Selection between internal and external membranes in MBR technology

In-Tank vs. External Tubular MBR Membrane: A Guide for MBR Technology Selection

MBR (Membrane Bioreactor) technology has revolutionized wastewater treatment, with the MBR membrane being its core component. When choosing an MBR system, selecting between in-tank MBR membranes (e.g., PTFE immersion-type) and external tubular MBR membranes is a critical decision that directly impacts system efficiency, cost, and maintenance. This guide compares the two types to help you make an optimal choice for your wastewater treatment needs, whether for industrial projects, municipal upgrades, or retrofits.

In-tank MBR membranes, especially PTFE-based models, stand out for their compact design and streamlined workflow. Thanks to their ability to handle high sludge concentrations (up to 20-30g/L), the overall volume of the bioreactor can be significantly reduced. Unlike traditional systems or external tubular membranes, in-tank MBR membranes eliminate the need for additional equipment like sand filters, sedimentation tanks, and even civil engineering work in retrofit projects. For example, if you’re upgrading from a tubular membrane system to an in-tank MBR setup, you only need to place the membrane modules directly into the existing aerobic bioreactor—saving time, space, and construction costs. In contrast, external tubular MBR membranes require more complex piping and dedicated installation space, increasing both the footprint and initial investment of the MBR technology system.

Performance and longevity are other key differentiators. In-tank PTFE MBR membranes offer an impressive 5-year warranty and a minimum service life of 5 years, with a flux decay rate of no more than 5% after 5 years—ensuring consistent performance over the long term. They also excel at solids retention, with an SS (Suspended Solids) rejection rate exceeding 99%, which guarantees stable effluent quality and avoids adverse impacts on subsequent processes like nanofiltration. On the other hand, external tubular MBR membranes have a shorter warranty (1-2 years) and service life (2 years), with an annual flux decay of 10%-15%. Their SS rejection rate is less than 75%, which can compromise effluent quality and disrupt downstream treatment steps—a major drawback for applications requiring high-purity water output.

Operational costs, particularly energy consumption and maintenance, further favor in-tank MBR membranes. For a system treating 200 tons of wastewater per day, an in-tank PTFE MBR membrane system consumes only 230 kW of power daily, while an external tubular system uses a staggering 1500 kW—translating to an annual electricity savings of approximately 500,000 yuan. Maintenance for external tubular membranes is also more demanding: they require strict inlet water quality control (including mandatory security filters) and extensive chemical cleaning (with large chemical dosages and long cleaning times). In contrast, in-tank MBR membranes have no special inlet water requirements (no need for filters) and can be cleaned online in just 2 hours with minimal chemical usage—reducing both maintenance time and costs, and maximizing MBR technology system uptime.

The image illustrates the structural differences between in-tank and external tubular MBR membrane systems. In-tank PTFE MBR membranes are immersed directly in the aerobic bioreactor, with simple auxiliary equipment (e.g., self-priming pumps, roots blowers) integrated into the existing tank—minimizing space usage. External tubular MBR membranes, however, require separate external pressure vessels, complex circulation pipelines, and additional pre-filtration units, leading to a larger and more intricate system layout. This visual contrast highlights why in-tank MBR membranes are the preferred choice for space-constrained or cost-sensitive MBR technology projects.

Energy Consumption Comparison for 200 Ton/Day MBR Membrane Systems (Table)

Choosing the right MBR membrane is pivotal to unlocking the full potential of MBR technology. In-tank PTFE MBR membranes offer superior space efficiency, longer lifespan, lower operational costs, and more stable performance—making them ideal for most wastewater treatment scenarios, especially retrofits and projects with tight budgets or space constraints. External tubular MBR membranes, while suitable for specific high-pressure applications, fall short in terms of cost-effectiveness and long-term reliability. By prioritizing in-tank MBR membranes, you can build a more efficient, economical, and sustainable MBR technology system that meets your treatment goals for years to come.