Two delivery formats, very different engineering
In water treatment, activated carbon is used in two fundamentally different formats: granular activated carbon (GAC) in fixed-bed contactors, or powdered activated carbon (PAC) dosed directly into the process stream and removed by clarification or filtration.
GAC in fixed-bed contactors
A GAC contactor is a vessel filled with granular carbon — typically 1–3 metres of bed depth — through which water flows continuously. As the carbon adsorbs contaminants over time, its capacity decreases. When breakthrough occurs (when effluent quality degrades to the point of non-compliance), the carbon must be replaced or reactivated.
GAC is the choice for continuous, high-volume water treatment — municipal drinking water plants, industrial process water, and effluent polishing. The capital cost is higher, but the operating cost is typically lower per unit volume treated.
UCI RC830 and RC1240 are Rajindra’s primary water treatment GAC grades — designed for consistent iodine number, controlled mesh, and the hardness required to withstand backwash cycles.
PAC in continuous dosing
Powdered carbon is dosed into the water stream at a point before clarification — allowing the carbon to contact the water, adsorb contaminants, and then be removed along with other settled solids. It offers flexibility: dose rate can be adjusted rapidly in response to changing contamination levels. It requires no dedicated contactor vessel.
PAC is preferred for seasonal or episodic contamination events — algal toxin outbreaks, taste and odour episodes, contamination incidents. The ability to vary dose and respond quickly outweighs the higher carbon cost per litre treated.
Which to choose
Choose GAC when: contamination is continuous, volumes are large, capital investment is justified, and the treatment target is consistent over time. Choose PAC when: contamination is variable or episodic, flexibility is required, or the treatment plant has no room for contactors.