of monovalent ions (e.g. Cl-, Na+)

Retention of organic compounds

Separation of components with lower and higher molecular

weight in aqueous solutions

Membrane Technology

- Characteristic features of reverse osmosis

Reverse Osmosis (RO)

Operation mode cross-flow-operation

Operating pressure 5 – 70 bars (transmembrane), up to 120 bars

Separating mechanism Solubility/diffusion

Molecular separation size Dissolved matter: < 200 Dalton

Membrane types Asymmetric polymer or composite membrane

Module types Spiral-wound, tube, plate, cushion disc-tube modules

Membrane Technology

- Typical applications of reverse osmosis

Industrial wastewater treatment

concentration of drainage water from mines containing CaSO4

concentration of cellulose washing water

recovery of phosphoric acid

treatment of wastewater from bleacheries

treatment of landfill leachate

Membrane Technology

- Classification of membranes

Membrane

Synthetic

Liquid Solid

Organic

Non-porous Porous

Inorganic

Porous

Biological

Origin

Material

Morphology

Membrane Technology

- Membrane structure

Symmetric membranes – homogenous structure all over the

thickness of the membrane

Membrane Technology

- Membrane structure

Asymmetric membrane – made up of two layers

Active layer – determines the separation behavior of the

membrane

Support layer – ensures the mechanical stability of the

membrane

Membrane Technology

- Membrane structure

Asymmetric membrane (cont’d)

Also manufactured as phase inversion membranes (active

layer and supporting layer made from the same materials)

Membrane Technology

- Membrane module forms

Membrane form

• Module form

Tubular

• Tube module

• Capillary module

• Hollow-fiber module

Flat

• Spiral-wound module

• Cushion module

• Plate module

• Disc-tube module

Membrane Technology

- Tube module

Membrane Technology

- Capillary or hollow-fiber modules

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- Spiral-wound modules

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- Cushion module

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- Disc-tube module

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- Membrane Arrangement

Series connection

Parallel connection

- Membrane cleaning on flow (@ constant pressure)

Reference Journals:

Reference:

- Pinnekamp, J. & Friedrich, H. (eds.) 2006. Municipal Water and Waste

Management : Membrane Technology for Waste Water Treatment, Aachen:

FiW VERLAG.

- Desalination Journal

- Journal of Membrane Science

- Separation & Purification Technology

- Water Research

- Membrane Technology