The MBR membrane bioreactor is one of the commonly used water treatment devices, and a key focus in MBR research is maximizing membrane flux. This approach allows for a smaller membrane footprint, ultimately reducing both the infrastructure and operational costs of the MBR system. These factors are determined by the specific parameters of the membrane bioreactor. Let’s now take a closer look at the key parameters that define an MBR system.

　　MBR membrane bioreactors use materials categorized into organic and inorganic membranes. Organic membranes are widely preferred in membrane bioreactors, with commonly used materials including polyethylene and polypropylene. Separation-type membrane bioreactors typically employ ultrafiltration membrane modules, which usually block molecules ranging from approximately 200,000 to 300,000 Daltons. While larger molecular-weight cutoffs generally result in higher initial membrane flux, this doesn’t necessarily translate to consistently high long-term flux performance.

　　How does an MBR membrane operate?

　　If a membrane is selected, it also determines the material properties, making operational practices a key factor influencing membrane fouling in membrane bioreactors. Parameters such as sludge concentration and mixed-liquor viscosity not only affect membrane flux but also impact the overall filtration performance of the mixed liquor itself (e.g., characteristics of activated sludge and microbial community composition), directly contributing to the decline in membrane permeability over time. Research findings indicate that adding powdered activated carbon (PAC) and coagulants can enhance sludge-water separation, leading to the formation of bulky, less viscous flocs that reduce the likelihood of membrane clogging. However, excessive addition of coagulants may inhibit sludge activity, negatively affecting the reactor's treatment capacity and overall effluent quality.

　　What are the hydraulic characteristics of MBR membranes?

　　Improving the hydrodynamic conditions of the liquid near the membrane surface, increasing the fluid inflow velocity, and minimizing concentration polarization help ensure that solutes are efficiently carried away by the flow. Separated-type membrane bioreactors typically employ an improper cross-flow filtration method, while integrated membrane bioreactors essentially rely on dead-end filtration. Cross-flow filtration is far more effective than dead-end filtration in preventing fouling and deposition on the membrane surface. Therefore, designing a well-optimized channel structure—such as enhancing the upward liquid flow between membranes to generate greater shear forces—can significantly improve the cross-flow filtration performance and reduce fouling on the refined membrane surface. This approach is particularly critical for submerged membrane bioreactors.

　　What are the uses of MBR membranes?

　　1. Wastewater Treatment: China is a water-scarce country, making wastewater treatment and reuse essential measures for effectively developing water resources. After being treated using advanced equipment like membrane bioreactors, urban and industrial wastewater can be repurposed for non-potable applications such as landscaping, laundry, and replenishing ornamental water features—while still meeting high-quality standards when intended for drinking or other critical uses. Since urban and industrial wastewater sources are typically located close to treatment facilities, this approach eliminates the need for long-distance transportation. By treating wastewater locally, we maximize water resource utilization while minimizing the risk of leaks during transit that could contaminate underground water supplies. Wastewater reuse has already been widely adopted in many water-stressed regions around the world and is regarded as one of the most practical wastewater treatment technologies of the 21st century.

　　2. Comparison of Inlet and Outlet Water Quality:

　　Typical urban wastewater design influent water quality: BOD5

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