This guide addresses design inputs, material and equipment selection, instrumentation and control, factory acceptance testing (FAT) and site acceptance testing (SAT), commissioning and start-up, and operation and maintenance for industrial electro-membrane systems. It is intended for project teams to reference during design reviews and acceptance.
Design Inputs: Basic Data Determining System Configuration
- Complete water quality analysis: major cations and anions, COD, hardness, pH, temperature, and seasonal fluctuation ranges.
- Water quantity conditions: daily treatment capacity, peak factor, continuous or intermittent operation, and annual operating hours.
- Product requirements: target concentration, allowable impurity levels, reuse destination, and storage conditions.
- Site and utilities: available area, power supply capacity, cooling water, compressed air, and drainage conditions.
- Discharge and compliance requirements: concentrate discharge volume, concentrate destination, and local environmental standards.
The most commonly underestimated design input is the range of water quality fluctuations. If the system is selected based only on average water quality, it is highly likely to exceed design boundaries under peak and abnormal conditions, leading to flux decline, frequent cleaning, and even shutdown.
Key Points for Material and Equipment Selection
- Membrane materials: determine membrane type and material based on feed pH, temperature, oxidizing substances, and organic matter content.
- Membrane stack structure: determine the number of membrane pairs, stages, and parallel grouping based on treatment scale and product concentration.
- Power supply and electrodes: the voltage regulation accuracy of the DC power supply and the corrosion resistance of electrode materials directly affect operational stability.
- Pumps and piping: Select pumps based on flow rate, head, and medium corrosivity; piping materials must be compatible with the medium.
- Pretreatment unit: The configuration of filtration, hardness removal, residual chlorine removal, and heat exchange should match the membrane stack requirements.
Instrumentation and Control System
- Flow and pressure: Online monitoring of inlet and outlet flow, pressure, and differential pressure at each stage is used to determine the degree of fouling.
- Conductivity and concentration: Online monitoring of the conductivity of dilute, concentrate, and product streams is used to assess desalination and concentration performance.
- pH and temperature: Monitoring of pH and temperature of acid and alkali products and feed is used for process adjustment and safety protection.
- Current and voltage: Recording of membrane stack operating current and voltage is used to calculate energy consumption and determine membrane stack status.
- Safety interlock: Abnormal conditions such as overcurrent, overvoltage, water shortage, and overtemperature should trigger alarms and execute shutdown or load reduction.
FAT and SAT: Two acceptance stages
FAT (Factory Acceptance Test)
- Check equipment appearance, nameplate, material certificates, and factory inspection reports.
- Check membrane stack assembly quality, sealing, and piping connections.
- Power-on and no-load trial run: check the power supply, instruments, control logic, and safety interlock actions.
- Clean water circulation test: check for leaks and whether instrument readings are normal.
SAT (site acceptance test)
- Installation-in-place verification: confirm piping, electrical, grounding, and utility interfaces.
- Trial run with feed: gradually increase the load using the actual feed solution, and record flux, product concentration, and energy consumption.
- Continuous operation test: operate continuously under design conditions to verify stability and the cleaning cycle.
- Product specification verification: confirm item by item against the product requirements in the design input.
Commissioning, Operation, and Maintenance
- During commissioning, increase the load gradually to avoid instantaneous fouling of the membrane surface caused by bringing it to full load at once.
- Establish an operation log: record flow rate, pressure, conductivity, current and voltage, and cleaning time as a basis for trend analysis.
- Cleaning management: trigger chemical cleaning based on pressure difference and flux decline; cleaning agents and concentrations must be compatible with the membrane material.
- Shutdown protection: keep the membrane stack wet during short-term shutdowns, and take protective measures according to membrane material requirements during long-term shutdowns.
- Spare parts inventory: membrane elements, gaskets, filter cartridges, and other consumables should be stocked in advance according to the cleaning cycle and supply cycle.
The long-term performance of electromembrane systems depends largely on how well O&M is standardized. Keeping solid operating logs and cleaning records often extends membrane life more than simply upgrading equipment specifications.