Last Updated on May 11, 2025 by Kevin Chen
Membrane Bioreactor (MBR) systems have gained widespread popularity due to their stable effluent quality, compact footprint, and high level of automation in wastewater treatment. However, one key parameter that is often overlooked but determines the efficiency of an MBR system is Dissolved Oxygen (DO).
Why Is DO So Important?
The MBR process relies on active microorganisms within the sludge to degrade organic pollutants, and these microorganisms require sufficient oxygen to maintain metabolism. DO levels directly impact the following:
- Low DO: Insufficient oxygen limits microbial activity, reduces organic and nitrogen removal, and can shift the system toward anoxic or anaerobic conditions, lowering treatment efficiency.
- High DO: Leads to energy waste, sludge bulking, poor settling, and inhibition of denitrification, ultimately affecting total nitrogen removal.
In MBR systems, aeration supplies oxygen and plays a vital role in membrane scouring, making DO control more complex and sensitive than conventional systems.
What is Impacting DO Control in MBR Systems?
Effective DO control requires more than just operator experience. It must consider multiple interacting factors:
1. Influent Water Quality
Organic and nitrogen loading determine oxygen demand. Fluctuating influent conditions require responsive DO adjustments to avoid under- or over-aeration.
2. Mixed Liquor Suspended Solids (MLSS)
Higher MLSS increases oxygen demand. MBR systems typically run at high MLSS (6000–12000 mg/L), requiring tighter oxygen control to avoid oxygen limitation or sludge bulking.
3. F/M Ratio (Food-to-Microorganism Ratio)
Low F/M can reduce oxygen demand and promote endogenous respiration, while high F/M increases oxygen requirements. Continuous monitoring helps optimize energy use and performance.
4. Temperature & pH
Low temperatures reduce microbial activity and oxygen transfer efficiency, increasing DO needs. pH affects nitrification efficiency and should be factored into DO strategies.
5. System Design & Recirculation
In systems like AO or A²/O, DO distribution across zones is critical. Anoxic zones should maintain 0.2–0.5 mg/L DO, while anaerobic zones should be near zero. Excess DO can inhibit denitrification and biological phosphorus release.
Smart DO Control Strategy for MBR system
As a professional MBR membrane and system provider, we recommend:
- Installing online DO sensors integrated with control systems for automated aeration adjustment.
- Linking DO control with MLSS, sludge settling ratio, membrane flux, and effluent quality.
- Ensuring even aeration and minimizing dead zones: to avoid localized oxygen deficiency.
- Defining zone-specific DO targets, especially in membrane tanks and biological zones, to balance energy use and treatment performance.
In an MBR system, DO is more than just an oxygen supply indicator—it’s a process control signal. Precision in DO management is key to unlocking the full potential of MBR systems in terms of performance, stability, and energy efficiency.
SPERTA has specialized in producing water treatment products for many years. If you need further assistance, please get in touch with our technical team for customized MBR solutions or further process optimization advice.
