Membrane Bioreactor (MBR) technology has revolutionized the way we treat wastewater, especially in areas where space is limited and high effluent quality is required. In this article, we’ll explore what MBR is, how it works, and why it’s increasingly being adopted around the world — all based on the insights I shared in my YouTube video.
What Is an MBR System?
MBR stands for Membrane Bioreactor. It is a modern wastewater treatment process that combines:
- Biological treatment (activated sludge)
- Membrane filtration (ultrafiltration or microfiltration)
This combination allows for the separation of treated water from solids and microorganisms without the need for a conventional settling tank. Instead, membranes physically retain the biomass and suspended solids, allowing only clean water to pass through.
How Does MBR Work?
The process involves two main components:
1. Biological Treatment
The raw sewage first enters a biological reactor where bacteria break down organic matter (BOD and COD). This step is similar to conventional activated sludge systems.
2. Membrane Filtration
Instead of using gravity to separate solids from water, MBR uses membrane modules that act as physical barriers. These membranes are either:
- Submerged inside the biological tank (internal/submerged MBR), or
- Located outside the tank in a separate loop (external/side-stream MBR)
The membranes allow clean water to pass through while retaining sludge, bacteria, and pathogens.
MBR Stages
1. Rotatory Screen
- Purpose: Initial coarse screening of the influent.
- Function: Removes large debris (rags, plastics, etc.) to protect downstream equipment.
2. Anoxic Stage
- Purpose: Denitrification.
- Function: Nitrate (NO₃⁻) is converted to nitrogen gas (N₂) in the absence of oxygen by denitrifying bacteria. This step reduces total nitrogen in the effluent.
3. Anaerobic Stage
- Purpose: Phosphorus removal and hydrolysis of complex organics.
- Function: Under completely oxygen-free conditions, specific bacteria (like PAOs) release phosphorus and break down large organic molecules. This improves overall biological nutrient removal (BNR).
4. Aerobic Stage
- Purpose: Organic matter degradation and nitrification.
- Function: Aerobic bacteria use oxygen to break down BOD (biochemical oxygen demand) and convert ammonia (NH₄⁺) to nitrate (NO₃⁻).
5. MBR Modules
- Purpose: Solid-liquid separation.
- Function: Hollow-fiber or flat-sheet membranes filter out suspended solids and pathogens, producing high-quality effluent. Acts as a physical barrier.
6. Chemical Cleaning Tank
- Purpose: Maintenance of membrane modules.
- Function: Holds cleaning solutions (like sodium hypochlorite or citric acid) used periodically to remove fouling on the membrane surfaces.
7. Outlet
- Purpose: Final treated water discharge.
- Function: Delivers permeate (clean effluent) suitable for reuse or safe discharge, depending on regulations.
✅ Advantages of MBR Systems
- High effluent quality: Suitable for reuse (irrigation, toilet flushing, even some industrial uses)
- Compact footprint: No need for large clarifiers or secondary settling tanks
- Better sludge retention: You can maintain higher mixed liquor concentrations
- Reduced odor and visual impact
- Efficient nutrient removal: Longer sludge age helps remove nitrogen and phosphorus
⚠️ Challenges of MBR
Like any technology, MBR has its drawbacks:
- Membrane fouling: A major operational challenge; membranes need periodic cleaning
- Higher energy consumption: Due to air scouring and pumping
- Higher capital and operational costs compared to conventional systems
- Need for skilled operators to manage cleaning cycles and membrane lifespan
Fouling Control and Cleaning
Regular cleaning is crucial to manage membrane fouling using:
- Air scouring to reduce buildup
- Relaxation cycles (pausing filtration intermittently)
- Backwashing (reversing flow through membranes)
- Chemical cleaning, including:
- CIP (Cleaning in Place) with solutions like sodium hypochlorite or citric acid
- Maintenance cleaning weekly or monthly
- Recovery cleaning when membranes are severely fouled
Proper cleaning strategies can extend membrane life to 8–10 years if done correctly.
When to Choose MBR?
MBR is an excellent choice for:
- Urban areas with limited space
- Projects requiring water reuse
- Resorts, airports, hospitals, and high-end housing
- Decentralized or containerized treatment systems