The testing process for tubular ultrafiltration membranes is a comprehensive quality assurance system covering the entire lifecycle of production, delivery, and operation. It focuses on the integrity, separation performance, physical strength, and hygiene safety of the membrane module, ensuring consistent and reliable product performance through standardized methods.
★ Production Stage Process Inspection
This stage aims to ensure that each membrane tube meets design requirements in terms of structure, pore size, and basic performance.
• Appearance and Geometric Dimension Inspection: Visually inspect the inner and outer surfaces of the membrane tubes to confirm the absence of defects such as cracks, scratches, and bubbles. Simultaneously, use calipers, thickness gauges, and other tools to measure length, outer diameter, and wall thickness to ensure dimensional tolerances are within acceptable limits.
• Support and Membrane Layer Bonding Inspection: Verify the sealing performance of the interface between the support and the separation layer through hydrostatic or pneumatic testing to prevent delamination during operation.
• Basic Performance Testing: On a dedicated testing platform, using pure water as the medium, the initial pure water flux is measured under a specified pressure difference to provide a benchmark for subsequent performance evaluation.
• Comprehensive Performance Testing Before Shipment: Before shipment, the finished product undergoes comprehensive testing to verify whether it meets the nominal performance and application requirements.
★ Integrity Testing: This is a crucial step in verifying the absence of defects in the membrane structure. Common methods include:
• Bubble Observation Method: Pressure is applied to one side of the immersed membrane module. If continuous bubbles are observed on the permeate side, a defect exists.
• Pressure Decrease Method: After pressurizing to a set value, the membrane is sealed, and pressure changes are monitored. If the pressure drop exceeds a threshold within a specified time, it is considered unqualified.
• Separation Performance Testing: The membrane's molecular weight cutoff is calibrated by testing the rejection rate of specific standard substances (such as polyethylene glycol PEG, bovine serum albumin BSA) to ensure it meets design requirements.
• Mechanical Strength and Pressure Resistance Testing: Pressure is applied to individual membrane tubes or modules on a dedicated device to test their rupture pressure and pressure resistance, ensuring safe operation under design conditions.
• Batch Sampling Testing: Each batch of product is sampled and the above key tests are repeated to verify the consistency and stability of the overall product performance.
• Third-Party Authoritative Testing: For membrane products used in drinking water, pharmaceuticals, food, and other fields, a more comprehensive hygiene and safety assessment is usually commissioned to a third-party organization.
• Testing Process: Includes sample receiving and pretreatment, physical performance testing, chemical safety testing, microbiological safety assessment, and comprehensive performance and durability testing.
• Testing Content: Focuses on assessing whether the levels of leached heavy metals and organic matter meet standards, as well as the retention capacity for microorganisms such as E. coli, and issues an authoritative testing report.
• Online Monitoring and Maintenance Testing During Operation: After the membrane system is put into operation, its performance changes and health status need to be assessed through online monitoring and periodic testing.
• Online Monitoring: Real-time monitoring of transmembrane pressure difference (TMP), permeate flow rate, influent and effluent turbidity, and COD. An abnormal increase in TMP or a decline in permeate water quality indicates potential membrane fouling or damage.
★ Shutdown Inspection and Maintenance
• Integrity Re-inspection: Regularly use the bubble observation method or pressure decay method to check for new damage or seal failures that may occur during operation.
• Fault Diagnosis: When the permeate water quality is abnormal, the damaged membrane tube can be located and replaced using the single-tube troubleshooting method.
• Performance Evaluation: Through standardized flux testing, evaluate the cleaning effect and membrane performance recovery rate to provide a basis for optimizing the cleaning program.
