If you’ve worked with MBR membranes, you know they’re game-changing for wastewater treatment—compact, high-efficiency, way better than traditional activated sludge for most applications. But let’s be real: those membranes get dirty fast, and skipping the right cleaning routine will kill their lifespan, slash flux, and turn your whole system into a headache. As a supplier who’s talked to hundreds of operators (from small municipal plants to food manufacturing facilities), I’ve seen every mistake people make when cleaning MBRs. Today, I’m breaking down exactly how to do it effectively, no fancy jargon, just real stuff we use every day. MBR Membrane
First, let’s get one thing straight: not all fouling is the same. If you grab the same cleaning recipe for every dirty membrane, you’re wasting time and money. I’ve had a plant owner call me panicking because their membrane flux dropped 40%—turns out they used acid to clean organic fouling, and it did nothing. So, before you even touch chemicals, you need to figure out what’s clogging those fibers. The two main culprits are organic fouling (think leftover sludge, bacteria, food waste, that slimy gunk that builds up on surfaces) and inorganic fouling (scaling from hard water, heavy metals, salts, or even tiny silt particles that get stuck in the pores). Sometimes you get both, which is even trickier.
How do you tell which is which? Do a quick check: pull a small sample of membrane fibers (wear gloves, they’re fragile!) and rinse them with tap water. If they still feel slimy or gross, it’s organic. If they feel rough or have white, crusty spots, that’s inorganic. Most cases are a mix, so you’ll likely need a two-step clean later.
Now, let’s talk about the two types of cleaning: routine regular cleaning and deep (offline) cleaning. Regular cleaning is what you do every few days/weeks during normal operation to keep minor fouling from building up, and deep cleaning is for when flux drops 15-20% from baseline, which is when you can’t just do the daily stuff anymore.
Starting with routine cleaning—this is non-negotiable, and it’s way easier than fixing a bad deep clean later. The go-to here is usually a low-concentration chemical solution, plus some physical shearing. Wait, shearing? Yeah, that’s just the force that lifts gunk off the membrane surface, usually from aeration. Most MBR systems have coarse bubble aeration running 24/7, but turning up the intensity during routine cleaning for 30-60 minutes a few times a week makes a huge difference. I tell my clients to bump aeration to 1.5x normal during routine cleanings—just don’t crank it so hard it breaks fibers, that’s a waste.
For chemicals in routine cleaning, we stick to mild stuff so we don’t damage the membrane’s PVDF material (most MBRs are made of PVDF, by the way, never use anything that eats at that plastic). Common options are sodium hypochlorite (bleach, but not the smelly old laundry kind—use food-grade or industrial-grade, no additives) at 500-1000 ppm, or citric acid if there’s a hint of scaling. I’ve had a small brewery client who only ran routine cleaning with 750 ppm bleach once a week, and their membrane lasted 4 years with zero deep cleans before that. Pro tip: don’t mix bleach with anything else—vinegar, ammonia, whatever—it makes toxic fumes that will ruin your day.
Now, deep offline cleaning—this is when you need to take the membrane module out of the tank, or at least isolate it, to do a heavy clean. A lot of people make the mistake of trying to deep clean the membrane still in the tank, and they just don’t get the gunk out of the pores. Let’s split this into organic fouling deep clean and inorganic fouling deep clean, since they need totally different chemicals.
Organic fouling deep clean: For this, you want a stronger bleach solution, usually 5000-10,000 ppm, plus a surfactant to help the solution get into those tiny pores. Surfactants break up that slimy biofilm so the bleach can kill the bacteria and dissolve the organic matter. The process here is: first, rinse the module with clean water to get rid of loose sludge, then soak it in the bleach-surfactant solution for 1-4 hours (don’t leave it longer than 4—bleach can eat at PVDF over time if left too long). After soaking, do a light physical scrub with a soft brush on the surface (never hard-bristled, that will scratch the membrane) and then rinse thoroughly until the water runs clear. I always tell clients to test the pH after rinsing—bleach will make pH high, so you need to get it back to neutral before putting the module back.
Inorganic fouling deep clean: This is all about acid, because inorganic gunk is usually mineral scale. Citric acid is our go-to here, since it’s milder than hydrochloric acid and less likely to damage the membrane. Mix a 2-5% citric acid solution (warm it up to 30-40°C, that helps it dissolve scale faster—hot works better than cold) and soak the module for 2-3 hours. If the scale is really bad (like white crust that won’t budge), you can bump citric acid to 10% max, but never go higher than that, and never use sulfuric acid unless you’re 100% sure your membrane is compatible. After soaking, rinse well and check pH again—acid will make it low, so get it back to neutral before reassembling.
Wait, what if you have both organic and inorganic fouling? That’s the messy middle case, super common for municipal plants that deal with all kinds of wastewater. Do the organic clean first, then the inorganic, not the other way around. If you do acid first, it will dissolve some inorganic gunk, which might release stuff that reacts with the bleach later and makes it less effective. Trust me, I had a city plant mess this up and end up with a membrane that smelled like bleach for weeks—avoid that order.
Now, let’s talk about mistakes I see all the time, because even if you know the steps, cutting corners ruins membranes. First, overusing chemicals. A lot of operators think if a little is good, more is better—nope. Too high concentration of bleach will break down the PVDF fibers, make them brittle, and they’ll start tearing after a year or two instead of 5-7. Same with acid: too strong etches the membrane pores, which lets smaller particles pass through, ruining filtration efficiency. I once had a client who used 15,000 ppm bleach for a deep clean, and their flux never came back—they had to replace the whole module 6 months later. $20k wasted because they thought more chemical = better clean.
Second mistake: not replacing the cleaning solution. If you’re soaking a module in old bleach that’s lost its strength, that’s useless. Test the concentration of your cleaning solution before you use it—bleach breaks down over time, so if it’s been sitting in a bucket for a week, it’s probably half as strong as you think. Same with citric acid: if it’s cloudy or has sediment at the bottom, make a new batch.
Third mistake: skipping post-clean aeration and flush. After you clean, you need to run high aeration for another 30 minutes to flush any leftover gunk and solution out of the membrane. If you just put it back online right away, residual chemicals will mess with your wastewater treatment process, and any leftover small particles will clog the system again.
Also, a quick note on online vs offline cleaning for new operators. For most small to medium systems, you don’t need to pull modules out for routine or even semi-deep cleans. You can run online cleaning by dosing the chemical into the tank, turning aeration up, and recirculating for a few hours. That’s way less work than offline. Only do offline when online cleaning doesn’t bring flux back to baseline, or when you have really heavy fouling that’s stuck in the pores.
Let’s add a real example to make this concrete. Last year, a food processing plant (they make frozen veggies, so their wastewater has lots of organic matter and fine silt) called me because their flux dropped 35% after 18 months of operation. I had them test a fiber sample—slimy, so organic fouling, plus a little white scaling from the water they use. We did an online routine clean first with 800 ppm bleach, turned aeration up to 1.5x normal, ran it for 2 hours—flux came back 10%, still low. Then we did an offline deep clean: 7500 ppm bleach + surfactant soak for 2 hours, followed by 3% warm citric acid soak for 2.5 hours. After rinsing and reinstalling, their flux was back to 98% of baseline, and they’ve been running great for another year. That’s the kind of result you get when you match the clean to the fouling.
One last pro tip: keep a cleaning log. Write down when you do routine cleans, what concentration you used, when you do deep cleans, what the flux was before and after, and any notes about the water (like if it’s been cold lately, or if the wastewater source changed). This helps you spot patterns—like if flux drops every time your plant has a big batch of processing waste, you can adjust your cleaning schedule before it gets bad. I’ve had clients who kept logs and cut their deep clean frequency by half just by bumping up routine cleans during busy periods.
Now, if you’re new to MBR membranes or just tired of dealing with fouling that won’t budge, don’t guess at what to do. We work with all kinds of facilities, from small industrial operations to large municipal plants, to help them tailor cleaning routines that fit their specific setup. Whether you need help troubleshooting a bad clean, ordering the right cleaning chemicals, or just want to learn how to extend your membrane lifespan, we’re here to help. Reach out to discuss your system and find the best cleaning plan for you.
Cartridge Filter References
- “Membrane Bioreactors for Wastewater Treatment: Principles and Practice”
- “Fouling Control in Membrane Bioreactors: A Review of Current Strategies”
- “PVDF Membrane Compatibility with Common Cleaning Agents for MBR Applications”References
- Membrane Bioreactors: Fundamentals and Applications, Elsevier, 2018
- Fouling Mitigation Strategies for Submerged Membrane Bioreactors, Water Research, Vol. 127, 2017
- Compatibility of Polyvinylidene Fluoride Membranes with Alkaline and Acidic Cleaning Solutions, Journal of Membrane Science, Vol. 515, 2016
- Operational Guidelines for MBR Cleaning: Routine vs. Offline Protocols, Water Environment Federation, 2019
Nantong Delta Filtration Material Co., Ltd.
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