During long-term operation of reverse osmosis (RO) systems, various types of fouling may occur, among which microbial fouling (also known as biofouling) is one of the most insidious and common. It refers to the adhesion, growth, and reproduction of microorganisms such as bacteria, fungi, and algae on the membrane surface or inside the system, leading to the formation of a biofilm. This type of fouling is difficult to detect and can cause continuous degradation of system performance and membrane lifespan. Microbial fouling typically originates from microorganisms that are not completely removed during the pretreatment process and rapidly proliferate under favorable environmental conditions, posing a hidden threat to the stable operation of the system.
The formation of microbial fouling is not an instantaneous process but a gradual biological progression. Initially, microorganisms in the feed water adhere passively to the membrane surface or inner pipe walls, causing little noticeable impact on performance. Over time, however, these microorganisms secrete extracellular polymeric substances (EPS) that form a sticky biofilm structure. The biofilm adheres tightly to the membrane surface, providing a protective and nutrient-rich environment for microorganisms, allowing them to survive and reproduce even under unfavorable conditions. Meanwhile, the biofilm continuously traps organic matter and suspended particles from the water, making the fouling layer thicker and denser. Eventually, the membrane surface becomes fully covered by the biofilm, resulting in a decline in water flux and an increase in system pressure drop.
Once microbial fouling develops, it can lead to a series of severe consequences. The most direct effect is a significant decline in water production, as the biofilm hinders water permeation through the membrane. To maintain output, the system must operate at higher pressure, which increases energy consumption. In addition, the biofilm interferes with ion transport across the membrane surface, reducing the salt rejection rate and deteriorating permeate quality. More critically, the biofilm is highly adhesive and difficult to remove through conventional chemical cleaning; if not properly controlled, it can cause irreversible damage to the membrane. As microorganisms spread through the system, pipelines, filters, and storage tanks may also become contaminated, creating a vicious cycle of secondary pollution.
Preventing microbial fouling requires a comprehensive approach from source control, system operation, and maintenance. In the pretreatment stage, disinfection and sterilization processes-such as sodium hypochlorite dosing, ultraviolet light, or ozone treatment-should be enhanced to minimize the number of active microorganisms entering the RO system. During operation, flow velocity and pressure should be optimized to avoid dead zones or stagnant areas where microbes can accumulate. During shutdowns or intermittent operation, protective solutions should be circulated through the system to inhibit bacterial growth in standing water. Regular cleaning is also essential; specialized biofilm-removal cleaning agents can effectively eliminate fouling layers and restore membrane performance. Continuous monitoring of differential pressure, permeate flow, and SDI (Silt Density Index) helps detect early fouling trends and prevent major failures.
To address the challenges of microbial fouling, fouling-resistant membranes have been developed with advanced surface structures and chemical properties that reduce microorganism adhesion and growth, effectively delaying biofilm formation. These membranes require less frequent cleaning and maintain more stable performance under complex water conditions, providing users with a more efficient and durable water treatment solution. Our company's anti-fouling membranes are specifically designed to target microbial contamination. By optimizing membrane surface hydrophilicity and anti-adhesion properties, they significantly reduce the risk of biofilm formation, extend membrane lifespan, and ensure reliable system operation.
