Granular Activated Carbon
Granular activated carbon (GAC) consists of porous carbon particles graded by size. Its grains are larger than powdered activated carbon and can form a filter bed.
Molecules are retained mainly on the internal pore surfaces. Grain size affects water flow through the bed, while the raw material and pore structure determine adsorption properties.
Technical Specifications
| Physical form | Irregular granules |
|---|---|
| Feedstock types | Coal, wood and coconut shell |
| Iodine number | 916 mg/g |
| Moisture | 3.7% |
| Effective particle size | 0.725–0.925 mm |
| Uniformity coefficient | 1.85 |
| Abrasion number | 76.12 |
| Tamped apparent density | 0.55 g/cm³ |
| Bulk density (ASTM D2854) | 460–530 kg/m³ |
| Hardness | 95.9% |
| Ash content | 5.2% |
Application and use
- In drinking-water and process-water treatment, water passes through a carbon bed to reduce adsorbable dissolved organic compounds.
- Pressure or gravity filters can use GAC as a polishing stage after upstream treatment.
- Suitable grades also treat liquid food-processing streams for color and organic impurity reduction.
- Flow, bed contact time and backwash conditions are considered together when establishing filter operation.
Frequently asked questions
Does backwashing restore exhausted adsorption capacity?
No. Backwashing cleans and conditions the bed; suitable spent carbon is replaced or considered for thermal reactivation.
Why can black fines appear after a new fill?
New carbon can contain fines. Follow the selected grade's wetting, rinsing and backwash instructions before service.
Is the finest granule always the best choice?
No. Assess size and distribution against target-compound contact, filter flow, pressure drop and backwash capacity.
Can GAC remove free chlorine from water?
A suitable GAC bed can reduce free chlorine through a reaction at the carbon surface. Suitability depends on inlet concentration and contact conditions.
How is the carbon replacement time determined?
Monitor the target compound in treated water for breakthrough. Replacement or reactivation timing depends on actual loading and the required outlet quality.