Ultrafiltration membranes can reliably upgrade municipal wastewater to high-quality reuse standards—removing solids, pathogens, and emerging contaminants—by optimizing air scouring, filtration cycles, solids concentration, and low-dose acid cleanings to dramatically reduce fouling and enable long-term, high-flux operation.
Move the sliders and watch what happens! Higher Flow Speed = faster fouling. Higher Air Bubbles = less fouling. Higher Solids Level = less clogging. Click Clean Membrane to simulate a chemical wash. The graph now zooms in so even small changes in pressure (TMP) are clearly visible.
If you’ve ever wondered how cities can safely reuse wastewater for irrigation, agriculture, or even industrial processes, ultrafiltration membranes (UF) are quickly becoming the star of the show ⭐. A recent study explores how ultrafiltration membranes can step in—not just as a tertiary treatment, but even as a quaternary polishing step—to push water quality to the next level.
Let's unpack how ultrafiltration membranes performed in real municipal wastewater treatment plants (WWTPs), what challenges they faced, and how researchers overcame them to achieve crystal-clean water 💧✨.
Water scarcity is tightening its grip globally 🌍. With 40% of the world in arid or semi-arid regions, and freshwater sources stretched thin, reclaimed wastewater is becoming an essential water source.
But here’s the problem:
Traditional tertiary treatments often fail to remove modern contaminants, like:
Enter Ultrafiltration membranes, with tiny pores around 0.03 µm—small enough to remove bacteria, suspended solids, many viruses, and even microplastics.
This research explores whether ultrafiltration membranes can take over existing tertiary systems and help cities meet strict new regulations like the EU’s 2020/741 on water reuse.
Spoiler: they can. And they do it well. 😎
Researchers didn’t just simulate this in a lab—they installed a semi-industrial ultrafiltration membranes system at a real WWTP in Spain 🇪🇸 that treats municipal wastewater.
The supernatant from the secondary settler—water already partially cleaned, but still containing dissolved organic matter, colloids, SMPs, and pathogens.
Researchers tested how different variables influence fouling and filtration performance:
Their mission?
To maximize water production while minimizing fouling and energy use.
Fouling is the arch-nemesis of membranes 😈.
This study found much more fouling than expected, even at modest fluxes (10–17 LMH). The culprits?
Mostly from SMPs (Soluble Microbial Products) that cling to the membrane surface.
Mainly from scaling—especially phosphate-based precipitates.
Surprisingly, fouling looked more like that in membrane bioreactors (MBRs) than in typical post-settlement tertiary systems. Why?
Because the supernatant still contains sticky organic molecules and colloids that love clogging membranes.
But the researchers didn’t stop there—they fought back 💪.
Here’s where the engineering magic happens ✨.
The team tested multiple long-term strategies to keep the membranes clean and productive.
Raising air flow from 0.1 to 0.25 m³/m²·h:
❌ Reduced TMP growth by over 50%
⏱️ Doubled operational time without chemical cleaning
✔️ Improved removal of reversible fouling
Air bubbles create turbulence, shaking off foulants like dust off a carpet 🌬️.
Shorter filtration cycles plus more frequent permeate backwashing = major fouling relief.
Going from 300s filtration / 60s relaxation (BW every 10 cycles) to 150s filtration / 30s relaxation (BW every 5 cycles).
💥 Fouling rate dropped from 31.9 → 3.7 mbar/day.
Small changes, huge impact!
This part was counterintuitive 🤔
You’d think more solids = more fouling, but the opposite happened.
Raising TSS from 0.4 → 3–4 g/L:
⬇️ Fouling dropped from 100 mbar/day → 0.3 mbar/day
🛑 SMP/TSS ratio fell drastically
⚫ Extra particles help “capture” colloids that would otherwise foul the membrane.
Think of it like adding gravel to stop mud from clogging a drain—surprising, but it works! 🪣
To tackle irreversible fouling, researchers tried:
Citric acid was highly effective at eliminating scaling.
Even better?
Low concentrations used every 15 days were enough.
This drastically reduced chemical usage and made the process much more economical.
After combining all optimal strategies, researchers ran a final long-term test:
🎉 Result:
A ridiculously low fouling rate of 0.024 mbar/day, enabling:
👉 35+ days of continuous operation with almost no fouling
👉 Theoretical continuous operation of 1+ year without major chemical cleaning
This is a game changer for real-world UF operation 🔥.
Here’s what the ultrafiltration membrane removed:
| Parameter | Removal |
|---|---|
| Suspended solids (TSS) | 100% |
| Turbidity | 92% |
| COD | 56% |
| BOD₅ | 60% |
| E. coli | 100% |
| Nematodes | 100% |
| Legionella | 100% |
| DNA residues | Below detection |
This meets the EU’s highest standard for reused water (Class A)—suitable for:
🌾 Agricultural irrigation
🌴 Landscape watering
🔧 Industrial reuse
🔄 Nutrient recovery processes
Safe. Clean. Reliable.
This study shows that ultrafiltration membranes can realistically replace or complement existing tertiary treatments—but with smarter fouling control strategies.
✔️ Higher water reuse rates
Cities can reclaim more water safely.
✔️ Better removal of emerging contaminants
Including microplastics and some pharmaceuticals.
✔️ Better integration with nutrient recovery
No solids = easier ammonia and phosphate recovery.
✔️ Lower energy & chemical use
Thanks to optimized air sparging and low-dose CEB.
✔️ Scalability
Researchers used commercial ultrafiltration membranes modules, meaning this setup can be replicated at full scale.
The study suggests several areas for future engineering research:
🧬 Analyzing how SMP composition affects UF fouling
💎 Understanding phosphate scaling mechanisms more deeply
👷 Life cycle assessment (LCA) to evaluate long-term cost and sustainability
🧪 Exploring hybrid processes: UF + ozone, electrooxidation, or MBRs
💧 Optimizing flux ranges for different wastewater compositions
Ultrafiltration membranes is not just a filter—it’s a cornerstone technology in the emerging circular water economy.
This research makes one thing clear:
Ultrafiltration membranes are ready to upgrade municipal wastewater treatment into a more sustainable, reliable, and high-performance system.
With smart operation strategies—especially controlling fouling—UF can deliver top-tier reclaimed water quality with long-term stability. This puts us one step closer to a world where wastewater isn’t wasted 🌍💙.
Ultrafiltration (UF) Membrane 🧽 A thin, porous filter that lets water pass through while blocking tiny particles like bacteria, solids, and some viruses—kind of like a super-powered coffee filter.
Transmembrane Pressure (TMP) 🎚️ The pressure difference across a membrane that pushes water through it; higher TMP usually means the membrane is getting clogged.
Flux (LMH) 💧➡️ The flow rate of water passing through a membrane, measured in liters per square meter per hour—basically the membrane’s “productivity speed.”
Fouling 🧫 The buildup of unwanted material (like organic goo, particles, or minerals) on the membrane surface that slows filtration and raises energy use. - More about this concept in the article "Higher Performance Cleaning 🚰 How Supercharged Nanofiber Membranes Are Changing Wastewater Treatment".
Reversible Fouling 🔄 Fouling that can be easily removed by simple cleaning methods like backwashing or relaxation.
Irreversible Fouling 🚫 Hard-to-remove buildup deep in membrane pores that requires chemical cleaning to fix.
Air Sparging (SAD) 💨 The injection of air bubbles near the membrane to shake off particles and reduce fouling.
Backwashing 🔁 Pushing clean water backward through the membrane to clean off accumulated dirt.
Filtration/Relaxation (F/R) Cycles ⏳ Alternating between filtering water and briefly “resting” the membrane so accumulated particles can loosen and wash away.
Chemically Enhanced Backwash (CEB) ⚗️ A cleaning step where mild chemicals (like citric acid) are added during backwashing to remove tougher foulants.
Soluble Microbial Products (SMPs) 🧬 Tiny organic molecules released by microorganisms that tend to stick to membranes and cause fouling.
Total Suspended Solids (TSS) ⚫ Particles floating in water, like silt, sludge, and organic bits—UF membranes are great at removing them. - More about this concept in the article "Turning Waste into Watts 💧💡 How Smart Control is Powering Energy-Free Wastewater Plants!".
COD/BOD5 ⚗️ Measures of how much organic pollution is in water; high values mean dirtier water, while lower values mean cleaner water.
Secondary Settler Supernatant 🌊 Partially treated wastewater that has already gone through settling tanks—cleaner than raw sewage, but not ready for reuse yet.
Scaling 💎 Mineral precipitation (like phosphate crystals) on membrane surfaces that causes irreversible fouling.
Source: Acebrón, Á.S.; Revert-Vercher, J.; Sanchis-Perucho, P.; Borrás, L.; Seco, A. Use of Ultrafiltration Membranes as Tertiary/Quaternary Treatment for Wastewater Reclamation in Municipal WWTPs. Water 2025, 17, 3453. https://doi.org/10.3390/w17243453
From: Universitat de València.
