If you’ve worked with Membrane Bioreactor (MBR) systems, you know they’re a game-changer for wastewater treatment: they combine biological treatment with solid-liquid separation, produce high-quality effluent, and take up less space than conventional activated sludge systems. But one challenge that’s plagued MBR operators since they moved beyond niche industrial use is biofilm formation on the membranes. As an MBR supplier with over a decade of hands-on experience helping facilities tweak their setups to run smoother, I’ve seen this issue turn a well-performing system into a maintenance headache— and I’ve also seen how proactive, informed strategies can turn it around. Today, I want to break down exactly what biofilm does to MBR membranes, the good (yes, there is some), the bad, and what we as a supplier bring to the table to help operators balance performance and cost. MBR Membrane Bioreactor Systems
First, let’s get on the same page about what biofilm in MBRs actually is. It’s not just “gunk” on a filter. Biofilm is a structured community of microorganisms— bacteria, fungi, protozoa, even algae in some cases— that stick to the membrane surface (or to each other) and embed themselves in a slimy matrix of extracellular polymeric substances, or EPS. That EPS is key: it’s made of proteins, polysaccharides, nucleic acids, and lipids, and it’s what lets the biofilm adhere tightly to the membrane, resist cleaning agents, and protect the microbial community from changes in the wastewater environment. It starts small, too: first, organic matter and ions from the wastewater adsorb to the hydrophobic or slightly charged membrane surface within minutes of startup, creating a conditioning film. Then, planktonic (free-floating) bacteria stick to that conditioning film, multiply, and build out the full biofilm within days, sometimes hours, depending on the wastewater feed.
Now, the effects of this biofilm— and they’re split right down the middle, which surprises a lot of new operators. The first, and often least talked about, is the beneficial side. MBRs rely on the entire biological process to break down contaminants, and some of the biofilm on the membrane surface is part of that treatment ecosystem. Biofilm microorganisms often have higher metabolic activity for slowly degrading compounds— like persistent organic pollutants (POPs) or complex pharmaceuticals— than planktonic bacteria, because they’re held in a stable, nutrient-rich environment right at the separation interface. In fact, a thin, controlled biofilm (measured in micrometers, not millimeters) can even improve membrane performance slightly by preventing fine suspended solids from embedding deep into the membrane pores. It acts as a buffer between the bulk wastewater and the membrane surface, so you don’t get irreversible pore blockage from large particulate matter. We’ve seen this firsthand at facilities treating municipal wastewater for small towns: when biofilm is kept to a consistent thickness of 5–10 micrometers, COD (chemical oxygen demand) removal rates stay 2–3% higher than systems with no surface biofilm at all.
But let’s be honest— this is a tiny fraction of the story. The harmful effects of excessive biofilm are why biofouling is one of the top three reasons MBR systems experience downtime, right after pore blockage and scaling. The biggest hit is to membrane permeability, which is the measure of how easily water passes through the membrane. As biofilm grows, it builds up a layer of EPS and trapped solids that add an extra resistance to water flow. We quantify this as trans-membrane pressure (TMP): as fouling increases, TMP rises, and higher TMP means more energy is needed to push water through the membrane. For a medium-sized MBR system (5,000 m³/day), a 10 kPa increase in TMP can add $15,000–$20,000 a year in electricity costs alone. Over time, excessive biofilm can also narrow or even fully clog membrane pores— that’s irreversible fouling, because the EPS and trapped biomass get stuck in the tiny, 0.04–0.4 micrometer pores of most MBR membranes, and even harsh cleaning agents can’t dislodge it. We had a customer last year who skipped routine biofilm monitoring, and their TMP jumped 30 kPa in six months; by the time they called us, 15% of their membrane modules were irreparably fouled and needed replacement.
Another underdiscussed negative effect is increased maintenance frequency. Operators used to run chemical cleaning every six months, but with heavy biofilm, you might need to do a citric acid or sodium hypochlorite clean every three months— or even more often for high-strength industrial wastewater. Each cleaning cycle uses chemicals, takes the system offline for 12–24 hours, and shortens the lifespan of the membrane itself. The average MBR membrane lasts 7–10 years, but heavy biofouling can cut that lifespan by 2–3 years, which adds $50,000–$100,000 in capital costs over the system’s life. There’s also the operational headache: biofilm can slough off in large chunks, which can flow downstream and contaminate the effluent, or clog other parts of the MBR process, like the aeration tanks or permeate lines. We had an industrial food processing customer a few years back that had to shut down their entire system for 48 hours when a biofilm slug blocked their permeate outlet, leading to a $12,000 loss in product (they treat wastewater that’s reused for process water, so downtime meant no new reuse for their production line).
Now, why does biofilm form so differently in MBRs vs. other wastewater systems? It all ties back to how MBRs operate: constant aeration for biological treatment, high cross-flow velocity (in most designs) to keep solids suspended, and a high concentration of mixed liquor suspended solids (MLSS) in the tank— often 8,000–12,000 mg/L, compared to 2,000–4,000 mg/L in conventional activated sludge. That high MLSS means more microorganisms are in contact with the membrane surface, and the aeration creates shear force that, when balanced correctly, can keep biofilm thin, but when unbalanced, can also cause shear to vary across the membrane module, leading to patchy biofilm growth. We’ve found that a lot of new MBR operators don’t tune their aeration rates correctly for their specific wastewater: for example, a system treating municipal sewage needs a different aeration setpoint than one treating pharmaceutical wastewater, because the latter has slower-growing microorganisms that stick more tightly to the membrane.
As an MBR supplier, our job isn’t just to sell membrane modules and walk away— it’s to help customers manage biofilm effects before they become problems. Over the years, we’ve developed a suite of proactive, data-backed solutions that work better than generic “clean more often” strategies. First, we work with each customer to do a custom biofilm risk assessment: we test their wastewater feed for nutrient levels (nitrogen, phosphorus, which fuel biofilm growth), their MLSS concentration, and even the microbial community in their system to predict how fast biofilm will form. For example, if we find a customer has high levels of EPS-producing bacteria in their feed (common in textile wastewater), we adjust our recommended membrane aeration rates to maintain consistent shear across the module, which prevents biofilm from building up in uneven layers.
Second, we offer continuous monitoring tools that track not just TMP, but biofilm thickness and composition. Our latest system integrates a small, in-situ sensor that measures the optical density of the membrane surface, which tells us if biofilm is at a healthy, thin level or if it’s growing too fast. That lets operators adjust aeration, add small doses of non-oxidizing biocides (gentler than harsh chlorine, which can damage membranes) only when needed, instead of on a rigid schedule. We’ve seen customers who adopted this tool reduce their chemical cleaning frequency by 40% and cut their energy costs by 18% in the first year.
Third, we recommend proactive membrane maintenance strategies that target biofilm specifically, rather than generic fouling. Instead of waiting for TMP to spike to 20 kPa before doing a chemical clean, we guide customers to do “maintenance cleans” when TMP is only 5–10 kPa, using a milder citric acid solution that removes biofilm EPS without damaging the membrane surface. We also offer modular membrane designs that are easier to access and clean, so operators can perform routine checks without shutting down the entire system. For industrial customers, we even help them adjust their biological process to select for microorganisms that are less likely to form heavy biofilm— things like adding a small anoxic zone in the aeration tank, which promotes denitrifying bacteria that don’t adhere as tightly to membranes.
I’ll be the first to say biofilm isn’t an enemy in MBR systems— it’s a natural part of the microbial ecosystem that we just have to manage smartly. The key is distinguishing between the thin, useful biofilm that boosts treatment performance and the thick, problematic biofilm that eats into your operational budget and uptime. Over our years in this space, we’ve worked with everything from small municipal MBRs serving 10,000 people to large industrial facilities processing 100,000 m³/day of high-strength wastewater, and the one thing that’s consistent is that proactive, customized management of biofilm effects is what makes an MBR system deliver on its promise.
If you’re dealing with biofouling in your MBR system, or you’re looking to install a new MBR system and want to build biofilm management into your design from the start, we’re here to help. Our team has decades of experience troubleshooting biofilm issues, optimizing aeration and maintenance schedules, and offering tailored solutions that keep your MBR running at peak performance, without unnecessary downtime or costs. Reach out to our team to learn more about how we can support your MBR system needs.
Other Sewage Treatment Equipment References
- Judd, S. (2018). The MBR Book: Principles and Applications of Membrane Bioreactors for Water and Wastewater Treatment (2nd ed.). Elsevier.
- Liao, B. Q., Kraemer, J. T., & Bagley, D. M. (2006). Biofouling in membrane bioreactors for wastewater treatment: A review. Water Research, 40(7), 1225–1242.
- Rosenberger, S., Laabs, C., Lesjean, B., Gnirss, R., & Kraume, M. (2006). Biofouling in membrane bioreactors – Characteristics, impacts and control. Desalination, 192(1-3), 82–88.
- Meng, F., Zhang, H., Yang, F., Liu, L., & Fujii, M. (2017). Fouling in membrane bioreactors: An updated review. Water Research, 114, 151–180.
- Wu, J., & Stuckey, D. C. (2016). A review of microbial extracellular polymeric substances (EPS) in anaerobic membrane bioreactors: Characteristics, effects on fouling, and control. Water Research, 105, 578–596.
Shandong Lingke Environmental Technology Co., Ltd.
Address: 100 Meters South of the Intersection of County Road 042 and National Highway 309, Changle County, Weifang City, Shandong Province
E-mail: aileenlin@sdlingkegroup.com
WebSite: https://www.lkecotech.com/
