MBR Operation and Maintenance Guide
Membrane Bioreactors, also referred to as MBRs, present a new type of wastewater treatment process by combining membrane separation technology and biotechnology. This process greatly increases the concentration of activated sludge while offering independent control of Hydraulic Retention Time (HRT) and Sludge Retention Time (SRT). A typical MBR system consists of pretreatment systems, bioreactors, aeration systems, MBR membrane modules, a chemical cleaning system, and more. It operates following this process flow:
Proper maintenance is key to ensuring an MBR System’s long service life. With it comes not just longer membrane life and consistently high-quality effluent but also fewer emergencies and reduced filtration costs over time. Here are some operation and maintenance tips from Membrane Solutions:
1. Intermittent Suction Operation
To secure stable performance of the MBR system, it is essential to perform an intermittent suction operation. If the suction pump continuously operates without any stop intervals, particles, colloids, sludge blocks and other substances in the membrane tank will accumulate on the membrane surface, therefore affecting flux and operation of the membrane module.
Generally, keep suction time within 9 minutes with at least 1 minute stop interval. For normal operations, it is recommended to run 8 minutes of the suction process with a 2-minute stop interval, done while aeration is continuously being carried out.
2. Chain Reaction Shutdown Settings
It is best to program an emergency stop function for suction pumps in MBR Systems. If a running blower suddenly shuts down because of an unprecedented issue while the suction pump continuously works, the sludge will quickly accumulate and stick on the membrane surface resulting in a rapid increase in the system pressure difference. For this reason, if the air blower is stopped, the system must have a chain reaction setting that would also automatically halt the suction pump simultaneously – sending an alarm signal if there are any changes in air flow or air blower pressure.
The valve design of the permeate pipeline must avoid siphoning during a shutdown. When the system is in an intermittent suction operation state, such as in a suction pump stop interval, siphoning occurs in the permeate pipes due to gravity. This can happen while the membrane modules are in a filtering state and the transmembrane pressure difference is rising. Considering this unusual shutdown state, it is necessary to install an automatic stop valve on the permeate pipe or set a siphon gate valve at the outlet to the suction pump to ensure that the membrane module immediately stops filtering when the suction pump stops.
The suction pressure of the membrane module needs to be monitored in real-time so that it does not exceed the set value. If the resulting value goes beyond the set value, the system should signal an alarm to quickly carry out chemical cleaning that would restore the pressure difference.
3. Chemical Cleaning
For MBR Systems, three types of chemical cleaning to consider are: Chemically Enhanced Backwashing (CEB), maintenance cleaning, and recovery cleaning. For optimal filtration performance of the membrane system, it is advised to do Chemically Enhanced Backwashing three times a week, supplementary to the monthly maintenance cleaning. Both of these cleaning methods inject chemical solutions from the side of the suction pump into the membrane module.
If the MBR System deals with organic pollutants, use NaClO as a cleaning agent. If the system undergoes extended operations, inorganic pollutants might accumulate and therefore would require acid cleaning.
- Chemically Enhanced Backwashing (CEB)
Achieve stable membrane system operation with regular CEB, managed through a PLC system, that removes clogs on the membrane surface and controls increase in Transmembrane Pressure (TMP). We recommend doing CEB three times a week or when the suction pressure surpasses the set value. During this cleaning process, aeration should be stopped.
- Maintenance Cleaning
Maintenance cleaning needs to be done every month or when the suction pressure exceeds the set value or point. This ensures regular removal of contaminants that have accumulated on the membrane surface or internal surface, minimizing membrane fouling.
When fouling is addressed, TMP restores its initial value. If the TMP difference is still high after maintenance cleaning, it can be an indicator of inorganic contamination that would require acid cleaning.
- Recovery Cleaning
If maintenance cleaning cannot restore the TMP difference or if the membrane surface adheres to the sludge due to mechanical equipment failure, it is necessary to remove the membrane module and soak it in a cleaning tank.
The whole membrane assembly should be immersed in a chemical cleaning tank to remove pollutants. The main purpose of recovery cleaning is to restore the TMP difference to its initial value. In general, recovering cleaning is better than maintenance cleaning.
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