MBR membrane maintenance

MBR Membrane Chemical Cleaning Procedure: Complete Offline CIP Cleaning Guide 1.  Overview This procedure applies to the MBR membranes used in wastewater treatment systems. The membranes are cleaned once per year as part of routine MBR membrane maintenance. The purpose of this MBR membrane chemical cleaning procedure is to remove organic, biological, and inorganic foulants, restore membrane permeability, reduce transmembrane pressure (TMP), and extend membrane service life. Although commonly referred to as MBR CIP cleaning, this is an offline / in-tank chemical cleaning procedure because the tank is drained and the membranes are soaked in cleaning solutions. The complete cleaning typically requires two technicians and two days.   2. Safety and Pre-Cleaning Requirements Isolate the MBR system and apply lockout/tagout (LOTO) before work. Wear appropriate PPE: chemical goggles or face shield, acid/alkali-resistant gloves, apron, and boots. Ensure adequate ventilation. Gas station wastewater may contain volatile organics; monitor for flammable or toxic gases if required. Never mix acid with sodium hypochlorite. Acid addition to hypochlorite can release dangerous chlorine gas. Confirm chemical compatibility limits with the membrane manufacturer before MBR membrane cleaning, especially for chlorine concentration, pH, and temperature. Remove free oil/grease and floating debris, if present, before chemical cleaning. Neutralize and dechlorinate all waste cleaning solutions before discharge.   3. Cleaning Chemicals and Equipment Sodium hypochlorite (NaOCl) Sodium hydroxide (NaOH) Citric acid Clean water or permeate pH meter and chlorine test kit Aeration blower / coarse-bubble diffusers Cleaning tank or isolated membrane tank Hoses, pumps, valves, PPE, and neutralization chemicals   4. MBR Membrane Cleaning Procedure Step 1 – Drainage, Sludge Removal, and Pre-Rinse Shut down the MBR system and isolate the membrane tank. Pump out the tank water and transfer sludge to the sludge handling system. Remove loose sludge, debris, and floating oil/grease. Pre-rinse the membranes with clean water or permeate to remove gross solids. Drain the rinse water and inspect membranes, piping, and aeration diffusers.   Step 2 – Alkaline / Oxidative Cleaning Fill the tank with clean water until the membranes are fully submerged. Add sodium hypochlorite to a concentration of 2,000 ppm as available chlorine, or as recommended by the membrane manufacturer. Add NaOH to adjust the pH to approximately 11. Soak the membranes with gentle coarse-bubble aeration for about 6 hours. Monitor pH and chlorine concentration during soaking; adjust if necessary. Drain the cleaning solution to a neutralization or holding tank.   Step 3 – Intermediate Rinse Rinse the membranes and tank thoroughly with clean water or permeate. Continue rinsing until residual chlorine is low and the pH is near neutral, approximately 6–8. Drain the rinse water completely before proceeding to acid cleaning. This step is critical to prevent acid contact with residual hypochlorite.   Step 4 – Acid Cleaning Fill the tank with clean water. Add citric acid to a concentration of 1% w/w. Adjust the pH to approximately 1 using citric acid or NaOH if needed. Soak the membranes with gentle aeration for 5–6 hours. Monitor pH during soaking and maintain the target range. Drain the acid cleaning solution to the neutralization tank.   Step 5 – Final Rinse and Return to Service Rinse the membranes thoroughly with clean water or permeate. Continue rinsing until the pH is 6–8 and no residual cleaning chemicals remain. Drain the final rinse water. Restore valves, instruments, and aeration equipment. Perform a membrane integrity test or leak check if applicable. Restart the MBR system gradually and monitor TMP, permeability, and effluent quality.   5. Key Control Parameters Stage Chemical Concentration pH Aeration Duration Alkaline / oxidative cleaning NaOCl + NaOH 2,000 ppm as available chlorine 11 Gentle coarse-bubble aeration ~6 hours Intermediate rinse Clean water / permeate — Neutral, 6–8 — Until neutral Acid cleaning Citric acid 1% 1 Gentle aeration 5–6 hours Final rinse Clean water / permeate — Neutral, 6–8 — Until neutral   6. Manpower and Schedule Manpower: 2 technicians Duration: Approximately 2 days Day 1: Isolation, drainage, sludge removal, pre-rinse, alkaline/oxidative cleaning, intermediate rinse Day 2: Acid cleaning, final rinse, neutralization, system restoration, integrity check, and restart   7. Waste Handling Dechlorinate NaOCl-containing waste using sodium thiosulfate or bisulfite. Neutralize acid waste with NaOH or another suitable alkali. Adjust combined waste to pH 6–9 before discharge. Comply with local discharge regulations for gas station wastewater treatment.   8. Acceptance Criteria Final rinse water is neutral and free of residual chlorine. Membrane permeability or TMP is restored or improved. No leaks or integrity failures are detected. Effluent quality meets the required standard after restart. Cleaning records are completed, including chemical batches, pH, chlorine concentration, soaking time, rinse results, and maintenance photos.   9. Optimization Notes Always follow the membrane manufacturer’s maximum chlorine exposure and pH limits during MBR membrane chemical cleaning. Use permeate for final rinsing where available to reduce contamination risk. Maintain a moderate cleaning temperature, typically 20–30°C, unless otherwise approved by the manufacturer. If fouling is severe, repeat the alkaline or acid stage separately, but avoid excessive chlorine exposure. Ensure uniform aeration without excessive air scouring that could damage the membranes. Keep acid and hypochlorite systems completely separated during storage, preparation, and cleaning.

What’s the essentially 3 operations of MBR System   MBR System Operating Parameters    There are essentially 3 main operations of a membrane bioreactor (MBR) system during wastewater treatment. They are as follows:   Membrane permeability daily maintenance Microbiology maintenance and proper operation Membrane filtration and sludge transfer   Of these, maintaining membrane permeability is one of the most significant factors affecting the overall performance and stable operation of an MBR wastewater treatment plant.   Operation Purpose Key Indicator Biological treatment Degrade pollutants MLSS, DO, SRT Membrane filtration Produce treated water Flux, TMP Aeration/scouring Supply O₂ + control fouling Air flow, DO Backwash/cleaning Restore permeability TMP recovery, permeability   Membrane Premeability Daily Maintenance     The daily maintenance of MBR membrane permeability includes the following:   a) MBR cleaning: Both physical cleaning, such as relaxation and clean-water backwash, and membrane air scouring are important for maintaining membrane performance. For example, a relaxation time can be designed as 7 minutes of working and 1 minute of relaxation. During air scouring, coarse bubbles rise along the membrane surface and create shear force to remove accumulated sludge and foulants, helping keep the MBR membrane clean.   b) Chemical cleaning – CEB (Chemically Enhanced Backwash):** Backwashing with chemical dosing through the pipeline helps remove foulants that cannot be effectively removed by physical cleaning alone.   c) Chemical cleaning – CIP (Clean-In-Place): CIP is a recovery cleaning procedure for the MBR membrane modules. The membranes are cleaned in the tank using chemicals and aeration to help restore membrane permeability. Microbiology Maintenance and Proper Operation   Biological treatment, or biodegradation, is an essential part of MBR wastewater treatment. Maintaining healthy activated sludge growth in the biological system is very important for stable operation.   The activated sludge in the bioreactor consumes organic matter, nitrogen, and phosphorus. This is the “bioreactor” half of an MBR system. Proper MLSS, DO, SRT, and nutrient balance should be maintained so that the microorganisms can perform their treatment functions effectively.   For typical MBR operation, the MLSS can be maintained at around 6000–8000 mg/L, with DO generally around 1.5–3 mg/L, together with appropriate SRT and nutrient balance.   How to operate the MBR System for Wastewater Treatment and set the running Parameters Membrane Filtration and Sludge Transfer   The MBR membrane modules physically separate treated water from biomass and suspended solids, replacing the secondary clarifier used in a conventional activated sludge plant. This process is driven by a suction pump or gravity head, and its performance is mainly tracked by TMP (transmembrane pressure) and flux.   Discharging sludge from the MBR tank is a routine but critical operation. Unlike conventional systems, MBR systems operate at relatively high MLSS concentrations, so sludge must be periodically wasted to maintain the appropriate biomass concentration and help prevent membrane fouling.   If the MLSS increases above approximately 8000 mg/L, the membrane can become more susceptible to fouling and clogging, making proper sludge management important for stable MBR operation. Hinada is ready to discuss your wastewater treatment needs, MBR membrane selection, system design, or maintenance requirements. Our technical team is here to help. Contact us to discuss your application.