Clean water in
Ultrafiltration (UF)
Particles and microbes out. Minerals stay in.
Ultrafiltration is a membrane filter with pores far finer than any sand bed — fine enough to stop bacteria and colloids — yet open enough to let dissolved minerals through. It needs only low pressure and wastes little water.
What it means
A UF membrane is a bundle of thousands of hollow fibres, each like a thin straw whose wall is full of microscopic pores, typically around a hundredth of a micron to a tenth. Water is pushed through the fibre walls; what is bigger than the pores stays behind.
That pore size is the point. It is small enough to hold back suspended solids, colloids, bacteria and most cysts, giving clear water with a consistently low turbidity. It is large enough that dissolved salts and minerals pass, so the water keeps its character.
UF is often used just before an RO plant: it hands the RO membranes clean, particle-free water, which is what they need to last.
How it works
Step by step, as drawn in the diagram above.
- 1
Feed water in
Pre-filtered water is pumped into the UF module at low pressure.
- 2
Through the fibre walls
Water passes through the pores in the hollow-fibre walls; particles, colloids and bacteria are held on the surface.
- 3
Clean permeate out
The filtered water — the permeate — collects and leaves the module.
- 4
Backwash
At intervals, permeate is pushed back the other way to lift what has gathered on the fibres and flush it to drain.
Keeping the fibres clean
UF runs in short cycles: filter, then backwash, with occasional chemical cleaning.
- 1 Filtration Water passes through the fibre walls; solids build up on the surface.
- 2 Backwash Permeate is reversed through the fibres to lift the layer off, often every few tens of minutes.
- 3 Chemically enhanced backwash Periodically a dilute chemical is added to the backwash to remove what water alone cannot.
- 4 Clean-in-place Occasionally the module is soaked in cleaning solution to restore its flow.
What it takes out
- Suspended solids and turbidity
- Colloids
- Bacteria and most cysts
- Much of the larger organic matter
What it does not
- Dissolved salts and minerals (TDS)
- Hardness
- Dissolved gases and some dissolved organics
Where it is used
- Safe water where TDS is already acceptable
- Pre-treatment ahead of RO
- Apartments and campuses
- Food and beverage pre-treatment
- Recycled water polishing
What we size it on
- Required flow of filtered water
- Turbidity and solids in the feed
- Feed water temperature
- Backwash frequency and the water it uses
Looking after it
- Keep pre-filtration working — UF should not see heavy silt
- Watch trans-membrane pressure; a steady rise means cleaning is due
- Carry out chemical cleaning as scheduled
- Integrity-test modules periodically
Questions, answered
What is the difference between UF and RO? ＋
UF stops particles, colloids and bacteria but lets dissolved minerals through, at low pressure and with little waste. RO also removes dissolved salts, needs a high-pressure pump and produces a reject stream.
Does UF reduce TDS? ＋
No. Dissolved salts pass through UF membranes. If TDS is high, an RO is needed.
Why put UF before an RO? ＋
RO membranes foul quickly when particles reach them. UF delivers consistently clean feed, so the RO runs longer between cleans.
The rest of the treatment train
Clean water in
Water Softeners
Hardness out. Scale, white spots and failing geysers with it.
Clean water in
Sand & Carbon Filters
Particles out with sand. Chlorine, odour and colour out with carbon.
Clean water in
Industrial RO Skid Systems
Dissolved salts out — the one thing no filter can touch.
Clean water out
Sewage Treatment Plants (STP)
A building’s sewage, treated well enough to use again.
Clean water out
Effluent Treatment Plants (ETP)
Industrial effluent, treated to meet discharge or reuse norms.
Send us your water report
Or tell us where your water comes from — we design the treatment train, install it and stand behind it.