Some images are technical illustrations. Real installation photographs where marked.
Overview
The CG BAF™ (Biological Aerated Filter) is a fixed-film aerobic treatment system where biological oxidation of dissolved organic pollutants and physical filtration of suspended solids occur simultaneously in a single bed of engineered plastic or mineral media. Microorganisms attached as biofilm to the media surface degrade BOD and carry out nitrification, while the media itself acts as a depth filter capturing suspended solids. This dual function makes BAF one of the most compact secondary or tertiary treatment technologies available — it eliminates the secondary clarifier while delivering both biological and physical treatment. BAF is widely used for municipal sewage treatment, industrial effluent polishing, and upgrading overloaded plants where additional capacity is needed without new land.
Working Principle
In the downflow BAF configuration, pre-treated wastewater is evenly distributed over the top of the filter media bed. Air is introduced through nozzles at the base to supply oxygen to the biofilm. As wastewater percolates downward, organic pollutants are oxidised by biofilm and suspended solids are mechanically captured between media particles. Periodically (every 24–72 hours), combined air scour and water flush backwash the media, stripping excess biofilm and captured solids. Backwash takes 15–30 minutes and can occur without interrupting overall plant operation when multiple BAF cells operate in parallel.
Key Technical Features
- Combined biological treatment + physical filtration
- No secondary clarifier required
- BOD removal: 85–95%
- Nitrification: NH₃-N removal >80%
- 50% smaller footprint than conventional activated sludge
- Upflow or downflow media configurations
- Media: polypropylene, expanded clay (LECA), or mineral
- Automated air/water backwash — no manual cleaning
- Short HRT: 30 min – 2 hours
- Modular cell design — easy capacity expansion
Design Parameters
| Parameter | Value |
|---|---|
| Flow Range | 50–5,000 m³/day |
| Inlet BOD | 50–500 mg/L |
| BOD Removal | 85–95% |
| NH₃-N Removal | >80% |
| HRT | 0.5–2 hours |
| Media | PP/LECA/Mineral |
| Backwash Cycle | Every 24–72 hrs |
Applications
- Municipal sewage secondary treatment
- Industrial effluent polishing after primary biological stage
- Upgrade of overloaded activated sludge plants
- Nitrification of ammonia-rich streams
- Tertiary treatment before reuse or sensitive discharge
- Hotel, hospital, and institutional sewage
- Pre-treatment before membrane systems
Advantages
- Smallest footprint of fixed-film aerobic systems
- No secondary clarifier — capital cost saving
- Automated backwash — no operator-intensive cleaning
- Modular — cells added as flow increases
- Suitable for tertiary polishing to very low BOD
- Robust to variable loads — biofilm adapts rapidly
Frequently Asked Questions
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