Inside-out ultrafiltration membrane (also called an inner-pressurized UF) is a hollow-fiber membrane in which raw water enters the lumen of each fiber and permeate flows from the inside to the outside through the membrane wall under a low trans-membrane pressure (TMP). Particles, colloids, and bacteria are retained on the lumen side, while clarified water passes the pores and is collected on the shell side.
1) Inside-out ultrafiltration membrane — working principle & flow direction
Flow path for inside-out UF: feed → fiber lumen → filtration across the wall → permeate collected on the outside → concentrate leaves via the lumen. End-potting (e.g., epoxy) seals both ends so feed cannot bypass into the permeate channel. Compared with outside-in, inside-out typically operates at lower pressure and allows quick backwash/air scour to recover flux.
2) Construction & operating essentials
- Hollow fibers in parallel with sealed potting separate feed and permeate safely.
- Low TMP at ambient temperature is sufficient; stable TMP is key to lifetime.
- Backwash & chemical cleaning: periodic backwash with permeate, optional air scour, and CIP (acid/alkaline) restore performance after fouling.
3) Benefits & limitations
- Benefits: low energy, high automation, up to ~95% water recovery (application dependent), compact footprint, and simple O&M.
- Limitations: oil/viscous feeds or high fouling loads may clog fibers; reliable pretreatment and a realistic cleaning strategy are necessary.
4) Typical applications
- RO pretreatment: seawater/brackish water, surface water, and well water polishing (turbidity/Silt Density Index control).
- Drinking water polishing: mineral/spring water and municipal polishing before disinfection.
- Process water: pure/ultrapure water trains (incl. post-EDI polishing) for bacteria/colloid removal.
- Water reuse & ZLD steps: municipal/industrial reuse, cooling/condensate recovery.
- Pharma/electronics/food & beverage: bioburden control, clarification, haze removal.
- Public & residential: point-of-entry/point-of-use systems, aquaculture recirculation water.
5) Inside-out vs outside-in UF (quick comparison)
| Aspect | Inside-Out UF | Outside-In UF |
|---|---|---|
| Feed path | Feed in lumen; permeate flows inside → outside | Feed on shell side; permeate flows outside → inside |
| Operating pressure | Generally lower | Typically higher |
| Backwash/air scour | Fast and effective | Depends on module design |
| Where it fits | RO pretreatment, polishing, reuse | Similar domains—choose by feed quality & footprint |
6) Selection checklist (what to confirm before sizing)
- Feed quality: turbidity/SS, colloids/organics, oil, iron/manganese.
- Targets & scale: permeate flow, recovery, outlet specs (turbidity/SDI/bacteria).
- Polymer & module: common materials include PVDF and PES—check chemical and thermal limits.
- Pretreatment & dosing: coagulation/clarification, fine filtration, oxidants, acids/alkalis/reductants (ensure compatibility with the membrane).
- Cleaning strategy: backwash interval, CIP recipes/temperature, safety handling.
- Lifecycle cost: energy, chemicals, consumables, labor and planned downtime.
7) Design & O&M quick notes
- Set backwash correctly based on ΔP/flux trend; add air scour where allowed by the module.
- CIP trigger lines: run cleaning when normalized flux drops or ΔP rises to your threshold (e.g., ~10–15% change).
- Normalization: correct for temperature/viscosity before judging performance.
- Safety & compliance: chemical storage/dosing, neutralization & discharge, hygiene and lock-out/tag-out during service.
8) FAQs
Q1. Is an inside-out ultrafiltration membrane better than outside-in?
Each has its place. Inside-out often wins for low-pressure operation and quick backwash, but the best choice depends on feed quality, space, and existing utilities.
Q2. What recovery can I expect?
With suitable pretreatment and tuning, water recovery can reach around 95% in many applications; confirm with pilot data and vendor guidelines.
Q3. How does UF compare with NF/RO?
UF is a screening process that removes suspended solids, colloids, and bacteria at low pressure. NF/RO target dissolved salts and small organics and require higher pressure/energy.
Q4. Can UF be used directly for drinking water?
UF sharply lowers turbidity and microbes, but potable use typically requires post-disinfection (UV/chlorine) and compliance with local regulations.
Q5. How do I minimize fouling?
Stable pretreatment, optimized coagulant dosing, disciplined backwash/CIP, and excluding oil/large particles. Track TMP/flux/SDI to act before fouling becomes irreversible.
9) Next steps (RFQ & resources)
Een offerte aanvragen - RO dimensioneringscalculator - UF/RO systems - UF consumables & accessories - Stainless-steel tanks & skids
Engineering notice
Always confirm membrane chemical limits, compatibility and cleaning windows with the specific module supplier. Pilot testing is strongly recommended when feed quality varies seasonally or contains oil/organics.
Samenvatting
This guide explained what an inside-out ultrafiltration membrane is, how it works, and when to choose it over outside-in. Combine realistic pretreatment, conservative flux and clear cleaning triggers to achieve reliable SDI control and long membrane life—then scale with pilot data for confident CAPEX and OPEX planning.
Referenties en verder lezen
- WHO - Richtlijnen voor drinkwaterkwaliteit - ISO 20468-1 – Guidelines for water treatment systems