2. What Are Membranes?
Membranes are thin films of synthetic organic
or inorganic (ceramic) materials, which can
bring about a very selective separation
between a fluid and its components. The
fluid may be a gas or a liquid but in
Environmental Engineering we are more
concerned with water and wastewater.
6. Applications of Membranes in
Wastewater Treatment
• Pressure driven solid liquid separation processes
• Tertiary treatment of wastewaters following
secondary sedimentation
• Production of high quality effluent in re-use
schemes
• Alternative to sedimentation tank for solid/liquid
separation in:
– aerobic biological treatment
– anaerobic biological treatment
9. Advantages of Membrane Processes
• They are usually continuous
• Comparatively low energy utilisation
• No phase change of contaminants
• Small temperature change
• Modular design
• Minimum of moving parts
• Physical separation of contaminants
12. Microfiltration Design Considerations
• High flux
• Back-flushable
• High membrane area/volume ratio allowing low pressure
drop whilst maintaining high tangential velocities
• Simple installation and continuous operation with
minimum supervision
• Low operating pressure
• Easy maintenance and simple membrane replacement
• Low energy consumption
• Relatively low capital costs
13. Microfiltration Applications
Current Future
Wine Drinking Water
Dextrose clarification Hydrocarbon Separation
Haze removal from gelatin Milk-fat Separation
Beer clarification Food and Beverage
Pharmaceutical/biological Industrial Wastewater
Municipal Wastewater Treatment Paint
Biotechnology
14. Ultrafiltration Applications
Current Future
Juice clarification Domestic wastewater
Increase cheese yield More industrial wastewaters
Gelatin concentration Protein harvesting
Electroplating wastewater Petroleum processing
Protein from cheese whey Wastewater re-use
Concentration of oil emulsions Potable water (THM concern)
Pharmaceutical industry Abattoir (blood recovery)
“Grey” water Pulp and paper industry
Industrial Wastewater etc etc
15. Reverse Osmosis
Very different process to MF of UF. It is a
solubilisation diffusion technique that makes use
of a semi-permeable membrane which in turn acts
as a barrier to dissolved salts and inorganic
molecules.
It also confines organics with molecular weights
greater than 100
RO membranes do not have identifiable pores as in
MF or UF (i.e. too small - atomic size)
16. Applications of Reverse Osmosis
Current Future
Desalination for potable water
,, from sea water Chemical process industries
,, from brackish water Metals recovery
,, for effluent re-use Food processing WWT
Ultrapure water for semiconductors Textile wastewater re-use
,, ,, for pharmaceuticals Pulp and paper WWT
,, ,, for medical use Contaminated land
remediation
Boiler feed water Dairy industry WWT
Treatment of hazardous materials
17. Comparison of Membrane Processes
Ultrafiltration Reverse Osmosis Microfiltration
Operates on difficult Requires extensive pre- Rapidly fouled by colloids
colloidal water treatment of colloids giving high replacement costs
Low pressure (2-6 bar) High pressure (10-30 bar) Low pressure (2-4 bar)
Low energy consumption High energy Low energy
High recovery (up to 95%) Low recovery (50-80%) 100% recovery
Chemical tolerance pH 1-13 pH 2-11 pH 1-13
High temperature up to 80oC 45oC max. High temperatures possible
High resistance to oxidising Limited resistance to High resistance to oxidising
agents oxidising agents agents
Stream sterilisable Stream sterilisation not Stream sterilisation possible
membranes available possible
Hygienic module designs Modules not as hygienic Hygienic designs available
available
18. Some Properties of Typical Commercial
Ultrafiltration Membranes
Material pH Maximum Pressure Maximum Temp.
(bar) (bar)
Polysulphone 2-12 15 70
Polyarcylonitrile 2-10 10 60
Cellulose Acetate 3-6 25 30
Polyethersulfone 2-12 30 70
Fluoropolymer 2-12 10 60
Polyvinylidene fluoride 2-12 10 70
Poly vinyl chloride 2-12 10 50
