Ultrafiltration as RO Pre-Treatment
Hollow-fiber ultrafiltration (0.01 micron absolute) installed upstream of reverse osmosis removes colloids, suspended solids and bacteria that cause silt fouling, keeping RO feedwater at a low silt density index (SDI), reducing RO cleaning frequency and extending element life. U.S. Bureau of Reclamation life-cycle analysis of seawater RO plants found membrane pretreatment lowered total water cost 4-8% versus conventional media filtration.
RO elements fail mainly by fouling: colloids and biofilm plug the feed spacer long before rejection drops. Coagulation and cartridge filtration often cannot hold SDI low enough on surface water. A 0.01 micron PVDF UF stage removes the foulants physically - no chemicals in the barrier step - and is backwashable, so the protection does not expire after one season.
What filtration rating do I need before an RO membrane?
0.01 micron absolute (UF), not 1-5 micron nominal (MF). RO feedwater targets SDI15 below 5; nominal cartridges pass the colloids that drive silt fouling. SDI - not turbidity - is the practical indicator of RO fouling potential.
Does UF pretreatment really reduce RO cleaning and element replacement?
Published plant data says yes. The U.S. Bureau of Reclamation seawater RO pretreatment study reported significantly lower RO cleaning frequency with membrane (micro/ultrafiltration) pretreatment versus media filtration, and a 4-8% lower total water cost on a life-cycle basis. Actual gains scale with feedwater quality.
How do two UF modules clean each other?
Two H-1 modules can be plumbed so each periodically backwashes the other using filtered water - the arrangement commonly used on coin-operated water vending machines. No chemical tank, no operator round, no power at the membrane stage.
Typical configuration
H-1 Whole-House UF Water Purifier
Horizontal whole-house ultrafiltration purifier in food-grade 304 stainless steel, with a uniform Φ168 mm cylinder and flow options from 3000 to 10000 L/h. PVDF or PVC membrane at 0.01 micron, no electricity required.
- · Coarse load capture
R-A1 5-Stage RO System 100 GPD
Five-stage reverse osmosis system with booster pump: PP, UDF, CTO, a 100 GPD RO membrane and T33 post-carbon, rated 45 W at 200 V / 50 Hz. Modular interchangeable cartridges and a 400 × 180 × 465 mm under-sink footprint.
3,000 / 5,000 / 8,000 / 10,000 L/h · 0.01 micron; washable element
Frequently asked questions
Does the UF stage need electricity?
No. H-1 runs on inlet water pressure from 0.1 MPa (about 1 bar / 145 psi - normal mains pressure) with no power at the membrane stage.
How do I clean a fouled UF element?
Remove and rinse; the stainless housing is washable and the PVDF element tolerates brush cleaning and standard CIP solutions. Rated element life is up to 24 months depending on feedwater load.
Does UF remove dissolved salts?
No - that stays the RO stage job. UF is the particle, colloid and bacteria barrier upstream of RO, never a replacement for it.
Source: U.S. Bureau of Reclamation, Research Report 106: Evaluation of Membrane Pretreatment for Seawater Reverse Osmosis Applications. https://www.usbr.gov/research/dwpr/reportpdfs/Report106.pdf
Work out the numbers
Send us your feedwater analysis or a worst-case description - we size the UF stage against your RO recovery target.