Two forms of the same material
Granular activated carbon (GAC) and powdered activated carbon (PAC) are chemically identical — the difference is purely in particle size. GAC is 0.4–4 mm. PAC is typically less than 150 microns (0.15 mm). This size difference has profound consequences for how each is used.
GAC: continuous flow, fixed infrastructure
GAC is placed in a vessel and the contaminated stream flows through it. The carbon stays in place; the fluid moves. This is efficient for high-volume, continuous applications because a single carbon charge can treat millions of litres before replacement is needed.
PAC: flexible dosing, no fixed infrastructure
PAC is added directly to the stream as a powder or slurry, allowed to contact the fluid for a defined period, and then removed by filtration or sedimentation. No dedicated contactor vessel is needed. Dose can be changed at any time. But the carbon is single-use in most processes.
The decision framework
| Factor | Choose GAC | Choose PAC |
|---|---|---|
| Volume | Large — millions of L/day | Small to medium |
| Contamination | Consistent, predictable | Variable or seasonal |
| Capital budget | Available for vessels | Limited or not justified |
| Response time needed | Hours/days (bed design) | Minutes (dose adjustment) |
Many water treatment plants use both. GAC contactors handle the baseline load year-round; PAC dosing is activated during seasonal contamination events — algal blooms, agricultural runoff peaks — when the GAC alone cannot respond fast enough.
Cost comparison
Per kilogram, PAC costs more than equivalent GAC because of the grinding step. For high-volume continuous applications, the lifecycle cost of PAC vastly exceeds that of GAC. For batch pharmaceutical applications where the total volume is small and flexibility matters more, PAC is clearly more economical.