Membrane Technology Bernard A. Agana, PhD University of Santo Tomas Faculty of Engineering
Dec 31, 2015
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
- 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
- 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