1. Reverse Osmosis Ultrafiltration Microfiltration
MEMBRANE PROCESSES
Reverse Osmosis
Ultrafiltration
Microfiltration

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.

3. Microfiltration
Dead-end Filtration
Feed
Filter Cake
Membrane
Permeate

4. Microfiltration Crossflow Microfiltration Feed Retentate Membrane
Permeate
Notes: The retentate may be recirculated to the feed
A “dynamic” membrane may be created by adding Lime or KMnO4 to the feed, to precipitate MnO2 on membrane

5. Membrane Operation Feed Concentrate 100% 50% ! Membrane Permeate 50% !
Suspended Solids
Colloids
Dissolved Solids
Concentrate
Suspended Solids
Colloids
Dissolved Solids
100%
50% !
Membrane
Permeate
Low molecular
weight dissolved
solids
Liquid
50% !
To River, Sewer or Re-use

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

7. Aerobic Biological Treatment with Membrane Separation
Final Effluent
BOD <2 SS
Aerobic
Biological
Process
Sed
Tank
Pretreatment MF
Influent
BOD 300 SS
TKN 50 PO
Primary
Sludge
Secondary
Sludge

8. Membrane Anaerobic Reactor
Influent
Effluent
UF/MF Unit
Anaerobic Reactor
Wastage
Recycle
Gas

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

10. Filtration Range
micro-molecular
coarse
particles
Ionic range
macro-molecular
microorganisms
Reverse Osmosis
Ultrafiltration
Nanofiltration
Microfiltration
MWCO
microns

11. APPLIED PRESSURES Reverse Osmosis: 100-800 psi 1000-5500 kPa
Ultrafiltration: psi
kPa
Microfiltration: Low

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 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
Polyarcylonitrile
Cellulose Acetate
Polyethersulfone
Fluoropolymer
Polyvinylidene fluoride
Poly vinyl chloride